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.
Regular elemental powders were used in warm flow compaction instead of the expensive micron-sized powders to fabricate cross-shaped parts. Debinding behaviors,sintering properties and shape consistency of the sintered parts were studied. Binder removal was accomplished by heating green compacts at intermediate temperatures with optimal heating rates until the debinding temperature was reached. Results show that by controlling debinding process,complex parts with good shape consistence can be obtained by warm compaction of binder-treated powder. Fine and shiny surface was obtained and no surface defect can be observed for sintered parts debinded at 2 ℃/min,while defect can be observed in sintered parts debinded at 4 ℃/min.
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.
Some flow stress models was used to simulate the compaction of a cylindrical specimen.A new flow stress model was presented by analyzing and summarizing the powder compact experiment with different initial densities.Compared with other models,the new model fits better with the experiments.The compaction process of a synchronizer hub was simulated with new model and the synchronizer hub shape was improved by the simulation results.The density distribution was measured and compared with the simulation results of splitting the samples into pieces.The comparison shows that the model could be used to simulate the powder compact process in an efficient and accurate manner.And the results indicate that the density distribution is homogenous after optimization.
