UK-based Precision Technologies Group (PTG) — the manufacturer of the Powerstir range of friction-stir welding (FSW) machines (
www.holroyd.com) — has introduced a number of dual-weld-head FSW models specifically for use in the high-volume production of automotive battery-tray-floor assemblies from extruded aluminium panels.
PTG has long used its knowledge of the FSW process to help automotive OEMs produce lightweight, robust and ‘aesthetic’ components for battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs).
Aimed directly at manufacturers of ‘skateboard chassis structures’, the dual-weld-head process developed by PTG ensures that a ‘tight weld-flatness tolerance’ is achieved during battery-tray floor construction.
The company says that a tight weld-flatness tolerance is essential to ensure that each battery cell sits perfectly level within its housing, and that its Powerstir dual-weld-head FSW machines provide an even and stable welding
process — thanks to its ‘matched’ dual-force control systems and balanced upper- and lower-head welding parameters.
“The result is exceptionally stable friction-stir welding by both the upper and lower weld heads, producing matched weld seams with balanced heat input.
“This in turn minimises post-weld distortion and equips each welded assembly with a significantly improved flatness tolerance, when compared to existing conventional single-side FSW techniques.”
Because aluminium extrusion lines usually produce panels that are 300-600mm wide, PTG has also developed a fully automated high-output Powerstir FSW production cell for the rapid friction-stir welding of multiple extrusions, to create single structures for fabrication into battery-tray floors. These structures are typically up to 2.4m wide.
Equal heat dispersionPTG’s Powerstir regional sales director, Mark Curran, said: “Our dual-weld-head FSW technologies, whereby both sides of an extrusion are welded simultaneously, not only remove the time-consuming process of lifting and turning extrusions between welds but also allow for equal heat dispersion, which results in minimal distortion.
“In the PTG Powerstir dual-weld-head FSW process, typically four to 12 individual ‘child-part’ extrusions are brought together for assembly.
Following gantry loading, each extrusion is automatically positioned and clamped ready for friction-stir welding, after which the partially completed vehicle component is automatically repositioned, ready for the next panel to be welded in place.
“In addition to providing automotive OEMs with a ‘state of the art’ means of joining metals and achieving extremely high-strength results, it is important to consider that — in many instances — the use of friction-stir welding also allows for reduced wall thickness — a key element of reducing vehicle weight.
“As the friction-stir welding process generates very little heat, the crystalline structure of the metal remains unchanged, so it retains its original strength. Moreover, there is no need for an inert gas, no need for post-weld heat-treating, and no requirement for additional surface finishing.
“In addition to building Powerstir machines specifically for the production of battery-tray floor assemblies, we are creating FSW techniques for the production of coolant units, control box panels and car body panels, as well as body panels and components for commercial vehicles.”
Consistent welded seamsThrough the use of industry-standard CNC systems (equipped with PTG Powerstir software, data-logging and interpolation technologies), 2-D welding — guided by laser tracking — can be carried out on precise tool paths, with force control ensuring consistent welded seams.
Furthermore, QR codes are used to identify each extrusion before welding commences, and each completed panel is then DMC-coded to identify the panel, thereby offering complete and on-going traceability throughout the manufacturing cycle.
PTG says that friction-stir welding combines frictional heat with precisely controlled forging pressure to produce extremely high-strength joints that are virtually defect-free.
Moreover, because the welding temperature is very low, mechanical distortion is practically eliminated, the heat-affected zone is minimal, and an excellent surface finish is achieved.
PTG highlights the fact that friction-stir welding transforms the parent metal from a solid to a plasticised state resulting in a high-integrity full-penetration welded joint, and that the Powerstir FSW process is effective on flat plates, cylindrical components — and even on parts of irregular thickness.
Though used primarily for joining aluminium, the Powerstir process can also be applied to magnesium, copper, titanium and steel alloys.