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10/05/2006
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A hybrid rapid prototyping and rapid tooling technique has been developed that can handle series production of complex, plastic parts. Dean Palmer reports
A patented hybrid technique that uses rapid tooling and rapid prototyping technologies, has been developed that offers low cost, simplified moulding tools made from aluminium.
The technique uses CAD software and high speed CNC machining methods, working from the client's CAD model data. With these moulds, the customer can call off both prototypes and batches of plastic components in production intent materials.
Ideal for complex parts, Protoform's patented 'Space Puzzle Molding' (SPM) process has also passed its graduation examination for series production as a fast and easy shortcut to polymer products of all kinds.
Using the Space Puzzle Molding process, Protoform Konrad Hofmann concentrates on producing one-offs as well as prototypes in small numbers or short series. In the company´s plastic injection moulding plant, plastic parts are produced piece-by-piece, mostly by hand, as well as in batches of up to 3.000 pieces.
Compact, inexpensive to build SPM-moulds are manufactured at Protoform. Puzzle is installed by a lifting device in standard injection moulding machines. The mould is fixed in a standard frame and prepared for the injection moulding process.
Following the injection moulding process, the complete mould is released and lifted out with a handling device. On a special workbench with a holding device, the mould is opened and disassembled (manually) to release the plastic part. Production parameters of the injection moulding process are adjusted and controlled carefully to satisfy customers and quality assurance requirements. Parameters are documented to assist future series production.
This rather complicated manual process is rationalised to a large extent in Protoform's production. In fact, it takes trained personnel only minutes to re-assemble the SPM-mould for the next part to be produced. Locking force used for the injection moulding machines is from 300 to 6,500kN. Because internal pressure can develop up to 1,000 bar or more, which the SPM-mould and machine-integrated mould frame must withstand, plastic parts (such as automobile centre consoles) are limited to 800 by 400mm in size and 2,200g in weight.
Typical plastics are PC+ABS, PEEK and PP, but mainly PA, PBT, and PPS are used. More frequently, customers also express a desire for reinforcement with fillers. Moulds manufactured in such cases have proven their performance.
SPM has long supplied one-offs, a few unique pieces, or short series up to 500 parts. Now the procedure is advancing into series production. Its advantage: after a few working days a fully functional mould that can supply authentic parts in original materials is available for production.
Release of the plastic parts form the mould is usually associated with a varying degree of disassembly of the mould which sets some limits on the maximum output. In some cases, the number of parts produced has been sufficient, because no mass production was required, for example, in medical appliances, such as computer tomographs. So far, the output produced in the SPM procedure was 500 to 1,000 parts.
The first case in which this limit was exceeded significantly and therefore shifted into the series range, was a project for US company Pitney Bowes. There, Protoform helped solve an emergency, because a series injection mould was not available in time. With a large SPM tool, 3,000 units of a complex plastic housing insert for a paper sorting machine were produced very quickly.
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Author
Tom Shelley
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