Design Simulations and Verification Experiments of the Novel Extrusion Die and Dummy Blocks
Date Issued
2016
Date
2016
Author(s)
Liu, Cheng-Hsien
Abstract
Abstract In the past, there were many defects occurred in the direct extrusion process has not been solved for a long time. Such as surface coarse grain layer, back-end funnels or axial hole defect, inner oxide ring, etc. These defects will cause scrap increased and quality problem. We developed the Ex-ECAE (Extrusion + ECAE) process using the conventional direct extrusion press to scale up ECAE process and eliminate the surface coarse grain layer of the extrudate. Consider the capacity of the existed extrusion press and the arrangement of the production line, the Ex-ECAE process with die angle of 120° and route C were a choice. The billet was AA 6063. The experimental results show that the surface coarse grain layer and the grain in the core of the rod billet were refined by the different causes of shear stress. Both of the inner and outer corners of the die channel were filled with the extruded material, because the rod billet was supplied continuously and the high friction of the channel surface (equivalent to back pressure) in the Ex-ECAE process. Therefore a dead metal zone cause by the friction of the channel was built at the corners. This brought about the surface coarse grain layer flowed through the channel along the boundary of the dead metal zone. To keep the continuity with the dead metal zone along the boundary, the surface coarse grain layer was imposed by the high intensity shear stress. The grain of the surface coarse grain layer would be refined. As part of the grains in the core of the rod billet would be refined and became elongated grains by the extrusion process. There were many substructures has already been built inside these elongated grains. With the help of the simple shear, the substructure built during the extrusion process would translate into subgrains of high angle grain boundaries. Then those elongated grains would become fine equiaxed grains. Except the grain refinement, adopt the Ex-ECAE process to scale up the ECAE process includes the other advantages. First, the billet-to-billet loading method makes the Ex-ECAE process become as a continuous process. Secondly, it may be difficult via ECAE process to produce an extrudate with a specified shape. As we need a rod billet of a specified shape first. But this kind of rod billet may be hardly to produce by machining, or maybe the cost of the machining is too high. The textures of the Ex-ECAE sample at various segments are measured. The results reveal that the first segment of the Ex-ECAE sample has a perfect fiber texture which consists of a mixture of strong <001> and weak <111>. The texture of the second segment is a mixture of strong {1 1 0} <1 -2 1> and weak {0 1 1} <2 -1 0>. Finally, the texture of the extrudate (the third segment) is reversed to an incomplete fiber texture which consists of the strong {0 0 1} <-1 -1 0> and the weak {1 1 1} <1 -1 0>. Using the direct extrusion press to perform the Ex-ECAE process, some congenital defects, e.g. back-end funnel defect and inner oxide ring, will occur. No one tried to eliminate or avoid these defects by the design of the dummy block. However, we designed a hot top and beveled edge dummy blocks to eliminate or avoid back-end funnel defect and inner oxide ring, respectively. And the experimental results showed that these two designed dummy blocks could eliminate or solve these two defects as expect, respectively. In the design of the hot top and beveled edge dummy blocks, with the help of FEM (Finite Element Method) simulation, we could obtain the effect of the design parameters quickly. Finally, more severe conditions of ECAE (such as die angle of 90° and increase process passes) can be performed and scaled up by the direct extrusion if the capacity of the press is high enough.
Subjects
Direct Extrusion
Finite Element Method
Surface Coarse Grain Layer
Back-End Defect
Type
thesis
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