Extrusion through two die openings: A 2D upper-bound analysis checked by plasticine experiments

Abstract The design of extrusion dies, meant for the manufacturing of aluminium profiles of complex shape, is today mainly built upon experience and the results of numerous experiments. Typical problems are the determination of the lengths of the bearing lands and the optimal positions of the die openings. These problems must be solved simultaneously in order to obtain a feasible die resulting in the same exit velocity for different parts of the cross-section. If the bearing land is not designed in a proper way the extrudate might assume a curved, and not the desired straight, shape. If the die opening is positioned in an incorrect way the difference between bearing lengths, characterizing the bearing land, will become unnecessarily large and the required force high. In order to study these kinds of problem by means of a 2D analysis, the extrusion through a die with two openings of different sizes has been studied. Also, the influence of the hole positions is analyzed. The upper-bound method is utilized and the proposed velocity fields are optimized numerically. In this way bearing lands giving the same velocity of the two extrudates are found for different positions of the die openings. To check the results, plasticine experiments were performed. Qualitative agreement was found and it is concluded that this kind of approach is useful for increasing know-how within the filed of die design.