All you need to know about injection moulding - on the outside of a box!22 January 2007If you’re a product designer or manufacturing engineer with little or no experience of plastic injection moulding, UK based rapid injection moulding company Protomold would like to send you a box of...nothing. Nothing, that is, on the inside. On the outside, however, it’s a box crammed with useful information on how (and how not) to achieve the best possible results from injection moulding. The box in question is Protomold’s new sample part; an innovative piece that travels flat but folds into a palm-sized 63.5mm (2½-inch) cube using hinges and two kinds of moulded-in clips (locking and non-locking).
First distributed in huge numbers at Euromold 2006 (5000 samples in 5 days), the highly sought after Protomold Cube is now available to anyone who wants one, showing examples of what can be done in a straight-pull mould. The clips and hinges are just a few of the many sample features scattered across the surfaces of the cube.
For example, if you want to see a range of available surface finishes, from highly polished SP1-A2 to the matte finish of medium bead-blasted PM-T2, get a cube! They’re all there for you to see and touch. Want to know what happens when bosses are too thick for the surrounding surfaces? They’re likely to cause sink, and now you can see for yourself. And if you want to see some better ways to strengthen those bosses – gussets, ribs, and attachment to walls – the Protomold Cube has examples of those too.
Ever wonder whether thick, freestanding features should be cored out? They should, and the new sample shows you why. But thick isn’t the only thing to watch for; thin has it’s problems too, and the sample cube shows some examples of what can happen when a section gets too thin. And while ribs are a nice, lightweight way to strengthen a part, if they’re not sized right for the rest of the part, they can cause sink.
And what about knit lines, the cosmetic blemishes that form when streams of cooling plastic meet behind an obstruction? The sample part has some through holes formed by posts in one of the mould halves, and there’s a distinct possibility of knit lines behind such an obstruction.
A particularly noteworthy feature is a small channel running along one face of the part, the sort of thing you’d run an axle through, for example. It looks like it would require a side action, but it didn’t. The hole definitely runs horizontal to the direction of mould pull, but it was formed in a straight-pull mould. A close up look will reveal how it was formed. And, of course, there are those clips and hinges mentioned earlier, as well as the “footprints” of a lot of well-placed ejector pins.
Of course it is, as we’ve mentioned already, a box, which makes it ideal for holding up to 256 cubic cm (approx. 15 cubic inches) of odds ‘n’ sods of your choice. And all you have to do to get one of your very own is go to the Protomold website and request your free Protomold sample cube.
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