| Selective Laser Melting(SLM) of high temperature alloy powder is the key research object of today’s 3D rapid prototyping manufacturing and has been widely used in fields like aerospace and biological treatment at present. But during SLM process laser react with powder violently that may form a larger temperature gradient and cause a large thermal stress inducing defects affect the quality of forming parts. Therefore, the exploring the forming mechanism of high temperature alloy powder SLM and analyzing the temperature field and stress field distribution, SLM forming technology of high temperature alloy powder has important guiding significance.In this thesis, three-dimensional transient finite element model has been constructed by finite element modelling software. The heat source was approximated as Gaussian distribution. Birth-death element and APDL parametric language command flow considering latent heat of phase change and material nonlinear problems has been designed. The temperature field and residual stress field during SLM process of nickel-based super alloy GH4169 has been simulated.By analyzing temperature field of single-pass scanning of single-layer block forming, properties like temperature distribution of scanning procedure, scan line change to transfer and temperature changes trend with time have been studied. Effects of scanning speed and laser power on temperature fields have been discussed. The size of melting pool increases with the increase of laser power. The instantaneous highest temperature decreases with the increase of scanning speed. The temperature gradient in front of melting pool is larger. Based on these analysis, mechanism of the change of temperature and temperature gradient has been deduced and elected suitable process parameter.Based on the results predicted by temperature field simulation. The changing rule of the stress field distribution has been studied. The stress distributions of scanning procedure, scan line change to transfer and stress changes trend with time have been studied. It is found that stresses on the surface of forming part are mainly about tensile stress, however, pressure stress on substrate. Stress concentration during scanning procedure occurs mainly in areas between scan lines and scanning line change to transfer. Residual stress σx during procedure of cooling down temperature is mainly about tensile stress which focus on boundary and the four corners of forming part. The highest tensile residual stress σy occurs on scanning line change to transfer. Von Mises equivalent stress concentrate on boundary and the four corners of forming part too, and that is the main reason why warp and crack show up.SLM Experiment of nickel-based super alloy GH4169 has been performed to validate results from simulation. The correctness of simulating method was validated. With the parameter obtained from simulating results, block parts with good density has been produced. At last part of this paper, factors affecting process of SLM and defect easy to occur has been studied. Results show that the method using finite element modelling to predict defect during forming process turns to be effective. |
