Efficient prediction of workpiece-fixture contact forces using the rigid body model

Prediction of workpiece-fixture contact forces is important in fixture design since they define the fixture stability during clamping and strongly influence workpiece accuracy during manufacturing. This paper presents a solution method for predicting the normal and frictional contact forces between workpiece-fixture contacts. The fixture and workpiece are considered to be rigid bodies, and the model solution is solved as a constrained quadratic optimization by applying the minimum norm principle. The model reveals some intricate properties of the passive contact forces, including the potential of a locator release and the history dependency during a sequence of clamping and/or external force loading. Model predictions are shown to be in good agreement with known results of an elastic-contact model prediction and experimental measurements. This presented method is conceptually simple and computationally efficient. It is particularly useful in the early stages of fixture design and process planning.