Numerical Simulation And Experimental Verification Of Extrusion Molding Of Tungsten-based Alloy Feed

Powder extrusion molding is one of most important way to prepare large slenderness ratio tungsten-based alloy bars. Developing of the process parameters in traditional methods always faces significant limitations i.e. long experiment period and high cost. However, modern simulation technology can effectively reduce the experimental cycle. In order to improve the reliability of simulation and accelerate the developing cycle of tungsten-based alloy bars, it is necessary to analyze the mechanical properties of feed under different conditions. In this work, the models of forward extrusion and screw extrusion of tungsten-based alloy feed were systematacially investigated and technological parameters were optimized.The friction angle and adhesion of tungsten-based alloy feed were measured by the electro-hydraulic servo testing machine. The stress-strain curves of tungsten-based alloy feed under different temperatures were measured by the WSM-200KN mechanical testing machine. Thermal physical parameters between20～90℃were measured by Germany NETZSCH DSC200F3differential scanning calorimeter. The forward extrusion process and screw extrusion process of tungsten-based alloy feed as well as the influence of process parameters on the extrusion products were simulated and analyzed by MSC.Marc and Deform-3D software, respectively. The tungsten-based alloy extruded bars were prepared by YH41-25C-hydraulic machine and Dorst V15spHv vacuum extrusion machine. The fracture of extruded bars was analyzed by Scanning Electricity Microscope(SEM).The results are as follow:(1) The feed friction angle of the forward extrusion tungsten-based alloy is17.3°. The adhesion is4.9MPa.The shear yield strength of feed increases with increasing the positive stress.(2) The results of simulation of tungsten-based alloy feed forward extrusion indicate that the cracks are easy to be observed on the extruded bars when the forward extruding speed is too slow. Otherwise, the density of the extruded bars will be uneven and the resistance of deformation will go up. The displacement gradient will appear when the friction coefficient goes up, leading to an inhomogeneous deformation of the extruded bars. Under the condition of small extrusion ratio, the extruded bars will not have enough density. Otherwise, the deformation resistance will be too large, which lead to the stress concentration phenomenon. When die structure is cone, extrusion speed is2.5mm/s, friction coefficient is0.1and extrusion ratio is11, the simulating results of tungsten forward extrusion are basically consistent with the actual results.(3) The results of simulation of tungsten-based alloy feed screw extrusion indicate that the deformation resistance and thermal stress will be too large when the extrusion temperature is too low. Otherwise the feed will be softened excessively which can lead to low strength of bars. When the extrusion speed is too slow, the densification of bar and efficiency of extrusion will be low. Otherwise the bar will be non-homogeneous. When the extrusion temperature is70℃, and speed is5mm/s, the simulation results are well consistent with the actual results.