A novel protection-type porthole die for manufacturing multi-cavity and thin-walled extrusion profile: numerical simulation, optimization design, and experimental validation

The structure type of porthole die has a crucial impact on metal flow balance in die cavities, strength of seam weld, and die strength. At present, there was little industrial case for the application of protection-type porthole die. In this study, a novel combined porthole die which includes protection, upper, and lower dies was designed to manufacture a multi-cavity and thin-walled profile. The plastic deformation behavior and flow velocity distribution of metal in die cavities were examined by numerical simulation. Seam weld strength and porthole die strength were quantitatively analyzed. In order to eliminate extrusion defects, multiple structure modifications for protection-type porthole die were proposed to balance metal flow and improve seam weld strength. Extrusion experiments were carried out on the horizontal extruder to validate the accuracy of numerical model and the rationality of modified dies. The research results showed that the relative velocity difference at die exit corresponding to the theoretical flow velocity for the designed die is at the range of -54.96 similar to 5.86 mm/s. The weld strength at the outer edges of profile is larger than that at the connecting edges of profile. The comprehensive effect of above factors that leads to an uneven front end, bending defect and seam weld cracking in extruded profile. After optimization, the relative exit velocity difference is decreased to at the range of -1.478 similar to 1.641 mm/s. The welding pressures on the concerned welding planes are obviously improved. The maximum stresses on the optimized porthole dies are both far less than the yield strength of H13 tool steel. The simulated front end shape for extruded profile agrees well with experimental one as well as the grain size and distribution on different observation positions are relatively uniform, which validate the rationality of design method for protection-type porthole die.