Modeling, Analysis, and Verification of Optimal Fixturing Design

Abstract

Fixture design is an important manufacturing activity which affects the quality of parts produced. In order to develop a viable computer-aided fixturing tool, the fixture-workpiece system has to be accurately modeled and analyzed. This paper describes the modeling, analysis, and verification of optimal fixturing configurations by the methods of force closure, optimization, and finite-element modeling (FEM). Force closure has been employed to find optimal clamping positions and sequencing, while optimization is used for determining the minimum clamping forces required to balance the cutting forces. The developed FEM is able to determine in detail what are the reaction forces, workpiece displacement, deformation in the workpiece and fixtures. In order to produce a more accurate model for predicting the behavior of the fixture-workpiece system, the developed FEM includes fixture stiffness, which past models have assumed as rigid bodies. The reaction forces on the locators are experimentally verified. A sensor-embedded experimental fixturing setup was developed to verify the modeling and the data was used to compare with the FEM. Note to Practitioners-In practice, the machinist applies excessive force to hold the part on machine table, so that it does not move when machining is carried out. However, while machining flexible parts or clamping on finished surfaces, care must be taken so that only necessary and optimal clamping forces are applied, to avoid deforming the part or damaging the surface. Therefore, in this study, we have developed a mathematical model to characterize the mechanics and conditions for a fixture to hold a given part. The developed mathematical model computes the optimal clamping forces required to hold the part in position, given the cutting conditions. The result obtained was verified by conducting the machining test using the developed sensor-embedded experimental fixture setup. The FEM was also developed to predict the behavior of fixture-workpiece system and the results obtained were encouraging.