FINITE ELEMENT MODELLING AND ANALYSIS OF WORKPIECE-FIXTURE SYSTEM

Abstract

The fixture design and analysis lead-time is always a major influencing factor for the bottleneck between product design and manufacturing. With advent analysis and simulation tools, there is a lot of potential to expand the scope of optimization of fixture elements to achieve the objectives such as ‘maximizing rigidity’ and ‘minimizing weight’ of a fixture assembly. There are many sources which affect the rigidity of fixture assembly. The rigidity of fixture assembly mainly depends upon various factors such as material properties, geometry of individual components, stability against thermal distortions, clearances or plays on fixture elements (to facilitate loading and unloading of workpiece), contact deformations at contacting surfaces, etc. Among these, contact deformations at contact interface are one of the important sources of errors in precision fixture design. These contact deformations are measure of contact stiffness and therefore needed to be studied in accordance with workpiece-fixture contact. In this paper, a numerical model of fixture unit assembly is presented using the FEA tool ANSYS. ANSYS contact elements CONTA175 (8 node element) and TARGE170 (8 node quadrilateral element) are utilized to represent contact stiffness at contact interface. This model simulates the behavior of contacting surfaces of fixture assembly for different values of surface roughness, coefficient of friction (μ) and contact stiffness with very little modelling or computational efforts and time. This work establishes the FEA model of fixture unit assembly to predict fixture unit stiffness and FEA model of rough surface contact to predict contact stiffness. Based on this study, the database of fixture stiffness and contact stiffness is built up and further can be used in computer aided fixture design (CAFixD).