Half a croissant, on a plate, with a sign in front of it saying '50c'
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reconfigerable mass injection molding

  (+6, -2)
(+6, -2)
  [vote for,

molds for plastic injection molding cost up to 5 thousand dollars each.

Which is bloodly expensive from an investment standpoint of a product.

What if you can readjust the mold via moving an array of metal pins. While somehow keeping the pins close together to prevent leakage.

mofosyne, Feb 19 2011

Baked http://etheses.nott...rew_Pin_Tooling.pdf
Rapid Manufacturing of Vacuum Forming Components Utilising Reconfigurable Screw-Pin Tooling [AntiQuark, Feb 19 2011]


       A rather shapely convex bun [+}
FlyingToaster, Feb 19 2011

       Hah. //somehow keeping the pins close together to prevent leakage.//   

       (For those of you who haven't ever done injection molding, be aware that what [Akimbomidget] has proposed is full-on industrial grade magic, complete with a vacuum wand and a pointy hat.)   

       Maybe, if you keep the plastic extra viscous (barely melted), and the pressures low... 'course, you can't push viscous plastic at low pressure... (although I always liked the smell of shear-burned polycarbonate. Reminded me of marshmallows, for some weird reason.)   

       How about a thin (inexpensive!) metal liner, supported by the pins? That would seal, but I'm afraid you'd have problems at the edges. And the heat transfer would be as difficult as a fly rod in a VW...   

       What kind of machine you got, anyway? One of those 1.5 ton hand-cranked Boy key-ring makers? Pins would never hope to support the pressure on one of those multi-hundred ton clamp force jobs, like a big Cinci or Netstal.
lurch, Feb 19 2011

       Could such a pin array be used for vacuum forming of sheet plastic? The strength and sealing requirements would be much less.
spidermother, Feb 19 2011

       This is a nice idea, but I think it would not work.   

       First, the products would be "pixellated". In some cases, this would not matter, but it would prevent you making anything very precise, even if the pins were 0.1mm across (which means a 10 x 10cm object would need a mould with 1 million pins). It would also prevent you making objects with a nice finish, where this matters.   

       Second, you'd be limited to objects that don't re-curve (ie, you can't make overhangs, except in very simple cases). Again, many moulding machines do this, and even simple two-part moulds often produce shallow recurving lips (for example, to allow parts to be clipped together), which can be released thanks to the flexibility of the set plastic.   

       Third, the mould would be very fragile - one inadvertent knock to the pins, and they'd have to be replaced.   

       Fourth, I'm not sure how easy it would be to release the object after moulding, given the textured nature of the pin surface, even if no plastic squeezed in between the pins.   

       Fifth, commercial moulds are often fitted with many complex features including water cooling channels and retractable pegs etc, both to allow more complex products to be made, and also to speed the moulding cycle. You couldn't do this with a pin array.   

       ON the other hand, I am now looking at one of those pin- matrix toys (carrying an impression of a hamster, as it happens). A slightly finer version which could be locked and used for vacuum sheet forming, as per [spidermother]'s suggestion, would make an interesting toy or hobby device.   

       So, [+]
MaxwellBuchanan, Feb 19 2011

       The pins, I imagine, would be hexagonal.
FlyingToaster, Feb 19 2011

       If the pins were fine enough you could even get a decent reverse surface on vacuum forming. That being said, it might work for one or two parts- prototypes or one offs. But in quantity, wear and de-molding difficulties would offset the advantages. Also you are going to be very limited in the detail of features, since you're clean side will be the un-molded side. And deep drafts are going to be just about impossible.   

       It would also be extremely expensive (what's supporting the pins, a small motor each? a stepper multi part solenoid?) or extremely difficult/time consuming to reconfigure.   

       Since you can get a decent low volume mold (wood or polyurethane foam usually) for ~500- 1000, and a good high volume mold for 5000, I doubt this very expensive tooling will pay for itself. Full up injection molds are usually noticeable more expensive than 5k though, which is why you only go to them if you've got the volume to support it. 10k for a mold isn't all that much if you're expecting to produce 100 million units.
MechE, Feb 19 2011

       And if you actually read through anti-quarks] link, you find they use the initial pin formed part as a near net shape, which they then coat with a filler material and machine into shape for a mold. Considering you can machine a mold from raw stock for less effort and barely more cost, it's not worth it.
MechE, Feb 19 2011

       [Max] Why don't you use your hamster directly as the vacuum forming mould?
spidermother, Feb 19 2011

       Because, if hamsters behave anthing like cats, once you've pumped all the air out they're never quite the same afterwards.
8th of 7, Feb 19 2011

       It was a stuffed hamster. Derrr!
MaxwellBuchanan, Feb 20 2011


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