Predicting and compensating for part distortion caused by residual stresses occurring during 5-axis machining operations
When metal parts are being manufactured, the workpieces go through heating and cooling phases, in which they are exposed to considerable fluctuations in temperature. Through high-temperature methods such as casting or forging, internal compression and tensile stresses, so-called residual stresses, are introduced into the material at various locations. During the shaping of the final geometry by a milling process, parts of the material are removed. The forces arising from the internal stresses in the remaining material lose their equilibrium as a result of the material removal. Consequently, there is a change in the residual stresses within the part, resulting in variations in the structure of the material and in the volume of the part. This frequently leads to change in the shape of the part, which is referred to as distortion.
Serious residual stress distortion, which is an important factor in lightweight engineering design, occurs particularly in the case of large-scale parts and parts with thin walls. An option to reduce part distortion is to straighten the distorted parts following a mechanical machining operation. This entails bending the workpiece into the required shape. However, straightening is a very complex process and not always possible, particularly in the case of complex geometries. Reducing or eliminating distortion is always time-consuming and costly; it is not uncommon for the workpiece to have to be scrapped in the end, even after considerable effort has been made to salvage it.
The aim of the "VoKoES" research project is to predict and compensate for part distortion caused by residual stresses during 5-axis milling operations and to reflect this in the CAM programming.
The research project has been divided into four sub-tasks in order to achieve the aims of the project:
- Development of a simulation which will determine the residual stress states in semi-finished goods.
- Development of an algorithm for FEM simulation of part distortion in the course of 5-axis milling operations.
- Development of methods to compensate for part distortion during 5-axis milling based on the previously developed prediction methods.
- Development of an adaptive clamping system capable of detecting and relaxing part distortion.
Finally, the researchers will implement the compensation methods they have developed in a CAM module.
Within the “VokoES” project, the researchers at SLA will develop an advanced FEM simulation tool for the prediction of part distortion. To reduce computational time, the novel FEM modification Finite Cell Method (FCM) is implemented. With this method, the computational mesh and the part geometry are decoupled and remeshing is no longer required. Since the component geometry changes permanently during the simulation of a milling process, omitting constant remeshing results in a considerable reduction of simulation time.
- Fraunhofer Institute for Production Technology IPT
- Access e. V., Aachen
- RWTH Aachen, Institute of Structural Mechanics and Lightweight Design (SLA)
- Innoclamp GmbH, Aachen
- Module Works, Aachen
- BoTech GmbH, Mönchengladbach
The research project is funded by the European Fund for Regional Development (EFRE) 2014-2020. (Project Number: EFRE-0801634)