Energy-efficiency increase through hybridization of solid forward extrusion with electrical resistance heating - Modeling the contact between electrodes and workpiece

研究的重点是WZL开发的混合温固相正向挤压工艺。在此过程中，通过电阻加热在成形过程中对工件进行加热。根据工艺的性质，局部加热发生在易受内人字形裂纹影响的区域。与传统的热固体正向挤压工艺相比，这导致了更高的能效。到目前为止，混合热固体正向挤压产生的提高能效的效果还不能在工业上使用。造成这种情况的原因有两个。首先，由于工件与凸模、凸模之间的接触区域存在复杂的电热机械叠加现象，导致升温时间波动较大。这比典型的冷固体正向挤压加工时间要长。其次，对于接触区的刀具侧，观察到了表面粗糙度变化和边缘质量损失的烧损现象。烧损会降低工具的使用寿命。高的、波动的升温时间以及烧损导致工艺稳定性降低。本研究旨在广泛地解释凸模、对冲头和工件接触系统中的电热-机械相互作用。这一知识使接触系统的全面推导具有更短的升温时间和更少的烧损。

Focus of examination is the hybridized warm solid forward extrusion process developed at WZL. In this process the workpiece is heated during forming through resistance heating. Determined by the nature of the process local heating takes place in the area susceptible to inner chevron cracks. This results in a higher energy-efficiency compared to the conventional warm solid forward extrusion processes. As of now the effects within the hybridized warm solid forward extrusion causing increased energy-efficiency cannot be used industrially. There are two reasons for this. Firstly, due to complex superimposed electro-thermal-mechanical phenomena in the contact area between workpiece and punch as well as workpiece and counterpunch highly fluctuating heating-up times occur. These are greater than typical cold solid forward extrusion process times. Secondly, as for the tool-side of the contact area a burn-off is observed in the form of a changing surface roughness and a marginal mass loss. The burn-off reduces the tool lifetime. The high, fluctuating heating-up times as well as the burn-off result in a reduced process stability. This research aims at extensively explaining the electro-thermal-mechanical interactions within the contact system of punch, counter punch and workpiece. This knowledge enables the comprehensive derivation of a contact system with shorter heating-up times and reduced burn-off.