A new model for describing the compaction process of iron powder was proposed based on the continuum hypothesis and elliptical yield criterion.To simulate the densification behaviour,the constitutive model was implemented in Marc computer program.For the relationship between load and displacement,different models were compared and the influence of the parameters in the constitutive equations was determined by means of simulation and experiments.The density distribution of a balancer was measured and simulated.The results show that the parameterηadopted plays a modification role for the load-displacement curve,and compared with other models the present model fits better with the experimental data in the later stage of the compaction process mainly due to the different parameters A and B.The friction on the contact surface contributes to the inhomogeneous density distribution under large deformation of the workpiece.The comparison between the simulation and experimental data indicates that this model can be used to predict the powder compact process precisely and effectively.
The constitutive relation of powder material was derived based on the assumption that metal powder is a kind of elasto-plastic material, complying with an elliptical yield criterion. The constitutive integration algorithm was discussed. A way to solve the elastic strain increment in each iteration step during elasto-plastic transition stage was formulated. Different integration method was used for elastic and plastic strain. The relationship between model parameters and relative density was determined through experiments. The model was implemented into user-subroutines of Marc. With the code, computer simulations for compaction process of a balancer were performed. The part is not axisymmetric and requires two lower punches and one upper punch to form. The relative density distributions of two design cases, in which different initial positions of the punches were set, were obtained and compared. The simulation results indicate the influence of punch position and movement on the density distribution of the green compacts.
