Identification of Tribological Mechanisms of Shot Peened Steel Surfaces for an Application in Sheet-Bulk Metal Forming

Author:  Maria Löffler, Ulf Engel, Kolja Andreas, Marion Merklein
Source:  ICSP-13
Doc ID:  2017043
Year of Publication:  2017
Abstract:  
Abstract: An increasing demand on highly-integrated high-strength lightweight components,especially in the automotive industry, motivates the need for the development of the new class of manufacturing processes sheet-bulk metal forming (SBMF). The use of SBMF for producing those components leads to many challenges. This is due to the fact that the processes are characterized by a successive and/or simultaneous occurrence of different load conditions regarding stress and strain states. These conditions influence the material flow and thus the geometrical accuracy of the produced parts. To improve the product quality, methods to control the material flow are needed. One possible approach is given by the local adaption of the tribological conditions. Within the present study shot peening as a method to impede the material flow and thus to increase the friction is investigated. The aim was to identify the tribological relevant effects determined by the surface properties. Thus, surfaces with different characteristics regarding roughness, work hardening and residual stress states were generated by peening. The influence of the varying surface properties on the material flow was identified using two laboratory friction tests. The results show that with increasing roughness and work hardening the friction increases. For the higher roughness values this can be explained by an enhanced interaction of the roughness peaks of tool and workpiece surface. To identify the influence of work hardening a numerical model of the pin extrusion test with an adapted modelling of the workpiece was used. The results revealed that a hardened surface layer leads to reduced flow velocities in lateral direction what is an indicator for an impeded material flow.