The production of square bars with curvature requires additional processes such as bending press after extrusion, so the process is complex and uneconomical. Recently, many researches have been conducted to improve the production process of a curved square bar by using the cold extrusion method. However, these studies also had to build an additional process infrastructure such as the use of guide rolls, and they were limited in that the process could not be simplified based on a single platform. The curvature extrusion method proposed in this paper is a method to control the curvature by adjusting the shape of die to be extruded. Unlike the usual die shape, it creates a tilt angle on the die to induce a difference in speed between the upper and lower sides of the extrudate by inducing the internal stress difference between the upper and lower sides of the billet to induce the curvature. This difference in internal stress is caused by the stress concentration effect occurring in the non-flow region near the edge of the die. In the past, the influence of the non-flow part was analyzed by the application of the upper bound method or the slab method, but the reliability tends to be lower because the material flow, stress and strain are not taken into consideration. Recently, finite element analysis has been applied to solve these problems. In order to use the curvature induction method by controlling the die shape, a systematic analysis process for the above effect was studied. The influence of non-flow region occurrence(DEAD METAL ZONE) was analyzed through Deform-3d analysis program. The billet is set as a tetrahedral element and the symmetry plane is set in the entire simulation model to save the computer memory and time required for the experiment. The friction coefficient condition was set to be Coulomb friction condition, and the same friction coefficient value was the same regardless of the area where the experiment was performed.
In the experiment, the simulation was performed under the tetrahedral element billet condition. Therefore, when there is no fillet of proper value in the extrusion design, the pull-out phenomenon is observed and the constituent elements of the non-flow region are erased. However, in the actual experiment, pull-out phenomenon was solved by giving a fillet in the simulation condition because there is a difference in friction coefficient depending on the place, unlike the Coulomb friction condition. However, since the lubricant was used in the experiment, it is difficult to measure the original friction coefficient . Therefore, in this experiment, By comparing and analyzing actual experimental results and simulation results, a simulation platform of a new curvature extrusion process was constructed by proving the effect of fillet in actual experiments and then studying the friction coefficient applied when setting experimental model to simulation condition.
Simulation results show that when the coefficient of friction is 0.4, the fillet is 0.4, the friction coefficient is 0.6, the fillet is 0.5, the friction coefficient is 0.6, the fillet is 0.8, and the friction coefficient is 0.8. When the fillet was 0.8mm, the result showed the same result as the experimental value. When the curvature value was numerically analyzed, the fit was best when the fillet was 0.4mm when the coefficient of friction was 0.4.