A parameter-free strain estimation method to prevent occurrence of splits in sheet forming of complex CAD designs

Abstract. Early detection of manufacturability issues in the design stage is key to avoid long lead times in product development. For various sheet forming processes a critical issue is the occurrence of splits, due to forming beyond the intrinsic formability properties represented by the Forming Limit Curve (FLC). Nevertheless, within industrial engineering practice a detailed manufacturing process simulation including forming limit prediction is not obvious. While commercial Finite Element analysis tools for sheet metal forming are readily available on the market, because of current limitations in availability of accurate data, companies may be rather inclined to choose experimental verification over process simulation analysis. For formability analysis, the required accurate data comprises both material data (hardening data, plastic anisotropy data, FLC data) as well as process data (e.g. non-linear friction data in lubricated system; static or dynamic tool elasticity properties).Therefore, we propose a first-order approximation of the forming deformation, without any parameter (e.g. for material, friction), based solely on conformal flattening of the CAD sheet surface. In this work, we show the usefulness of this method in hydroforming of complex-shaped, industrial parts (bipolar plates). It is shown that from the strain estimation, we can identify the most critically strained regions for individual categories of strain, as formability is known to be greatly dependent on strain mode. The tooling assists to compare design alternatives in terms of formability in the absence of FLC or even basic material data.