Improved FE simulation of the shear cutting process by a temperature and strain rate dependent extension of the MMC model

Shear cutting is an established process for chipless cutting and is used for the cost-effective production of components. The quality of the cut surface achieved during shear cutting depends on material, tool and process parameters. In order to achieve the desired cutting result, the process design is usually based on experience or within the framework of time-consuming and cost-intensive experimental test series. Therefore, the numerical representation of the shear cutting process has a high potential to spare these practical tests. Up to now, finite element (FE) simulation systems with simplified calculation algorithms have been applied to describe material failure and crack propagation, which only allow limited predictions regarding the cutting surface geometry. Therefore, the overall objective of this research project is to further develop the modified Mohr-Coulomb (MMC) failure model to improve a realistic calculation of material failure, thus predicting the cut surface quality more reliably.

In the first phase of the project, material characterisation was performed for various steel materials (DC04, DP600, DP1000 and 1.4301) in the temperature range from 20 °C to 300 °C and at strain rates from 0.01 s-1 to 80 s-1. However, a numerical analysis of the shear cutting process showed that strain rates of up to 750 s-1 and temperatures of up to 519 °C occur, which represent a significant influencing variable for a realistic numerical process mapping with regard to damage modelling as well as flow behaviour. Therefore, in the second phase of the project, the flow and damage behaviour will also be determined experimentally at higher temperatures and strain rates.

Furthermore, so far only one specific stress triaxiality range (0.0 < η < 0.67) has been considered for the parameterisation of the damage model. In the second phase of the project, an experimental methodology developed at IFUM is to be used to consider the negative stress triaxiality range (-0.1 ≤ η ≤ 0.0) and to increase the number of support points for the failure characterisation in the range (0.0 ≤ η ≤ 0.33) of shear stress. In addition, the shear-cutting model will be built up three-dimensionally and a modified MMC failure model will be implemented, taking the lode angle parameter in a strain-rate and temperature-dependent form into account. To validate the developed models, shear cutting tests will be carried out on a forming press. A variety of different materials, cutting gaps and sheet thicknesses are used to represent a wide range of different operating conditions. Finally, the cut edges are measured laser-optically and examined by means of metallographic micrographs. The data will be used for the final validation of the numerical simulation results.