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09/01/2005
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A revolutionary injection moulding process has been developed that cuts cycle times and assembly costs. Dean Palmer reports
 A revolutionary injection moulding process has been developed that cuts cycle times and assembly costs. Dean Palmer reports
A patent-pending injection moulding process has been developed that uses a revolutionary 'twin cube' system, allowing manufacturers to achieve improved efficiencies, faster cycle times and reduced assembly costs. The technology looks almost certain to be adopted by high volume parts manufacturers in the packaging, medical and telecoms industries.
German company Forboha's twin cube system incorporates a mould which comprises two rotating cubes positioned between the two halves of the mould. In effect, these cubes function like two separate moulds. The twin cube has three closing parts in which different working processes can occur simultaneously, guaranteeing the efficient production of parts.
After simultaneously injecting the cavities of the first and third closing part, each by an independently-operated injection unit, both closing units are opened, the cubes (including the injection moulded parts) are rotated by 90 degrees and then re-closed. The next injection moulding process now follows. At the same time, the pieces which have been injected cool off on the side facing the operating side. Following the next injection process, the mould opens again and both cubes are rotated together by a further 90 degrees.
Both lots of injected pieces of the first and third closing parts are now facing each other in the second closing part. When the twin cube is closed, the two sets of injected pieces are mechanically fitted together (in-mould assembly) using a separate core puller. Due to the separate assembly process, parts assembly is mostly independent of the closing process of the machine, so that operation is achieved with maximum speed.
In the next machine cycle, both cubes are again rotated by 90 degrees, but the finished parts are now transferred outside by one of the cubes, where they can be removed. At the free station of the first cube, labels or metal parts for in-mould assembly can be inserted into the mould, using some kind of feeder mechanism.
Forboha developed a special drive and coordination mechanism to effect the opening and closing of both cubes. The tricky bits are the different opening times of the closing units which ensure an efficient rotation of the cubes without loss of the machine's opening stroke.
The benefits of the twin cube system look appealing, especially when it comes to storing assembly processes in the mould. Considerable cycle time can be saved because assembly operations occur during the injection process when the mould is closed. This eliminates the costs of external assembly operations and results in large savings in space and investment. Instead of purchasing two separate injection moulding machines, only the twin cube system is required.
Logistics becomes easier too since an intermediate zone or 'buffer' is no longer required. And, high precision and quality are guaranteed, as assembled parts are from cavities that are ideally adapted to each other.
According to Forboha, in tests on a 2 x 16 cavity mould, each top and bottom parts of a two-part thin wall packaging were injected and assembled simultaneously. The top parts of the packaging were supplemented with in-mould labelling. During one cycle, 16 complete parts of polypropylene were injection moulded, labelled and assembled within a cycle time of around 6.2s.
Pointers
* The twin cube system simultaneously injection moulds and assembles parts leading to faster cycle times and reduced assembly costs
* On a 2 x 16 cavity mould, 16 complete parts of polypropylene were injection moulded, labelled and assembled in just 6.2s
* The process looks certain to be taken up by high volume manufacturing industries such as telecoms, packaging and medical devices
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Author
Tom Shelley
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