Optimization of tool path in two points incremental forming

In recent years, the sheet incremental forming process was characterized by a very fast development. Several sheet incremental forming techniques and strategies have been designed and studied. In fact, analyzing the literature, it is possible to distinguish between the sheet incremental forming without die, like Single Point Incremental Forming (or “dieless forming”, patented by Leszak since 1967), and the sheet incremental forming with negative or positive die (either full or partial), like Two Points Incremental Forming. The research presented in this paper reports an experimental optimization of the tool path in two points incremental forming applied to the manufacturing of an automotive component. The applied technique uses a full negative die and a shaped blankholder. Three different tool paths have been investigated and its effects on part integrity, surface quality and dimensional tolerances have been analyzed. In the first one, the tool path was realized with a series of incremental paths with constant step depth. In this case the step depth was varied from 1 mm to 0.2 mm. The second tool path was made by a series of incremental contours but with a variable step depth in order to minimize the set value of the so called scallop. The values of the step depth were the same used for the first tool path type, while two levels of scallop values were investigated: 0.1 mm and 0.02 mm. Finally, a spiral path was investigated. This path was characterized by a simple pressure up to the maximum depth in the center of the part, followed by a spiral path when the bottom is reached. All the investigated paths were generated using commercial 3D CAD-CAM software. As far as the results are concerned, the influence of the tool path on the geometry of the part, on the surface quality and roughness was analyzed. A high product quality have been obtained, showing how it is possible to obtain safe parts respecting the shape and geometry tolerances using this innovative sheet metal forming technique.