Abstract
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.
Highlights
Extrusion welding is a process that generally is characterized by co-extrusion of two or more metals [1] or, even, by different flows of the same metal
Different aluminum alloys have been worked through this technique; at the investigated process is physically possible with all wrought aluminum [2]
Several works have been carried out to highlight the influence that die design has on the extrusion process [3,4]
Summary
Extrusion welding is a process that generally is characterized by co-extrusion of two or more metals [1] or, even, by different flows of the same metal. Due to the porthole die complexity, experimental analyses usually require time consuming for the equipment construction and, besides, it results to be expensive to verify different geometrical solutions From this point of view, simplified equipments were proposed in literature [12]. Experimental data, found in literature [13], were used in order to validate the numerical results Both FE and NE methods were used in order to simulate the process starting from 2D analyses; for this investigation, a significant section was extrapolated by the complete die. Both FEM and NEM results were conducted and their results were compared with the experimental ones In this phase, isothermal analyses were carried out in order to reduce the computational time fixing the billet temperature to 510°C; the model simplification can be justified considering that along the welding plane the material presents a narrow temperature variation.
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