Efficient Build-Up of High-Strength Aluminum Structures Using Friction Stir Additive Manufacturing

Abstract

Friction Stir Additive Manufacturing (FSAM) is a novel process with which large-scale aluminum structures can be produced from high-strength alloys such as the 7xxx series. Due to the prevalence of these alloys in airplanes and rockets, the process offers high application potential, for example in fabricating stringers and stiffeners. The building process in FSAM is characterized by sequentially stacking and friction stir lap welding (FSLW) metal sheets. Before adding the next layer, the surface is machined (i.e., by milling). So far, this is a necessary step to enable gap-free welding of the layers, which results in increased costs and reduced layer heights. The investigations described in this paper were aimed at improving the weld surface quality to enable defect-free FSAM without the additional machining step. For this, FSLW was conducted using different welding tools. The resulting welds were evaluated based on superficial and internal characteristics as well as the mechanical properties (shear strength). With a welding tool in which both a rotating and a stationary shoulder were combined, defect-free weld seams with a mean underfill and a mean flash height of 0.07 mm were produced. In a subsequent study, it was proven that defect-free FSAM without surface machining is possible up to the fifth layer using the combined welding tool.

A Comprehensive Review of Friction Stir Additive Manufacturing (FSAM) of Non-Ferrous Alloys

“…Meanwhile, tools T1, T3, and T4 result in good material mixing on the advancing side of NZ (with some microstructural defects), but not on the retreating side. Similarly, M. Sigl et al [ 67 ] used double-scrolled stationary and rotating tool shoulder to perform FSAM, and announced the combined rotating and stationary tool shoulder produced defect-free Al-7075 structure.…”

“…Similarly, the same type of defects were observed by H. Venkit [ 93 ] during fabrication of alternative gradient composite structure containing multiple sheets of Al-6061 and Al-7075. M. Sigl et al [ 67 ] used FSAM to improve weld top surface and quality (micro-defects). The study’s main goal was to reduce machining costs while maintaining maximum and gap-free building height by adding the next plate without machining or milling.…”