Computer Simulation Of Powder Metallurgy Process

Powder metallurgy is a process in which various types of materials and products are prepared by forming and sintering from metallic powder or mixed powder(metallic powder mixed with non-metallic powder).Compacting is an important step in powder metallurgy production.The traditional process design of compacting mainly adopts the "experiential trial and error method",which has a long design cycle and high cost.Therefore,it is an inevitable trend to introduce computer simulation technology into the powder compacting process.In this thesis,the process of powder forming is simulated by computer.As a supplement,the process of spark plasma sintering(SPS)is also simulated.This thesis summarizes two ways of modeling powder forming at present,and introduces in detail the mechanical models and related theories involved in each way.The difficulties in numerical simulation of powder forming were analyzed on the basis of summarizing the research status of various ways of modeling powder forming at home and abroad.It is determined that the modeling approach adopted in this thesis is based on the micromechanical method of densely packed spherical particles.The applications of main simulation software(Abaqus,MSC.Marc,ANSYS,DEFORM)in powder forming were reviewed.Through the comprehensive comparison of four simulation software,the optimal simulation software for this study is selected as Abaqus.Given that Abaqus software provides users with Abaqus script interface.In this study,the generation principle of dense packing spherical particle model was proposed,and Python script was written to realize the establishment of random distribution three-dimensional dense packing spherical particle model.The finite element analysis software Abaqus was used to simulate the powder compaction process on a microscopic scale.The accumulation behavior of randomly distributed three-dimensional dense spheres of loose powder particles was studied.The friction coefficient and compression method were discussed.The influence law of density of embryos,The effects of friction coefficient and pressing method(one-way suppress,two-way double punch pressing)on powder accumulation behavior and density of pressed embryo were discussed.The simulation results show that the essence of powder material accumulation is to reduce porosity and increase density.The powder stacking process can be divided into two stages :(1)the powder particles have displacement and elastic deformation;(2)plastic deformation of powder particles due to extrusion.The method of bidirectional pressing and lower friction coefficient are beneficial to the uniformity of the blank density.This conclusion has certain guiding significance to the research of powder compaction forming theory.Spark Plasma Sintering(SPS)is a new rapid sintering technology developed in recent years.From the perspective of simulation,SPS simulation involves temperature field,electric field and displacement field at the same time,and the simulation process is very complex.As a supplement,this paper established a multi-field coupling model with electric field,temperature field and displacement field by using the finite element analysis software Abaqus 6.14,SPS simulation was conducted for the core parts of the sintering system,and the discharge plasma sintering process of conductive powder and non-conductive powder was compared.The simulation results show that :(1)the highest temperature at the final state of sintering is located at the position where the pressure head contacts the mold,the lowest temperature is located at the upper surface of the upper electrode and the lower surface of the lower electrode,and the other parts are between the two.(2)the heating rate of conductive powder materials is faster than that of non-conductive powder materials,but the temperature distribution of non-conductive powder materials is more uniform than that of conductive powder materials.