Design And Development Of System On Prediction & Analysis Of Shrinkage/porosity Defect In Castings

Shrinkage /porosity is a common defect in castings and one of main causes making products waste. The ultimate aim of the numerical simulation on temperature field in castings solidification process is for eliminating shrinkage /porosity or limiting them within the user's permission. The main task of the thesis is that prediction&analysis system of shrinkage /porosity defect in a casting,which is oriented to foundry engineering application,was preliminary developed based on ANSYS. The three-tier developing hierarchy structure was adopted in this system by operation visualization,parametric design,and function modularization.On the basic of the detailed analysis on main causes and main prediction methods of casting shrinkage/porosity,we put forward two methods to describe the solid phase rate of materials solidification. One is liner-distributing method,and the other is parabola-distributing method. And then,we apply the former to the system. We also put forward to realistic arithmetic of temperature gradient method and niyama criterion method. These methods are flexible in use.This thesis gives a system of defects sorting and a flow of defects reasoning and analyzing on physical field. By building a knowledge-base,a reasoning mechanism,a explaining mechanism and a defects information coding,the defects analysis system integrate defects information and defects analysis function,which include defects inquire,defects causes analysis,measure &suggestion of defects preventingand knowledge-base maintenance.The key to prediction of casting shrinkage/porosity lies in ascertaining the critical value of temperature gradient and niyama criterion. The thesis put forward two methods to ascertain the value,one is which is positive-direction and the other is negative-direction.We verify the realistic arithmetic of temperature gradient method and niyama criterion method by experiment,and we can draw a conclusion that the arithmetic is correct and reasonable in most cases and choice of developing tool is sound. At the same time,critical values of them are obtained. But niyama criterion method is not suitable for the prediction of shrinkage/porosity of high-chrome iron casting.