Friction and lubrication modelling in sheet metal forming: Influence of local tool roughness on product quality

To improve the accuracy of forming simulations, advanced friction models are increasingly used in the industry. These models account for the physical properties of the sheet, tool and lubrication and describe the tribological conditions during the forming operation. One of the main influencing factors on the tribology system, and therefore the friction coefficient, is the surface roughness of the tools. Until now, it is often assumed all tools have the same uniform surface roughness. In reality however, the tool might have different surface conditions dependent on the type and location of the tool. That is, the blank holder might be differently polished than the punch, and sharp radii might have a different tool roughness compared to flat areas. This paper investigates a significant number of tool measurements from different tool sets from Volvo Cars, and quantifies the effect of local surface conditions on product quality.