A Method to Determine the Optimal Checking-Fixture Layout for Gauge Repeatability

This paper proposes a method for finding the optimal fixture layout to achieve acceptable gauge repeatability in the inspection process of a non-rigid part. Currently, there are no rigorous means of evaluating the effectiveness of a fixture layout for a part in terms of gauge repeatability until actual parts and gauges are available late in the product development process. Changes to the part design or modifications to the gauge at this late stage are usually costly and can result in program delays, incurring substantial costs. This paper proposes an approach to arrive at the best locator layout for gauge repeatability early in the part design phase thereby avoiding costly and time-consuming changes during the build phase. The method is implemented using a commercially available tolerance stack software with finite element analysis combined with a specially coded genetic algorithm. The method’s effectiveness is demonstrated through the improvement in gauge repeatability from an arbitrary datum scheme to the optimal datum scheme in a notional design problem as well as an actual production part. We also demonstrate that the commonly accepted datum scheme of using a primary plane along the largest dimension of a part may be highly suboptimal for gauge repeatability.