A model to predict minimum required clamp pre-loads in light of fixture-workpiece compliance

The determination of minimum required clamp pre-loads is an important process in the design of machining fixtures. This paper presents a linear, clamp pre-load (LCPL) model that can be applied to fixture-workpiece systems whose compliance is load invariant. The model considers the static deformation of the fixture-workpiece system in response to the clamping process and the machining process. Sources of compliance throughout a fixture-workpiece system are considered. The model computes the minimum required pre-loads necessary to prevent workpiece slip at the fixture-workpiece joints throughout the machining process. This paper also describes an experimental study that was used to characterize the accuracy of the LCPL model with regard to the application of a ramping external load to a fixture-workpiece system. Over the contact conditions tested, the LCPL model was observed to overestimate the minimum required clamp pre-loads by an average of 7%. This experimental study also revealed the sensitivity of the computed pre-loads to the relative compliance of the fixture elements as well as the coefficient of friction.