Studies on Optimization of Laser Materials Processing by Pulse Shaping

1)确定激光加工的最佳脉冲形状(由A.Matsunawa和S.Katayama进行)奥氏体不锈钢和铝合金被认为是难以焊接的材料，因为形成各种缺陷，如气孔和裂纹形成，特别是在脉冲激光焊接中。为了消除或抑制这些缺陷，在考虑激光辐照条件和材料常数的基础上，进行了理论和实验工作，确定了每种材料的最佳脉冲形状及其相关参数，以彻底消除缺陷的形成。2)脉冲激光焊接的熔化和凝固特性及数学模型的建立(由A.Matsunawa，T.Takemoto和S.Katayama主持)建立了考虑熔化潜热的导电式激光点焊的熔化和凝固以及激光快速淬火焊缝金属的微观偏析的数学模型，并计算了…实验验证了较大的枝晶生长速度和微观偏析的分布。3)脉冲成形激光在易切削不锈钢焊接中的应用(由S.Katayama和O.Miyata进行)在易切削不锈钢中，添加了硫化物和铋等元素来改善金属的切割性能，但由于凝固裂纹，极大地恶化了熔焊的可焊性。4)优化和改进了脉冲可整形YAG激光电源和光纤光束传输系统(松川、M.Saitoh和T.Uchida等人进行的光纤光束传输)，研制了一种能够实现脉冲整形的激光电源，并通过实际焊接优化了其电路常数，并改进了光纤光束传输系统，以获得焦点处的最佳功率密度分布。较少

1) Determination of Optimum Pulse Shape for Laser Processing (Conducted by A.Matsunawa and S.Katayama)Austenetic stainless steels and aluminium alloys are known as difficult materials for welding because of formations of various defects such as porosity and crack formations, particularly, in pulsed laser welding. In ordert to eleiminate or suppress these defects, theoretical and experimental works were conducted by considering laser irradiation conditions as well as material's constants, and optimum pulse shape and its allied parameters for each material were determined to drastically eliminate defects formation.2) Fusion and Solidification Characteristics of Pulse Shaped Laser Welding and Construction of Mathematical Model (Conducted by A.Matsunawa, T.Takemoto and S.Katayama)Mathematical models of fusion and solidification of conduction mode laser spot welding and microsegregation of laser rapidly quenched weld metal were developed considering the latent heat of fution, and the calcul … More ated growth rate of dendrite and distribution of microsegregation were experimentally verified. The developed models were proved to be effective to predict the optimum shape to suppress the solidification crack.3) Application of Pulse Shaped YAG Laser to Welding of Automotive Parts used Free Cutting Stainless Steel (Conducted by S.Katayama and O.Miyata)In free cutting stainless steels, elements such as Sulpher and Bismas are added to the metal to improve the cutting propertiy but it greatly deteriorates the weldability in fusion welding because of solidification cracking. In this work, the newly developed pulse shaped YAG laser welding was applied to weld the free cutting stainless steel to ordinary austenetic stainless steel in automotive part, and crack free weld was obtained successfully.4) Optimization and Improvement of Power Source of Pulse Shapable YAG Laser and Beam Delivery by Optical Fiber (Conducted by A.Matsunawa, M.Saitoh and T.Uchida)A power source which enabled the pulse shaping of YAG laser was developed and optimized its circuit constants by actual welding, and also improved a beam delivery system by optical fiber to obtain the optimum power density distribution at the focal point. Less