Studies on Optimization of Laser Materials Processing by Pulse Shaping

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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