Modelling of Oxide and Surface Contaminant Removal in Ti-6Al-4V Linear Friction Welds

Linear friction welding (LFW) is a solid-state welding process that is finding increasing interest from the aerospace industry as a method for fabricating near-net-shaped (NNS) titanium alloy (Ti-6Al-4V) components. This is primarily due to the high strength and integrity of the welds produced, and the significant cost savings that can be achieved. If a linear friction weld is to be free from oxides and surface contaminants, which can compromise component performance, it is essential that the interface material of the work pieces to be joined is entirely expelled from the weld into the flash.

Using the finite element modelling (FEM) code DEFORM, computational models were developed to investigate the influence of the process inputs and work piece geometry on the interface material expulsion. The models were validated by experiments and captured many of the experimental trends, such as the flash thickness and interface expulsion rate, thus giving a good insight into the LFW process.

Key results demonstrated that a smaller burn-off was required at higher forging pressures and rubbing velocities for complete expulsion of the interface material. When the rubbing velocity and forging pressure were kept constant, a reduction in the width of the work pieces in the direction of oscillation also decreased the required burn-off. Interestingly, the peak temperature of the weld increased as the forging pressure was decreased and/or the rubbing velocity increased.

An understanding of these phenomena is of particular interest for the industrialisation of NNS components of various geometries and sizes.