Tape sandwich for greater stiffness, less weight and low production costs

The focus of the ENGEL Mobility Days 2023 – supported by KTM Technologies – mid-June in Austria is change and sustainability. The two-day conference sees industry experts discussing solutions for future mobility. And this includes a global premiere: a motorcycle seat base produced using the new tape sandwich process. Development partners ENGEL and KTM Technologies have made it possible to combine greater stiffness, despite a more compact part design and less weight, with low production costs. Via the two development partners, the new composite technology is also available for applications in other companies.

The aim of the joint development work was to make a seat base for motorcycles more compact and lighter while retaining at least the same part properties. "We are accommodating increasing numbers of electronic components on the vehicle and need space for them," says Hans Lochner, Head of Material and Applications at KTM Technologies in Anif, Salzburg, explaining the challenge. Due to drivetrain electrification, this trend is not just impacting on bicycle and motorcycles OEMs, but on the entire mobility industry.

In order to offer added value for the mass markets in addition to the technical advantages, a cost-efficient production process is needed. ENGEL and KTM Technologies are combining their expertise for this. ENGEL is contributing its expertise in lightweight production technologies and industrialization, while KTM Technologies is responsible for conception and product-specific technological development. The third partner in the alliance is mould maker Feronyl, who is based in Belgium.

Thus far, the seat bases for KTM motorcycles have been purely thermoplastic injection moulded parts. The required stiffness is achieved by geometric stiffening – for example via ribs – which leads to a relatively high part thickness of up to 9 mm. To reduce the necessary installation space and free up more space for the electronics, KTM Technologies took a close look at composite materials and production processes and, in cooperation with ENGEL, established a production process that is characterised by a particularly high level of efficiency. The result is tape-sandwich technology.

"In the tape sandwich process, we work with very thin, single-layer reinforcement materials such as tapes and fabrics with polypropylene matrix, which are inserted into both cavity halves of the injection mould without preheating before the cavity is filled with polypropylene," as Franz Füreder, Vice President Automotive & Mobility at ENGEL headquarters in Schwertberg, Austria, explains. "Due to the specific mechanical properties of the sandwich structure, we can already meet the stiffness required for motorcycle seat bases with a single-layer UD-tape. This means that the tape sandwich process requires significantly less energy and simpler production cell technology than conventional fibre-reinforced plastic composite processing methods. At the same time, the production costs drop."

In the case of this technology demonstrator, the seat bottom, with identical stiffness, the necessary installation space could be reduced by 66 percent and the weight by about 26 percent. "The new sandwich structure, in which the reinforcing fibres are as far away as possible from the neutral fibre, offers maximum stiffness while minimising the number of fibres required," says Lochner.

Another advantage of the sandwich structure is that standard thermoplastics can be used in components exposed to high mechanical stresses, since the part performance is driven exclusively by the tape structure. And that boosts cost efficiency, too.

The development partners have tested a variety of injection moulding materials, including bio-based and recycled PP grades in addition to conventional PP from fossil sources. The global warming potential (GWP) was determined for the various material combinations. Compared to the series production version – a seat made entirely of fossil PP – the tape sandwich technology reduces the GWP by 27 percent when also using fossil PP. This value is achieved solely by reducing the material. With polypropylene from renewable sources, the GWP value is reduced by 85 percent. The component weight was reduced by 26 percent in each case. This is possible because even very thin components achieve high stiffness.

The consistent single grade plastic approach also contributes to the reduction of greenhouse gases in the overall view. In combination with tapes from a PP matrix, parts can be created which can be recycled at the end of their service life. "This new development sees us open up an affordable and sustainable solution for future mobility," Füreder emphasises.

The first step will be to set up tape sandwich technology for use in the KTM family of motorcycles. Besides this, ENGEL and KTM Technologies have their sights set on many other lightweight applications in a wide range of mobility disciplines. The two development partners are offering the tape sandwich process jointly, and developing solutions tailored precisely to the specific use case.

ENGEL and KTM Technologies jointly organised the two-day Mobility Days event. The networking event is bringing together more than 500 experts from the automotive, micro-mobility, aerospace and transportation sectors in Linz and St. Valentin in Austria. With a top-class conference program and forward-looking machine exhibits, the event is promoting a cross-industry expert exchange.