Distribution analysis of deterministic clamping and positioning error for machining of ring-shaped workpieces considering alignment uncertainty

In the machining of aero-engine gearbox ring-shaped parts, deterministic positioning is often achieved by general fixtures combined with manual alignment due to various sources of error. However, manual intervention leads to discontinuous and inefficient production. To improve this situation, workpiece alignment is centralized on alignment table equipment, and then the workpieces are transferred to the machine tools by robots for processing. In this case, the accuracy of clamping and positioning on the alignment table is extremely important. In this paper, a simulated model is constructed to predict workpiece clamping and positioning accuracy error distribution by combining manual alignment and the GD&T of process system. Firstly, an error transfer chain for the non-deterministic positioning alignment table is constructed based on assembly layers and features. Secondly, the alignment process is modeled and integrated into the established chain. Through the update of the error transfer chain, the deterministic clamping and positioning model are developed. The model shows excellent accuracy by comparing simulated results with the experimental measurements. Furthermore, an experimental scheme is designed to evaluate the influence of different types of alignment on the positioning accuracy of clamping in the assembly system. Through this experimental evaluation, the key alignment error factors affecting positioning accuracy are identified, and a quantitative metric is provided to assess the impact of workpiece and equipment alignment on the precision of workpiece fixturing and positioning. Based on these findings, the optimization suggestions for tolerance design of alignment are provided.