Just two years after the launch of its range of Powerstir ‘dual weld-head’ friction stir welding machines, UK-based Precision Technologies Group (PTG) reports achieving double-digit sales of these specially developed FSW technologies for electric vehicle OEMs.

Designed specifically for use in the volume production of automotive battery tray floor assemblies from extruded aluminium panels, the company’s dual weld-head process is aimed directly at manufacturers of skateboard chassis structures and ensures that a tight weld-flatness tolerance is achieved during battery tray floor construction.

PTG has been a leading name in the manufacture of friction stir welding machine tools for transport applications ever since its Powerstir range was launched at EMO Hannover some 20 years ago. More recently, however, it has used its considerable knowledge of the FSW process to assist automotive OEMs in producing lightweight, robust and aesthetic components for both battery electric vehicles (BEV) and plug-in hybrid electric vehicles (PHEV).

“We are delighted to have achieved this level of sales for our new dual weld-head Powerstir machines in such a short space of time and during such a challenging trading period for manufacturing industry,” comments PTG sales director, Mark Curran. “Clearly, the benefits of the PTG Powerstir dual weld-head process have made us a major contender among organisations that are looking to invest in advanced FSW technologies for the manufacture of electric vehicles.”

Ensuring a tight weld-flatness tolerance

A tight weld-flatness tolerance, as provided by PTG Powerstir dual weld-head machines, is essential to ensure that each EV battery cell sits perfectly level within its housing. The PTG dual weld-head method achieves an even and stable welding process – something that is made possible thanks to PTG’s unique ‘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.

High-output production cell

As aluminium extrusion lines usually produce panels of 300 mm to 600 mm 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 2.4 metres wide.

“Our dual weld-head FSW techniques, 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,” comments Mark Curran. “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 also important to consider that in many instances, the use of friction stir welding also allows for reduced wall thickness – an important aspect in reducing vehicle weight,” he adds. “As the friction stir welding process generates very little heat, the crystalline structure of the metal remains unchanged, retaining its original strength. There is no need for inert gas, no need for heat-treating post weld, and no requirement for additional surface finishing.”

PTG is widely considered to be a leader in the development of FSW technologies for transport applications. Organisations involved in the manufacture of aerospace components and the production of aluminium carriage panels for high-speed trains were among the first to recognise the benefits of Powerstir friction stir welding. Working with 5000 and 6000 Series aluminium alloys, and magnesium alloys from 3 mm to 6 mm in thickness, PTG is currently developing new FSW processes for several automotive OEMs.  Through the use of industry standard CNC systems, equipped with PTG Powerstir software, data-logging and interpolation technologies, 2D welding – guided by laser tracking – can be carried out on precise tool paths, with force control ensuring consistent welded seams. QR codes are used to identify each extrusion before welding commences. Each completed panel is then DMC coded to identify the panel, for complete and ongoing traceability throughout the manufacturing cycle.

Coolant units and body panels

In addition to building Powerstir machines specifically for the production of battery tray floor assemblies, PTG is also 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. Through its recently opened friction stir welding research centre, the company is also assisting a number of organisations in developing FSW processes for specific manufacturing challenges.

High-strength joints with minimal Heat Affected Zone

Friction stir welding combines frictional heat with precisely controlled forging pressure to produce extremely high-strength joints that are virtually defect free. Due to the very low welding temperature, mechanical distortion is practically eliminated, with minimal Heat Affected Zone (HAZ) and an excellent surface finish. Friction stir welding transforms the parent metal from a solid to a plasticised state. This occurs during a process that involves mechanically stirring the materials to be joined together, to form a high integrity, full-penetration welded joint. The Powerstir FSW process is effective on flat plates, cylindrical components and even on parts of irregular thickness. Although used primarily for joining aluminium, the Powerstir process can also be applied to magnesium, copper, titanium and steel alloys.

PTG Powerstir FSW manufacturing applications for electric vehicles include:

• Battery tray floor assemblies
• Battery trays and boxes
• Chassis and structural components
• Control box panels
• Vehicle body panels
• Brake regeneration systems
• Coolant units and heat exchangers