RepRap/injection molding question

I wanted to ask the community about a thought I had for an injection molding idea.

I have ther need to create a small part , a box that is 30mmx20mmx20mm (hollow) 2mm walls (@ 3 grams of ABS), and want to do it injection style for strenghth and looks, not to mention speed.
so I wondered if I could convert or use a reprap style extruder/hotend to do the job. I'm not opposed to building a small injection machine, but the whole machine seems like it would be a bit much for what I want to produce, and it would take some time to re-coop the money spent building it.

My biggest concern is feeding fast enough and having enough pressure to fill the mold.
the idea was to create a hotend with an orifice large enough to flow quickly. Perhaps rotate the heat cartridge to it is parallel with the hotend giving a longer hot zone. and a wades style exturder.

I have also thought about feeding 2 filament into one hotend to increase flowrate.
Before I begin a project, that in my head works, I thought I would ask if I am way off the mark in my thoughts. I have no experence with with injection molding, but have been researching the topic. it seems pretty straight forward, but again, so do so many other things I have failed at.

If someone could point out the flaws with my idea. I'm sure I am missing something - my guess is the amout of force it takes to fill the mold in a timely manner.

Thanks

You wont have enough pressure to push the plastic into the corners. In addition the filament driver wheel will slip as the pressure increases.
Take a look at some videos of the hand toggle operated injection molds, you will see that quite a bit of force is being exerted to push the plastic in.

But I like to see people try, you never know, you could come up with an easy hack to make it work, but simply placing the nozzle of a typical hot end into a mold and expecting it to fill, I don't see it happening.

Edited 1 time(s). Last edit at 08/02/2014 10:32AM by A2.

You can print it at your highest resolution and solid infill then put it in an acetone vapor bath.

The acetone should "melt" the layers together enough to get closer (or all least closer) to injection molding strength.

That's about as close as you can get for larger parts. There is an instrustable with a guy that uses his makerbot to injection mold but it. Was with small parts.

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Small part injection molding with a 3d printer
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Look for a resin that has a low viscosity, i.e. flows like water, less your object requirements dictate otherwise.

While injection molding can work at low pressure (similar to sandcast molding), substantial part of the process is to fill the cavity in one rush. Else the material solidifies before it reaches the more distant places of the mold.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Thanks for the replies.

Quote
gmh39
You can print it at your highest resolution and solid infill then put it in an acetone vapor bath.

I did think about that, but I need a clean, professional looking product. I don't think the vapor bath would give me the finish I am looking for.

A2 I swear you live in a reseach facility, you always have great and detailed answers.

Traumflug - you have given me hope.

I have thought about heating the mold to help off set the quick cooling and get a full fill.

I'm going to give it a try, If it doesn't work, we'll put that on the failure pile and hope my wife doesn't see the receipts.

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cat.farmer
[...] hope my wife [...]

Try to make some ornaments or similar and she might even help you :-)

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

A company is going to KS (no idea when) with a 3d filament printer that can injection mold, only $8500.00. I've read that they also have a patent on a nozzle for filament extrusion, but one might assume there is a crossover to the hot end nozzle.

So give it a try, and see how far you get.