Compensation for tool deformation and expansion in virtual try-outs of hot stamping tools

The mechanical properties of hot-stamped parts strongly depend on the tool's cooling performance. The cooling rate hinges on sufficient temperature gradients and on an excellent contact conductance between tool and workpiece. A uniform distribution of the contact pressure is the key to an even cooling behaviour, and hence, a homogenous micro structure of the formed part. Elastic deformations of machine and tool components under load are a major influence on the pressure distribution between tool surface and hot-stamped part. This applies to hot and cold forming tools. An additional difficulty in hot stamping are superimposed thermal expansions and contractions of the tool, which also affect the part's mechanical properties due to their influence on the normal contact pressure. Manual die spotting needs to compensate for all these undesired effects and makes tool try-out a large time and money-consuming factor in the development of hot forming tools. This paper presents methods to transform the spotting of hot forming tools into a virtual production reality in order to reduce manual labour and lower costs. It gives details on the numerical compensation of tool surfaces for elastic tool and machine deformations and for temperature-induced tool expansions and contractions. The authors critically analyse necessary and achievable accuracies of computed surfaces and point out required improvements for the future implementation of virtual try-outs into tool development and manufacturing processes.