Simulation of Porthole Die Extrusion Process comparing NEM and FEM modelling

Porthole die extrusion is a process typology that can give great advantages in the forming processes. Due to the complexity of the die assembly, experimental analyses are often carried out in order to investigate the parameter influence on the quality of the final parts. Finite Element Analyses, however, have been often used for the cost reducing and for a better local investigation of variables like pressure and effective stress inside the welding chamber. In spite of that, up to now, commercial FE codes present a "structural" limit during the welding phase due to the impossibility to simulate element joining when material reaches the required process conditions. From this point of view, the Natural Element Method (NEM) provides significant advantages; in fact, the meshless characteristic of NEM is "natively" able to simulate joining of free surfaces, as it occurs during porthole die extrusion, simulating the welding line formation inside the welding chamber. In this paper, using experimental tests recognizable in literature, the authors tried to validate the effectiveness of this technique; moreover, even a comparison between NEM and FEM results was carried out. More in detail, different geometries of the welding chamber were analyzed; in some cases, the process conditions were suitable to guarantee material welding while, in other cases, the material came out from the porthole die without joint formation. The variable that was used to verify the process goodness is the maximum pressure inside the welding chamber. Furthermore, to evaluate the effectiveness of 2D analyses, even in a complex shape, a significant section was extrapolated for each die, performing a NEM vs. FEM assessment of the results. A good comparison was obtained between the two different methods that, moreover, were in agreement with the experimental tests.