Papers by Author: R. Kopp

Abstract: This paper describes the basic investigation on material behaviour of cold working steel X210CrW12 in semi-solid state concerning the semi-solid forging. It includes a study of flow behaviour and microstructure by means of a high temperature isothermal upsetting test applying a special cylinder sample with a shell, which is designed to avoid collapsing of samples during the compression. The flow curve of the semi-solid steel is determined by an inverse modelling via FEM using the obtained load curve of the samples and the separately obtained flow stress of the shell material. An extensive microstructure study of the compressed samples provides a comprehensive understanding on the flow mechanism of the semi-solid steel. At the end of the paper some general restrictions and remarks for the semi-solid forging process are given based on the gained results.

Abstract: Transmission electron microscopy (TEM) was used to assess the microstructural changes accompanying semisolid molding of a creep resistant Mg-5%Al-2%Sr alloy. It was revealed that the processing created thixotropic morphologies with globular solids of α-Mg, having well-developed sub-structures. The quickly-solidified liquid fraction, enriched in Al and Sr, led to the formation of increased volumes of a lamellae type Al4Sr phase, surrounding the secondary α-Mg. Traces of Mg17Al12 still existed, predominantly as irregular shape compounds located mainly in grain interiors. Both the primary solid and high melting point precipitates of Mn-Al modified with Sr, acted as nucleation substrates for secondary α-Mg grains.

Abstract: We introduce a simulation procedure for through-process texture and anisotropy prediction, in particular for AA5182 sheet production from hot rolling through cold rolling and annealing. The FEM package ‘T-Pack’ based on the software LARSTRAN served as a process model. It was combined with physics based microstructure models for deformation texture (GIA), work hardening (3IVM), nucleation texture (ReNuc), and recrystallization texture (StaRT). The terminal sheet texture was used for a FEM simulation of cup drawing. A new concept of interactively updated texture based yield locus predictions was employed. The simulation predictions were compared to experimental data. The procedure can be applied to a wide variety of Aluminum alloys.

Abstract: Light weight construction is a construction philosophy which aims at maximum weight reduction. Reasons for light weight construction can be very diverse. One main cause can be to improve fuel efficiency. This can be achieved by use of load optimised sheet thicknesses. Another reason can be the increasing demands on crash performances by optimisation of local properties. This paper presents two production processes of flexibly rolled blanks, one with longitudinal and the other one with latitudinal thickness transitions. Both of them have been developed at the Institute of Metal Forming (IBF) and yet found their way into series production. The potential of these processes is already proved by a large range of products, especially in automotive industries. Some special deep drawing tests with flexibly rolled blanks have been conducted and their results are presented. Also process simulation has been carried out at the IBF and will be explained. One possibility with regard to optimise these products is shortly introduced. Completing this paper an outlook is given.