Influence of workpiece tolerances on the fixtures design. Case study

Abstract

The tolerances of a part influence both the operation of the assembly of which it is part and the technological manufacturing process. High tolerances can lead to an assembly that does not work at the designed parameters, and low tolerances require additional machining operations that increase the cost of the part. The manufacturing series is another factor that influences the technological process. Large series production requires special facilities in terms of processing and control equipment which are needed in the manufacturing process. The paper presents a case study on the influence of tolerances of a part being produced in large series on the construction of the orientation and clamping device used in machining. Starting from the dimensions indicated in the design drawing, a first version of the fixture is proposed in which the parts are fixed and the tolerance of the closing dimension of the assembly of parts is analysed using the Worst Case and Root-Sum-Square methods. Since the closure size tolerance is outside the recommended range, another variant of orientation and fixture is proposed. By re-analysing, the closing dimension tolerance by the two methods mentioned above it was confirmed the necessity of modifying the part width tolerance. The analysis of the tolerance of the closing quota is resumed by the two methods mentioned above and the result confirms that it is necessary to change the tolerance to the width of the piece. The tolerance verification of the closure dimension of the assembly formed by the parts fixed in the device is performed by Monte Carlo simulation.