Hytec Cape Town recently designed and constructed a 400-ton thermoplastic press for composite materials supplier AAT Composites, a Recaro Group subsidiary based in Somerset West. The press is capable of deep-moulding composite materials up to 1 m2 used in the manufacturing of components, such as seat pans and interior panels in the aerospace industry.
The contract was awarded in the face of considerable competition from international manufacturers. Hytec, with the assistance of a local mechanical engineering company and an electrical company, was able to supply a complete, integrated press machine, a turnkey solution from a single supplier that was tailored to suit AAT Composites’ specific production requirements, as opposed to modifying an imported press.
Resin-impregnated cloth is first suspended in trolley frames for moulding. The machine has an infeed-loader to pre-load trolleys whilst a cycle is in operation, plus an automated feeding system to transfer the trolleys precisely from one station to the next. A preheater with two sliding drawers, each containing 99 ceramic heating elements, preheats the resin-impregnated cloth to 450°C prior to moulding and curing. The material then has to be transferred into the press within three seconds and the pre-heated moulds closed quickly in order for moulding and curing to take place at a maximum temperature of 280°C.
Once the thermo-forming duration has been completed, the press opens and the part is transferred to the out-feed station for manual removal. All of these functions require precise real-time control, as neither of the individual functions has the same operating duration. The machine design includes a range of safety and operator protection and a scada system to provide visualisation and control of the production process.
“Special consideration had to be given to avoid heating of the press structure, and in particular the platens and guides, as any fluctuations would alter the 0,2 mm flatness tolerance of the platens,” explains systems engineer, Max Hoffmann. “An insulating layer together with cooling platens enables the heating of press moulds as opposed to press platens. This also serves to reduce energy consumption as heating is limited to the size of the moulds installed. Press platen cooling was excluded on request of the customer, however can be easily retrofitted.”
A range of Bosch Rexroth hydraulic components are used across the system. These include a standard press-control manifold with the latest EU safety features such as double load-holding and spool-position monitoring on all critical directional valves, and proportional displacement and pressure control with a 30 kW electric motor on the hydraulic power unit.
The main ram, supplied by sister Hytec Group company Hytec Engineering, is a single-acting displacement unit with a 450 mm diameter and 700 mm stroke. Fast extend and retract utilises two 80/50x700 slave cylinders (one with LVDT for position monitoring) which also aid in pressing. The automated feeding system is powered by two VSD drives with a pneumatic in-feed loader.
“This was an exciting project to be a part of, and is a great advertisement for the technical competency and capabilities of the Hytec Group to the country and the world,” Hoffmann concludes.
For more information contact Max Hoffmann, Hytec,+27 (0)21 551 4747, [email protected], www.hytecgroup.co.za
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