Feeding Type Laser Cladding Forming The Three-dimensional Temperature Field Numerical Simulation Research

In recent years, powder-feeding laser cladding forming techonology has beenwidely applicated in the field of component forming and repairing. Becauselaser cladding forming is a complex physical and metallegical process, and thereare many parameters affecting the forming quality, the forming quality thedifficult to control. The temperature field and stress field of laser claddingforming, especially the temperature gradient，cooling rate and stress distributionhas a direct influence on the quality and cracking of the cladding layer. However,because laser cladding forming is a rapid melting and solidification process, it isvery difficult to measure the variation of the temperature and stress fields.Therefore, numerical simulation are combined with experimental method tostudy the temperature and stress field, in order to reveal the microstructure andcracking mechanism of laser cladding forming.Firstly, powder-feeding single track, multi-track overlapping and multi-layerlaser cladding three dimensional transient temperature field models were set upwith ANSYS APDL parametrical programming. The temperature fielddistribution, the temperature-time history of different node points, and thecontour and temperature variation were analyzed. A kind of measuring methodwas developed to measure the depth of the melting pool. It is shown from theresearch results that the temperature field of the laser cladding presenteddifferent characteristics. The temperature of the node points at both ends of thecladding layer is higher than that at the middle of the track, which presents aphenomenon of “end effect”. The temperature gradient and cooling rate of thelaser cladding process is very high, which is about10~5℃/s and10~3℃/s,respectively. The influence of the temperature gradient on the microstructure andits growth direction were studied through the analysis of the temperaturegradient distribution on different node points, which provided a theoretical basisfor the optimization of the powder-feeding laser cladding forming processparameters.Secondly, on the basis of the finite element simulation and analysis of thetemperature field, thermo-mechanical coupling analysis of multi-layer laser cladding was carried out. It is shown from the results that the tensile stress alongthe laser scanning direction (the forward direction of X axis) is the largest;therefore, the cladding layer is liable to crack perpendicular to the interface ofthe bonding face. The stress at the interface between the cladding layer and thesubstrate and the end of the cladding layer is relatively high, where cracking iseasy to initiate. Through the study of the plastic strain along the three directionsof certain point, two kind of cracking patterns as hot cracking and solidificationcooling cracking were discovered. The factors influencing the forming of thecracks were analyzed, which provide a theoretical basis for the decreasing andelimination of cracks.Finally, through the experiments of laser cladding forming, the microstructureand cracking behaviors of laser cladding forming were analyzed. Theexperimental result was well coincided with that of the numerical simulation,and the results of the numerical simulation were verified.