Multi-field Numerical Simulation And Experimental Study Of SLM Laser Cladding

The laser selective melting(SLM)process can realize the additive manufacturing of complex cavity parts with high precision,high strength and high quality,and has been developed and applied in the fields of aerospace,rail transportation and bioengineering.However,in the actual forming process,the flow and heat transfer of the molten pool formed after the powder melting directly affects the quality of the formed parts,and the thermal fluid behavior of the molten pool and related physical mechanisms are not fully understood,which makes it difficult to control the forming process stably,and typical metallurgical defects such as pores and cracks often exist in the formed parts,which limits the wide application of SLM technology and its formed parts.In order to understand the various physical mechanisms in the SLM forming process,investigate the causes of defects,and then improve the quality of the formed parts,numerical simulations of the SLM single melt channel laser cladding forming process are conducted,and the main research contents and conclusions are as follows:(1)Combining the discrete element theory and the real characteristics of stainless steel316 L powder particles,a three-dimensional powder bed model is established;the Gaussian planar heat source model is used as the light source,and the fluid dynamics software and the physical parameters of the powder material are combined to establish the melt pool dynamics model under mesoscopic scale.(2)Numerical simulations of light-powder coupled heat and mass transfer in SLM singlepass forming process are conducted to study the changes of laser power,scanning speed and energy density on the morphological dimensions,temperature field and flow field of SLM single-pass forming melt channel: the temperature,melt width,melt depth and flow rate of the melt pool increase with the increase of laser power and energy density,and decrease with the increase of scanning speed.Along the laser scanning path direction,the temperature of the upper and lower observation points of the cross-section of the melt pool is positively correlated with the laser power and energy density,and inversely correlated with the scanning speed.(3)The accuracy of the numerical simulation is verified by comparing the actual forming of a single melt channel with a simulated channel under different process parameters.The causes of spheroidization and unevenness are explained,and it is qualitatively analyzed that the spheroidization and unevenness can be effectively improved by increasing the energy input appropriately.