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Creating a stir

For automotive manufacturers, friction stir welding machines stir the imagination for electric vehicle production

According to Inside EV, a digital publication that tracks all U.S. electric vehicle sales, September 2018 marked the 36th consecutive month for year-over-year monthly sales gains for electric vehicles. As sales of hybrid and all-electric vehicles continue to gain momentum – all around the globe, in fact – engineering firms and equipment manufacturers are keen to assist automotive OEMs in tackling the many challenges associated with developing components for these new fossil-fuel alternatives.

A closeup of a weld head on a PTG Holroyd Powerstir friction stir welding (FSW) machine.

PTG Holroyd, a U.K.-based organization, is among those forward-thinking equipment manufacturers. The company is busy applying its considerable knowledge of friction stir welding (FSW) to the difficult-to-join materials so often found in hybrids and all-electric vehicles. PTG Holroyd builds FSW equipment, and its Powerstir line of machines, in particular, is receiving increasing numbers of inquiries from businesses involved in the manufacture of battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs).

As a result, and in addition to developing new FSW machines specifically for the automotive sector, PTG Holroyd has also expanded its sub-contract FSW capability to provide prototyping and component development services for BEV and PHEV OEMs.

“Improved battery range and reduced vehicle weight through the greater use of plastics and aluminum panels have long been the goals of vehicle manufacturers,” says Steven Benn, PTG Holroyd’s regional sales director. “The recent, rapid growth in the development of BEV and PHEV technologies, however, has presented new challenges and opportunities as motor manufacturers prepare to build electric vehicles in higher volumes.

“The use of a ‘skateboard’ chassis architecture,” he says, as an example, “integrates vehicle battery packs at the body-in-white stage rather than treating battery enclosures later as add-ons. This has resulted in orders and inquiries from organizations requiring highly efficient FSW techniques specifically for the fabrication of enclosures capable of housing multiple battery modules side by side.”

Quality standards

PTG Holroyd, which planted its roots in 1860 in Hulme, Manchester, as a machine tool and textile machinery manufacturer, clearly has a long-standing reputation for building robust equipment. When the company launched its Powerstir line of FSW equipment about 20 years ago, it didn’t take long to become an acknowledged leader in the use of FSW technologies for joining metal.

Working with 5000 and 6000 Series aluminum alloys and magnesium alloys 3 mm to 6 mm thick, all to industry-recognized FSW quality and inspection requirements including microstructure analysis, the company is currently developing a number of FSW techniques for automotive OEMs, such as dual-head welding technology. These efforts result in joints that are aesthetically pleasing and provide low welding temperature input.

“To date, we have developed FSW machines specifically for the fabrication of lightweight, robust and highly aesthetic battery trays and housings,” Benn says. “While 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 FSW allows for reduced wall thickness – an important aspect in reducing vehicle weight. As the process generates very little heat, the crystalline structure of the metal to be welded also 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.”

A multiple-axis Powerstir single-sided gantry-type FSW machine in operation.

As a result of PTG Holroyd’s ongoing investment in research and development, coupled with its considerable expertise in FSW processes, the company is able to provide automotive OEMs with highly viable manufacturing solutions.

“We are also developing FSW technologies for the production of coolant units, control box panels and car body panels as well as body panels and components for commercial vehicles,” Benn adds.

By using industry-standard CNC systems, equipped with PTG Powerstir software, data logging and interpolation technologies, 2-D and 3-D welding – guided by laser tracking – can be carried out on precise toolpaths. The use of force control ensures consistent welded seams.

“Our work surrounding the production of automotive battery enclosures, associated electronics housings and coolant units is not simply exciting, it also challenges many conventional attitudes toward vehicle construction,” Benn explains. “It is enabling vehicle design engineers to achieve both structural rigidity and reduced weight in components that benefit from high-strength welded joints.”

Planes, trains and EVs

Since their launch, Powerstir FSW machines have attracted considerable interest from sectors requiring an innovative, alternative way of creating superior metal-to-metal joints. Organizations involved in avionics and the manufacture of aluminum railway carriage panels were among the first to recognize the benefits of Powerstir FSW.

For example, the organization has built a number of large-scale Powerstir FSW machines for railway carriage manufacturers. Each equipped with a 30-m-by-4-m gantry, these machines are used to create what are believed to be the longest single FSW railway panel welds in China, at more than 15 m long.

Powerstir friction stir welding of aluminium railway car panels, with laser tracking along the seam and a deflashing brush for burr removal.

The drive to reduce vehicle weight coupled with the need to manufacture new, lightweight components for use in today’s and future generations of electric vehicles has resulted in PTG Holroyd developing new highly advanced Powerstir FSW models specifically for the automotive sector. In reality, though, almost anywhere high-speed, high-quality welding with low distortion and superior joint strength is required, the company has a solution.

From small, intricate components to automotive products, aircraft manufacturing, railway carriage panels and shipbuilding, Powerstir FSW machines provide a clean, highly aesthetic alternative to traditional welding – a method that delivers guaranteed weld quality, excellent mechanical properties and virtually no porosity. Although used primarily for joining aluminum, the Powerstir process can also be applied to magnesium, copper, titanium and steel alloys.

Patented by TWI (The Welding Institute), FSW combines frictional heat with precisely controlled forging pressure to produce extremely high-strength joints that are virtually defect free. Due to the low welding temperature, mechanical distortion is practically eliminated, with a minimal heat-affected zone and excellent surface finish. FSW transforms the parent metal from a solid to a plasticized 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 process is effective on flat plates, cylindrical components and even on parts of irregular thickness.

Typical Powerstir FSW applications for electric vehicle manufacturers include battery trays and boxes, chassis and structural components, control box panels, vehicle body panels, brake regeneration systems, and coolant units and heat exchangers. Other applications include heat sinks and electronic enclosures, aluminium train and carriage panels, aircraft fuselage and avionics development, boat and ship panel sections, pipelines and heat exchangers, and electric motor housings.

Closeup of a weld head on a 5-axis, gantry-type Powerstir FSW machine fitted with a vision tracking weld seam guidance system.

Additional end product examples include truck bodies, caravans and space frames as well as flat and cylindrical fuel tanks and bulk liquid containers. Finally, the process is well-suited for producing aluminium bridge sections, architectural structures and frames.

Incorporating the brands of Holroyd, Powerstir FSW and Holroyd Precision Rotors, PTG has established itself at the forefront of high-precision machine tool design, build and supply for specialized applications.

PTG Holroyd

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