Magneti Marelli’s First-Ever Carbon Fiber Steering Knuckle Slashes WeightMagneti Marelli’s First-Ever Carbon Fiber Steering Knuckle Slashes Weight

Magneti Marelli collaborated with thermoplastic supplier Solvay to create this first-of-a-kind carbon fiber part.

Dan Carney, Senior Editor

April 25, 2021

3 Min Read
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Magneti Marelli

As carmakers leap to reach increasingly higher-hanging fruit in the effort to trim weight from new vehicles, advanced materials and manufacturing processes confront cost constraints.

Magneti Marelli’s solution is to employ carbon fiber that includes 40 percent recycled material. As there is not an abundance of carbon fiber products returning from the end of their useful lives, recycled carbon fiber is normally excess material recovered from manufacturing processes for other parts.

Automotive steering knuckles, also known as hub carriers or suspension uprights, are typically heavy parts because of the forces involved supporting the car’s weight and withstanding steering and braking forces that transfer through the part.

These have traditionally been made of cast iron, and cast aluminum is a rarely seen lightweight alternative used mostly in expensive sports cars. With that cost constraint in mind, the idea of moving on to carbon fiber could be unrealistic, but Magneti Marelli says it thinks it has a solution with this component.

“Our first idea with this project was to combine the really high mechanical performance of carbon fiber laminates with the very complex geometry that can be achieved with injection molding,” explained Salvatore Sottile, Advanced Materials Application Engineer, Composite Specialist, and Project Leader for Magneti Marelli. “The use of recycled carbon fiber enables us to reduce the cost of the product itself and to decrease our environmental footprint during the manufacturing process. Besides the possibility to achieve the lightweight target compared to the aluminum counterpart.”

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Casting is normally used for steering knuckles because of their complex shapes, an attribute that brings additional challenges to the idea of using carbon fiber. Magnetti Marelli worked with Solvay’s Composite Materials Global Business Unit in an effort to marry the strength of composites with the shapability of injection-molded materials.

The carbon fiber knuckle is made using Advanced Sheet Molding Compression (ASMC), which is a high-volume, high-pressure method suitable for molding complex, high-strength materials. The resulting part is as strong as traditional carbon fiber and is even more resistant to cracking. Compared to the usual cast iron, the Magneti Marelli knuckle is 50 percent lighter and is even25 percent lighter than the aluminum equivalent.

Of course, the durability of those traditional materials is well established, so Magneti Marelli’s Ride Dynamics team has performed extensive testing, analysis, and validation to confirm the durability of the suspension knuckle, developing prototypes using a 1500-ton press.

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The combination of chopped carbon fiber with ASMC permits complex structural parts that meet performance requirements that can be produced in a one-shot, net-shape process, resulting in cycle times that Magneti Marelli describes as suitable for automotive production.

The part employs compression molding and overmolding processes using a combination of Solvay’s Amodel PPA thermoplastic compound and Evolite PPA thermoplastic composites. These products were developed specifically for high-temperature automotive functional applications such as this steering knuckle.

“We are proud of our contribution to this prototype. This is a successful combined application of Solvay’s Amodel and Evolite PPA thermoplastic composite technologies which meets the rate and process flexibility expected by automotive manufacturers” said Gerald Perrin, Global Automotive Director at Solvay Composite Materials Global Business Unit.

Now, we have to wait to see the first production application of the component. Given Magneti Marelli’s longstanding ties to various low-volume Italian sports car manufacturers, one of those companies seems a likely candidate to debut the carbon fiber steering knuckle.

About the Author

Dan Carney

Senior Editor, Design News

Dan’s coverage of the auto industry over three decades has taken him to the racetracks, automotive engineering centers, vehicle simulators, wind tunnels, and crash-test labs of the world.

A member of the North American Car, Truck, and Utility of the Year jury, Dan also contributes car reviews to Popular Science magazine, serves on the International Engine of the Year jury, and has judged the collegiate Formula SAE competition.

Dan is a winner of the International Motor Press Association's Ken Purdy Award for automotive writing, as well as the National Motorsports Press Association's award for magazine writing and the Washington Automotive Press Association's Golden Quill award.

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He has held a Sports Car Club of America racing license since 1991, is an SCCA National race winner, two-time SCCA Runoffs competitor in Formula F, and an Old Dominion Region Driver of the Year award winner. Co-drove a Ford Focus 1.0-liter EcoBoost to 16 Federation Internationale de l’Automobile-accredited world speed records over distances from just under 1km to over 4,104km at the CERAM test circuit in Mortefontaine, France.

He was also a longtime contributor to the Society of Automotive Engineers' Automotive Engineering International magazine.

He specializes in analyzing technical developments, particularly in the areas of motorsports, efficiency, and safety.

He has been published in The New York Times, NBC News, Motor Trend, Popular Mechanics, The Washington Post, Hagerty, AutoTrader.com, Maxim, RaceCar Engineering, AutoWeek, Virginia Living, and others.

Dan has authored books on the Honda S2000 and Dodge Viper sports cars and contributed automotive content to the consumer finance book, Fight For Your Money.

He is a member and past president of the Washington Automotive Press Association and is a member of the Society of Automotive Engineers

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