Investigation on the scale effects of initial bulk and machining induced residual stresses of thin walled milled monolithic aluminum workpieces on part distortions: experiments and finite element prediction model

Thin walled monolithic milled aluminum workpieces are commonly used in the aerospace industry, because of their good properties such as a high overall strength-to-weight ratio. After machining those parts distortions occur. Residual stresses (RS) are the main driver for those distortions. Two types of RS, the initial bulk residual stresses (IBRS) and the machining induced residual stresses (MIRS), contribute to the part distortion. In this study, the scale effects of each RS type and their combined effects on the distortion of milled thin walled aluminum workpieces are evaluated for different wall thicknesses, different IBRS conditions and different MIRS. In this context a finite element model (FEM) is developed to predict the distortion due to the measured RS. A 3D linear elastic model, considering both types of RS as input is presented. The simulation outcome is validated by experiments. It was found that both RS types contribute to part distortion. For parts containing high IBRS, those IBRS dominate the distortion. For stress relieved parts, containing low IBRS, the MIRS dominate the distortion. The investigations showed that the shear RS induced by machining are crucial for the distortion. The developed FEM model is able to predict the distortion due to both RS types.