Analysis of workpiece locating error using geometric fixture model: A theoretical and experimental study

Document Type : Research Article


1 Faculty of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran

2 Tarbiat Modares University, Mechanical Engineering Department, Tehran, Iran


Investigation of the robustness of the locating layout is an important analysis which is usually conducted in the verification stage of the fixture design procedure. In such an analysis, workpiece locating error is modeled by considering its sources in the workpiece and locating elements. The main focus of the present study is to investigate the robustness of the locating layout which is designed for the workpiece in the machining fixture, both theoretically and experimentally. Geometric model of the fixture is employed for theoretical analysis of errors in locating a workpiece using the well-known 3-2-1 locating principle. For validation, computer-aided assembly model is designed for calculating the workpiece locating error and comparing the results to the theoretical predictions. Experiments are also designed and conducted for validation of the theoretical predictions. Two types of the machining workpiece (with polyhedral and freeform geometry) are incorporated as case studies for the validation process. Maximum error values equal to 3.6% and 6.1% are obtained between the theoretical predictions for the workpiece locating error and results of the CAD model and experiments, respectively. Results of the present study confirmed that the locating layout with the maximum distance between its locators provided the minimum locating error value for the workpiece. Agreement between the theoretical predictions and results of the computer-aided assembly model and experiments confirmed the applicability of the geometric fixture model and credibility of its results.


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