A new sheet-bulk metal forming process for the production of bulk components out of a flat sheet has been developed. Superimposed oscillation has been applied to the new process. By this means, process limits regarding better mould filling were expanded, and forming forces could be reduced. In order to investigate the effects of superimposed oscillation on material behaviour, plane strain and ring compression tests were carried out. The superimposed oscillated plane strain compression test showed a reduction in biaxial flow stress and thus in plastic work. Furthermore, reduced friction and roughness were verified in ring compression tests using superimposed oscillation.

The novel sheet-bulk metal forming (SBMF) technology allows the production of solid metal components with various functional design features out of flat sheet specimens. However, due to the high working pressures arising during the forming process the efficiency of SBMF is tightly related to the tool service life, which is mainly limited by die wear. In the forming processes involving high contact pressures (e.g. SBMF) the influence of contact normal stresses on the die wear can be overestimated. In order to provide a realistic estimation of the die wear, the shear friction stress must be considered. The presented paper introduces a die wear model that intends the tangential component of contact stress and its implementation in the commercial FE code.

Internal die cooling during forging can reduce thermal loads, counteracting surface softening, plastic deformation and abrasive die wear. Additive manufacturing has great potential for producing complex geometries of the internal cooling channels. In this study, hybrid forging dies were developed combining conventional manufacturing processes and laser powder bed fusion (L-PBF) achieving conformal cooling channels. A characterisation of the used hot-work tool steel’s AISI H10 powder material was carried out in order to determine suitable parameters for L-PBF processing and heat treatment parameters. Additionally, the mechanical properties of L-PBF-processed AISI H10 specimens were investigated. Furthermore, the influence of different internal cooling channels regarding a possible structural weakening of the die were analysed by means of a finite element method (FEM) applied to a hot-forging process. The numerical results indicated that the developed forging dies withstood the mechanical loads during a forging process. However, during the investigation a large dependency between the resulting stresses and the chosen parameters were observed. By choosing the best combination of parameters, a reduction of the equivalent stress by 1000 MPa can be achieved. Finally, a prototype of the hybrid-forging dies featuring the most promising cooling channel geometry was manufactured.

In industrial hot forging processes, the forging dies underlie cyclic thermo-mechanical loads, which can lead to failure of the tools. Besides die wear (abrasive and adhesive) on the surface, fatigue crack initiation with a following fracture of the tool is one of the most frequent failures occurring in hot forging processes. In this study an industrial hot forging process is considered for fatigue analysis. Tool geometry is designed for a defined life time until crack initiated failure of the tool. Material characterization tests in form of tensile tests as well as cylindrical compression tests and low cycle fatigue tests were carried out. The data will be implemented in a commercial software-system to realize a qualitative good prediction of die life regarding crack wiation.

Within the scope of the transregional collaborative research centre TCRC73, the effects of an oscillation superimposed forming process for the production of a demonstrator component are investigated. Previous studies in this field were limited to a consideration of the process-related parameters such as the influence of the plastic work and the friction or the component-related parameters such as the influence of the surface quality and the mold filling. This research concentrates on the consideration of the mechanical vibration resistance of components that were manufactured superimposed oscillated. For this purpose, Wöhler tests are conducted in which the fatigue strength of superimposed oscillation pre-stretched test samples and oscillation-free pre-stretched test samples are investigated. First, Wöhler curves are generated in the tensile threshold range for tensile samples made out of the steels DC04 and DP600. Subsequently, tensile specimens are pre-stretched superimposed oscillated and oscillation-free. These specimens are subjected to a tensile threshold load until they break. The influence of the superimposed oscillation forming on the long-term fatigue of components is derived from the comparison of the bearable load cycles. Investigations of the microstructure of the specimens are conducted in order to draw conclusions about the influence on the long-term strength.