Advances in Prediction of Part Distortion and Tool Deflection of Machined Components

Machining-induced stresses and the removal of bulk stresses drive part distortion in machined plates, forgings and castings. In the aerospace industry machined monolithic components incur part distortions arising from machining-induced stresses on thin walls, ribs and webs. Bulk stresses arising from heat treat and forging processes are removed during machining and contribute to distortion of both thick and thin section parts. Machined automotive components experience distortion due to high forces and interrupted cuts on complex cast parts. Tool deflection and improper clamping conditions can further exacerbate distortions during machining. The result is increased scrap and expensive part rework. To alleviate these problems manufacturers often resort to part flipping processes or small, incremental material removal with low forces as distortion and tool deflection control mechanisms.

This paper presents advances in physics-based models for predicting tool deflection and part distortions by considering the appropriate physics for each problem. Dynamic cutting forces predicted by physics-based machining models, and tool compliance properties are incorporated into a detailed linear elastic deflection model in order to predict in-process deflections along a computer numerical control (CNC) machining toolpath. Distortions in ribs, webs and stiffeners due to stresses created during milling are predicted for various machining conditions. Changes in processes such as climb and conventional milling and radial depth of cut are taken into account. Predictions are validated against experimental measurements of distortions.