Andreas Sterzing

Severe plastic deformation by incremental bulk metal forming

Incremental bulk forming technologies are investigated with respect to the creation of ultrafine-grained aluminium material. Based on first investigations of spin extrusion the technology of gradation rolling for rod shaped billets was developed. High strain generation as precondition for grain refinement is caused by the so called knead effect during processing in incremental rolling. Cross sections of processed billets show a demarcated area of different reflexion behaviour and a corresponding increase in hardness. In this area a gradient with decreasing grain size in surface direction is shown by crystallographic mapping. A several millimetre thick layer of refined material has been obtained.

Comparison of Material Behavior and Economic Effects of Cold and High Temperature Forming Technologies Applied to High-Strength Steels

The focus of forming high-strength steel at elevated temperature is to improve its forming properties like elongation and to reduce the power requirements during the forming process in opposite to cold forming. Because of the undefined and large spring-back effects parts made by cold forming are not able to achieve the demanded dimensional accuracy, which is necessary for laser welding operations in car body assembly. The reduction of the spring-back behavior is another advantage of the temperature controlled forming technology. On the other side the forming at elevated temperatures requires increased costs for forming tools and tempering equipment. For a fundamental evaluation of this technology, expenditures for the complete process chain have to be considered.

New methods for more accurate material characterization

In order to ensure better process design and tool optimization, it makes sense to describe material behavior in the context of phenomenological plasto-mechanics. To achieve this, it will be necessary to determine material behavior comprehensively and also to a high level of precision, in order to determine accurately the start of flow and to put forward specific variables relative to the forming process. At Fraunhofer IWU these endeavors have been expanded to form a main research area, with the aim, for example, of making the necessary material variables available under actual process conditions, detailed and accurate, for a range of different simulation programs.

Resource efficiency in bodywork parts production

The need for even greater efficiency in handling resources is coming to be seen as a public duty in politics, commerce and research. At the same time this raises the question of what options are open to companies in the manufacturing industries - and, in particular, the OEMs and suppliers to the automotive industry - for reducing costs as well as deployment of resources and emissions. In addition to illustrating and analysing the relevance of this topic as far as forming technology is concerned, the following article discusses a selection of approaches that are being adopted in the Fraunhofer Institute for Machine Tools and Forming Technology with a view to reducing the consumption of resources, particularly in the bodywork parts production sector.