Experimental assessment of a clamp actuation intensity analysis model

The application of a clamp actuation intensity analysis (CAIA) model is a rough cut technique used to compute the minimum clamp pre-loads necessary to keep a workpiece from slipping within a fixture throughout a machining cycle. A CAIA model is based on the simplistic assumption that a fixture-workpiece behaves as a system of contacting rigid bodies subject to Coulomb friction at the joints. To date, little research has been carried out to ascertain how well these models predict minimum pre-loads for actual applications, or how their limitations can be overcome in order to improve their performance. This paper describes an experimental study that was used to the assess: (1) the impact of including all contact regions, regardless of rigidity, within a CAIA model, (2) the sensitivity of the CAIA model to known variations in coefficient of friction, and (3) the accuracy of predicted pre-loads for actual milling operations. The major conclusions drawn from this study are: (1) only the stiffest contact regions of a fixture-work-piece system should be included in a CAIA model, (2) there is nearly a one-to-one correspondence between the variation of the clamp pre-loads computed by the CAIA model and the variation of the inputted friction coefficients, (3) the clamp pre-loads computed by the CAIA model for a series of milling experiments were within 25% of the actual values for the majority of experiments, and (4) a reduction in the coefficient of static friction at fixture workpiece joints appears to occur during the application of milling forces, this is especially true for planar tip fixture elements.