Research Group Materials Testing
The materials testing group is responsible for the determination of material properties and process boundary values, as well as their preparation for the use in process simulation and material modelling tools. The properties can be determined either directly from the measured data or by a subsequent inverse modelling. A particular focus of the group is the process related characterization of microstructure evolution.
The goal of the hot-gas-bulge test project is to deliver accurate material data for the virtual testing and design of hot stamping processes. Hot-stamping is a quite new process, which is mostly used by the automotive industry for the production of high strength components. The high strength levels are achieved by simultaneous forming and quenching of hot steel sheets with initial temperatures up to 950 °C.
For the material testing, a pneumatic bulge test is developed within this project. The bulge tests consists basically of two rings fixing a sheet metal. The sheet metal is then loaded with a controlled gas pressure, which causes the sheet to bulge through one of these rings. Although the controlled gas forming of sheets is challenging, flow curve in the temperature range of 600 to 950 °C can be obtained at constant strain rates of 0.5 s-1. Future goals are the increase of the strain rate up to 5 s-1 and testing of the meta stable austenite.
For further information, please contact Alexander Braun.
Investigation of Bond Formation and Failure of Metallic AlloysIBF
Roll bonding enables the targeted combination of different materials and thus their mechanical and thermal properties in a single material composite. However, the connection created under pressure load can tear up again due to shear stress at the end of the roll gap. Thus, industrial production requires very long process chains, which are often determined by trial and error. In order to allow for a knowledge based design of such process chains, a basic experiment was developed at the Institute of Metal Forming to characterize bond formation and failure. In this test, the connecting partners are heated inductively and joined under combined pressure and shear stress. After bond formation, the strength can be tested at deformation temperature under a combination of tensile, compressive and shear stress. The procedure thus enables testing under near-process conditions.
For further information, please contact Jens Dierdorf.
Thermal Characterization of Surface ContactsIBF
For the simulation of hot forming processes, the knowledge of the heat transfer between the tool and the work piece is of importance. Currently the determination of the interfacial heat transfer coefficient is carried out via inverse methods in transient condition, which sometimes provides only insufficient results. Therefore, a test stand for the steady state heat conduction is being developed at the IBF in cooperation with the Department for Industrial Furnaces and Heat Engineering. Thereby, various influencing variables such as atmosphere, contact pressure, temperature and surface roughness may be varied in order to model the corresponding processes as application-orientated as possible. Particular focus is placed on lower contact pressures at higher temperatures, which allows the modeling of processes such as annealing of coiled metal strips or the slab transport on the roller conveyors.
For further information, please contact Jürgen Nietsch.
Friction Determination With Extended Conical Tube-Upsetting TestIBF
The conical tube-upsetting test is used to determine the friction coefficients for different friction models. Similar to the ring compression test, which is also available at the institute, the geometric change of the specimen is measured and evaluated by means of nomograms. The conical contact surface suppresses the occurrence of static friction and thus enables more homogeneous test conditions, even under high prevailing friction. In addition, a blue line laser has been added to the test setup in order to record the contour change during forming. These measured values can be used on the one hand for the inverse determination of the prevailing friction and on the other hand for the examination of the change in friction during the compression process. The test setup allows the testing of workpiece temperatures up to approx. 1200 °C. In addition, the tools can be preheated to temperatures of up to 300 °C.
For further information, please contact Marco Teller.
Determination of Wear Characteristics With Compression-Torsion-TribometerIBF
For the determination of wear parameters, a self-constructed compression-torsion-tribometer is used. The steel specimen, which is optionally coated and / or lubricated, can be pressed onto a counter body under a maximum axial load of 18 kN. An engine realizes a relative movement between the two specimens. By measuring the transmitted torque and controlling the axial force, rotational speed and number of rotations, the wear behavior, for example with regard to adhesion and abrasion, can be investigated under a controlled load spectrum. In addition, an encapsulation of the specimens allows higher contact pressures and thus the approximation of load collectives during extrusion of aluminum. The tribometer is used, for example, for examining dry extrusion of pure aluminum.
For further information, please contact Marco Teller.
Specific Shaped Copper Windings Manufactured by Forming TechniqueIBF
The electrical wheel hub motor is a promising technology for the development of future urban mobility. Specific shaped copper windings with a rectangular cross section offer the potential of a better exploitation of the available coil assembly space, causing a higher power density of the electric motor. At the institute of metal forming, briefly IBF, the production of these specific shaped copper windings using forming technology is investigated. Thereto, different manufacturing approaches were developed. The advantages and disadvantages of these manufacturing approaches are examined practically. The main objective of the project is a good efficiency of the manufacturing chain, so that an economic benefit of a production with high quantaties is ensured.
For further information, please contact Daniel Petrell.