Obtainable Accuracies and Compensation Strategies for Robot Supported SPIf

摘要

Single point incremental forming (SPIF) is a flexible forming method allowing to shape sheet metal without the need for die. This process is particularly well suited for rapid prototyping and small series production. The classical setup for incremental forming is a specialised rig mounted on a standard milling machine. While this is an economic solution for small to medium size workpieces, large parts require the availability of a big and therefore expensive machining centre. A cheap solution consists in using a robot, which typically has a much better workable range to cost ratio. Unfortunately a robot is usually not a stiff machine, with the consequence that during forming, due to the forming forces, the deformation of the robot can be orders of magnitude greater than the accuracy of the process. In consequence the accuracy of the achieved part is significantly affected. To overcome this problem, a strategy for compensating the deflection of the robot at the level of the tool has been implemented. To support this strategy, two variables have to be examined: the forming forces on one hand and the stiffness of the robot on the other. In this paper it is demonstrated how, based on robot kinematics, the tool deflection can be computed from the knowledge of compliance of each joint in terms of angle deflection versus the moment load applied to the joint. Experimental results illustrate the effectiveness of this approach.