Composite volume production: lightweight material challenge

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While everyone agrees composites could be a good fit for automotive – at least when it comes to lightweighting – producing parts in the volumes needed is an area that continues to challenge.

All of the major automotive original equipment manufacturers (OEMs) are examining the feasibility of replacing the metals they use to produce the body-in-white (BiW) of their vehicles with carbon fibre-reinforced plastics (CFRPs). These light, stiff composites could be a vital part of these carmakers’ strategies to increase fuel efficiency and reduce emissions. However, only BMW – with its ‘i models’ and, more recently, with its 7 Series – is using CFRPs in anything approaching high volumes.

CFRPs are expensive and the processes used to convert them into parts and components has traditionally been too slow for use in mass-production. But the suppliers of these materials are working hard to remove these roadblocks.

According to one such supplier – Cytec Industrial Materials – the company's current composites solutions are viable for production rates of 30,000–50,000 vehicles a year, and it is targeting even higher volumes than this. To assist in this goal, Cytec has opened a £9.2 million application centre at its site in Heanor, UK.

The purpose of this centre is to drive the development of these materials to the speed, cost, performance and manufacturing levels required for part production in large volumes by OEMs and their suppliers. Crucially, the centre will provide a venue for Cytec to work directly with those manufacturers to develop the technology needed to make it viable.

“There’s a learning curve that any new customer would need to make, to make the switch from one material choice to another, and perhaps different customers will have a different view on what the lowest risk/highest reward approach is for making that switch,” says Timothy Wybrow, an application research and engineering manager for Cytec Industries. “So our role here is to facilitate that change, to try and de-risk that process with them, to try and help build their understanding, to give them the confidence in taking that technology forward.”

The centre currently plays host to a wide variety of automated manufacturing cells, each of which demonstrates liquid and compression moulding technologies developed by Cytec and its partners to make the production of composite parts cheaper and more efficient. These cells can be modified or swapped out depending on the projects the company is working on.

Alexander Aucken, the global automotive manager of Cytec Industrial Materials' parent company Cytec Industries, adds: “We’re trying to attack this from both angles. We’re doing the fundamental research and development work to take it to a successful TRL (technology readiness level), and also coming at it from another direction with the larger tier-1s and tier-2s who are going to have to take that technology and introduce it into the OEMs at production rates.”

While these technologies are useful in isolation, Aucken and Wybrow are keen to point out that the best results are achieved when they are used in combination. For example, one of the cells – developed as part of the Composites Innovation Cluster’s ACTIVATE project – enables the automated production of cross-ply prepregs with localised slashing, which improves the drapability in a tool without impacting mechanical performance.

This cell comprises an Assyst Bullmer cutting machine and a 6-axis ABB robot fitted with a vacuum end effector. Using these machines, two rolls of prepreg are unrolled side-by-side at 0° on the cutting table. These prepregs are then slashed via kiss cutting with an ultrasonic knife, which enables the prepreg to be cut without damaging its backing paper.

The first roll of prepreg is then cut into squares that are picked-up by the end effector and the backing paper is removed. The surface tack of the prepreg has been modified to ensure that it does not get stuck to the end effector. These squares can then be placed on top of the second roll of prepreg at 90°, to create a 0/90° crossply prepreg that can be off-wound.

These crossply prepregs can be processed further in another cell designed for the manufacture of tailored blanks. The prepreg is unrolled on a Zund flatbed CNC cutting machine, which is fitted with an ultrasonic knife and is capable of cutting speeds of 1–1000 mm/s.

The prepreg is cut into kit plies that are laid-up on an adjacent turntable, using a 6-axis ABB robot fitted with a pick-and-place end effector featuring individually actuated suction cups, to form 2D blanks.

These tailored blanks can then be laid-up on a membrane for double-diaphragm forming, which Cytec says is affordable – at less than £35 per kilogramme of material processed – and can be operated with a five minute takt time. The process is particularly suitable for the production of floor pans, sidewall panels, crush cans and body panels.

Using this cell, the membrane containing the blank is placed in a frame and a vacuum is applied. This blank is then preheated within the diaphragm forming fixture, which enables the production of parts with complex geometries, and compression moulded in a Schubert 350t up-stroking hydraulic press where it undergoes a five minute cure cycle at 140°C. Finally, the part is demoulded before final inspection and trimming.

Working with Jaguar Land Rover (JLR) and Penso – a composite part manufacturing company in which Cytec Industries has recently acquired an equity position – the centre has also developed a recycling process for prepreg off-cuts generated by any primary manufacturing process.

The resulting ‘recycled’ material demonstrates similar mechanical properties and processing characteristics to sheet moulding compounds (SMC), and it can be used to produce non-structural parts or can be co-moulded with conventional prepregs.

Going large

The largest manufacturing cell at the application centre is the Langzauner 1600t down stroke press, which can be used with hot compression moulding, thermoforming and high-pressure resin-transfer moulding (HP-RTM) processes.

Cytec is using this press to evaluate and characterise its XMTR750 epoxy, a two-part system developed specifically for high-rate manufacture of components using HP-RTM.

The epoxy system possesses a low viscosity, which enables injection times of less than 30s with HP-RTM moulding equipment, and Cytec claims that parts can be made in a total cycle time of five minutes or less at 120–130°C. These parts can be demoulded while hot.

The company has also invested in a Formaplex HP-RTM tool featuring integrated sensors that enable the study of cure distortion and the analysis of resin flow, which could help with the design of its customer’s manufacturing processes.

Much of Cytec’s work is with thermosets, but Carmelo Lo Faro, chief technology officer of Cytec Industries, describes the company as ‘materials agnostic’ and adds it is happy to work with thermoplastics too.

The application centre boasts a cell – developed as part of the UK-ECOPROCESS project – for the production of low-cost, near-net shaped thermoplastic preforms reinforced with glass, carbon or aramid fibres.

The cell features an ABB 6-axis robot fitted with a ChopCot HC TRL 6 chopping gun and alignment device. The base materials employed are chopped rovings made from a thermoplastic and the chosen reinforcement.

These rovings are sent through the chopping gun and sprayed in an oriented way onto a vacuum preform screen, which captures and stabilises the chopped fibres. The properties of the component can be optimised by adjusting the chopped length and orientation of the fibres.

The hybrid chopper is able to process around 100 tonnes of glass based rovings without the need for maintenance, and is able lay down up to several kilogrammes of chopped material a minute. This means that the process is capable of producing large amounts of thermoplastic composites in a cost-effective manner.

The resulting preform is consolidated, and then subjected to heat and pressure in a high-speed press to produce a part.

Indeed, Cytec's work with thermoplastics is likely to increase in the future. In December 2015 Cytec Industries was acquired by Belgian chemicals giant Solvay in a deal worth around $6.4 billion. Solvay generated sales of €10.2 billion in 2014.François Hincker, the manager of Solvay's Integration Management Office, says: “We have the resources, the financial commitment, to invest in the industry to make the adoption of composites even bigger than it is today.”

Lo Faro is keen to stress that Solvay is taking a long-term view with regard to Cytec’s composites business; that it could take decades before CFRP is being used widely in the automotive industry and that many challenges remain.

Author
James Bakewell

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