FE-based springback prediction of sheet metal forming processes of lightweight materials considering anisotropic hardening

• Applicant: Professorin Dr.-Ing. Marion Merklein
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 403835472

The overall objective in the second project phase is to improve the numerical design of deep drawing processes at elevated temperatures as a function of the strain rate. According to previous investigations, aluminium alloys of the 7000 series show both a tensile-compression asymmetric and strain-rate sensitive material behaviour. These aspects influence not only the temperature but also the hardening and springback behaviour. For this reason, a phenomenological material model is being developed, taking into account the anisotropic hardening as a function of the temperature and the strain rate, in order to be able to numerically represent the specific material behaviour of high-strength aluminium alloys. Based on the results from the first project phase, it is only possible to a limited extent to investigate the stress-state dependent forming behaviour of AA7020-T6 and AA7075-T6 at temperatures above 100 °C with the given test setups. It is therefore necessary to modify the test setups in order to investigate the material behaviour in a temperature range relevant for 7000 aluminium alloys. Using this analysis, the material model to be developed in the first phase will be extended by one term as a function of strain rate and temperature. By modelling the anisotropic hardening behaviour in correlation to the forming rate and forming temperature an improved representation of the material behaviour is given. In order to validate the material model, deep-drawing tests with a circular cup at elevated temperatures and different forming speeds are performed. The validation is based on the sheet thinning and the force-displacement curve during the deep drawing process. In addition, the springback behaviour with open cross profiles and open T-profiles are to be determined. Since the friction between tool and workpiece influences the deep drawing process, the corresponding friction coefficients are determined in the strip drawing test. Thus, after successful validation of the material model as a function of the forming speed and temperature, the numerical mapping accuracy and prediction quality of warm and hot forming processes can be improved with regard to the springback behaviour. As a result, process design time is saved, because expensive experimental iteration loops are avoided.

• DFG Programme: Research Grants