November 2021

38 | Plant & Works Engineering www.pwemag.co.uk November 2021 Production Engineering Talking Industry Extra F riction welding is an efficient and cost- effective means for joining a wide variety of materials. Advantages of the process include joint strength and weld integrity, very low risk of failure for safety-critical joints, fast weld times and the ability to weld dissimilar materials. However, despite the process affording significant advantages, its use remains relatively low. Many engineers out there haven’t heard of rotary friction welding or linear friction welding. To discuss and promote the process and answer questions, we assembled an excellent panel, chaired by DFA Manufacturing Media’s consultant editor and featuring speakers from TWI, AFW & KUKA Systems UK. Collectively, they demonstrated a wealth of expertise. They tackled questions such as how the process is best applied, and whether it is best to purchase a machine or use a subcontractor. Jayne Shimwell, technical services manager at KUKA Systems UK, was the first speaker. She explained how KUKA got into friction welding machines, via the acquisition of Thompson Friction Welding from Rolls-Royce way back in 1993, while she herself joined a year later. Shimwell showed some photographs of the types of components that are routinely friction welded and also the combinations of dissimilar metals involved. Friction welding touches nearly everybody’s everyday life through one component or another. At KUKA, there is a specialist team of approximately 100 people working in friction welding - designers and engineers, with a facility to offer the process also as a subcontracting service. Kate Bennett (senior project leader – Friction and Forge Processes, TWI) then described the basics of the friction welding process and how it compares to other welding processes. She handed over to the second speaker from KUKA Systems UK, head of sales and market development (AWS) Nick McCarthy. He explained the typical markets and sectors where the process has found most traction. The first of our two speakers from the USA was John Fischer, speaking from specialist subcontracting company American Friction Welding in Oklahoma. He outlined the business case for the process and the circumstances where it makes sense to subcontract the process, and when an outright machine purchase can be justified. And finally, no discussion of welding Extra: Rotary Friction Welding As a fabrication process, welding has been used within manufacturing for decades. Traditional welding methods, however, aren’t always suitable for components intended for use within high-impact applications, such as offshore drilling, automotive components, or power generation. Andy Pye, PWE’s consulting editor, reports. would be complete without a discussion of the metallurgy behind it. Jeff Price, manager of North American operations, Thompson Friction Welding, covered the role of the metallurgy laboratory, how to determine the integrity of the weld (including heat-affected zones, and the formation of embrittling intermetallic compounds when interlayers between two different materials are used. In fact, it was emphasised all the way through that welding of dissimilar metals is one of the great strengths of the process, provided that the process is conducted and monitored correctly. Perhaos unexpectedly, the session generated over 60 questions from the audience (see a selection below), one of whom almost purchased a machine there and then. Because of that, the session ran for around 95 minutes, well above the average figure for a Talking Industry event. Among the most interesting elements of the later discussion was the consideration of how to friction weld “difficult” dissimilar metals, an example being steel and titanium. It was pointed out that such examples were very much the exception, but this would be done by using a suitable interlayer material, while care would need to be taken about the formation of intermetallic compounds, which can lead to embrittlement. Zoom Chatbox Please read these edited and re-ordered comments in conjunction with the on-demand version of the webinar (www.talkingindustry.org) , where many questions were also answered or amplified. General process questions Erkan Bedir: What are the issues to be developed in friction welding technology or machines today? Anon: What are the advantages of FSW over Vacuum Brazing? Daniel Mann: Would you explain the difference between Friction Stir, Linear Friction vs. the Rotary Friction. Bruno Fita: What is the HAZ size of friction welding vs other welding processes, such as GTAW, SMAW, GMAW? NIJLINGAPPA MUDDAPPA: Does FW machine comes with lathe features? if yes, can it be expanded to a bar feed feature? Simon Welburn: Flash trap geometry - am I right in thinking this is designed into the pre-welded components to ‘capture’ internal spoil that can’t be cleaned up post welding? Ben Rutter: Is much debris created during a friction weld? How do you control/deal with this during automation? Dimensions Simon Welburn: Did I hear minimum tube wall thickness of 25mm? If so, is this driven by the ‘friction’ face areas or buckling stress during the process? John Fischer: Minimum wall is dependent on the size of the welding machine. It could be as small as .090in. Jayne Shimwell: The tube wall of 25mm was given as an example of max for a 220mm OD tube. Thin wall tubes can be friction welded, subject to materials and overall geometry. Specifications and welding codes Bruno Fita: Which welding codes are being used to weld and qualify these various alloys? Jayne Shimwell: BS15620:2019 Friction Welding of Metallic Materials John Fischer: Other specifications include AWS C6.1 and C6.2, ISO 15620, ASME Section XI, AWS B4.0, AWS B2.1, ASME E8 Daniel Mann: Another testing consideration may be ASTM 262 corrosion testing.