Advanced DIC for accurate part deflection measurement in a machining environment

Structural aluminium alloy parts used in aeronautics are manufactured in several steps, from forming processes and heat treatments to final machining. Some of the process steps generate residual stresses. For highly-alloyed thick aluminium plates manufactured with closed-die forging parts, material removal during machining can release residual stresses, leading to part deformations. Such deformations may lead to a geometrical non-conformity of the machined workpiece. It is thus of primary importance to control this phenomenon. For this purpose, the present work aims to define a reliable experimental technique to measure part deformations during the machining of large aeronautical parts. The backbone of the technique relies on Digital Image Correlation (DIC), which enables the non-destructive measurement of part deformations during machining. Moreover, DIC provides a full-field measurement in one shot. This is faster than other available measurement techniques. This work discusses more particularly problems related to the use of DIC in a machining environment for a large machined workpiece. Indeed, the technique involves using the entire captured image to compute the displacement field, and the large size of the studied workpiece can give rise to optical distortion, which can corrupt the results. In order to control optical distortion problems, a specific calibration method, which takes advantage of the machine tool environment, is proposed.