Application of the Armstrong friction model to study dynamic transient response in workpiece-fixture systems

Abstract

Dynamic interactions in the tool-workpiece and workpiece-fixture systems significantly impinge on the quality of machined workpieces. The dynamics of these systems are determined by many factors including fixture layout and frictional contact at the workpiece-fixture interface. In this paper, a multi-body flexible model of a frictional workpiece-fixture system is developed. A combination of the bristles concept with a modified version of the Armstrong friction model is employed to study dynamic interactions in the system. This analytical model enables the study of presliding and microsliding in the contact region along the transient dynamic response of the workpiece-fixture through an impact hammer test. Studying the behaviour of the bristles for various clamping forces indicates that the frictional damping decreases at higher clamping forces, which is due to increase in difference between the phase angles of oscillating bristles representing surface asperities. The model is validated by reproducing published experimental results. The presented modelling and solution methodology assists in detailed investigation of the contact region behaviour and can lead to optimal design of fixture elements specifically for delicate work parts and microelectromechanical systems (MEMS). The observed phase angle phenomenon can be utilized for determination of the optimal dynamic clamping forces. The simulated displacement history obtained via the presented modelling is very suitable for using to improve machining stability by extracting chatter stability lobes.