Numerical Simulation And Experimental Investigation On The Selective Laser Melting Process Of Invar Alloy

The rapid development of the selective laser melting forming technology(SLM)provides a new idea for the forming of Invar alloy parts.However,the forming process of SLM involves many process parameters,which have an important influence on the forming quality and mechanical properties of SLM parts.At present,there are few reports on the research of SLM forming process of Invar alloy.Therefore,in order to promote the engineering application of SLM forming technology for Invar alloy,it is necessary to conduct in-depth research on the SLM process of Invar alloy and the optimization of process parameters.In this thesis,the combination of numerical simulation and experiment was used to study the distribution of temperature field and stress field during the SLM forming process of Invar alloy,and the influence of some process parameters on them.Based on this,some SLM process parameters ware selected and optimized.The following are the main research contents and innovative work of this thesis:(1)Finite element simulation was performed to study the temperature field in Invar alloy SLM process,the basic characteristics of temperature field distribution,and the SLM process parameters’(laser power and scanning speed)influence on the temperature field.In view of the shortcomings in the selection and optimization of process parameters for the existing SLM numerical simulation research,this thesis established a model of the relationship between the main process parameters(laser power and scanning speed)and the size of the molten pool by BP neural network,and used the genetic algorithm to optimized the process parameters.(2)A new method was proposed to improve the consistency of the molten pool size during the SLM processing,and worked well both in the simulation and forming test.Finally,the Invar alloy SLM parts,which has smooth surface and don’t contain defects such as voids,warps and cracks,were manufactured in this way.(3)A 3D sequentially coupled finite element model was developed to investigate the distribution characteristics of the stress field and the influence of laser power and scanning speed on the stress field during the SLM process of Invar alloy.(4)The Finite element simulation of multi-layer SLM process was carried out on In625 alloy by ANSYS Additive 19.1.The basic distribution characteristics of the stress field during the multi-layer SLM process were analyzed.The influence of four common hatch angles on SLM stress field was studied.It has been found that a 45° hatch angle allows the molten layer to have small residual stresses both in X and Y directions simultaneously,and minimizes the difference in stress between the two directions.