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3D printing can be used to make injection molds of unimaginable complexity but which kind of 3D printing process is suitable when?

Suppose that a part is to be made using injection molding in large quantity for an extended period of time, what Additive Manufacturing (AM) process will be the best, such that the mold does not give way too soon?

Also, suppose that the part to be made is custom and only has to be made in small quantities - that is to say that the injection mold will be used limited number of items and then thrown away - which is the best AM technique then? Best in the sense of economic feasibility, lower cost, lower capital investment etc.?

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    $\begingroup$ This is one of those questions that qualifies as too broad to be answered in a practical manner. Even the question is segmented into so many parts as to indicate clearly how broad the scope. I suggest to focus on specific examples with easily determined problems for which solutions can be described. $\endgroup$ – fred_dot_u Dec 12 '16 at 22:41
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Yes, this is very broad. That said...

For high detail you want SLA. i.e. jewelry. If you just want a prototype of a mold, you can do a standard FDM style printer (95% of printers are FDM, and that number is a guess)

Really, you should be asking what material you need for your mold, but you can open a second question for that.

Do more research on injection molding. There is a great deal of information on how molds are made, i.e. How It's Made Plastic injection molds.

You will see there is a vast difference between a plastic, or silicon, mold and an injection molding machine. You are thinking that injection molding as a single mold, when it is really it is a system composing of several pieces of heavy duty machinery that can pump out hundreds of items a day automatically. However, it usually starts at 20k USD for the tooling for injection molding. Your costs could be a fraction of that or could be several times that. This is just a generality. So, if you are making 100 units you won't want to go down that route. For 10,000 units, on the other hand, it would be acceptable.

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  • $\begingroup$ Just to clarify... the 20k - is that cost (i.e. $20,000), or quantity (i.e. 20,000 units)? $\endgroup$ – Greenonline Dec 13 '16 at 14:47
  • $\begingroup$ $20,000 USD which is the cost. It is also a random number based off a general knowledge. It could be half that, could be 10 times that. $\endgroup$ – StarWind0 Dec 13 '16 at 16:28
  • $\begingroup$ It is also worth mentioning that my local hackerspace has offered classes on injection molding. One by you may as well. $\endgroup$ – StarWind0 Dec 14 '16 at 22:56
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Stratasys offers a 3D printing system specifically for producing injection molds. They claim their Polyjet/Digital ABS line of printers can produce prototype injection molds good for 10-100 shots of the same mold and that the material can be used with regular injection molding machines.

Of course, the molds still wear out quickly and are only suitable for prototyping and/or extremely small production runs.

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Injection molds generally require tooling and are not usually cast from 3D prints. Depending on the size of your part - costs can easily skyrocket to over $60,000. The price per part is sometimes lower than other methods. Other possible methods (depending on the part) are Thermo-Forming, Vacu-Forming, and different Casting methods - sandcasting (investment casting), flexible casting (rubber, urethane, and alginate), and hard casting (printing mold negative). Some have immediate use of 3D Printed parts...others have work flows in place to convert your files for use. You can print a mold negative, prep it, use mold release, and cast shapes from that mold... certainly the casting material would be flexible or the mold would need the proper relief- But it is certainly possible.

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