Investigation of Incremental Sheet Forming (ISF) using Advanced Numerical and Analytical Approaches

Abstract

The incremental sheet forming process (ISF) is a suitable candidate for manufacturing lightweight components while achieving cost-effectiveness for low volume production. The critical difference that incremental forming presents compared to the conventional sheet metal forming process is that it does not require dedicated equipment such as a press and specific dies for each shape of the part. The equipment is replaced by a robust setup on a CNC milling machine or a robot in incremental forming. This setup includes a finger-type tool mounted on the head of the CNC or the robot and a clamping system to hold the initial blank. The process is called single point incremental forming (SPIF). For parts with complex geometries, it uses two point incremental forming (TPIF), where the setup includes a back die to support forming the three-dimensional shape. Despite their robustness and low-cost manufacturing, ISF processes are facing challenges in their large-scale adoption because of a lack of understanding of the material-tool interaction and, consequently, lack of possibilities to optimize the process for zero errors. In ISF, the tool-material interaction has a nonlinear relationship dependent on a series of process parameters and local contact conditions, enabling enhanced formability compared with conventional processes. There are currently limited analytical models and finite element models that allow extraction of the relationships between process parameters and material response and prediction of the formed geometry and the defects. However, limited experimental results for complex geometries are an obstacle in the validation of these models. Thus, ISF is still using trial and errors to find the right process parameters to form parts within the given design tolerance. Hence, any attempts to eliminate the trial and error associated with the forming process contribute significantly to the cost reduction related to manufacturing the part by reducing the amount of material, tooling, and workforce required in the process. Advancement of numerical modeling, such as multiscale modeling approaches, is a current solution for understanding the forming mechanism of ISF and gives answers to the material defects found during the forming process. Understanding how the instabilities are formed makes it possible to predict what combination of process parameters leads to such conditions and minimize their occurrence. Once the mechanism of incrementally forming is understood is possible to build reduced-order models capable of accurately predicting the geometry and thickness with significantly less computational cost comparing with finite element models.