Determining material model parameters by optimization for temperature controlled friction stir additive manufacturing

Abstract

Friction stir additive manufacturing (FSAM) is a novel process with the potential of being used for efficiently fabricating large aircraft structures. It is based on the repeated stacking and friction stir lap welding of metal sheets. Recent studies have reported that temperature-related defects occur in the upper layers of the builds, which are explained by changed thermal conditions. The temperatures during fabrication can be calculated by a digital twin of the process. A precise material model is necessary for this purpose. This paper presents and discusses several strategies used to determine Johnson-Cook material model parameters for the aerospace aluminum alloy EN AW-7075. Using only the process data of two welding experiments, suitable material model parameters (C of -0.14161, m of 0.66863) were determined by solving an optimization problem. For these parameters, the mean absolute temperature error was less than or equal to 4.07 K for unknown test data. The method therefore enables the inline calculation and control of the welding temperature during FSAM, thus ensuring stable thermal conditions and high-quality parts.