Simulation of metal powder bidirectional compression in a pressing tool with a floating die

The process of bidirectional compression of a powder titanium sponge in a pressing tool with a floating die is considered. The paper studies powder screenings of titanium sponge of TG-100 grade according to GOST 17746-96 with a fraction of -3 + 1 mm. A new design of the pressing tool is proposed to implement the process of bidirectional compression. The simultaneous movement of the upper and lower punches relative to the sectional die is achieved by placing the die between two rubber springs. The pressing tool provides an efficient compression due to the implementation of a synchronous vibration-free movement of the lower and upper punches relative to the sectional die, as well as a uniform compression unloading on all sides, which eliminates the occurrence of splitting cracks. Numerical simulation of the process was performed using a finite element analysis. In the simulation, it was assumed that the elements of the pressing tool have properties of an absolutely rigid body. The powder material is considered as a continuous compressed elastoplastic medium with initial isotropic properties. The powdered material yield condition is described by the Modified Drucker-Prager Cap yield model. The rate of plastic deformation is proportional to the voltage at the current moment, the stress state determines the instantaneous increments of plastic deformation components. The associated plastic flow rule is fulfilled. Mooney-Rivlin hyperelastic material model was used as a model of the material (SKU-7L rubber) of the spring elements. As a result of the simulation, the calculated density distribution in the cross-section of the compacted powder workpieces at different compression pressures was obtained. The dependence of the average relative density of the powder workpieces on the compression pressure was investigated. For the compacts obtained at different compression pressures (100 and 500 MPa), a micrographic study of the microstructure of the samples longitudinal sections surfaces was performed. The change in the shape and size of pores in the lower and upper parts of compacts was studied. In order to assess micromechanical properties of the obtained workpieces, kinetic microindentation of thin section surfaces of the longitudinal axial sections was carried out, which allowed determining the microhardness values, the creep characteristic, and the reduced modulus of elasticity. It is shown that the proposed design of the pressing tool allows obtaining workpieces with a more uniform density distribution in comparison with those manufactured using monodirectional compression.