Linear Friction Welding for Near Net Shape Manufacturing of Titanium Alloy Ti-6Al-4V Aerospace Components

Titanium alloy aerospace components are typically machined from oversized ingots, forgings and extrusions. This is an expensive process due to the proportionally large amount of material that is purchased compared to the amount that remains after machining. For example, buy-to-fly (BTF) ratios of 20:1 are not uncommon. Linear Friction Welding (LFW), owing to its economic and environmental benefits, has been identified as a disruptive technology for producing these parts. This paper provides an overview of the ground-breaking work on LFW undertaken by TWI Ltd. The microstructure and mechanical properties of titanium alloy Ti-6Al-4V welds are analysed; the results show that the weld microstructure is refined and the mechanical properties are often superior to the parent material. Moreover, examples of the types of components that can be produced, along with the achievable cost savings, are presented. The purpose of this paper is to inform the manufacturing and aerospace industries of the benefits of LFW, so that this innovative manufacturing process may be better exploited.

I. Introduction

Linear Friction Welding (LFW) is a solid-state joining process (i.e. no melting occurs) which works by oscillating one workpiece relative to another while under a compressive force. Friction between the oscillating surfaces produces heat, which causes the interface to soften and plasticise. The placticised material is then expelled from the interface causing the workpieces to shorten in the direction of the applied force. During the shortening, the interface contaminants, such as oxides, are expelled from the weld interface into the flash. Once free from contaminants, pure metal to metal contact occurs resulting in an integral bond [1]. A schematic of the process is shown in Figure 1(a) and a completed weldment in Figure 1(b).