The University of Nottingham in the UK has commissioned precision metering technology as part of short fiber compression molding process.

Plans are for the university to use the process, developed by a team from the EPSRC Future Composites Manufacturing Research Hub, to make composite parts for the automotive industry.

Researchers say that they have developed an out of autoclave (OOA) manufacturing technology that can use lower cost, short fiber formats. It uses a liquid resin spray (LRS) system to apply the resin matrix to short form (25 mm) carbon fiber activated by an air stream. In this way, the resin and the fibers make complete and uniform contact with each other without the need for mechanical application.

It could be used to make complex-shaped under bonnet and suspension parts at a lower cost, the university said.

The technology has been supplied by UK pump manufacturer Slack & Parr. "Being able to accurately meter each ingredient means we can mix the resin matrix to a viscosity that can be sprayed reliably and effectively without having to rely on the overuse of solvents," said Professor Nick Warrior, who has led the research. "Varying the percentages even slightly at this stage can result in a resin that may not spray or cure correctly, so accuracy is crucial here.

"We can also adjust the metering pump to create new resin systems with different characteristics, for example faster curing and better mould release to help us achieve our target 30-second cure cycle."

Slack & Parr says that that metering pumps are built around hardened steel involute gears which are machined to precise tolerances of one or two microns. This results in extremely small, controlled clearances – measuring less than a human hair – between the gear and mating components, ensuring almost no internal slip even at high pressures. This level of precision means the pump is able to control or meter the flow with extreme accuracy and repeatability.

In the university’s system, each part of the resin matrix is held separately to prevent curing and mixed only at the point of application, the company said. The metered matrix is then sprayed directly from the resin mixing tank onto the short form carbon fiber filaments which are simultaneously propelled into a controlled air stream via a robot head. The resin-coated carbon fibers are subsequently moulded to form a composite component.

The University of Nottingham’s application requires three different fluids with different viscosities to be brought together at the same rate and in the right ratios to achieve the desired resin matrix and to ensure consistency and repeatability of the process. Using Slack & Parr’s gear pump technology, the university team was able to achieve a consistent flow throughout the process despite varying pressures linked to the different viscosities of the fluids.

"Our pump solutions are relevant to every area of the composites industry where the need to precisely determine the fibre-to-resin ratio is key to the manufacture of consistent composite materials and parts," said Neil Anderton, hydraulics and industrial director at Slack & Parr. "Importantly, the technology can also be extended out to other polymer resins and plastics to offer the same level of performance."