Manufacturing variation modeling and process evaluation based on small displacement torsors and functional tolerance requirements

抄録

The aim of this paper is to study the modeling method of the geometric variations which occur at the successive set-ups of the machining process by relying on the small displacement torsor (SDT) and its transfer formula, and to develop the machining process evaluation method based on the limitation of functional tolerances. The proposed method firstly considers the machining process of the mechanical part as a mechanism mainly consisted of machine-tool, part-holders, machined part, and cutting tools; Then, the SDT parameters are employed to represent the geometrical variations of the part caused by the positioning errors and machining operations during successive machining set-ups; the SDT chains are used to model the deviation propagation between different set-ups. During the whole modeling, there are three kinds of torsors need to be defined which are the global SDT of the part-holder, machined part or machining operation relative to their respective nominal positions, the gap torsor between two contact surfaces, and the deviation torsor of the associated surface relative to their respective nominal positions on the part-holder, machined part or machining operation. After obtaining all SDT chains based on the process planning of the part, an evaluation method is developed to verify the effectiveness of machining process by cumulating the impacts of various manufacturing variations on the respect of functional tolerances. Finally, an example is given to illustrate how to use the proposed method to model the manufacturing variations and evaluate the machining process of the part in the field of CNC milling machining.