JOB KNOWLEDGE 29 SPOT WELDING Figure 5. Cross section macrograph of RFSSW aluminium alloy. Figure 6. Skin stiffened panel joined using RFSSW technology. Figure 4. RFSSW process probe-plunge variant


microstructural composition of these zones are dependent on the material and processing conditions (parameters and tool design, for example).


APPLICATIONS


RFSSW has been mainly used to join heat treatable aluminium alloys, without and with surface protection, for example anodized or coated. Dissimilar combinations between aluminium and other engineering materials, such as magnesium, steel, titanium, copper and carbon fibre composites, have also been explored with successful results. Welding of polymers and polymer composites have also proven possible. As a single-spot welding process, RFSSW is an alternative solution to replace mass-adding fastening processes, such as rivets, and to address challenging material combinations for fusion spot welding processes. Although this technology is only currently being used for research and development applications, possible industrial sectors for this technology include:


• Shipbuilding and Marine panels for decks, sides, bulkheads and floors • Aerospace


Skin/stringer applications Fuselage and wing structures


• Railway industry Rail stock vehicle floor, side and roof panels, namely for high-speed trains railway tankers • Automotive


engine chassis cradles car body structures


ADVANTAGES


Refill friction stir welding offers many advantages over current spot joining processes, especially when joining aluminium alloys:


• Remaining in the solid-state, avoiding many of the defects associated with melting and solidification during fusion welding, such as pores and solidification cracks.


• The peak temperatures are lower, allowing a reduction in distortion and shrinkage.


• No filler material or third body is added to the weld.


SUMMARY


TWI Ltd has developed experience and knowledge in the RFSSW process across various industry sectors. If you would like to know more about the process, please contact friction@twi.co.uk


www.awd.org.uk | WeldingWorld1 • No exit hole and the


roughness of the spot weld is lower than the base material.


• Being able to join many ‘non- weldable’ aluminium alloys, namely from the 2xxx and 7xxx series.


• No fumes, porosity or spatter are generated.


• Easily automated, making the process suitable for production.


• Energy efficient.


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