KraussMaffei Partners with Taiwanese Composites Specialist to Realize Carbon Rims

Golf clubs, bicycles — and now automotive, too: Together with KraussMaffei, Taiwanese composites specialist Advanced International Multitech (AIM) is expanding its portfolio to include high-pressure resin transfer molding (HP-RTM). AIM is now producing automotive carbon rims on a complete system with sophisticated tools.

Anyone who plays golf and is keenly aware of the importance of club weight has probably held an AIM product in their hands. The company has a global market share of around 80% for carbon-fiber golf clubs (under various brand names), and also has a track record in the bicycle market. For around 30 years, various composite technologies have been part of the standard repertoire. When AIM first ventured into the automotive sector, however, know-how from KraussMaffei was in demand, as this would be the first time it put an HP-RTM system into operation. Carbon-composite wheels have emerged as a hot topic of late. OEMs such as Jaguar Range Rover, Chevrolet, and Hyundai all offer the option on select vehicles.

High pressure, high quality, high cost

In comparison to low-pressure processes, HP-RTM requires more complex dosing technology, but also delivers consistently high-quality components with exceptionally precise surface quality — all in short cycle times, which are particularly important in the automotive industry. In the beginning, the AIM team first wanted to get to know the new technology of the system. As Tyson Hsiao, R&D manager at AIM, explains: “Fredrick Su, our sales partner at KraussMaffei, listened carefully, and then put together a package that we could use in an HP-RTM cell to recreate both high-pressure transfer molding as well as wet molding and compression RTM for small production series. We were really impressed by this.”

Related:Carbon Composites Usher in New Era of Rocket Manufacturing

A concrete project soon followed. Carbon rims tend to occupy a niche in the automotive sector yet are extremely lucrative because they are in the high-price segment. A material mixture is common in this case: A rim body made of carbon-fiber-reinforced plastic (CFRP) to which the visually appealing aluminum wheel spider is bolted. These wheels are approximately 20 to 30% lighter than those made of pure aluminum and, at the same time, are around 20% stronger than all-aluminum rims. Sporty and ambitious drivers can accelerate faster thanks to the reduced weight and, with more of the unevenness of the road dampened by the suspension, the driving experience is also more pleasant. If you want to deck out your vehicle with carbon rims, you have to dig deep into your pockets, though: €10,000 to 15,000 ($11,000 to 16,600) per set is common.

Robotic assistance, modular tool design

The HP-RTM cell package consists of an MX press with a clamping force of 10,000 kN, a RimStar Compact 8/4 HP-RTM metering system, two robots for metering and handling (with different grippers), and a sophisticated mold solution. The system’s 16 x 12-meter (52.5 x 39.4-ft) footprint represents a relatively compact design.

The entire production cell for the carbon rims measures a compact 16 x 12 meters (52.5 x 39.4 ft), including the enclosure. Image courtesy of KraussMaffei.

The tooling set applies a master mold and uses several mold packages for the different rim diameters. This gives the customer a lot of flexibility.

 A carbon preform, prepared by the customer, is placed over the inner core of the mold, and four sliders, which form the round outer contour of the rim, then move simultaneously. The press closes and the epoxy matrix material is metered through a distribution star. After a curing time of approximately 15 minutes, the mold opens, the sliders open, and an ejector ring presses the rim body, which has shrunk to the core (20 inches in diameter), upwards. The mold is flexible from 18 to 22 inches in diameter with a rim width from 8 to 12 inches. The tool weighs in at 4.9 tonnes and delivers incredibly precise concentricity of 20 µm. 

Know-how in the mold

The many moving parts in the mold were cause for the greatest challenge, which was to seal the complete system at a high cavity pressure. Normally, the pressing force alone is sufficient to seal a mold, where the horizontal sealing surface is located solely between the upper and lower parts of the mold. In the case of the rim project, however, the undercuts and C-shaped contours of the part required four sliders to enable demolding, not to mention the moving ejector ring.

Road-ready carbon-composite rims emerge directly from the mold carrier. Image courtesy of KraussMaffei.

To retain the vacuum in the mold and prevent low-viscosity material from escaping, the team strove to achieve the best possible manufacturing precision and with it a good design. The locking force is generated by four barrels on the top of the master mold and locking elements mounted underneath, which move into recesses on the sliders and block them. With a mold temperature of 120 to 130°C (248 to 266°F), protection of the pneumatic and electronic components with insulation boards was necessary.