Laser Institute of AmericaActa Medica Okayama1042-346X3712025High-quality welding of copper and aluminum by angled laser irradiation and insert metals012041ENYasuhiroOkamotoFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityYukiYamadaGraduate School of Environmental, Life, Natural Science and Technology, Okayama UniversityAkiraOkadaFaculty of Environmental, Life, Natural Science and Technology, Okayama UniversityMasakiMiyakeKataoka CorporationTakeshiYamamuraKataoka CorporationKatsutoshiNagasakiKataoka CorporationNorioNishiKataoka CorporationCopper is an important material in order to use electricity effectively, and aluminum is also an attractive material to perform lightweight construction. Laser welding of copper and aluminum is required, and there are some reports to weld copper and aluminum firmly by laser irradiation from the aluminum side. On the other hand, laser irradiation from the copper side requires high power density to generate a keyhole, which causes the strong convection of molten aluminum into copper. Thus, brittle intermetallic compounds with rich aluminum result in the deterioration of joining strength. Angled laser irradiation enables mild heat input to the aluminum side, and the combination of angled and superposed irradiation of blue and near-infrared (NIR) lasers achieved a remarkable increase of breaking strength. However, the breaking strength is still lower than the base materials. Therefore, insert materials between copper and aluminum plates were investigated by the angled irradiation of blue and NIR lasers from the copper side. The breaking strength with insert materials showed higher values in the order of titanium mesh, nickel foil, and nickel mesh, and its value with the nickel mesh was close to the tensile strength of aluminum in a cross tensile test. Further improvement of breaking strength is possible by inserting the nickel mesh between copper and aluminum plates in the case of angled irradiation of blue and NIR lasers even from the copper side.No potential conflict of interest relevant to this article was reported.Springer Science and Business Media LLCActa Medica Okayama0043-22886782023Study on joint characteristics in laser butt welding of AMed and wrought Ti6Al4V plates19972005ENYasuhiroOkamotoOkayama UniversityTogoShinonagaOkayama UniversityYoshitoTakemotoOkayama UniversityAkiraOkadaOkayama UniversityAkihiroOchiOkayama UniversityRyuyaKishimotoOkayama UniversitySisaPityanaNational Laser Centre, CSIRNanaArthurNational Laser Centre, CSIRPeterOmoniyiUniversity of JohannesburgRasheedatMahamoodUniversity of JohannesburgMartinMainaJomo Kenyatta University of Agriculture and TechnologyEstherAkinlabiUniversity of JohannesburgTitanium 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 f 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.No potential conflict of interest relevant to this article was reported.IOP Publishing LtdActa Medica Okayama2631-8644422022High-quality micro-shape fabrication of monocrystalline diamond by nanosecond pulsed laser and acid cleaning025301ENYasuhiroOkamotoGraduate School of Natural Science and Technology, Okayama UniversityTubasaOkuboGraduate School of Natural Science and Technology, Okayama UniversityAtsuyaKajitaniGraduate School of Natural Science and Technology, Okayama UniversityAkiraOkadaGraduate School of Natural Science and Technology, Okayama UniversityThe flat plane of small surface roughness below 0.1 mu m average roughness was obtained for monocrystalline diamond by nanosecond pulsed laser irradiation of 1060 nm and post-process acid cleaning, at a laser fluence around the material removal threshold value. The glossy and flat plane at the bottom of the micro-groove was parallel to the top surface of the 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 produced a shallower micro-groove with a wider, flatter bottom compared with the round beam in Gaussian mode. The creation method of the 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 did not create a flat plane with constant depth. Therefore, a 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. The newly proposed two-step scanning method was practical and useful to create a widely flat plane with small surface roughness, and the two-step scanning method provided superior control over the micro-groove depth. This proposed method can reduce the surface roughness in addition to the shape creation of monocrystalline diamond, and it can be used as a high-quality micro-shape fabrication method of monocrystalline diamond.No potential conflict of interest relevant to this article was reported.Japan Laser Processing SocietyActa Medica Okayama1880-06881622021Formation and Its Mechanism of High-speed Micro-grooving on Metal Surface by Angled CW Laser Irradiation109114ENNozomiTauraGraduate School of Natural Science and Technology, Okayama University, JapanAkiyaMitsunobuFaculty of Engineering, Okayama University, JapanTatsuhikoSakaiNIPPON STEEL CORPORATION, JapanYasuhiroOkamotoGraduate School of Natural Science and Technology, Okayama University, JapanAkiraOkadaGraduate School of Natural Science and Technology, Okayama University, JapanIn general, pulsed lasers with high peak power have been used for the micro-groove formation. However, the processing speed is limited by the pulse repetition rate. On the other hand, CW laser can be expected to perform the high-speed processing by continuous energy input. The mechanism of micro-groove formation by CW laser was investigated by high-speed observation and the thermal fluid analysis. In the perpendicular irradiation of CW laser, the molten metal flows symmetrically around the keyhole to the backward direction, and micro-grooves remain at both edges of molten region. In contrast, in the angled irradiation, the molten metal at the reflection-side scatters as spatters. The remained molten metal flows from the reflection-side to the incident-side through the bottom of keyhole, since the recoil pressure is generated from the reflection-side to the incident-side. In addition, high-speed scanning contributes to keeping the sufficient time and force to move the molten metal in the backward direction. Then, the micro-groove remains at the reflection-side, while the upheaval is formed at the incident-side by gathering the molten metal from the reflection-side and the front of keyhole. Asymmetrical behavior of molten metal flow in angled irradiation of CW laser can create micro-groove in the reflection-side. No potential conflict of interest relevant to this article was reported.Elsevier B.V.Acta Medica Okayama092401362992021Effects of Superposition of 532 nm and 1064 nm Wavelengths in Copper Micro-welding by Pulsed Nd:YAG Laser117388ENMartin RuthandiMainaNontraditional Machining Laboratory, Okayama UniversityYasuhiroOkamotoNontraditional Machining Laboratory, Okayama UniversityKazukiHamadaNontraditional Machining Laboratory, Okayama UniversityAkiraOkadaNontraditional Machining Laboratory, Okayama UniversityShin-ichiNakashibaKataoka CorporationNorioNishiKataoka CorporationUnstable and low absorption of laser energy is experienced in copper welding at around 1000 nm wavelength. At 532 nm wavelength, there is stable and high laser absorption by copper. Past researches have shown that transitional processing condition between keyhole and heat conduction welding results in a stable micro-welding process characterized by good surface quality and deep penetration. In order to adapt laser welding to copper using pulsed Nd:YAG lasers, investigations of welding quality and efficiency were addressed. Processing was done under transitional processing condition between heat conduction and keyhole welding. Copper C1020 specimens were processed using superposed laser wavelengths of 1064 nm and 532 nm. Effects of irradiation delay and power density on the process were clarified by taking measurements of absorption rates and molten volumes, and by analyzing the weld beads. In addition, the dynamics of molten area and keyhole formation were investigated through three-dimensional FEM analysis. A stabilized laser absorption and increased molten volume was achieved by superposition using 532 nm laser of an appropriate high power density coupled with a short irradiation delay for the 1064 nm laser, which resulted in high-efficiency welding of copper.No potential conflict of interest relevant to this article was reported.SpringerActa Medica Okayama0043-22886462020Effect of numerical aperture on molten area characteristics in micro-joining of glass by picosecond pulsed laser937947ENYasuhiroOkamotoGraduate School of Natural Science and Technology, Okayama UniversityZhiyongOuyangGraduate School of Natural Science and Technology, Okayama UniversityTakumiFujiwaraGraduate School of Natural Science and Technology, Okayama UniversityAkiraOkadaGraduate School of Natural Science and Technology, Okayama UniversityGlass products with precise and sophisticated shapes are highly demanded in the field of MEMS due to their excellent properties. Ultrashort pulsed laser has been expected to be a powerful and reliable tool for micro-welding of glass. Focusing condition such as numerical aperture (N.A.) is a critical parameter that controls how ultrashort laser pulses interact with and propagate in glass, and it has a great influence on the laser micro-welding characteristics of glass. In order to investigate the quality of welding process, it is important to understand the dependence of the mechanical strength of molten area created in glass specimen with various numerical apertures. Therefore, the mechanical strength of molten area with various numerical apertures was evaluated in micro-welding of glass by picosecond pulsed laser. Higher bending strength could be obtained under an appropriate volume ratio of molten area and glass specimen, when continuous molten areas were formed. In addition, high density and large size of molten area without crack led to higher breaking stress. It is concluded that superior focusing characteristics such as N.A. 0.65 enable a long region of high power density in beam axis, which can satisfy both high mechanical strength and high processing speed.No potential conflict of interest relevant to this article was reported.MDPIActa Medica Okayama972019Influence of Numerical Aperture on Molten Area Formation in Fusion Micro-Welding of Glass by Picosecond Pulsed Laser1412ENZhiyongOuyangGraduate School of Natural Science and Technology, Okayama UniversityYasuhiroOkamotoGraduate School of Natural Science and Technology, Okayama UniversityYutaOginoGraduate School of Natural Science and Technology, Okayama UniversityTomokazuSakagawaAkiraOkadaGraduate School of Natural Science and Technology, Okayama University Focusing condition such as numerical aperture (N.A.) has a great influence on the creation of molten area and the stable welding process in fusion micro-welding of glass. In this study, a picosecond pulsed laser of 1064 nm in wavelength and 12.5 ps in pulse duration was tightly focused inside a borosilicate glass using objective lenses of numerical apertures 0.45, 0.65, and 0.85 with spherical aberration correction. Influence of numerical aperture on molten area formation was experimentally investigated through analysis of focusing situation in glass, and movement of absorption point, and then molten area characteristics were discussed. It is concluded that N.A. of 0.65 with superior focusing characteristics can form a large and continuous molten area without cracks, which enables achievement of stable joining of glass material by picosecond pulsed laser.No potential conflict of interest relevant to this article was reported.Acta Medica Okayama000785066812019High surface quality micro machining of monocrystalline diamond by picosecond pulsed laser197200ENY.OkamotoGraduate School of Natural Science & Technology, Okayama UniversityA.OkadaGraduate School of Natural Science & Technology, Okayama UniversityA.KajitaniGraduate School of Natural Science & Technology, Okayama UniversityT.ShinonagaGraduate School of Natural Science & Technology, Okayama UniversityIn micro machining of monocrystalline diamond by pulsed laser, unique processing characteristics appeared only under a few ten picosecond pulse duration and a certain overlap rate of laser shot. Cracks mostly propagate in parallel direction to top surface of workpiece, although the laser beam axis is perpendicular to the surface. This processed area can keep diamond structure, and its surface roughness is smaller than R-a = 0.2 mu M. New laser micro machining method to keep diamond structure and small surface roughness is proposed. This method can contribute to reduce the polishing process in micro machining of diamond. (C) 2019 Published by Elsevier Ltd on behalf of CIRP.No potential conflict of interest relevant to this article was reported.Faculty of Engineering, Okayama UniversityActa Medica Okayama0475-0071351-22001Laser Welding of Slices of Magnetic Circuit2128ENVolodymyrS.kovalenkoYoshiyukiUnoYasuhiroOkamotoM.AnyakinA.LutayKhaled Al.Shubul10.18926/15348In electric power industry, there is a problem of achieving stable joint in different components using high productive and efficient technologies. One type of these components is packages of slices for magnetic circuit of electric motors, transformers etc., which need reliable means for their fixing. Laser welding is proposed to solve this problem as an alternative for existing technologies. The development of the laser welding process is presented based on process simulation, study of heat history and comparison with experimental results. Laser beam additional scanning technique is proposed to improve the quality and efficiency of the joining operation.No potential conflict of interest relevant to this article was reported.