Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1016/j.procir.2017.12.030

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In laser processing of silver nanowire transparent conductive film covered with an acrylic resin layer, effects of pulse duration on electrical insulation and surface quality were experimentally investigated by using nanosecond pulsed laser. The minimum laser fluence to achieve the stable electrical insulation by removal of silver nanowire became small with decreasing the pulse duration, but shorter pulse duration showed drastic change of removal trace area of silver nanowires at the boundary region of laser fluence to change conductive state to insulation one. In contrast, longer pulse duration around 200 ns indicated almost constant small removal trace area of silver nanowires, and wide processing window to perform the stable electrical insulation with small removal trace area of silver nanowires can be expected by using a proper long pulse duration in nanosecond pulsed laser processing. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmatprotec.2016.10.004

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Fuji Technology Press  

In laser cutting and drilling process, molten material was scattered as spatter, which deteriorates the surface integrity of a workpiece because of the thermal damage. It is expected that the control of assist gas flow can reduce the adhesion of spatter. In order to investigate the improvement method of thermal damage due to the adhesion of spatter, it is required to clarify characteristics of spatter. Therefore, a method was developed to collect and analyze spatter based on the use of high-speed video cameras in the lasermicro-drilling process, and the characteristics of spatter movement were numerically investigated by CFD analysis. The scattering velocity and angle of the spatter were investigated by recognizing and tracking spatter with the high-speed video observation. The movement of spatter was observed by using two high-speed video cameras, and analyzed by using a two-direction tracking method, in which the 3D tracking lines of spatter particles were reconstructed in the forward and backward frames, and the actual trajectory of individual spatter particle was obtained by averaging those tracking lines. These measurements revealed that the initial velocity of spatter was mainly distributed from 52 m/s to 200 m/s with an average velocity of 129 m/s. The initial angle of spatter was mainly distributed between 0 and 30 degrees from the workpiece surface in the upward direction. There was little correlation between the initial velocity and angle of spatter. The diameter of spatter was mainly distributed from 1 µm to 4 µm with an average diameter of 3.7 µm. It is important to use the processing conditions achieving the smaller spatter diameter in order to reduce the thermal damage caused by spatter. Although coaxial assist gas flow has an influence on the spatter behavior, that time period is very short. Therefore, it is important to control the spatter behavior outside of the coaxial assist gas flow by using an additional gas flow to prevent the thermal damage to the workpiece surface.

DOI： 10.20965/ijat.2016.p0874

Scopus

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Evolution of free-electron density in internal modification of glass by fs-laser pulses at high pulse repetition rates is simulated based on rate equation model, which is coupled with thermal conduction model in order to incorporate the effect of thermal ionization. Model shows that highly absorbing small plasma generated near the geometrical focus moves toward the laser source periodically to cover the region, which is much larger than focus volume. The simulated results agree qualitatively with dynamic motion of plasma produced in internal modification of borosilicate glass by fs-laser pulses at 1 MHz through the observation using high-speed video camera. The paper also reveals the physical mechanism of the internal modification of glass when heat accumulation is significant. (C) 2016 Optical Society of America

DOI： 10.1364/OE.24.025718

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN LASER PROCESSING SOC  

The internal modification technique for a sapphire substrate using a sub-nanosecond pulsed fiber laser of 180 ps was experimentally investigated with a normal achromatic focusing lens of 20 mm focal length, and the possibility of a singulation method with this internal modification technique was discussed. The laser beam of 1060 nm was focused in sapphire substrate of 0.4 mm thickness by passing through GaN epitaxial layer grown on the top surface of the sapphire substrate, and the internal modification zone was generated from the stain-finished surface as the bottom surface of sapphire substrate. The laser beam was absorbed from the stain-finished bottom surface, and the absorption point moved in the axis of laser irradiation without moving the focusing optics. The narrow internal modified line less than 5 mu m in width with a high aspect ratio of more than 30 was successfully obtained only by one laser scanning irradiation from the epitaxial layer side. A sapphire wafer could be broken from the internal modified line with less damage of the epitaxial layer by a stress sufficiently smaller than the tensile strength of sapphire. The breaking strength and its dispersion became smaller with increasing number of laser scans.

DOI： 10.2961/jlmn.2014.01.0011

Web of Science

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/MSF.783-786.2792

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Glass materials have been widely used in optics, MEMS, electronics and biomedical applica-tions because of their excellent optical, mechanical and chemical properties. Fusion welding by ul-trashort pulsed laser has been proposed as a promising technique for glass joining, since joining can be accomplished without an intermediate layer and mechanical contact. However, to apply a fusion welding technique by ultrashort pulsed laser as a reliable joining method, it is important to under-stand the mechanical properties of the weld seam since glass materials are very sensitive to tempera-ture gradients. Therefore, a method of evaluating the weld seam in the fusion welding of glass by picosecond pulsed laser was discussed, and its mechanical strength was investigated. A larger opti-cal contact area had a great influence on the shear load of the weld seam, while a smaller optical contact area could reduce the influence of the contact area on the measurement of shear load. There-fore, it was important to reduce the optical contact area to accurately evaluate the shearing strength of weld seam. The mechanical strength of the weld seam reduced at a low pulse repetition rate. High bending strength and shear stress could be obtained at a proper pulse repetition rate.

DOI： 10.2961/jlmn.2013.01.0013

Scopus

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Authorship：Lead author,　Corresponding author   Language：English   Publisher：Japan Society of Electrical-Machining Engineers  

CiNii Article

CiNii Books

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

Aluminum nitride and silicon carbide are expected as a useful material for the substrate in semiconductor industry because of their excellent properties. Precision micro-machining without crack and with little heat affected zone is required for their applications. Shorter wavelength makes it possible to remove a material with little heat affected zone because of its high photon energy. Therefore, effects of wavelength on machining characteristics of AlN and SiC in micro-drilling using Q-swithched YAG harmonics were experimentally investigated. The drilled depth increased with decreasing the wavelength. Under the reduced pressure condition, the drilled depth increased, and the better surface integrity could be obtained compared to the atmospheric pressure condition. The circumference region around the drilled hole was oxidized for all the case, and the oxidization in the case of fourth harmonic was more remarkable than that in second harmonic. In the initial stage of drilling for AlN with fundamental wavelength, the irradiated point expanded by the absorption of laser beam with increasing the number of laser pulse, and the processing was carried out by crumbling the grain due to the thermal expansion. On the other hand, the higher harmonics could make a hole at the irradiated point from the initial stage without thermal expansion.

DOI： 10.1299/jamdsm.2.661

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Language：Japanese   Publisher：The Japan Society for Precision Engineering  

Machining characteristics of aluminum nitride by various kinds of the harmonics of Nd:YAG laser, that is the fundamental harmonic (λ_1=1064nm), the second harmonic (λ_2=532nm), the third harmonic (λ_3=355nm) and the forth harmonic (λ_4=266nm), were experimentally investigated. Since the material removal is mainly performed by thermal processing in the case of long wavelength such as fundamental wavelength, the removal rate greatly decreases with increasing the distance from the focusing point to the tip of removal. Thus, the limit of removal depth was shallow, since the material removal was sensitive to the energy density of laser beam. On the other hand, when the photon energy of laser beam is larger than the bonding energy of material, the material is mainly removed by the photochemical reaction. Thus, the decrease of removal rate was small for shorter wavelength. Therefore, the removal rate increases with decreasing the wavelength of laser beam for long term irradiation under the same energy condition. In the case of deep hole drilling, the drilled depth increases proportionally with the number of laser shot at the beginning region. Therefore, the removal depth could be controlled by the number of laser shot in this region.

DOI： 10.2493/jspe.72.725

CiNii Article

CiNii Books

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Other Link： https://jlc.jst.go.jp/DN/JALC/00386431733?from=CiNii

Language：Japanese   Publisher：The Japan Society for Precision Engineering  

The stagnation pressure, which is the sum of static and dynamic pressures, has a great influence on machining performance in laser cutting. Therefore, increasing the velocity of assist gas is effective in reducing the height of dross. In this paper, Laval nozzle was newly designed, because it can increase the velocity of assist gas flow spouted from nozzle tip. Effects of Laval nozzle on assist gas flow and the machining results in precision cutting of thin metal plate by a pulsed YAG laser were experimentally investigated. Assist gas flow from Laval nozzle does not have Mach Shock Disk and goes more straight than a traditional convergent nozzle. Therefore, the pressure on a workpiece increases, since assist gas flow from Laval nozzle can utilize energy more efficiently. However, caution is necessary in setting the cylinder gas pressure, since Laval nozzle has many unstable regions, where the pressure on the workpiece changes periodically. Using Laval nozzle makes it possible to reduce the height of dross even under low cylinder gas pressure condition compared to convergent nozzle. Thus the consumption of flow quantity of assist gas can be reduced, when the same height of dross is desired. Moreover, it was pointed out that the convexed inner wall of nozzle leads to the reduction of dross generation and unstable region.

DOI： 10.2493/jspe.70.433

CiNii Article

CiNii Books

J-GLOBAL

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Publishing type：Part of collection (book)   Publisher：Springer Nature Switzerland  

DOI： 10.1007/978-3-031-73906-4_5

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Authorship：Last author,　Corresponding author   Language：Japanese   Publishing type：Research paper (international conference proceedings)  

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jmapro.2023.10.039

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：(一社)日本鋼構造協会  

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Laser Institute of America  

This study investigated the effects of laser beam intensity distribution on the reduction of dross height in fiber laser cutting of a steel plate with 3.2 mm thickness. A twin-spot beam was produced by splitting a single Gaussian beam into two beams using a special axicon lens, and these beams were set in the scanning direction for cutting experiments. The power ratio of two beams (R:F = Rear power:Front power) was varied to discuss the intensity balance for the effective reduction of dross. After cutting experiments, ray tracing analysis was conducted using an optical analysis to calculate the absorbed power density distributions in the kerf. A smaller dross height of 18 μm can be achieved at a power ratio of R:F = 8:2, and its value is lower than that by a single Gaussian beam. At a power ratio of R:F = 8:2, the front beam of lower power is irradiated at the upper part of the workpiece, and the rear beam of higher power is absorbed at the lower part of the workpiece. Thus, effective heat input to the lower part of the workpiece can contribute to a reduction of the dross height. Variation of power ratio in the rear and the front beams is effective in controlling the cutting front shape, and the uniformity of absorbed power in the thickness direction can be improved by setting the rear beam of about four times higher power to the front beam of lower power to obtain a smaller dross height in the case of a 3.2 mm steel plate.

DOI： 10.2351/7.0001097

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Laser Institute of America  

In order to achieve sustainable development goals, decarbonization and low-carbonization are required. Electric and hybrid vehicles are indispensable for the conservation of natural environment, and the lightweight construction and the effective transfer of electricity become important. Thus, copper and aluminum have been increasingly recognized as important materials because of their excellent materials’ properties. However, in the welding of these materials, it is difficult to obtain strong joints because there are problems in the brittle intermetallic compounds and the welding defects due to different melting points between copper and aluminum. Especially in the joining of copper and aluminum by copper side irradiation, aluminum-rich intermetallic compounds (IMCs) of brittle state result in the decrease of mechanical strength. Therefore, mild heat input from copper to aluminum would be necessary to reduce the brittle IMC. Angled irradiation might result in the mild energy input to aluminum because it can be expected that aluminum would be heated by the reflected light inside the keyhole generated in copper according to its high light reflection. In addition, stable welding can be expected by the superposed irradiation of blue and near-infrared lasers because of high light absorption rate of blue laser to copper. The angled and the superposed irradiation could achieve a stable welding state, and the generation of aluminum-rich IMC becomes smaller. Angled irradiation of a near-infrared laser showed equivalent joining strength to the superposed irradiation of two wavelengths, and the combination of angled and superposed irradiation achieved a remarkable increase of joining strength in a cross tensile test by 80%.

DOI： 10.2351/7.0001096

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Titanium alloy Ti6Al4V has been widely applied to medical, automotive, and aerospace industries due to its excellent properties such as high strength and excellent corrosion resistance. On the other hand, additive manufacturing (AM) technology can give the freedom of design of the products. In order to spread the AMed products, the joining of AMed and wrought products are required, and it is important to understand the joint characteristics. In this study, butt welding of Ti6Al4V plate was conducted by fiber laser in argon shielding, and the joint characteristics of laser weld wrought/wrought, AMed/AMed, and AMed/wrought Ti6Al4V plates were experimentally investigated. The AMed plate has higher tensile strength than wrought plate but the elongation of AMed plate is smaller, since AMed plate has α’ martensite due to rapid cooling during laser irradiation in AM process. Then, the laser weld joint of AMed/AMed plates has higher tensile strength, but smaller elongation than that of wrought/wrought plates. The weld joint of AMed/wrought plates shows good welding state, since small heat input leads to formation of small weld bead with higher hardness between wrought and AMed plates.

DOI： 10.1007/s40194-023-01533-3

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Other Link： https://link.springer.com/article/10.1007/s40194-023-01533-3/fulltext.html

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jmatprotec.2023.117866

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2351/7.0000740

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

The flat plane of small surface roughness below 0.1 µm average roughness could be obtained for monocrystalline diamond by nanosecond pulsed laser irradiation of 1060 nm and post-process of acid cleaning, at the laser fluence around the threshold value of material removal. The glossy and flat plane at the bottom of micro-groove was parallel to the top surface of specimen, although the round beam of Gaussian-mode was irradiated in the direction perpendicular to the top surface of specimen. The square beam of top-hat mode could obtain shallower micro-groove with wide flat bottom in comparison with the round beam of Gaussian mode, and then the creation method of flat plane with small surface roughness was discussed in the arrangement strategy of linear micro-grooving by the square beam of top-hat mode. Normal side-by-side repetition of linear micro-grooving could not create the flat plane of a constant depth. Therefore, two-step scanning method was proposed in order to overcome the problem in the normal side-by-side repetition of liner micro-grooving. Non-removal areas were partly retained between the processing lines in the first step, and the laser scanning was conducted on the retained area in the second step. Newly proposed two-step scanning method was practical and useful to create a wide flat plane with small surface roughness, and the controllability of micro-groove depth could be improved by the two-step scanning method. This proposed method can reduce the surface roughness in addition to the shape creation of monocrystalline diamond, and it can be used as the high-quality micro-shape fabrication method of monocrystalline diamond.

DOI： 10.1088/2631-7990/ac5a6a

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Other Link： https://iopscience.iop.org/article/10.1088/2631-7990/ac5a6a/pdf

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>The feasibility of joining laser metal deposited Ti6Al4V sheets using laser beam welding was investigated in this article. The additive manufactured sheets were joined using a 3 kW CW YLS-2000-TR ytterbium laser system. The mechanical properties and microstructure of the welded additive manufactured parts (AM welds) were compared with those of the wrought sheets welded using the same laser process. The welds were characterized and compared in terms of bead geometry, microhardness, tensile strength, fractography, and microstructure. The differences in characteristics are majorly found in the width of the bead and tensile strength. The bead width of AM welds appear wider than the wrought welds, and the wrought welds exhibited higher tensile strength and ductility than the AM welds.

DOI： 10.1038/s41598-022-08122-2

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Other Link： https://www.nature.com/articles/s41598-022-08122-2

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2526/ijem.27.35

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Laser Processing Society  

DOI： 10.2961/jlmn.2008.02.0007

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/mawe.202000314

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/mawe.202000314

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Titanium and its alloys, particularly Ti6Al4V, which is widely utilized in the marine and aerospace industries, have played a vital role in different manufacturing industries. An efficient and cost-effective way of joining this metal is by laser welding. The effect of laser power and welding speed on the tensile, microhardness, and microstructure of Ti6Al4V alloy is investigated in this paper. Results show that the microhardness is highest at the fusion zone and reduces towards the base metal. The microstructure at the fusion zone shows a transformed needle-like lamellar α phase, with a martensitic α’ phase observed within the heat affected zone. Results of tensile tests show an improved tensile strength compared to the base metal.

DOI： 10.3390/jcs5090246

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Laser Institute of America  

DOI： 10.2351/7.0000470

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.cirp.2021.04.063

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2584895

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： https://doi.org/10.1117/12.2584895

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Electrical Machining Engineers  

DOI： 10.2526/ijem.26.54

J-GLOBAL

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Laser Institute of America  

DOI： 10.2351/7.0000300

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Laser micro-grooving has excellent potential to improve the surface properties of metals. In this study, high-speed micro-grooving of the surfaces of mild steel SS400 and aluminum alloy A1050 was investigated using a single-mode continuous-wave fiber laser with an average power of 200 W. Experiments were conducted at laser beam scanning speeds of 1 to 6 m/s. The incident angle of the laser beam in the plane perpendicular to the scanning axis was varied from 0 to 60°. A relatively deep groove (approximately 30 µm in depth) and a high upheaval (10 µm in height) were formed along the scanning line at an incident angle of 45° on the SS400, whereas only shallow grooves were formed on A1050. The micro-groove formation mechanism was discussed on the basis of high-speed camera observation, groove shapes, and the thermophysical properties of the metal. Asymmetric molten metal flow and solidification around the keyhole are thought to play important roles in micro-groove formation. Although the laser irradiation conditions must be optimized according to the thermophysical properties of the material, angled laser irradiation has the potential to effectively form micro-grooves.

DOI： 10.3390/app10238333

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier BV  

High energy density of electron beam (EB) with diameter of about 60 mm is obtained in a large-area EB irradiation method. This method can be used for melting and evaporating material surface instantly, and highly efficient surface finishing of metals such as mold steels and biomaterials is possible. Furthermore, surface functions such as corrosion resistance, water repellency and wear resistance can be improved since a thin modified layer with fine microstructure is formed on the EB irradiated surface. It is expected that thick modified layer is effective to maintain their surface functions for long-term. However, the material surface is slightly removed in formation of modified layer. Therefore, control and prediction of removal and modified layer thickness are important in order to obtain appropriate modified layer thickness and to keep the shape accuracy for metals with different thermal properties. In order to predict the removal and modified layer thickness, it is necessary to clarify the temperature distribution in depth direction and its time variation in large-area EB irradiation. In this study, changes of removal and modified layer thickness on metal workpiece with different thermal conductivity are investigated by calculation of temperature distribution in large-area EB irradiation. It is made clear that the modified layer thickness of workpiece with low thermal conductivity is larger than that with high one, while the removal layer thickness is almost the same regardless of thermal conductivity. Furthermore, analytical removal and modified layer thickness obtained by our unsteady heat conduction analysis agree well with the experimental ones. Therefore, our unsteady heat conduction analysis model has high accuracy, and it is possible to predict variations of removal and modified layer thickness on workpiece with different thermal conductivity.

DOI： 10.1016/j.procir.2020.02.280

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier BV  

DOI： 10.1016/j.procir.2020.02.283

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/icesi.2019.8863016

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/icesi.2019.8863018

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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DOI： 10.3390/app9071412

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Electrical Machining Engineers  

DOI： 10.2526/ijem.24.21

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/jamdsm.2018jamdsm0100

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1016/j.procir.2017.12.031

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Electrical Machining Engineers  

DOI： 10.2526/ijem.23.38

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Society of Mechanical Engineers  

Silver nanowire transparent conductive film is expected as a new material for transparent electrodes because of its superior flexibility and electrical conductivity with high transparency at visible wavelength. Laser beam processing has been widely used for these application, and laser beam has the unique characteristic as an electromagnetic wave. Its feature has a great influence on laser-material interaction. However, these mechanism have not yet been clarified. Therefore, the polarization characteristics indicated by electric and magnetic fields were discussed, and effects of polarization direction on removal characteristics of silver nanowire transparent conductive film were investigated by using femtosecond pulsed laser with linear polarization.

DOI： 10.1299/jsmelem.2017.9.007

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Society of Mechanical Engineers  

In nanosecond pulsed laser processing, laser beam irradiation normally induces plasma generation, which leads to the reduction of laser energy absorbed into a specimen. Therefore, material removal characteristics are strongly affected by phenomenon of laser induced plasma. Plasma generation is affected by pulse duration and laser intensity, but influence of plasma generation on material removal characteristics has not yet been clarified sufficiently. In this study, influence of pulse duration and laser intensity on plasma was investigated by measurements of transmittance of laser energy through the plasma. Finally, effective energy to material removal characteristics was discussed with calculated laser energy relating to removal volume of mild steel.

DOI： 10.1299/jsmelem.2017.9.026

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Society of Mechanical Engineers  

Pure titanium (Ti) and Ti alloys have been widely used as biomaterials. However, they have the disadvantage of lacking for bioactivity. Thus, adding a new function to Ti and Ti alloys is required. One method for adding new functions is controlled cell spreading by formation of periodic surface nanostructures on the biomaterials. In this study, the nanostructures were formed on the pure Ti by ultrashort pulsed laser irradiation, and influence of laser parameters on surface profile and discontinuity of the nanostructures was discussed. Moreover, influence of the shape variation of the nanostructures on control of cell spreading was investigated.

DOI： 10.1299/jsmelem.2017.9.014

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Electrical Machining Engineers  

<p> A multi-layered artificial skin, which is mainly consisted of three layers of silicone elastomer, printed paper, and resin plate, is expected as sealing material of facial defects. However, sweating phenomenon from the surface of missing parts results in insanitary conditions to the skin surface, and micro-drilled holes are required to improve the breathability of the multi-layered artificial skin as human's sweat glands. High-efficiency processing is expected by using a high pulse repetition-rate laser. Although ultra-short pulsed laser is used, a continuous long time laser irradiation deteriorated the aesthetic quality of multi-layered artificial skin because of heat accumulation corresponding to the high pulse-repetition-rate. Therefore, laser irradiation method with the high-efficiency and good-aesthetic-quality was experimentally investigated by using picosecond pulsed laser of 1064 nm wavelength. The laser irradiation method, which can reduce the heat affected zone at the adhesion part between the print paper and the silicone elastomer, was effective in order to improve the esthetic quality of drilled hole for the multi-layered artificial skin. The discoloration area around drilled hole on multilayered artificial skin could be reduced by dividing method of laser shot number at the same irradiation point to provide non-irradiation time. A long non-irradiation time resulted in the reduction of discoloration area around drilled hole on multi-layered artificial skin under the similar heat input condition.</p>

DOI： 10.2526/ijem.22.8

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

In wire EDM (electrical discharge machining) process, it is important to smoothly exclude debris and bubbles generated in the working gap for keeping stable performance. Much debris stagnation in the gap would cause frequent occurrence of discharge concentration and secondary discharge, which results in unstable machining performance, such as frequent wire breakage, low removal rate, and low shape accuracy. Therefore, a jet flushing of working fluid using upper and lower jet nozzles has been conventionally applied for excluding the debris and bubbles from the machined kerf. Nevertheless, it is well known that the wire often breaks when the machined kerf length is a few mm from the start hole in 1st-cut wire EDM. The influence of machined kerf length on the flow field, the debris exclusion, and the wire behavior caused with hydrodynamic force by the jet flushing should be made clear. In this study, variations of flow field in the kerf, the debris accumulation state and the wire deflection caused jet flushing with machined length were analytically investigated by CFD (computational fluid dynamics) and structural analysis when 1st-cut wire EDM was done from a small start hole. Moreover, the effects of machined kerf length on the wire deflection and wire breakage were discussed. Wire breakage frequency experiments showed that wire tended to frequently break at a certain machined kerf length, where the wire deflection rapidly increased and the debris residence time in the gap became long.

DOI： 10.4028/www.scientific.net/KEM.749.130

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The characteristics of the molten area are attributed not only by laser energy condition but also the focusing condition. In this study, a picosecond pulsed laser of 1064 nm in wavelength and 12.5 ps in pulse duration was used as a laser source for joining glass material. Influence of focusing condition on micro-welding of glasses was experimentally investigated by using an objective lens with and without spherical aberration correction, and its molten area was characterized. The usage of objective lens with spherical aberration correction led to a larger molten area inside the bulk material of glass even under the same pulse energy, which related to the efficient micro-welding of glass materials. In addition, an optical system with the spherical aberration correction led to a stable absorption of laser energy inside the bulk glass material, stabilizing the shape of molten area, which resulted in the reliable weld joint. On the other hand, breaking strength of the specimens with spherical aberration correction was higher than that without spherical aberration correction. Therefore, it is concluded that the focusing condition with spherical aberration correction led to the larger and stable molten area, which resulted in higher joining strength in micro-welding of glass materials.

DOI： 10.1007/s00339-016-0026-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IGI Global  

In the present study, a three-dimensional finite element model has been developed to simulate the temperature, stress and deformation fields in continuous wave (CW) laser micro-welding of thin stainless steel sheet. The welding deformation was experimentally evaluated using a single-mode fiber laser with a high-speed scanning system. Application of developed thermal model demonstrated that the laser parameters, such as laser power, scanning velocity and spot diameter have a significant effect on temperature field and the weld pool. In the case of welding deformation, numerical simulation was carried out by an uncoupled thermo-mechanical model. The welding stress and deformation are generated by plastic deformation during the heating and cooling periods. It was confirmed that the residual stress is higher than yield strength and has strongest effect upon the welding deformation. The numerical simulated results have proved that the developed finite element model is effective to predict thermal histories, thermally induced stresses and welding deformations in the thin material.

DOI： 10.4018/IJMMME.2016040104

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Micro-welding characteristics of silicon and glass by pulsed lasers are described. In this study, four types of laser beam, which are nanosecond pulsed laser and picosecond pulsed laser of 532 and 1064 nm in wavelength, were used for joining monocrystalline silicon and glass. Influence of wavelength and pulse duration on micro-welding of monocrystalline silicon and glass was experimentally investigated under the same spot diameter, and the molten area of monocrystalline silicon and glass was characterized. Finally, the breaking strength was evaluated for the overlap weld joint with different pulse duration and wavelength. A splash area of molten silicon around the weld bead line was obvious in the nanosecond pulsed laser. On the other hand, there was no remarkable molten splash around the weld bead line in the picosecond pulsed laser. Breaking strength of specimens with 1064 nm wavelength was higher than with 532 nm wavelength in nanosecond laser, whereas breaking strength of laser-irradiated specimen by picosecond pulse duration was higher than that by nanosecond pulse duration. It is concluded that the combination of picosecond pulse duration and infrared wavelength leads to the stable molten area appearance of the weld bead and higher breaking strength in microwelding of glass and monocrystalline silicon.

DOI： 10.1007/s00339-016-9849-5

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Language：Japanese   Publisher：The Japan Society for Precision Engineering  

DOI： 10.11522/pscjspe.2016S.0_835

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Processing characteristics of transparent conductive film containing silver nanowires by ns pulsed fiber lasers with various pulse duration were experimentally investigated in the view-points of insulating state and surface quality. The laser fluence achieving the insulation state became smaller with decreasing the pulse duration. Appearance of removed trace area of silver nanowires was varied by the pulse duration, and the removal area ratio of removed trace area to the whole one was evaluated to discuss the surface quality. Small removal area ratio and good insulation state could be performed at a wide processing window at long pulse duration of 200ns. (C) 2016 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.procir.2016.02.189

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Effective shielding method for a wide area is required in the vertical-position remote laser welding of pure titanium. Therefore, shielding effects of ring-type nozzles with two layers for a wide area were numerically and experimentally investigated in the vertical-position setup of workpiece with argon gas. Prevention of incoming air flow outside a ring-type nozzle is effective to increase mass fraction of argon gas. Mass fraction of argon gas could be increased using a ring-type nozzle, in which shielding gas is supplied by open-side injection ports of proper angle at a proper flow ratio of two jetting layers. (C) 2016 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.procir.2016.02.230

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Surface finishing technology by EDM has recently progressed, and very small surface roughness can be readily obtained by controlling the electrical discharge conditions, or by using metal powder mixed working fluids. In addition, it was reported that EDMed surface using metal powder mixed fluids sometimes has high surface functions, such as high hardness, high corrosion resistance and so on. Therefore, the high functional EDM finished surface is well expected to be applied as a final metal mold surface. In this study, formation of chromium containing layer on the EDMed surface was tried by using chromium powder mixed fluid. Furthermore, the EDMed surface characteristics with chromium powder mixed fluid were experimentally evaluated. (C) 2016 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.procir.2016.02.277

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

In this study, the movements of thin tungsten wire electrode during fine wire EDM were investigated by direct observation using a high-speed camera. The results showed that the amplitude in the direction parallel to the machining direction was a little larger than that in the perpendicular one. Also, the backward wire deflection could be confirmed even in fine wire EDM. Furthermore, the wire vibration mode was found out by frequency analysis and the vibration amplitude could be reduced by adjusting the workpiece position to the 3rd order node of the vibration. In addition, the amplitude envelope of wire electrode during the process was clarified. (C) 2016 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.procir.2016.02.266

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Pure Titanium (Ti) and Ti alloys are the most used biomaterials. However, they have problem for bioactivity because metals have no biofunction. Therefore, adding new function to Ti and Ti alloys are necessary. One method to add new function is the creation of periodic structures on the biomaterial surfaces, which can control cell spreading. Femtosecond laser is one of the useful tools for creating periodic nanostructures, which can be created on metals and semiconductors by self-organizing in the laser focusing spot. In our previous study, the nanostructures could be formed on the Ti plate by using the femtosecond laser with fundamental wavelength of 775 nm. The periodicities of the nanostructures on the Ti plate was approximately 590 nm, which was shorter than the laser wavelength. Cells tests indicated that cell spreading clearly occurs along the grooves of the nanostructures. However, the influence of the periods of the nanostructure on cell spreading has not yet been investigated. It is expected that the periods can be varied by changing laser parameters, such as pulse widths, laser wavelengths, laser fluences, and number of shots. In this study, the periodic nanostructures are created on the Ti plate surface by using the femtosecond laser with fundamental wavelength of 790 nm. Then, influence of the pulse width and number of shots on the periods is investigated. In the experiments, laser beam is focused and scanned on the Ti plate surfaces. The laser irradiated areas are analysed by using a scanning electron microscope (SEM).

DOI： 10.1016/j.procir.2016.02.188

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Characteristics of the molten area in micro-welding of monocrystalline silicon and glass are described. In this study, 4 types of laser beam, which are nanosecond pulsed laser and picosecond pulsed laser of 532 nm and 1064 nm in wavelength were used for joining monocrystalline silicon and glass. Influence of wavelength and pulse duration on micro-welding of monocrystalline silicon and glass was experimentally investigated under the same spot diameter, and the molten area of monocrystalline silicon and glass was characterized. A splash area of molten silicon with 532 nm wavelength was wider than that with 1064 nm in a nanosecond pulse laser. However, its splash area of molten silicon with 1064 nm changed drastically at certain pulse energy of 11 mu J in a nanosecond pulse laser. On the other hand, 12.5 ps pulsed laser still kept a stable molten area appearance even at pulse energy of 11 mu J. A splash area of molten silicon around the weld bead line was obvious in the nanosecond pulsed laser. On the other hand, there was no remarkable molten splash around the weld bead line in the picosecond pulsed laser. It is concluded that the combination of picosecond pulse duration and infrared wavelength leads to a stable molten area appearance of the weld bead.

DOI： 10.1088/1757-899X/114/1/012039

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Electrical Machining Engineers  

A multi-layered artificial skin is mainly consisted of three layers of silicone elastomer, print paper, and resin plate. Sealing of facial defects with the multi-layered artificial skin causes perspired water from the surface of missing parts, which results in insanitary conditions to the skin surface. Therefore, the laser micro-drilling using nanosecond pulsed laser of 266 nm was investigated to provide the breathability for multi-layered artificial skin without human eye's recognition of drilled holes, which can satisfy both the breathability and aesthetic problems. The visibility of drilled hole was affected by the pitch distance of drilled holes, and its visibility decreased with increasing the pitch distance. A small color difference measured using a colorimeter led to the low visibility, and laser micro-drilling with small color difference is effective to obtain the breathable multi-layered artificial skin with low visibility of drilled holes, which can improve the breathability for the multi-layered artificial skin.

DOI： 10.2526/ijem.21.13

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Authorship：Corresponding author   Language：English   Publisher：The Japan Society of Mechanical Engineers  

Effects of edge intensity distribution in top-hat mode on removal characteristics of zinc oxide film was experimentally investigated by a nano-second pulsed fiber laser. The usage of mask could change the edge intensity distribution of laser beam. The combination of singlet lens and slit mask could perform the gradual edge and the sharp edge intensity distributions in parallel and perpendicular directions to a scanning line, respectively. This edge intensity combination could achieve high-quality removal with narrow damaged regions around the scribed grooves and reliable removal with stable electrical insulation states at more than a proper overlap rate.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Japan Society of Mechanical Engineers  

In this study, the controllability of multi-wire EDM slicing with the group power supplying method was investigated in order to apply this method regardless of workpiece resistance. In the case of monocrystalline silicon of 0.01Ω·cm, although peak current of electrical discharge pulse ideally changed with number of processing wire electrodes, kerf width, surface roughness and diameter of crater were approximately constant at almost constant cutting speed regardless of number of processing wire electrode. On the other hand, polycrystalline silicon of 2-3Ω·cm, resulted in ideal control of discharge current by applying sufficient no-load voltage, but its increasing ratio of no-load voltage must be larger than that of low resistance workpiece.

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The influence of the surrounding gas conditions on the surface integrity in the micro-drilling of silicon carbide was experimentally investigated using ns pulsed laser of 266 nm wavelength. Moreover, micro-machining characteristics were observed using high-speed shutter and video cameras in the micro-drilling of silicon carbide. The size and intensity of the laser-induced plasma were larger, and the plasma affected area was larger and deeper in argon than that in air. Although the intensity of the plasma was lower in helium than that in other gases, the surface around the drilled hole was roughened by the spread of the plasma in the vicinity of the drilled hole. Debris was removed along the flow field generated by laser shot in the opposite direction to the laser irradiation. The gas flow behavior and the spectrum and intensity of the laser-induced plasma were influenced by the surrounding gas type and pressure. The appearance of plasma generation affected the surface integrity at the circumference of the drilled hole, and the surface integrity was improved by reducing the pressure.

DOI： 10.1007/s00340-015-6060-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

A novel microwelding procedure to join Si-to-glass using ps-laser pulses with high repetition rates is presented. The procedure provides weld joint with mechanical strength as high as 85 MPa and 45 MPa in sample pairs of Si/aluminosilicate (Si/SW-Y) and Si/borosilicate (Si/Borofloat 33), respectively, which are higher than anodic bonding, at high spatial resolution (&lt; 20 mu m) and very high throughput without pre- and post-heating. Laser-matter interaction analysis indicates that excellent weld joint of Si/glass is obtained by avoiding violent evaporation of Si substrate using ps-laser pulses. Laser welded Si/glass samples can be singulated along the weld lines by standard blade dicer without defects, demonstrating welding by ps-laser pulses is applicable to wafer-level packaging. (C)2015 Optical Society of America

DOI： 10.1364/OE.23.003427

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Language：Japanese   Publisher：The Japan Society for Precision Engineering  

DOI： 10.11522/pscjspe.2015S.0_691

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DOI： 10.11522/pscjspe.2015S.0_689

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DOI： 10.11522/pscjspe.2015A.0_181

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DOI： 10.11522/pscjspe.2015A.0_185

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Language：Japanese   Publisher：The Japan Society for Precision Engineering  

In our previous studies, the possibility of thin ceramic film formation by using a large-area EB irradiation was shown. However, the film formation mechanism has not yet been clarified. In this report, the influences of magnetic and electrical conductivity of a jig supporting an alumina target tube on the film formation were investigated, and the spectrum of plasma generated on the substrate surface during the EB irradiation was measured in order to clarify the mechanism. As a result, it was made clear that the film was formed by sputtering target material with the plasma of workpiece material caused by EB Irradiation.

DOI： 10.11522/pscjspe.2015S.0_1077

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

It has been known that wavelength, power density, interaction time and material properties have great influence on processing characteristics in laser material processing, in which materials with higher reflectivity classify into difficult-to-weld materials. In electronic industry, aluminum alloy is widely used as structural components due to its high specific strength, and copper became an important material because of its excellent electrical conductivity. These materials have high reflectivity and high thermal conductivity, which results in instability of energy absorption and processing results. Therefore, welding defects might be noticed in the micro-joining of aluminum alloy and copper. In this paper, the smart laser micro-welding of difficult-to-weld materials such as aluminum alloy and copper were discussed. The combination of a pulsed Nd:YAG laser and a continuous diode laser could perform high-performance micro-welding of aluminum alloy. A pulsed Nd:YAG laser was absorbed effectively from the beginning of laser scanning by pre-heating Nd:YAG laser pulse with the superposition of continuous diode laser, and wide and deep weld bead could be obtained with better surface integrity. As for micro-welding of copper material, stable absorption state could be achieved using a pulsed green Nd:YAG laser, since its absorptivity showed almost constant values with change of power density. A longer pulse duration was effective to achieve not only high absorptivity but also low deviation of absorptivity. The pulse waveform with maximum peak at the early period and a long pulse duration led to stabilizing the penetration depth with less porosity.

DOI： 10.1117/12.2076232

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

In a large-area electron beam (EB) irradiation method developed recently, high energy EB can be obtained without focusing the beam, and large-area EB with almost uniform energy density distribution of 60mm in diameter can be used for instantly melting and evaporating metal surface. Then, the surface smoothing and surface modification of metal molds made of steel, cemented carbide and ceramics can be performed efficiently. When the large-area EB is irradiated to a sharp edge, the material removal remarkably progresses at the edge due to the heat accumulation and EB concentration there, which leads to the edge rounding. Our previous study clarified that micro-deburring was also possible by using this phenomenon. Moreover, this method would be effective for removal of discontinuous micro burrs generated by thermal machining processes, such as EDM and laser cutting. In this study, the possibility to completely remove micro burrs generated in EDM was experimentally investigated. The difference in micro-deburring characteristics with the type of workpiece material was also investigated. As a result, the EDM micro burrs with a height of about up to 50μm could be completely removed by this method. Furthermore, it was made clear that the magnetic property of workpiece materials greatly influenced the deburring characteristics, and the thermal property such as melting point and thermal conductivity also did.

DOI： 10.4028/www.scientific.net/KEM.656-657.369

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Electrical Machining Engineers  

Debris exclusion from the wire EDM gap has been conventionally done by jet flushing using nozzles but the debris stagnation area always presents near the wire with the conventional method. In this study, a new flushing method using tilting nozzle to wire running direction to reduce the debris stagnation in the kerf was proposed on the base of simulation results by computational fluid dynamics (CFD) analysis. The simulations and experiments clarified that the tilting jet flushing nozzle could decrease the debris stagnation area in the kerf and leads to smoother debris exclusion, resulting in higher removal rate. Furthermore, the wire deflection caused by hydrodynamic force due to the jet flushing was calculated by a structural analysis using the distributions of pressure acting on the wire surface by jet flushing flow obtained by the CFD analysis.

DOI： 10.2526/ijem.20.3

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Electrical Machining Engineers  

In this study, the thermal deformation of thin stainless steel sheet was investigated in bead-on-plate welding by using a single-mode fiber laser with Galvano scanning system. The numerical simulation was carried out to calculate temperature and stress fields, and its deformation characteristics were discussed. It was suggested that a specimen firstly deformed downward in the same direction of laser irradiation, and then deformed in the reversed direction after laser scanning. The final distortion angle in the negative direction, which is concave shape from the view direction of laser irradiation, was generated under the heat conduction and quasi-penetration welding mode, and the positive angle was obtained as the final distortion angle under the full-penetration welding mode. On the other hand, a small distortion could be achieved by the proper weld bead geometry in micro-welding of thin sheet, but the welding mode of minimum distortion conditions varied with specimen thickness. However, these relationships obtaining a small distortion could be understood by the relationship between aspect ratio of weld bead and distortion angle. Minimum angle of distortion could be achieved around maximum aspect ratio of weld bead regardless of specimen thickness and spot diameter, when an inflection point appeared in relationship between aspect ratio of weld bead geometry and distortion angle.

DOI： 10.2526/ijem.20.9

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Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Precision Engineering  

Removal characteristics of zinc oxide film used as a transparent conductive oxide were experimentally investigated using a square fiber and nano-second pulsed laser. Effects of the intensity distribution of the laser beam on removal phenomena were discussed with a combination of an achromatic lens and a single lens. An achromatic lens achieved better groove shapes with a narrow damaged region, but the electrical insulation state was unstable, in which scribed groove could not achieve insulation state even at a higher overlap rate around 80%. High-speed observation revealed a possibility of zinc oxide film remaining on the glass substrate, since dominant removal of zinc oxide film progressed uniformly inside the spot area in thickness direction of film. On the other hand, a single lens resulted in a wide damaged region, but the electric insulation was obtained stably at more than a certain overlap rate. Because zinc oxide film was removed from center to outer side inside the laser spot with pushing material in width direction, and zinc oxide film was almost completely removed at the center area of laser spot. Therefore, the combination of a singlet lens and a slit mask was proposed to attempt different intensity distribution in parallel and perpendicular direction to scanning line. This optical setup could achieve both stable electric insulation state and better groove shapes with a narrow damaged region at more than overlap rate of 60%.

DOI： 10.2493/jjspe.81.1033

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

High flow rate in nozzle jet flushing is effective for smooth debris exclusion from the wire EDM gap, but this leads to large wire deflection and vibration, resulting in the wire breakage and low shape accuracy. In this paper, the influence of nozzle jet flushing on wire breakage was experimentally investigated with varying the machined kerf length and machining conditions. Furthermore, the flow fields and debris residence time in the kerf, hydrodynamic stress distributions acting on the wire, and wire deflections were numerically analyzed. Based on the analyzed results, the causes of wire breakage were discussed. (C) 2015 CIRP.

DOI： 10.1016/j.cirp.2015.04.034

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

Glass materials are widely used in products such as optical components and semiconductor devices. In these products, precision welding techniques of glass are required to manufacture small and complicated shape. The laser welding method can perform the joining without an intermediate layer and an adhesive agent. In addition, an ultra-short pulse laser can reduce the heat affected zone with the high space accuracy. However, heating and cooling cycles are repeated even in the case of ultra-short pulsed laser. The temperature distribution and change of molten area are influenced not only by laser energy condition but also focusing condition. Therefore in this study, effects of focusing condition of laser beam on micro-welding characteristics of glass were experimentally investigated by using a picosecond pulsed laser. A usage of object lens with the spherical aberration correction led to a large molten area even at the same pulse energy, which related to the efficient welding of glass materials. An optical system with the spherical aberration correction led to stabilizing the shape of molten area, which resulted in the reliable weld joint.

DOI： 10.4028/www.scientific.net/KEM.656-657.461

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

EDM finishing techn ology has progressed recently, and very small surface roughness can be obtained by controlling the electrical discharge conditions. Also, EDM using powder mixed fluids can improve the surface characteristics. Therefore, the EDM finished surface is highly expected to be applied as a final metal mold surface. In that case, the characteristics of EDMed surface affects the molding performance and the life of metal molds. As a new surface finishing method by EDM, the characteristics of EDMed surface using a nickel powder mixed fluid was experimentally discussed in this study, since nickel coatings have been widely applied to improve the corrosion resistance and the mold releasability of metal molds. Experimental analysis clarified that the resolidified layer containing nickel content could be formed on the surface by EDM in nickel powder mixed fluid. Also, the water repellency and the releasability of molded resin from the EDM finished surface could be improved.

DOI： 10.4028/www.scientific.net/KEM.656-657.375

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

This paper describes the applicability of large-area EB irradiation method to a new surface modification for metal molds. The previous papers clarified that the surface roughness on wide area uniformly decreased to less than 1 mu m Rz in a few minutes by the large-area EB irradiation. Therefore, the large-area EB irradiation method has high practicability as an efficient surface finishing process for metal molds, and then the EB irradiation equipment has already been introduced into the market for practical use. In this method called EB polishing, the surface material melts and a very thin resolidified layer is formed on the surface. In this paper, the surface structure of EB polished metal mold steel SKD11 was first observed by TEM, and also component analysis was carried out by EDX. Then it was found out that the crystal grain size became small and chromium carbide is uniformly rearranged in the layer. Next, using heat conduction analysis model considering the electron penetration on the surface, the temperature distribution was calculated. The results showed that the surface temperature rapidly raised over its melting point until the end of EB irradiation, and cooled down rapidly. As the important practical surface characteristics for long life of metal mold, resistance to corrosion, water repellency, and the releasability of molded resin from metal mold surface were evaluated. The corrosion resistance and the water repellency could be improved by EB polishing, since the surface structure changes and Cr content distributed uniformly on the surface. Also, the releasability of molded resin from the surface became better. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmatprotec.2014.02.028

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER LONDON LTD  

In compression or injection molding of rubber products, small pieces of residual rubber often remain on the metal mold surface after releasing the product. This is caused by excessive localized adhesion to the mold surface. Therefore, cleaning of metal mold surface must be often performed, which results in longer molding cycle time, and the lifetime of metal mold is often reduced. In this study, the separation forces between molded rubber and metal mold surfaces are measured with a tensile tester to evaluate the releasability of molded rubber from the metal mold surface. Mold surfaces treated by various surface coatings and surface modification methods including EB polishing were tested and compared. Experimental results show that the separation force between molded rubber and metal mold surfaces depends on the true contact area between them and the chemical composition of the metal mold surface. The separation force decreases with a decrease in contact area. The chromium content at the metal mold surface significantly reduces the separation force. EB polishing is one of the most effective surface treatments for metal molds since the real contact area can be decreased while also decreasing the surface roughness of the tool surface in a short time. Electron beam melting is also shown to be an effective method of distributing chromium uniformly on the metal mold surface.

DOI： 10.1007/s00170-013-5415-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Internal modification process of glass by ultrashort laser pulse (USLP) and its applications to microwelding of glass are presented. A simulation model is developed, which can determine intensity distribution of absorbed laser energy, nonlinear absorptivity and temperature distribution at different pulse repetition rates and pulse energies in internal modification of bulk glass with fs- and ps-laser pulses from experimental modified structure. The formation process of the dual-structured internal modification is clarified, which consists of a teardrop-shaped inner structure and an elliptical outer structure, corresponding to the laser-absorbing region and heat-affected molten region, respectively. Nonlinear absorptivity at high pulse repetition rates increases due to the increase in the thermally excited free electron density for avalanche ionization. USLP enables crack-free welding of glass because the shrinkage stress is suppressed by producing embedded molten pool by nonlinear absorption process, in contrast to conventional continuous wave laser welding where cracks cannot be avoided due to shrinkage stress produced in cooling process. Microwelding techniques of glass by USLP have been developed to join glass/glass and Si/glass using optically contacted sample pairs. The strength of the weld joint as high as that of base material is obtained without pre- and post-heating in glass/glass welding. In Si/glass welding, excellent joint performances competitive with anodic bonding in terms of joint strength and process throughput have been attained.

DOI： 10.1007/s00339-013-8115-3

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Dynamic behavior of plasma in internal modification of glass using fs-laser pulses with high pulse repetition rates up to 1MHz is observed using high-speed video camera at 50,000 frames per second. High-speed pictures reveal striking fact that the localized plasma is produced with size much smaller than reported in literatures before, and changes its location, size, shape and brightness periodically at repetition rates of the order of kHz. The mechanism responsible for producing localized plasma and its long-term periodic motion is presented based on the analysis of free -electron density based on rate equation. (C) 2014 Published by Elsevier B.V.

DOI： 10.1016/j.phpro.2014.08.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Electrical Machining Engineers  

In a large-area electron beam (EB) irradiation method developed recently, high energy EB can be obtained without focusing the beam. Therefore, the large-area EB of 60mm in diameter with almost uniform energy distribution can be used for instant melting and evaporating of metal surface. The previous studies clarified that the surface smoothing of metal mold made of steel, cemented carbide and ceramics could be performed efficiently. Also this method can be applied to the surface finishing of biomaterials, such as stainless steel and titanium alloy. In this method, the sharp edge is possibly rounded to about half hundred microns in radius under relatively high energy density conditions, since the material removal remarkably progresses there due to the electron concentration and heat accumulation at the edge. In this study, the possibility of micro-deburring was investigated by using the preferential edge removal effect in the large-area EB irradiation. Experimental results showed that the micro-deburring was possible by large-area EB irradiation, and the burr height decreased with increasing energy density of EB and number of irradiation. The burr of about 50μm in height generated in EDM process could be removed completely. Furthermore, micro-burrs at the edge of several small holes within the wide area of 60mm in diameter could be removed simultaneously.

DOI： 10.2526/ijem.19.22

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Electrical Machining Engineers  

A laser singulation method by the superposition of a pulsed fiber laser and an SHG:YAG laser (SHG: Second Harmonic Generation) was proposed to perform the high-quality processing of semiconductor packages, which are consisted of thermosetting epoxy-resin with silica as the molding compounds and a glass epoxy board with insulator coatings for the semiconductor package. The superposition of the pulsed fiber laser and SHG:YAG laser with a high pulse repetition rate led to a straighter kerf shape with a smaller kerf width under the same pulse energy condition. A smaller kerf width was achieved by controlling the time-delay between the laser pulses compared with synchronized laser pulses. The heat affected zone from the cut surface was reduced by the superposition of the pulsed fiber laser and SHG:YAG laser. Moreover, synchronized laser pulses led to a smaller heat affected zone compared with unsynchronized pulses.

DOI： 10.2526/ijem.19.28

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Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Precision Engineering  

In micro-welding of aluminum alloy, its low melting point and high thermal conductivity make it difficult to obtain the large penetration depth with the good surface integrity. In order to perform the stable key-hole welding with little defects, it is important to understand the processing phenomenon near the boundary between heat conduction and key-hole type welding. Therefore, the boundary condition of key-hole generation in micro-welding of aluminum alloy was experimentally and numerically investigated with hybrid Nd:YAG laser system, in which a continuous diode laser (LD) of 808nm in wavelength was superposed in a pulsed Nd:YAG laser of 1064nm in wavelength. It became clear that the keyhole generation became stable when the continuous LD was superposed with pulsed Nd:YAG laser, and the shorter pulse interval time and higher continuous LD power led to the generation of the key-hole. The results of numerical analysis made it clear that the superposition of continuous diode laser is effective to stabilize the key-hole generation in micro-welding of aluminum alloy by pulsed Nd:YAG laser, since the continuous diode laser could keep the temperature near the boundary condition of key-hole generation appeared at the time when the temperature of welded bead was around the boiling point.

DOI： 10.2493/jjspe.80.419

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In order to reduce the debris stagnation in the kerf in wire electrical discharge machining (EDM), a new jet flushing method using tilting nozzle to wire running direction is investigated, based on the simulation results of flow field obtained by computational fluid dynamics (CFD) analysis. As a result, the tilting nozzle could decrease the debris stagnation area, and the removal rate could be improved.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society for Precision Engineering, ASPE  

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：The Japan Society of Mechanical Engineers  

Micro-drilling characteristics of SiC by harmonics of Nd:YAG laser were experimentally investigated in the viewpoints of wavelength and the surrounding gas type condition. Moreover, plasma and processing behavior were observed to discuss micro-drilling characteristics of SiC. The debris was removed away in the opposite direction of laser beam along the flow field generated by laser irradiation. The behavior, the spectrum and the intensity of laser induced plasma were influenced by the surrounding gas condition. The appearance of plasma affected the surface integrity at the circumference of drilled hole, and the surface integrity could be improved under the reduced pressure condition.

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：The Japan Society of Mechanical Engineers  

In laser cutting and drilling process, molten material was scattered as spatters, which deteriorate the surface integrity of workpiece due to the thermal damage. It is expected that the control of assist gas flow can reduce the adhesion of spatter. In order to investigate the improvement method of thermal damage due to the adhesion of spatter, it is required to clarify characteristics of spatters. Therefore, the collection and the analyzing method of spatters with high-speed video cameras in the laser micro-drilling were developed, and characteristics of spatter movement were numerically investigated by CFD analysis.

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Laser Processing Society  

DOI： 10.2961/jlmn.2013.01.0018

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

The sputter deposition of ceramic film on metal mold steel surface by large-area electron beam (EB) irradiation was discussed. The large-area EB has high energy density enough to generate plasma above the workpiece surface during the surface smoothing process, which causes the sputtering of target material set near the workpiece surface. The sputter deposition of target material with simultaneous surface melting and resolidification of workpiece surface by large-area EB would improve the adhesion between the deposited film and the workpiece. Short ceramic tube made of alumina or zirconia as a target was put on the substrate surface of steel, and large-area EB was irradiated to the surface. The workpiece surface component and structure after the irradiation were investigated using EDX and XRD analysis, in order to discuss the possibility of large-area EB irradiation as a new coating method. (C) 2013 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.procir.2013.03.053

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High efficient and precise slicing method is required for the slicing of silicon carbide ingot. The newly developed multi-wire electrical discharge slicing method would decrease the kerf width and the cracks generated on machined surface. However, much higher wire tension is required in order to reduce wire vibration and to perform a smaller kerf width. Thin wire electrode with round section does not have enough cross sectional area under the high wire tension condition. Therefore, a wire electrode with track-shaped section was proposed and applied to the wire EDM slicing of silicon carbide ingot. The running control of wire electrode with track-shaped section was experimentally investigated. The side support method with fixture plates could decrease the kerf width by brass coated steel wire electrode with track-shaped section. The parallel drawing type traverser and the short distance setting points of side support fixture plates could perform the smaller vibration of wire electrode with track-shaped section and the decrease of kerf width. (C) 2013 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.procir.2013.03.052

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Laser microwelding has been an essential tool with a reputation of rapidity and precision for joining miniaturized metal parts. In industrial applications, an accurate prediction of weld bead geometry is required in automation systems to enhance productivity of laser microwelding. The present work was conducted to establish an intelligent algorithm to build a simplified relationship between process parameters and weld bead geometry that can be easily used to predict the weld bead geometry with a wide range of process parameters through an artificial neural network (ANN) in laser microwelding of thin steel sheet. The backpropagation with the Levenberg-Marquardt training algorithm was used to train the neural network model. The accuracy of neural network model has been tested by comparing the simulated data with actual data from the laser microwelding experiments. The predictions of the neural network model showed excellent agreement with the experimental results, indicating that the neural network model is a viable means for predicting weld bead geometry. Furthermore, a comparison was made between the neural network and mathematical model. It was found that the developed neural network model has better prediction capability compared to the regression analysis model. © 2013 Mohd Idris Shah Ismail et al.

DOI： 10.1155/2013/415837

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In this study, the thermal deformation of thin stainless steel sheet was investigated in the bead-on-plate welding by using a single-mode fiber laser with a Galvano scanning system. The numerical simulation was developed to calculate the temperature and stress fields, and its deformation characteristics were discussed. It was suggested that the specimen firstly deformed downward in the same direction of laser irradiation, and then deformed in the reversed direction after laser scanning. The final deformation angle in the negative direction, which is concave shape from the view direction of laser irradiation, was generated under the welding mode of conduction and quasi-penetration for 50 mu m thickness sheet. On the other hand, the positive angle of final deformation angle was obtained under full-penetration welding mode, and the extreme small distortion could be achieved by the proper weld bead geometry in micro-welding of thin sheet. It was also confirmed that the similar weld bead geometry was resulted in both quasi-penetration and full-penetration welding mode for 20 mu m thickness sheet, but the final deformation angle tendency was different in 50 mu m and 20 mu m specimen thickness. It was clarified that the welding deformation was influenced not only by weld bead geometry but also by specimen thickness. (C) 2013 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.procir.2013.03.054

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Electrical-Machining Engineers  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Laser Institute of America  

The application of laser beam processing has been expected in the field of semiconductor devices because of its flexible cutting line and narrow kerf width. However, the deterioration of cutting quality would occur in the case of themosensitive materials due to the thermal damage, since the laser beam processing is mainly thermal process. Therefore, the laser singulation method by the superposition of pulsed fiber laser and green YAG laser was proposed to perform the high-quality processing for the semiconductor package, which is consisted of thermosetting epoxyresin with silica for molding compounds and glass epoxy board for semiconductor package with insulator coatings. The superposition of pulsed fiber laser and green YAG laser with high pulse repetition rates led to a straighter kerf shape with smaller kerf width under the same pulse energy condition. The smaller kerf width could be achieved by controlling the time delay between both laser pulses compared with synchronized laser pulses. The heat affected zone in singulation process could be reduced by the superposition of pulsed fiber laser and green YAG laser. Moreover, the synchronized laser pulses could lead to the smaller heat affected zone compared with unsynchronized one.

DOI： 10.2351/1.5062974

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Laser micro-welding has proven to be a very successful tool for micro-joining in the electrical and electronic industries, where the miniaturization, the high strength and the high heat resistance are constantly requested. Recently, a flexible printed circuit (FPC) is expected as a new connection technology between electrical conductors according to the improvements of reliability and controllability with the diversification of the design concept. In this technology, it is required to weld a several tens μm thickness of FPC and a several hundreds μm thickness of metal electrode. This material combination accompanies the difficulty to control the welding phenomenon due to the differences of thermal property and heat capacity. As a good alternative, laser micro-welding has advantages of non-contact tool, low heat distortion and consistent weld integrity. In this study, the overlap welding of thin copper circuit on a polyimide film and a thick brass electrode was experimentally and numerically investigated by using a pulsed Nd:YAG laser. In addition, the shearing stress of overlap welding was evaluated with and without the control of pulse waveform, which can provide a well-directed controlling of the heat input with high energy density. The results showed that a porosity was observed as the major weld defect in the welding process without a pulse control. However, the appropriate controlled laser pulse configuration of micro-welding could remove the weld defects in the molten zone, improve the weld penetration stability and increase the weld strength. The potential benefits of controlled pulse waveform were discussed for the direct laser micro-welding process. It is clarified that the direct laser micro-welding of a thin copper circuit on a polyimide film and a thick brass electrode could be successfully achieved by appropriate controlled pulse waveform and heat input. © KSPE and Springer 2012.

DOI： 10.1007/s12541-012-0041-3

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

A pulsed laser of 532 nm wavelength with ms range pulse duration was newly developed by second harmonic generation of diode pumped pulsed Nd:YAG laser. High electro-optical conversion efficiency more than 13% could welding be achieved, and 1.5 kW peak power green laser pulse was put in optical fiber of 100 mu m in diameter. In micro-welding of 1.0 mm thickness copper plate, a keyhole welding was successfully performed by 1.0 kW peak power at spot diameter less than 200 mu m. The frequency doubled pulsed laser improved the processing efficiency of copper welding, and narrow and deep weld bead was stably obtained. (C) 2012 Published by Elsevier B. V. Selection and/or review under responsibility of Bayerisches Laserzentrum GmbH

DOI： 10.1016/j.phpro.2012.10.076

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Scattering velocity and angle of spatter were investigated by recognizing and tracking spatter with the high-speed video observation. The spatter movement was observed by two high-speed video cameras, and analyzed by twodirection tracking method, in which the 3D tracking lines of spatter were constructed in the forward and backward frames and the actual trajectory of individual spatter was obtained by averaging those tracking lines. It made clear that the initial velocity of spatter was less than the speed of sound and mainly ranged from 75m/s to 200m/s. The velocity of spatter showed the slight correlation with the angle. (C) 2012 Published by Elsevier B.V. Selection and/or review under responsibility of Bayerisches Laserzentrum GmbH

DOI： 10.1016/j.phpro.2012.10.102

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

In laser drilling, an assist gas is often used to remove material from the drilling point. In order to design assist gas nozzles to minimize spatter formation, measurements of spatter trajectories are required.
We apply computer vision methods to measure the 3D trajectories of spatter particles in a laser cutting event using a stereo camera configuration. We also propose a novel method for calibration of a weak perspective camera that is effective in our application.
The proposed method is evaluated with both computer-generated video and video taken from actual laser drilling events. The method performs well on different workpiece materials.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

In a wire EDM using a thin wire electrode, better exclusion of debris from the machined kerf is important in order to maintain stable machining performance, since the area of spark generation is along a line and very small. When large amounts of debris stagnate in the gap, secondary discharges possibly occur and these discharges easily concentrate on the same location, which leads to unstable machining performance, wire breakage, low machining rate and a low shape accuracy.
Conventionally, the exclusion of debris is carried out by jet flushing with an upper and lower nozzle. However, the flow field of machining fluid in the kerf due to the jet flushing and the effect of jet flushing conditions from the nozzles on debris exclusion have not yet been sufficiently examined. This study aims to clarify the flow field in the machined kerf by computational fluid dynamics (CM) and to propose new jet flushing methods for smooth debris exclusion in the wire EDM. The effects of workpiece thickness and machined kerf length on the flow field of working fluid in the kerf under conventional jet flushing conditions are discussed. Then, jet flushing with a tilting nozzle is proposed in order to decrease the debris stagnation area near the wire electrode. As a result, by using the tilting nozzle, removal rate can be improved because of the smooth debris exclusion.

DOI： 10.4028/www.scientific.net/KEM.516.73

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：JAPAN SOC PRECISION ENGINEERING-JSPE  

Cemented tungsten carbide with nickel binder is often applied to the metal mold for electronic parts due to its non-magnetic feature. However, it is difficult to use conventional methods applied to metal molds made of steel for the surface finishing or modification of cemented tungsten carbides in some cases. The large-area EB irradiation for conventional cemented tungsten carbide with cobalt binder was studied in our previous papers. In this paper, surface finishing and modification of cemented tungsten carbide with nickel binder were investigated, and the effects of EB conditions on the surface characteristics were discussed. The experimental results indicated that the surface roughness decreased and the surface glossiness increased by the large-area EB irradiation. Also, the water repellency and the releasability of molded resin from the surface could be improved under proper EB conditions.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：JAPAN SOC PRECISION ENGINEERING-JSPE  

In this study, the thermal deformation of thin stainless steel sheet in laser micro-welding were experimentally and numerically investigated. The welding deformation was experimentally evaluated using a single-mode CW fiber laser with a high-speed scanning system. The numerical simulation was developed to calculate the temperature, stress and deformation fields. It was clarified that the laser irradiation condition has a significant effect on the welding mode and stress field. In addition, the thermal deformation was influenced by the weld bead geometry and residual stress distributions, and the final deformation was formed by residual stress and plastic deformation. It was found that the tensile stress was generated around the molten zone and balanced by the compressive stress in the base material.

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In the wire EDM using a thin wire electrode, the reduction of wire vibration is important to achieve a high-precision machining, since large amplitude of wire vibration leads to large kerf width, low shape accuracy, rough machined surface and high risk of wire breakage. In this study, the movements of wire electrode are directly observed by using a high-speed video camera in order to clarify the wire vibration in fine wire EDM for thin workpiece. The results shows that the wire vibration amplitude during the process increases with wire running speed and flow rate of jet flushing but decreases with wire tension. Also, the wire behavior during process is almost 1st order string vibration. Furthermore, the wire vibration frequency increases with not only the wire tension but also the discharge pulse frequency.

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Precision micro-machining without crack and heat affected zones is required in order to use high-performance materials such as silicon and silicon carbide, and it is expected that the higher harmonics of the Nd:YAG laser can perform precision micro-machining due to its high photon energy. However, even by using the harmonics of the Nd:YAG laser, a heat affected zone is inevitable due to the plasma generation. In order to reduce the influence of plasma on the processing results, it is important to understand the generation mechanism of plasma. Therefore, the laser induced plasma in micro-drilling of silicon carbide was observed by a high-speed shutter camera, and the influence of laser wavelength and surrounding conditions on the machining characteristics were experimentally investigated. The removal depth increased with decreasing wavelength and the surrounding gas pressure. The surface integrity was improved by the combination of shorter wavelength and reduced pressure conditions. The behavior of laser induced plasma was different from the wavelength of the laser beam and the surrounding gas pressure. Under atmospheric pressure conditions, the plasma grew greatly and affected the wider surface around the drilled hole with increasing wavelength. Under reduced pressure conditions, there was little difference in plasma size by wavelength, and the affected zone around the drilled hole became relatively smaller. It became clear. that a low surrounding gas pressure and shorter wavelength were important to obtain better surface integrity and highly efficient processing.

DOI： 10.4028/www.scientific.net/KEM.516.36

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Micro-drilling characteristics of silicon carbide by fundamental wavelength and three kinds of harmonic of Nd:YAG laser were experimentally investigated in the viewpoints of surrounding gas type and the pressure condition. Moreover, its characteristics were discussed by the observation of plasma behaviour, flow filed and debris behaviour on the specimen surface with a high-speed camera. The cracks were observed around drilled hole under the argon surrounding gas condition due to the generation of high intensity plasma. On the other hand, the helium surrounding gas kept the plasma in the vicinity region on the top surface of specimen, and the surrounding area of drilled hole was remarkably roughened. The better surface integrity could be obtained under the appropriate combination of surrounding gas type and the reduced pressure conditions.

DOI： 10.2351/1.5062420

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN LASER PROCESSING SOC  

The efficient welding of aluminum alloy has been strongly required for lightening the electronic products and automobiles, and a pulsed Nd:YAG laser is widely used for its application. However, the low absorption of a Nd:YAG laser makes it difficult to weld the aluminum alloy efficiently. Therefore, a pulsed Nd:YAG laser of 1064nm in wavelength and a continuous diode laser of 808nm in wavelength were spatially superposed, since the absorption rate of the continuous diode laser to the aluminum alloy is much higher than that of a pulsed Nd:YAG laser. The maximum temperature of specimen surface in the vicinity of laser irradiation area increased 50K by the superposition of continuous diode laser and pulsed Nd:YAG laser, and the energy of Nd:YAG laser was absorbed efficiently. Moreover, the thermal analysis indicated that the temperature of specimen surface with the continuous diode laser and the pre-heating pulse could be kept approximately 200K higher than that without these processes. The combination of pre-heating pulse and diode laser made it possible to increase the penetration depth even from the beginning of laser scanning. DOI:10.2961/jlmn.2011.03.0010

DOI： 10.2961/jlmn.2011.03.0010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

The nonlinear absorptivity of FOTURAN glass to ultrashort laser pulses is evaluated by experimental measurement and thermal conduction model at different parameters including energy and repetition rate of the laser pulse, translation speed and thermal properties of the sample. The mechanical strength of an embedded laser-melted sample and an overlapped weld sample is determined by a three-point-bending test and a shear test, respectively. The results are related to the average absorbed laser power W-ab. We found the mechanical strength of an overlapped weld joint to be as high as that of the base material for low W-ab, if the sample pair is pre-bonded to provide optical contact. (C) 2011 Optical Society of America

DOI： 10.1364/OE.19.022961

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In order to meet requirements in the next generation micro-processing, we have developed a 1.06μm pulsed fiber laser employing a MOPA (master oscillator power amplifier) configuration. This laser features broad pulse width flexibility ("100ps to 20ns), excellent beam quality (M2 ≦1.3), and a wide range of pulse repetition frequencies (50kHz to 1MHz). With these attributes of the laser, the optimum pulse width for P1 processing both (a)-Si (amorphous silicon) and CIS or CulnSe (copper indium diselenide) types of solar cells was studied. As a result, it was found that the pulse width of 10 to 20ns gives the best scribing quality on (a)-Si solar cells while the pulse width around 500ps leads to excellent results for CIS samples. The scanning speeds of 2500mm/s and 5000mm/s have been achieved for (a)-Si and CIS samples, respectively.this study, surface texturing of STAVAX, a through-hardening stainless steel for plastic molding, was also conducted. The surface roughness and water repellency on the STAVAX surface were controlled by adjusting the pulse width, number of scanning and assist gas condition.

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Cemented carbide has many excellent properties. However, it is sometimes difficult to apply conventional surface finishing or surface modification methods for the cemented carbide. The possibility of surface modification by large-area electron beam irradiation, namely EB polishing was discussed. The surface structure of the EB polished cemented carbide was observed by TEM. The hardness and the water repellency were tested. Also, the separation force of molded resin from the surface was measured for evaluating the releasability of the resin. The water repellency and the releasability of the molded resin could be improved by EB polishing, because the surface structure changed. (C) 2011 CIRP.

DOI： 10.1016/j.cirp.2011.03.107

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SHANGHAI JIAO TONG UNIV PRESS  

Recently, the laser dicing method has been expected to replace a blade dicing method because of its high flexibility. However, in the laser dicing, the heat affected zone yielding heat damage should be reduced in order to prevent the deterioration of semiconductor devices consisting of silicon chip. Therefore, the reduction of heat affected zone was experimentally investigated by using cooled assist gas. It is clarified that the combination of nitrogen assist gas in the coaxial direction of laser beam and cooled assist gas from the rear side of cutting direction led to the better cutting results with low heat affected zone.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

A pulsed Nd:YAG laser and a continuous diode laser were spatially superposed for higher absorption of laser beam to aluminum alloy. 12-20% increase in the bead width and 15-30% increase in the weld depth could be obtained by the superposition of continuous diode laser and pulsed Nd: YAG laser. Moreover, the unsteady thermal analysis with a key-hole effect indicated that the temperature of specimen surface with a continuous diode laser could be kept approximately 300K higher than that without a continuous diode laser. Therefore, it was clarified that the bead width and depth would increase greatly due to higher absorption of Nd: YAG laser to aluminum alloy by the superposition of a continuous diode laser.

DOI： 10.1299/jamdsm.4.875

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Precision micro-machining without cracks and with a narrow heat affected zone is highly required for the effective use of high-performance material. For this purpose, it is expected that the higher harmonics of Nd:YAG laser could perform the precision micro-machining by its high photon energy. However, even using harmonics of Nd: YAG laser, the heat affected zone is inevitable due to the plasma generation. In order to reduce the influence of plasma, it is important to understand the generation mechanism of plasma. Therefore, the laser induced plasma was observed by the high-speed shutter camera, and the influence of laser wavelength on machining characteristics was investigated.

DOI： 10.1299/jamdsm.4.867

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In this study, the characteristics of laser micro-welding with a high-speed scanning system on thin stainless steel sheets by using a single-mode CW fiber laser were experimentally investigated. It was clarified that the welding bead width and depth increased when increasing the scan velocity under a constant energy density condition, and high efficient welding was expected by using high-speed laser scanning with Galvano scanner. The utilization of assist gas is found to be very effective to obtain smooth fusion bead. In addition, the combination of micro beam spot and high-speed laser scanning made it possible to obtain good overlap welding of ultra-thin stainless steel sheets.

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A novel fusion welding technology of glass using ultrashort laser pulses with high pulse repetition rates has been developed, where the laser energy is selectively absorbed at the interface by nonlinear process to provide crack-free welding without pre- and post-heating. A laser-matter interaction model is developed to evaluate the distribution of the ultrashort pulse laser energy absorbed in bulk glass. A thermal conduction equation is derived to calculate transient 3-dimensional temperature distribution and dimensions of molten zone in glass. The mechanical strength of weld joint is evaluated taking into consideration of the attracting force of the optical contact between the glass plates needed for keeping the high-temperature plasma in the bulk glass. (C) 2010 Published by Elsevier B.V.

DOI： 10.1016/j.phpro.2010.08.171

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Pulsed Nd:YAG laser and continuous diode laser were spatially superposed for higher absorption to aluminum alloy. 12-20% increase in bead width and 15-30% increase in weld depth could be obtained by superposition of continuous diode laser and pulsed Nd:YAG laser. Moreover, the unsteady thermal analysis with key-hole effect indicated that the temperature of specimen surface with continuous diode laser could be kept approximately 300K higher than that without continuous diode laser. Therefore, it was clarified that the bead width and depth would increase greatly due to higher absorption of Nd:YAG laser to aluminum alloy by superposition of diode laser.

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Precision micro-machining without crack and with narrow heat affected zone is required in order to use high-performance material. For this purpose, it is expected that higher harmonics of Nd:YAG laser could perform precision micro-machining by its high photon energy. However, even using harmonics of Nd:YAG laser, heat affected zone is inevitable due to the plasma generation. In order to reduce the influence of plasma, it is important to understand the generation mechanism of plasma. Therefore, the laser induced plasma was observed by high-speed shutter camera, and the influence of laser wavelength on machining characteristics was investigated.

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Recently the welding of aluminum alloy has been strongly required for the lightening the electronic products, the automobiles and so on. Then the hybrid laser system was newly developed in order to perform the high efficiency and high quality welding of aluminum alloy. The high electric-optical conversion efficiency was achieved by the new diode pumped pulsed Nd:YAG laser. The hybrid system is consisted of a newly developed pulsed Nd:YAG laser and a continuous diode laser, and it can deliver two lasers by one fiber. Higher absorption of laser energy into the aluminum alloy can be expected under the continuous irradiation of diode laser (λ= 808 nm), since the absorption into aluminum alloy shows the maximum at λ= 850 nm. The suitable bead width and depth could be obtained with better surface integrity when the pulse waveform took the highest peak at the first period. The bead width and depth increased with increasing the power of continuous diode laser, which leads to overlapping welding even under high speed condition. Moreover, the high efficiency and high quality welding of aluminum battery case could be accomplished by the newly developed hybrid system, in which the suitable pulse energy and the peak power could be given even under the high pulse repetition rate.

DOI： 10.2493/jjspe.75.1222

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A newly surface treatment method was proposed by the combination of the high-speed laser scanning with Galvano scanner and the single-mode pulsed fiber laser with Master Oscillator Power Amplifier, and various periodic structures could be formed by this technique. The surface roughness of irradiated area increased almost proportionally with increasing the number of laser scan, and it could be controlled by the number of scan. The repellency of surface could be increased by the laser irradiation compared to that of ground surface under nitrogen atmosphere condition, while the hydrophilic property of surface could be improved by the laser scanning under air atmosphere condition. Moreover, it was found that the corrosion resistance of the surface could be improved by laser irradiation.

DOI： 10.4028/www.scientific.net/KEM.407-409.624

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Fraunhofer Institute for Laser Technology had developed the SHADOW (R) welding technique, in which high speed joining with minimal distortion is possible using a pulsed Nd:YAG laser. The possibility of high speed, high quality welding had been also reported by use of a single-mode fiber laser. The combination of micro-beam and high speed laser scanning offers potential advantages for thin metal sheet welding. Therefore, the characteristics of micro-welding for thin stainless sheet were investigated here by high speed laser scanning with both single-mode fiber laser and pulsed Nd: YAG laser. The results were a narrow welding region obtained using a laser beam with a large focus diameter of 160 mu m without pulse control, while a small focus diameter of 22 mu m was found in general to provide good control of the welding state. A small focus diameter can result in an excellent welding seam from the start, even without pulse control. The penetration depth could be controlled by the energy density with a small focus diameter. For the smaller beam foucus diameter, an unique periodic structure appeared at high beam scanning velocities. Moreover, by using a laser beam with a small focus diameter, the overlap welding of 25 mu m thickness sheet could be successfully performed, regardless of the presence of a small gap distance between two sheets.

DOI： 10.2961/jlmn.2008.02.0007

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This paper deals with the effects of the nozzle shape on cutting results and fundamental characteristics of laser cutting of solid type molded composite materials, which was composed of semiconductor board and epoxy-resin molding compounds, by Q-switched single-mode fiber laser. Experimental results clarified that high speed cutting of 16 mm/s could be carried out using a Laval throat nozzle with initial expansion zone, which also led to straighter kerf shape and narrower kerf width than other nozzles. Besides, Laval throat nozzle made it possible to reduce the kerf width, and the difference of kerf width between irradiation-side and exit-side became smaller. Nitrogen assist gas led to the narrow kerf width and straight kerf shape. Furthermore, the difference of kerf between substrate side and epoxy-resin side became smaller. Substrate side irradiation was more suitable for precision cutting than epoxy-resin side irradiation. These results proved that Q-switched single-mode fiber laser was useful for cutting of composite materials.

DOI： 10.1299/jamdsm.2.651

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Recently, since the size of component becomes smaller, then the welding of thin metal sheet has been required. Besides, the flexibility of process is important according to the accessibility especially for small components. Fraunhofer Institute for Laser Technology had developed the SHADOW((R)) welding technology, in which the high speed joining with small distortion is possible using pulsed Nd:YAG laser. The possibility of high speed and high quality welding had been reported by using single-mode fiber laser. The combination of micro beam and high speed laser scanning has the advantages for thin metal sheet welding. Therefore, the characteristics of micro-welding for thin metal sheet were investigated by high speed laser scanning, in which the welding was carried out by high speed scanner system with single-mode fiber laser and pulsed Nd:YAG laser. The proper welding region was narrow by the laser beam with a large focus diameter of 160 mu m without pulse control, while a small focus diameter of 22 mu m can control the welding state widely. A small focus diameter can perform the excellent welding seam from the extreme beginning without pulse control. The penetration depth can be controlled by the energy density with a small focus diameter of 22 mu m at the energy densities less than 1 J/mm(2). Besides, the unique periodic structure appeared at the high velocity of beam scanning with a small focus diameter. Moreover, the overlap welding of 25 mu m thickness sheet can be performed regardless of small gap distance between two sheets by the laser beam with a small focus diameter of 22 mu m.

DOI： 10.1117/12.722161

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Fiber laser has many advantages such as compact size, high conversion efficiency, good beam mode, air cooling and maintenance free. Therefore, it has high possibility as an industrial light source in the near future. The beam from fiber laser can be focused in a micro spot because of its excellent beam quality. However, the narrow kerf leads to the difficulty of outflow of melted material. Therefore, micro cutting by a single-mode fiber laser is considerably difficult, then the high performance nozzles are strongly required. In the previous work, authors developed a high performance nozzle, which can increase the velocity of assist gas flow and makes it possible to reduce the dross in the micro kerf. Therefore, high performance cutting by a single-mode fiber laser can be expected by using our newly designed nozzle. In this study, the effect of nozzle shape on the machining results in precision cutting of thin copper plate by a Q-switched single-mode fiber laser was experimentally investigated. It was found that the high speed cutting at 30mm/s could be carried out by the high performance nozzle under low pulse frequency condition. Besides, the reduction of the dross and good kerf shape could be attained in the case of nitrogen assist gas.

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The fundamental characteristics of laser cutting for thin copper plate by a Q-switched single-mode fiber laser were experimentally investigated, and the effects of the nozzle shape on cutting results are also discussed. In the case of traditional convergent nozzle with nitrogen assist gas, it was impossible to cut under any experiment condition, since assist gas pressure on workpiece was lower. On the other hand, high speed cutting of 30mm/s could be carried out using high-performance Nozzle Laval 800 and Nozzle Laval 800 IEZ, since high assist gas pressure could be supplied on the workpiece. In addition, the dross height using Nozzle Laval 800 and Nozzle Laval 800 IEZ was very small less than 10um, and the very narrow kerf and straight cut shape could be obtained. Therefore Q-switched single-mode fiber laser with high-performance nozzles proved to be useful for cutting of thin copper plate.

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DOI： 10.2526/jseme.40.21

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The fundamental characteristics of laser cutting for thin copper plate by a Q-switched single-mode fiber laser were experimentally investigated, and the effects of the nozzle shape on cutting results were also discussed. High speed cutting of 29mm/s could be carried out with a newly designed nozzle, since high assist gas pressure could be supplied on the workpiece without MSD. Nozzle Laval 800 makes it possible to cut more efficient, since the melted material in the kerf decreases compared to a traditional convergent nozzle. Using a Q-switched single-mode fiber laser, the kerf is very fine, and color change around the kerf is hardly observed by oxidation due to little heat conduction from dross. Therefore, it proved to be available in cutting of thin metal plate.

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A new slicing method of monocrystalline silicon ingot using wire electrical discharge machining was proposed for high efficiency and high quality slicing instead of inner diameter blade or multi-wire method. The effects of supply method of working fluid and wire speed on machining characteristics were experimentally investigated. It is clarified that the immersion method is superior than the nozzle supply method and the wire speed over 200m/min is desirable for stable machining. Besides, mounting of wire sub-guide is useful for obtaining better kerf shape.

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In YAG laser cutting process of thin plate, it is important to understand the assist gas flow from the tip of a convergent nozzle in order to improve the machining accuracy, since melted material is mostly carried away downward by the gas flow. Besides, it is considered that the nozzle shape influences the assist gas flow. In this paper, the effects of the nozzle shape on assist gas flow and machining results in micro machining by a pulsed YAG laser are experimentally investigated. There is an unstable region where the pressure on a workpiece changes periodically regardless of the internal shape and exit diameter of nozzle. The unstable region starts at low cylinder gas pressure and becomes smaller in range with increasing the exit diameter. Under middle and high cylinder gas pressure conditions over 300kPa, height of dross becomes smaller with the increase of the exit diameter for a nozzle of conical internal shape, since the pressure on workpiece increases. Furthermore, when the conical inner wall of nozzle is changed to a convex inner wall, it is possible to reduce the height of dross. Additionally, the height of dross becomes lower, when the curvature of the inner wall increases under the high pressure condition.

DOI： 10.2493/jspe.70.246

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In this study, the effect of the laser beam irradiation method on the deformation characteristics of laser forming for plastic material by YAG laser was experimentally investigated. In the case of area irradiation method, bending angle becomes smaller after the irradiation, since the amount of bending-down is large during the irradiation. Therefore, even if the number of laser beam irradiation increases, large bending angle can not be obtained. On the other hand, in the case of scan irradiation method, the bending angle becomes larger after the irradiation, since the amount of bending-down is small during the irradiation. As a result, the scan irradiation method makes it possible to obtain large bending angles up to 90 degrees by increasing the number of laser scan. Therefore, in order to obtain larger bending angles, the scan irradiation method is more effective than the area irradiation method.

DOI： 10.7791/jhts.30.47

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Plastic material can be also bent by laser forming in the same way as metal material, and larger bending angle can be obtained as compared to metal material. However, its deformation mechanism has not been yet clarified. Therefore, in this study, the machining characteristics and the deformation mechanism of plastic in YAG laser forming were made clear by experimental and numerical analysis. Small temperature gradient was obtained by thermal analysis in laser forming of high density polyethylene. The plastic material could be bent due to high viscoelasticity in spite of small temperature gradient. Specimen was first bent by the temperature gradient in thickness direction in a few seconds after the laser irradiation. Then, the temperature of specimen became almost the same in thickness direction, and the temperature gradient appeared only in side direction. Therefore, the deformation of specimen was occurred by the contraction of specimen in side direction and the effect of initial shape, which was deformed by the temperature gradient just after the laser irradiation. Besides, it was clarified that small thermal conductivity of plastic material lead to low cooling speed. Therefore, sufficient cooling time is necessary in order to control the deformation accurately, since the temperature of specimen should be kept equal before every laser irradiation.

DOI： 10.1117/12.596567

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In the Department of Mechanical Engineering at Okayama University, the manufacturing practice has been taken as an important subject, not only for educational manufacturing practice but also for introducing "Hands-on" fabrication. Therefore, this class was shifted from the second to the first grade year. Furthermore, the manufacturing of a simple shaped paperweight was altered to a complicated product, gyroscope. The analysis of questionnaire shows that the improvements in the subject are very effective in student's motivation for Hands-on fabrication. We hope that this subject will be a trigger for students to develop a creative ability.

DOI： 10.4307/jsee.51.5_58

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Effects of Laval nozzle on assist gas flow and the machined results in precision cutting of thin plate by pulsed YAG laser were experimentally investigated. Assist gas flow from Laval nozzle does not have Mach Shock Disk, and goes more straight than a traditional convergent nozzle. Therefore, the pressure on workpiece increases, since assist gas flow from Laval nozzle can utilize energy more efficiently. However, caution is necessary in setting of cylinder gas pressure, since Laval nozzle has many unstable regions in which the pressure on workpiece changes periodically. Using Laval nozzle makes it possible to reduce the height of dross even under low cylinder gas pressure condition. Thus the consumption of assist gas flow quantity can be reduced. Moreover, it was pointed out that the convexed inner wall of nozzle leads of reduction of dross generation.

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DOI： 10.2493/jjspe.68.1564

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In this study, the effect of specimen thickness on machining characteristics and deformation mechanism of laser forming for plastic material with YAG laser were made clear by the experimental analysis. Each specimen with different thickness can be bent to 90 degrees under proper machining conditions. The optimum laser power, in which bending angle takes a maximum under the same feed condition, increases with an increase of specimen thickness. In the case of thick specimen, the deformation occurs without a delay between the beginning point and the end one of irradiation just after finishing of laser scan. On the other hand, thin specimen is deformed from the beginning point of irradiation during laser scan at a small number of laser scan, since the rigidity of thin specimen is lower compared to that of thick specimen. Consequently, the bending angle per one laser scan is small in the case of thin specimen. However, the bending angle per one laser scan becomes larger at a large number of laser scan. Because it is considered that the increase of rigidity of specimen leads to the stable deformation, since the hardness of irradiated area increases with an increase of laser irradiation.

DOI： 10.2493/jjspe.68.466

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ITO film, which is a kind of transparent conductive film, has been used for LCD, PDF and so on. This film is mostly removed by wet etching method. However, this method needs many chemicals, numbers of process and large-size equipments. On the other hand, laser beam processing can achieve the dry process without chemicals and drastically reduces the number of process. Therefore, selective removal of ITO film on glass substrate by LD pumped Q-switch SHG YAG laser is experimentally investigated. Electric insulation across machined groove was successful. Better groove shape can be obtained by accurate control of defocused distance and feed rate under a constant average power. Using SHG YAG laser makes it possible to remove only ITO film without any damage to glass material as substrate, since SHG YAG laser of 532 nm in wavelength is easy to transmit the glass material. When laser beam is irradiated from ITO film to glass material, a non-removed portion of ITO film remains at the bottom of groove under long defocused distance condition. On the other hand, backside irradiation method, in which laser beam is irradiated to ITO film through glass material, can prevent from remaining a non-removed portion, since absorption of laser beam occurs from the boundary part between ITO film and glass material.

DOI： 10.1117/12.486573

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In this study, the slicing of silicon ingot by wire EDM is discussed, and the machining properties are experimentally investigated. Also, the accuracy of sliced wafer and the contamination on the machined surface are evaluated. Experimental results made it clear that the accuracy of wafer by this slicing method is almost the same as that by the conventional methods, and even higher slicing speeds are possible when multi type wire EDM slicing can be realized. Additionally, the contamination due to the adhesion and diffusion of wire electrode material into the sliced surface can be reduced by wire EDM under the condition of low current and long discharge duration. Therefore, wire EDM has a high potential as a new slicing method for monocrystalline silicon ingot.

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DOI： 10.2493/jjspe.66.891

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DOI： 10.2526/jseme.34.14

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YAG laser has widely been used for precision micro machining in many fields. However, adhesions of dress and spatter to the base material due to high energy beam machining lead to the deterioration of the surface integrity. It is important to understand the assist gas flow from the tip of a convergent nozzle in order to improve the surface integrity, since material is mostly removed away by the gas flow spouted in the same direction of the laser beam.
In this paper, effects of the nozzle shape on assist gas flow and the machined results were experimentally analyzed using the Schlieren method. There exists an unstable region in which the pressure on the workpiece changes periodically, and the region becomes wider with the reduction of the exit diameter. The pressure on the workpiece increases with an increase of the exit diameter, which makes the dress height smaller, However, it is necessary to select the nozzle shape according to the demand of the surface integrity, because the consumption of the assist gas increases and the kerf width becomes wider with an increase of the exit diameter. Moreover, it was pointed out that a kind of nozzle with a convex curve on inner wall of nozzle led to better surface integrity.

DOI： 10.1117/12.405759

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Laser forming of plastic materials with YAG laser is experimentally investigated. The bending angle increases rapidly in the cooling process just after laser irradiation and takes a maximum under a proper energy density. Slow feed rate and low power condition are recommended in order to obtain the better processing result, because the bending angle increases without reverse deformation at every laser irradiation scan and machined surface integrity under low power condition is better than that under high power one. Furthermore, in the case of plastics, the bending direction can be controlled by the selective painting of black resin on the top or bottom surface of specimen with only one-side laser irradiation, because heat is generated by absorbing laser beam energy into painted material. Therefore, various shapes can be obtained by varying both the laser scan and the painting part.

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DOI： 10.2493/jjspe.65.1471

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This article deals with high efficiency and high accuracy fine boring in a monocrystalline silicon ingot by electrical discharge machining (EDM). In manufacturing process of integrated circuits, a plasma-etching process is used for removing oxidation films. This process has recently been examined for use of monocrystalline silicon as the electrode to minimize the contamination. However, it is difficult to machine silicon accurately by the conventional diamond drilling method, because the material removal is due to brittle fracture. The machining force in the EDM process is very small compared with that in conventional machining, therefore, the possibility of high efficiency and high accuracy boring holes in silicon ingot by EDM is experimentally investigated. The removal rate of monocrystalline silicon by EDM is much higher than that of steel, while the electrode wear is extremely small. The improvement method leads to a better hole without chipping at the exit of hole or sticking of the insulator on the wall of hole. Furthermore, it is proved that even a high aspect ratio of about 200 boring is possible. (C) 1999 Elsevier Science Inc. All rights reserved.

DOI： 10.1016/S0141-6359(98)00029-4

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This paper deals with a new slicing method of monocrystalline silicon ingot by wire EDM. In manufacturing process of silicon wafer, ID blade and multi wire saw have conventionally been used for slicing of ingot. However, it is difficult to apply these methods for larger ingot such as 12(R) or 16 " expected to be used in the near future, since there are some problems in efficiency, accuracy, slurry treatment, contamination and so on. Therefore, a new slicing method is required as soon as possible. In this study, the possibility of slicing by WEDM was proposed and the machining properties as well as surface integrity were experimentally investigated. It was made clear that WEDM had the possibility as a new slicing method and that contamination due to adhesion and diffusion of wire electrode material to machined surface could be reduced by using the reversed polarity WEDM.

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DOI： 10.2493/jjspe.65.155

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In the manufacturing process of integrated circuit, graphite plate with many fine holes has been used as an electrode in plasma etching process. Recently, it is examined to use a single crystalline silicon as the electrode in order to minimize the contamination. However, it is difficult to machine accurately by the conventional methods, since the material removal is due to brittle fracture. The machining force in EDM is very small compared with that in conventional machining, therefore the possibility of high efficiency and high accuracy boring hole in a silicon ingot by EDM is experimentally investigated in this study. The removal rate of silicon is from 4 to 8 times higher than that of steel, while the electrode wear is from one-fifteenth to one-seventh times smaller. When the electrode advances at the exit of hole, stagnation region appears in which the electrode retracts suddenly and the machining becomes unstable. In order to prevent this phenomenon, the copper plate is closely attached under silicon ingot firmly. In this method, better hole can be obtained without chipping. Besides, there is no sticking of insulator which contains silicon oxide and copper oxide on the wall of hole in this case. Furthermore, it is proved that even high aspect ratio over 200 boring is possible.

DOI： 10.2493/jjspe.63.1725

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DOI： 10.2493/jjspe.63.1459

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In electrical discharge machining (EDM) process, the reduction of electrode wear is very important for high accuracy machining. It is reported that low electrode wear EDM can be achieved by the adhesions of workpiece material and heat resolved carbon from machining fluid to the electrode end surface, because of the protection effect of the latter which has large heat resistivity. Under a proper condition, even no electrode wear EDM is possible. Such adhesion phenomenon, however, is observed only on the condition that the pluse duration is relatively large. That is, it never occurs on the small pulse duration such as finishing condition. Therefore, no electrode wear EDM under finishing condition is impossible so far and the electrode wear in finishing EDM is practically allowed to be inevitable. It is reported that the heat resolved carbon from machining fluid adhering to the electrode end surface is turbostratic carbon. It has the chemical structure in which hexagonal lattice plane laminates irregularly, different from graphite structure. From these results, it is considered that no electrode wear EDM might be attained by using turbostratic carbon electrode under finishing condition.<br>In this study, EDM characteristics of a newly developed CVD-carbon electrode are experimentally investigated for higher performance EDM. Experimental analysis made it clear that low electrode wear EDM is possible by using CVD-carbon electrode even under finishing condition, since the heat resolved carbon from machining fluid has a stronger tendency to adhere to the end surface of CVD-carbon electrode than that of graphite one.

DOI： 10.2526/jseme.30.65_1

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DOI： 10.2493/jjspe.83.825

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