A new process design for performing hole-flanging operations by incremental sheet forming

摘要

Hole flanges are important functional elements in many sheet metal parts. They provide stiffness, allow for positioning and fixation, they guide cables etc. Hole flanging operations in sheet metal parts are typically performed using dedicated tooling. Recent publications proved that hole flanging by incremental sheet forming (i.e. incremental hole flanging) is an interesting alternative to the traditional operations with dedicated tools. In incremental hole flanging, limit hole expansion ratios of up to 4 were observed which are much larger than the typical expansion ratios of around 2. In addition, the high flexibility of the incremental sheet forming process is maintained, i.e. flanges can be formed using a universal CNC-driven forming tool without dedicated tooling. However, deficits in terms of process time and geometric accuracy still limit the industrial application. This paper investigates the process limits of incremental hole flanging and proposes two new approaches aiming to reduce current deficits. The first one is an adaptive blank holder that acts in the vicinity of the forming tool and reduces unwanted secondary deformation that would lead to deviations from the target geometry. The second one is a new process set-up that makes it possible to perform incremental hole flanging operations at high speed. Using these approaches, the flexibility of incremental forming and its advantages regarding high formability can be exploited, while the typical disadvantages such as geometric inaccuracies and long process times can be minimized.