Influence of a drawbead passage in deep drawing processes on surface values and the tribological system

Abstract

In recent times, lightweight design and functional integration in metal forming and especially in deep drawing operations lead to complex geometries. These geometries can cause variable defects in production. Especially with modern materials like AHSS or UHSS, deep drawing becomes more challenging. One common way to meet these challenges and manufacture sheet metal parts without defects is the application of drawbeads in the forming tool. Drawbeads are used for an exact control and forecast of the material flow during the deep drawing process. It was already shown, that different material parameters like the tensile strength and the fracture strain are changed significantly after running through a drawbead. In addition, there are various indications that the tribological system in a drawbead passage is also changed significantly and that this has further influence on the ongoing drawing process. This assumption is examined with an experimental setup derived from industrial deep drawing processes. Therefore, different sheet metal materials are drawn through a drawbead geometry under the same conditions like the blank holder force, the drawing velocity or lubrication. After the drawbead passage, 3D surface parameters are measured and compared to the values in its initial state. Following, conventional strip-drawing tests with preloaded strips are carried out. The variation of the friction coefficient after a drawbead passage is analysed and compared to the initial state. The results are correlated with the surface values. For these investigations, three different materials are used: A conventional deep drawing steel because of its wide application as well as an advanced high strength steel AHSS and an aluminium alloy of the 6xxx series as representatives for modern lightweight materials.