Machining strategies for distortion control during high speed machining

Airframe structural components that are machined from aluminium forgings or plate stock represent a significant contribution to the cost of both military and commercial aircraft. These components tend to distort due to heat treating induced bulk stresses and machining. Correcting these distortions increase costs and manufacturing lead times, especially for a high-volume, high-quality production company. In addition to this, variation in the residual stress profile from component to component is common due to variation in the condition of supply state. There is therefore a need to understand and model the effects of heat-treating and machining strategies on distortion and to predict, minimize, and control these distortions. This thesis addresses the modeling, data acquisition, and validation of residual stress and distortion models using different aluminium test cases. The project is divided into different technical studies to build the modelling capability: In the first study, aluminium 7050 material data and heat transfer coefficients were experimentally acquired. This data was to be used as an input to demonstrate the capability of Finite Element (FE) modelling as the main tool to predict and design robust strategies in the presence of residual stress variation due to processing or geometric differences. In the second study, the simulation study was performed to improve the machining distortion by using finite element (FE) modelling on varying residual stress profiles of aluminium coupons. Other studies included the influence of tool paths, the pocketing sequence, billet orientation and part location on machining distortion. Finally, utilizing the knowledge acquired, a machining process strategy for distortion control was proposed.