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I want to injection-mold several thousand of a part that fits in a 6" x 6" x 2" bed.

I would like to be able to use only tooling that I can make myself, so I can rapidly iterate on the tooling as production problems are discovered.

I know that typical injection-mold "hard tooling" is created using electrical discharge machining, which requires first CNCing a carbon positive and then using that as an electrode to spark-burn out a negative mold from hard steel.

However, I do not have the equipment for EDM. Instead, I would prefer to directly CNC the negative mold. I know that a soft enough steel to be CNCed will not last very long as an injection mold, but like I said, my run size is tiny, and I am ok with making a new mold every 500 units or so if necessary.

I am open to buying an endmill that is diamond-tipped, to work with harder steel, but then the limitation will probably be how much torque the CNC can produce on the endmill.

What are some recommendations or links to helpful resources? In particular, what is a good CNC with enough torque, and what blend of steel should I use? Thanks!

AlcubierreDrive
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  • Interesting question but I don't believe there is yet a relevant site to ask it on. This is probably off topic here, maybe it should be migrated to the proposed Digital Fabrication should it reach beta? – Joe Baker Jan 26 '13 at 05:51
  • The long list of CNC mills at http://reprap.org/wiki/MillStrap surely has at least a few suitable machines. – David Cary Jan 26 '13 at 07:55
  • I'm struggling to see how this is on-topic here... – Andrew Jan 26 '13 at 08:24
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    @Andrew: (a) people who make robots often use CNC machines to make robots, and more importantly, (b) CNC machines themselves are a kind of robot. – David Cary Jan 26 '13 at 20:02
  • I agree with @DavidCary that CNC machines are robots and roboticists frequently use CNC machines to make parts for their robots. However I don't see any robotics related questions. All the questions appear to be manufacturing related. As such I argue that this question is off-topic here. – DaemonMaker Jan 27 '13 at 04:00
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    CNC related questions are not directly on- or off-topic... but this question appears related to tooling rather than any robotics aspect.

    My comment was more of a hint to make it better - if I was decided I'd have closed it. I didn't (yet) but there are Votes...

     – Andrew Jan 27 '13 at 08:06
  • While it's not a great fit for here, I don't see anywhere better on the SE network at the moment. Not every question needs to find a home on SE, true, but it is still tangentially related, so I'd let it stand for the moment. But I'd encourage you to go and support the digital fabrication Area 51 proposal, and we can migrate the question once their beta goes live – ThomasH Jan 27 '13 at 11:57
  • @JoeBaker - I created the Digital Fabrication proposal as an attempt to see if a more vertical site could succeed where several more general robotics proposals had failed. Since this site went into beta I've come to the conclusion that many of the CNC, automation & 3d printer questions there would fit just as well here on robotics, now we have launched. – Mark Booth Jan 28 '13 at 11:48
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    Having said that, this question would be better if it weren't summarised at the end as if it were a shopping question however. – Mark Booth Jan 28 '13 at 11:50
  • @MarkBooth Yeah, it's definitely the most on-topic place we have right now to post it given the options. Maybe borrow it as a proposed question for Digital Fabrication? – Joe Baker Jan 28 '13 at 15:18
  • @JoeBaker - Feel free, I used up my 5 questions long ago. *8') – Mark Booth Jan 29 '13 at 02:18
  • @JoeBaker Yeah go for it. I would love for Digital Fabrication to come into its own. – AlcubierreDrive Jan 29 '13 at 03:42

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Answer from my MechE friend Sam who doesn't have an account:

First, I don't think you're going to have trouble with any CNC not having enough torque

Second I don't think you'll need diamond tipped. Tungsten carbide max.

I would look into using aluminum I believe it is viable for some molding.

And mild steel should definitely hold up. Easier to machine as well.

AlcubierreDrive
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