Concept for the Incorporation of Auxetics as Active Die Faces for Flexible Metal Forming Tools

Auxetic materials and cellular structures offer unique mechanical properties with respect to negative Poisson ratios, which essentially leads to elevated shear moduli and delivers superior mechanical resilience under specific mechanic and dynamic loading conditions. In the present study, we provide a literature review about auxetics, their specific properties and the resulting mechanical behavior. Systematically, we present concepts to apply these properties to the elementary functions of adjustable tools in groups of passive and active implementations of auxetic structures into forming tools. Conceptual application clusters are derived with respect to three scales of flexible forming tools: i) smallest adjustments of a surface layer to influence and control the material flow by pressure distribution, ii) intermediate adjustments to comply with manufacturing tolerances (e.g. elastic springback of the product) and iii) large tool surface adjustments by actuated substructures to produce variants. We present protype concepts of an elastically deformable cellular auxetic structure and a non-assembly mechanism with auxetic properties and quantify the benefits and limitations of both concepts. In future, we aim to apply these concepts to demonstrators used in sheet metal forming processes.