Energy- and resource-efficient process routes in hot sheet metal forming
Energie- und Ressourceneffiziente Prozessrouten in der Blechwarmumformung
In the last decade, press hardening has become a fully established technology in both science and industry for the production of ultra-high-strength structural components, especially in the automotive industry. Beside the improvement of the car performance such as safety and lightweight design, the production process is also one focus of technology development trends in press hardening. Because of the additional process parameter of temperature, the energy and resource efficiency of such processes is one of the most important challenges. This includes alternative process steps and process chains as well as zero defect manufacturing by intelligent process control. Beside the high energy effort for heating up the blanks to austenitization temperature, the production floor space requirement is also comparably high, especially for heating devices. Due to the growing product variety in automobile production, combined with shorter product life cycles, the flexibility of production processes becomes more and more significant, which is also true for press hardening. This includes production organization as well as flexibility of production devices. Another topic is part complexity. A trend in automobile car body design is to reduce the number of parts by increasing the complexity - to combine an assembled component to a single part with locally varying properties. By using tailored tempering, the press hardening technology enables a selective approach of material strength in one single component. There are different solutions in production, but the technical effort to create components with tailored properties is relatively high. The article will give an overview about alternative approaches for optimized process chains of press hardening and also includes pre- and post-processing in addition to the actual forming and quenching process. Investigations on direct contact heating technology show new prospects regarding fast and flexible austenitization of blanks at compact device dimensions. By application of high speed impact cutting (HSIC) for trimming of press hardened parts, an alternative technology is available to substitute the slow and energy intensive laser trimming in today's press hardening lines. Combined with stroke to stroke control based on measuring of process-relevant parameters, a readjustment of the production line is possible in order to produce each part with individual, optimal process parameters to realize zero defect production of property-graded press hardened components with constant high part quality. The significant research in the field of press hardening was carried out at the Fraunhofer IWU, in the hot forming model process chain which enables the running of experiments under conditions similar to an industrial scale. All practical tests where prepared by design of experiments and assisted by thermo-mechanical FE simulations.