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I am working on a project that requires an enclosure that I am thinking to prototype using a 3D printer (which is pretty easy and overall awesome).

My question is simply whether this same model can be used later on for mass production (i.e. mold injection)? What adjustment (if any) need to be done to model between prototype and mass.prod. stages? What areas in design to look out for that can make model viable for 3D printing non-viable for mass production?

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    $\begingroup$ What kind of 3D printing process are you thinking and which material (plastic or metal)? $\endgroup$ – 0scar Mar 23 '20 at 8:07
  • $\begingroup$ @0scar I guess PLA for material, and just common 3d printers like prusa i3 or similar. $\endgroup$ – Alexey Kamenskiy Mar 23 '20 at 8:09
  • $\begingroup$ Plastic injection molding, where hot plastic is injected into a mold under high pressure and typically from various places, will not have the internal layers & fill that 3D printing can have. So components will likely be heavier and balanced differently. I've not done any prints that were 100% fill (mostly because they take longer). If you are printing a part to make a mold from to use with other materials, like plaster or something, I guess that would not be so inportant. $\endgroup$ – CrossRoads Mar 30 '20 at 15:36
  • $\begingroup$ @CrossRoads I’m doing a prototype, but I am hoping that source step file can then be reused for mold injection without much changes (ideally none). The amount of possible changes is what this question is about not about making a mold itself where it would (hopefully) be done by a manufacturer. $\endgroup$ – Alexey Kamenskiy Mar 30 '20 at 15:40
  • $\begingroup$ You'd have to check with the manufacturer then to see if they can import whatever design files your creation software (such as Fusion360) can export. $\endgroup$ – CrossRoads Mar 30 '20 at 15:42
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I respectfully disagree with the hard no answer. There are many casting methods, some of which are not compatible with 3D printed parts and at least one that definitely is. See investment casting, aka lost wax casting. (Ref 1) Also search YouTube for "investment casting using 3D printing". Formlabs, the company that makes the Form 2 and Form 3 3D printers, sells a 3d printable resin specifically for investment casting. (Ref 2).

There is a whole world of casting, so I will describe, as an example, a very simple process that will make a replica of your 3D printed part. I will briefly address the steps necessary for making multiple copies at the end of my answer. First you need to add a cylindrical extension to the shape that will create a sprue. See the two models shown in the image below. Next make a foil cup a little larger than your 3D printed part and place your part in the cup, suspended by the sprue. Pour liquid plaster of Paris (POP) into the cup, covering the 3D printed part, with just the top of the sprue sticking out. Once the POP has hardened, you can remove the 3D printed part by dissolving it in an organic solvent (acetone for acrylic) or by heating the part to several hundred degrees C so it will burn out (convert to gasses). You will now have a block of POP with a void shaped like your 3D printed part plus a cylindrical hole to the outside that acts as a sprue. Once you have heated the POP to drive out any remaining water, you're ready to cast. Fill the void (via the sprue hole) with, for example, copper powder and heat it to well above its melting point. Once everything has cooled, lightly tap the POP with a small hammer or equivalent, to remove it, leaving your final part plus the sprue. You can remove any remaining POP with some warm baking soda and patience. The final step is to cut or saw off the sprue shape.

Please understand that the process described above is just to give you a basic idea of the process. There are many alternate or additional steps that may produce a better final product. Also, the process described should work of the rook model shown on the left of the image below, but not the model on the right, which has a small hole through the middle. There are ways to solve that issue, but as I said before, there is a whole world of this stuff.

Casting is a way to create parts out of materials that you otherwise could not 3D print directly (on a home budget). For mass production, you would need to start with an inverse of the final shape. For example, a cylindrical slug with a rook-shaped void. Then you would use the investment casting process to create a mold out of a rigid material that you could use to, for example, create rubber copies of the original part that could, in turn, be used as the "wax" for copies in the final material.

I urge you to experiment, maybe following one of the tutorials on YouTube. Good luck. enter image description here

Ref 1 - Investment Casting https://en.wikipedia.org/wiki/Investment_casting

Ref 2 - FormLabs 3D printable casting resin https://support.formlabs.com/s/article/Using-Castable-Resin?language=en_US

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  • $\begingroup$ Which part of my question did you disagree with? Also I don’t see how this answers my question. I asked about specific of CAD design. Not about manufacturing process. $\endgroup$ – Alexey Kamenskiy Mar 26 '20 at 5:30
  • $\begingroup$ @Alexey Kamenskiy, I was not disagreeing with you, but with the "hard No" answer. That answer seemed to imply that there is no way to use 3D printing for casting. I didn't expect my answer to be placed above the previous answer, so understand the confusion. I've edited the beginning of my answer to clarify that. $\endgroup$ – Vince 49 Mar 26 '20 at 6:01
  • $\begingroup$ I think that should’ve been a comment on that answer instead of new answer. Because this answer is implied to be to my question which it doesn’t answer. $\endgroup$ – Alexey Kamenskiy Mar 26 '20 at 6:03
  • $\begingroup$ It has been done. Spartan Games did print parts of their masters, then modeled on that, then took that master and made a latex mold from that, casting the result in resin. $\endgroup$ – Trish Mar 26 '20 at 9:50
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That's a hard No.

Models used in industrial injection molding are very specific to the process sometimes even the machine. When they build those molds they have to include constructs like spurs and runners; things to get the molten plastic to where it needs to go. Further the wall thickness of an injection molded part can only be so thick, because the plastic will contract when cooled, which will distort the final part if it is too thick.

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  • $\begingroup$ That’s a hard no even with adjustments? $\endgroup$ – Alexey Kamenskiy Mar 23 '20 at 13:11
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    $\begingroup$ I don't see how the second paragraph establishes the "hard no" claim. Rather it seems to suggest there are a number of constraints you could follow that would make it transformable to an injection mold with minimal changes. $\endgroup$ – R.. GitHub STOP HELPING ICE Mar 23 '20 at 14:16
  • $\begingroup$ @R..GitHubSTOPHELPINGICE, the changes are not minimal; that's why the hard no. $\endgroup$ – user77232 Mar 23 '20 at 18:06
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    $\begingroup$ If the initial design follows certain constraints about compatibility with injection molding, then it seems the changes needed should be minimal and mostly mechanical. $\endgroup$ – R.. GitHub STOP HELPING ICE Mar 23 '20 at 19:20
  • $\begingroup$ @R..GitHubSTOPHELPINGICE, The OP said that they are thinking about making a 3d printable model for the enclosure. When you design for manufacturing you start with the manufacturing process in mind. If your thinking starts as "this is for 3d printing", then that model can be simply used to create an injection mold later on. That answer is no; not without major modification that will amount to a complete redesign. $\endgroup$ – user77232 Mar 24 '20 at 12:22

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