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Ford, Warwick Manufacturing Group (WMG), Autotech and GRM Consulting have developed a composite rear suspension knuckle for a C-segment vehicle.
According to Ford, a combination of unique carbon fibre deployment and a bespoke manufacturing process results in a 50% weight reduction compared to the current fabricated steel component. The processing technology introduced in the project is said to be the first of its kind and offers a cycle time of less than 5 minutes. The design of the part is complete and manufacturing trials of the component are currently ongoing to develop the full-scale mass production process.
Collaboration is essential
The automotive industry across the globe is pushing for tighter mass targets in order to satisfy the ever increasing stringency over emissions, concern of depleting fossil fuels and customer demand for extended range of electric vehicles. Ford’s global Research and Advanced Engineering group teamed up with Chassis Engineering in the UK to redesign a serial steel suspension component to enable its manufacture as a lightweight composite component. The weight saving in this un-sprung component increases the effectiveness of the springs and dampers, leading to enhanced passenger comfort and driver handling. The newly developed composite part proved appropriate for a high performance C- segment vehicle.
The two-year project, Composite Lightweight Automobile Suspension System (CLASS), was part-funded by Innovate UK.
WMG used its extensive knowledge of material behaviour and state-of-the-art manufacturing cells to enable chassis manufacturer Autotech to design a component that meets the required functional requirements. GRM Consulting, which develops predictive tools for carbon fibre structures in the motorsport industry, made a significant contribution to the project by reducing the amount of physical testing required.
During the course of the project, the design of the composite part evolved from a single material part to a multi-material design. Initial surveys indicated that a composite lightweight knuckle could be realised by single material – sheet moulding compound (SMC). However, rigorous in-house testing of SMC samples highlighted two drawbacks, namely longer cure times and lack of mechanical properties to meet the load requirements. These issues led the design engineering team toward a multi-material system, where layers of prepreg give the required mechanical properties and co-moulding of SMC allows the complicated geometric profiles. Such a technology has been proposed in academia and in the aerospace industry, however the requirements for automotive applications are different and this project is likely to be the first time such technology is implemented. This has been possible as prepreg manufacturing costs are being reduced globally. The approach of combining uni/biaxial prepreg with SMC suggested that the composite component could satisfy the majority of the mechanical strength targets. The design was finalised after extensive simulation and experimental work, which involved optimisation for OEM durability and NVH targets.
Innovative manufacturing technology
A compression moulding technology has been developed capable of mass manufacturing the high strength, stiff and complex shaped suspension knuckle. This will be fully automated, achieving a cycle time below 5 minutes, with manufacturing trials producing a demonstration part for evaluation by physical testing. With the aid of a press, the pre-cut prepreg is preformed to the required shape in a die. The preform is then transferred to the compression moulding press. The compression moulding tool was manufactured by a UK-based tool maker and features sensors to track SMC flow, monitor process parameters and investigate the cure of the prepreg and SMC resins. The SMC is composed of 53% weight fraction and 15k filament count carbon fibre, and the prepreg is a woven fabric with 60% weight fraction and 12k filament count, all supplied by Mitsubishi Rayon. Prior to manufacturing the part, CLASS candidate carbon fibre materials were moulded at the Ford Research and Innovation Centre in Dearborn, US. This helped to optimise the process parameters so that the maximum mechanical performance and geometrical accuracy can be obtained.
Meeting the project’s cost objectives was the biggest challenge but the experience gained helped engineers understand how to strike the best balance between cost, performance and weight. The project started with an aim of developing a 100% SMC composite knuckle. As it progressed, the engineers learned that low cost composites cannot offer the required mechanical stiffness properties and therefore had to be more creative in the material selection to ensure that the manufacturing process could stay within the cycle times whilst meeting the objectives set out at the beginning of the project.
Image provided by Ford
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