On the Application of N-2-1 Locating Principle to the Non-rigid Workpiece with Freeform Geometry

Fixture design for non-rigid workpieces is performed based on the N-2-1 locating principle (with N > 3 base locators). Determination of the position and orientation of the application points of the locators are among the most challenging processes that fixture designers are encountered with, especially in case of the freeform workpiece without specific datum features. In this paper, the N-2-1 locating principle has been applied to a non-rigid freeform workpiece which is chosen from the aerospace industry. In this regard, four distinctive locating plans have been designed by alternating of two parameters: the quantity of the base locators (N) and the position of the locating points on the base locating surface. Numerical analyses have been conducted using finite element software in order to investigate the effects of the mentioned parameters on the fixturing characteristics under the application of the clamping forces. The output parameters can be elaborated as workpiece deformation, displacements of the locating points, stress values and the reaction forces generated on the locating agents. The best locating plan has been chosen by the application of the suggested decision-making model by incorporation of the calculated fixturing characteristics. Based on the results, reductions of almost 41.6% and 66% were observed respectively on the workpiece maximum deflection and cumulative locating points’ displacements by switching from the 3-2-1 to the N-2-1 (with N = 6) locating system without sensible change in the stress values.