Dirk Landgrebe

Influencing the gradient of material properties by gradation extrusion

Designing material characteristics by grain refinement using Severe Plastic Deformation (SPD) is an attractive way to create outstanding material properties. This paper presents a unique method which combines SPD and impact extrusion. The extrusion die is designed to create additional material deformation to a defined depth, resulting in a gradient from ultra-fine grained to coarse grained microstructure. Due to the large gradient the method is called gradation extrusion. The paper presents a new analytical calculation method and a numerical evaluation of the strain, showing the relationship between tool design and achievable effects and provides initial experimental results.

Inductive heating of glass fibre-reinforced thermoplastics using fibre- and wire-shaped stainless steel susceptors:

This article deals with an experimental and numerical study of the inductive heating of glass fibre (GF)-reinforced thermoplastics with susceptors made of stainless steel that are embedded in them. The objective of this article is to examine the links between individual process and system parameters and the heating behaviour of fibre-reinforced plastics. Two different susceptor designs were tested in relation to their heating capability. Furthermore, it was possible to experimentally study the dependency of the space between the specimens and inductors and therefore the impact of the generator output of the induction system and inductor attachments differing in their geometric shapes in terms of heating. Moreover, it was possible to use numerical simulation to examine the heating behaviour at different frequencies. These findings indicate that it is possible to heat GF-reinforced semi-finished products by fibre-shaped susceptors. Finally, it was possible to demonstrate that the heating process can be designed by means of the frequency of the induction system and directly controlled using the generator output.

Improvement of Formability in Single Point Incremental Forming of DP 1000 Steel by Induction Heating

This paper provides results from experiments to improve formability of DP 1000 steel in forming a complex profiles in single point incremental forming with induction heating. High attention is rewarded to the straight effect of induction power and tool settings, in order to determine if the heating temperature is sufficient for raising the formability. The steel sheet is formed by a punch in the upper side and synchronized by induction heating for the sheet on the lower side. Investigations show a maximum achievable wall angle of 70°, which was accomplished at 20 kW induction power for the two formed shapes pyramid and cone. The operational efficiency improved by reducing both the forming time and the induction power required obtaining an optimum heating temperature for the sheet blank. The presented method can be used to increase the formability of difficult-to-form metals by using a simple setup.