The Manufacturing Process Chain Consisting of Thick Sheet Forming and Peripheral Milling: Modeling of Residual Stress-Related Geometric Deviations

The sequential combination of thick sheet forming and peripheral milling is an alternative to machining from solid blocks, with the advantage of increased material utilization. After the forming stage, a complex residual stress field is present in the workpieces. During the milling stage, a disturbance of the stress equilibrium can lead to workpiece distortion. A virtual modeling approach to predicting the residual stress-related geometric deviations is presented. This approach can be used to evaluate the influence of process control variables on deviations and to identify suitable parameter values for reducing them. First, the initial residual stress field at the beginning of the milling stage is determined based on a physical-mathematical model of the forming stage, considering the elasto-plastic properties of the sheet material. Subsequently, the geometric deviations resulting from material removal are modeled using a series of equilibrium calculations. For comparison, the manufacturing process chain was implemented experimentally, and measurements of the workpiece geometry using a tactile coordinate measuring system were performed. The resulting geometric deviations for two target geometries were used to validate the model predictions. The virtual model enabled the magnitude of the geometric deviations and the effectiveness of a two-step milling strategy to be predicted.