Aluminum Mold Printing?

I have a small product that I test printed with shapeways using strong & flexible plastic, the design looks right and dimensions are correct. Now I've been looking into mold makers to machine an aluminum mold for injection molding (want to cast a lot of these in rubber or some rubber like material). Unfortunately it's been hard finding a mold maker that can make a mold for this design, since there's a lot of undercuts.

Then, I realized, since shapeways now offers aluminum 3d printing, shouldn't it be fairly easy, and also much faster and more affordable to 3d print the mold? I'm not at all from the world of 3d printing, mold making, modeling etc., so if there's something I'm not understanding, or missing let me know. But I have seen videos on 3d printing molds using other materials, so shouldn't it be possible to just print an aluminum mold?

And lastly, if so, does anyone here have the expertise or can anyone point me in the right direction to find someone who knows how to take an stl design and make the mold of it somehow (cut it in half and invert it?).

Thanks so much in advance!

So a couple of questions, did you design for mold release, parting line, draft? I design all kinds of that stuff that can not be injection molded, usually doing investments (lost wax) castings. Also how many is a lot? 50,000 pcs or 200. RTV tooling and casting (vinyl, silicon, resin) could be a good low production technique for you to scale your business. Printed aluminum could be as much as or more than a CNC'd mold, might even be too porous or thermally unstable. Other mfgs have printed tooling solutions but the design still has requirements for manufacturing. -S

Thank you for your response! I don't fully know what mold release, parting line and draft are. So probably not.

I just did a test and was able to create what should be a basic mold by just creating two blocks, inserting my piece and using boolean tool subtracting that shape for each of the blocks. Then I separated them into 2 stls and as a test uploaded one to shapeways to see what the price would be to print on shapeways, which is $246.45 (so X2 in order to do both sides, would be around $500, which is still drastically less than machining a mold traditionally (most places seem like they'd charge $5k and up for the mold). Is there any reason why this wouldn't work?? It's a very small piece, one half of the mold is 4.4cm x 4.68cm x 1.434 cm.

To answer your question on how many. Ideally I want to create probably between 2-10k and possibly more. But as a way to fund it along the way, if I can print a mold and create 500-1000 to start and then go from there, that would also work. But for it to work out the cost per piece can't be too high, hopefully not more than $1/ piece if it's a small run to start, and then obviously if it's a larger run they'd be less.

Anyway, thanks again for your help.

I don't know all that much about making moulds. I do admit to doing some ad-hoc experiments with stuff I had to hand (e.g. wooden moulds for acetone-softened polystyrine).
But I do know that shapeways aluminium parts are very rough. I think for it to have a chance at working you'd need to polish the parts really thoroughly and carefully. And you need the abutting edges to to fit together pretty precisely, so you'd need to allow for this loss.
If you're finding the professionals don't want to touch it, I'd say thats a clue that it's an awkward part, so probably not the best design to start off learning a production method with an untested approach.