Fixture clamping force optimisation and its impact on workpiece location accuracy

Workpiece motion arising from localised elastic deformation at fixture-work piece contacts owing to clamping and machining forces is known to affect si gnificantly the workpiece location accuracy and, hence, the final part qual ity. This effect can be minimised through fixture design optimisation. The clamping force is a critical design variable that can be optimised to reduc e the workpiece motion. This paper presents a new method for determining th e optimum clamping forces for a multiple clamp fixture subjected to quasi-s tatic machining forces. The method uses elastic contact mechanics models to represent the fixture-workpiece contact and involves the formulation and s olution of a multi-objective constrained optimisation model. The impact of clamping force optimisation on workpiece location accuracy is analysed thro ugh examples involving a 3-2-1 type milling fixture.