Study On The Optimization Of Techniques And Parameters Of Laser Transformation Hardening

Laser transformation hardening (LTH) has the obvious advantages of the traditional surface quenching techniques in the case of surface hardening for complicated structure parts, easy to distort or selected area of the part. This dissertation mainly studied on the optimum controlling of laser scanning technique and the parameters both with theoretical and experimental methods.The first, the paper gave a comprehensive discussion about the quality index of laser transformation hardening. According to their attributes, the quality indexes were classified to three different performance modules. Then, the paper gave a hierarchical structure for the LTH quality index system. And the decision-making framework model of the quality control was also set up.The second, based on the theoretical analysis of the temperature distribution characteristics and the actual hardened case distribution, the paper put forth that the simulation on the hardened case can be carried out with the temperature models respectively in the longitudinal and the cross section of the part. Furthermore, the paper put forward that by taking accessorial heat source to considering the influences of the boundary conditions and combining with the two temperature models, the simulation on three dimensions distribution of the case could be calculated much faster than pure numerical calculation.The third, with experimental and theoretical methods, the paper researched the relationships between the surface hardness, the case-depth and the laser power, scanning velocity. The researches aimed at the sensitivity of the variation of laser power and scanning velocity to the hardness and the case-depth. The reasonable explanation was put forward on the experimental results.The fourth, the theoretical and experimental researches were executed on the case distribution shape and the case discrepancy between the beginning and the ending boundaries of the part. The methods were also discussed to improve the uniformity for the hardened case distribution. The paper put forward feasible methods to improve the uniformity, which were the laser power and the scanning velocity optimum combination and the techniques of laser scanning with sectionally changing velocity along the scanning path. The fifth, taking the case-depth, surface hardness and the case distribution uniformity...