Molds Directly From a 3d Printer to an Injection Molder




About: I Make Stuff

In this Instructable I will document the process of an experiment i have been working on to test fairly low pressure injection molding using 3d printed molds.

You should be able to find everything you need for this project laying around your house:

-An initial concept and the ability to execute it in a digital format capable of exporting to a 3d printer

-a high res 3d printer

-an injection molder

-a handful of pelletized thermoplastic

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Step 1: Part Design

My teeny, tiny, cute, little injection molder is only capable of squirting out about 1/4 ounce of molten plastic at a time so i had to design a test part no larger than that. I was far more concerned with testing the process than actually making something useful so i just grabbed an existing 3-d file of my logo and converted it to a moldable form.

I used solidworks to extruded the shape in two directions with 7 degrees of draft  on both sides from the parting line.
the final part came in at a volume of 0.238268398 ounces.

Step 2: Mold Design

for this particular test i went with a really simple mold design, the mold would be split equally front to back with a few keys and a single direct injection point.

Step 3: Printing the Mold

I exported an stl file of my mold pieces and set them to a high gloss option for printing thorough an objet 3-d printer.
The out put is an acrylic photo-polymer mold.

Who knows if this is even going to work?
I might just crush the mold while trying to clamp up?
Or burn it up with molten plastic durring injection?
I might lose an eye?

Step 4: Molding

I was excited and in a rush to test out the process so i grabbed a handful of Cellulose Acetate i had laying around.

I heated my machine and ran a few ounces of plastic through it to purge out any old material that might be have been left in the  chamber.

I hit the mold surfaces with some spray silicone mold release and clamped it up.

-first shot was too short

-second shot similar to the first

-third shot, much better but still short

-fourth shot, better still but not perfect

-fifth shot... overpacked somehow i got too much plastic in there

-sixth shot BOOM!!! nearly perfect mold fill.

This is a relatively small number of shots to refine, temperature, injection speed and injection pressure before getting a good shot. I was really excited about that BUT i was far more excited that i just injection molded in to a 3-d printed mold!!!

Step 5: What Did I Learn?

I learned that it's possible to 3d print a mold with existing technologies for limited use.

after about 20 shots my mold started to show a few signs of stress but far less than i anticipated.
Most of the issues were showing around the area where my nozzle was pressing directly against the printed mold.

I believe there is a simple solution to this and i've already got some supplies to test my idea.
If i can fit my 3d printed molds in to an aluminum mold frame then the mold frame will help to absorb the barrel pressure and further extend mold life.

Clearly this is not a large volume manufacturing solution but perhaps for prototyping purposes or small volume needs this is a viable process. Imagine how useful this process might be for someone restoring rare automobiles or another industry that might need very limited volume but high tolerance plastic parts. There are certainly other options like cast resin but those options all have their own limitations. I look at this process as another possible tool to keep in my tool belt.

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    35 Discussions


    5 months ago

    Anyone know of a tutorial for making the 3D model of the mold? How do you go from the original 3D model to having a 3D model of the mold? Thank you!


    2 years ago

    What printer was used for this and what Material?

    1 reply

    5 years ago on Introduction

    This is really cool! Can't wait to be able to try it out ;)

    After finishing my 3D printer, an home made injection molder would be just awesome! I'll try to find out if it's possible... and if so, a new instructable will be born!

    But one step at a time...

    Congratulations for this very sucessfull experiment!


    6 years ago on Step 5

    Nice!!! Do you think we can use ABS or PLA material coming from a CubeX or Makerbot2?
    Ruben , Lima, Peru

    1 reply

    Reply 6 years ago on Step 5

    Your molding material will need to melt and flow at a temperature lower than the temperature at which the mold begins to soften and deform. With ABS and PLA molds you'd probably have more luck if you inject an RTV liquid resin using a plunger.


    6 years ago on Step 5

    Fantastic work! which mold injector are you using? I'm about to do some injection molds with my students.


    6 years ago on Introduction

    great tutorial ~

    the process layering of 3d printing + molding has a lot of promise

    case in point, this amazing pneumatic robot tentacle


    7 years ago on Step 5

    Wow, this is a really great result. And your idea to extend the process by using an aluminum frame will, if successful, make it a small-shop/short run production process, not just an experiment.

    I could imagine a small machine shop with a setup like this might have a mold for producing the odd part that is needed in small quantities, with a freshly RP'd mold ready to replace it if several orders come in a row.

    Thanks for sharing your results. Now I am even more anxious to get an injection molder!

    1 reply


    I've gotten a lot of criticism and questioning about why i wouldn't just 3d print all the parts in the first place.

    There are countless businesses that require small volume high quality parts with finish and material options that just aren't available in 3-d printing and this solution could be incredibly useful in those situations.


    7 years ago on Introduction

    That is a creative way to make a mold! I see that you were having trouble with overfilling the mold. I may suggest a possible solution.

    You could integrate relief passes into your mold. I am attaching photos of a similar epoxy mold, where plastic is allowed to pour from the sides before building up pressure.

    This way you could produce parts without stressing the plastic mold, and trim off excess material to get a finished part. For the box, you could make your mold round and fit it inside sections of cut up pipe.

    Levon Fiore @ Medium Machinery LLC, see our
    Small Manual Benchtop Plastic Injection Molding Machine

    2 replies

    further to my previous response, i just spent a bunch of time poking around your site. That is a fantastic machine you've designed.


    thanks for the tips, i think my biggest issue with over or under filling is simply the part size vs. shot capacity of my small machine.

    I think my part was little too big so i had to use every last bit of possible shot so i was doing a lot of tricky things to get as much material as possible in to the mold which meant that some times i ended up getting a little too much.

    I think with a little more experimentation and adjustments in my part size i could get good repeatability.


    7 years ago on Step 5

    This project is awesome. Now, if only there was an option for a cheap injection molder....

    The main advantage of injection molds over 3D prints is speed, right?

    6 replies

    speed, material selection, tolerance, cost, durability
    all depends on the requirements of the individual project.

    also, i could buy quite a few injection molders for the cost of my 3-d printer.

    are you asking where to buy an injection molder?
    ebay, a manufacturing equipment vendor, equipment auctions, the internet.

    we have two 3-d printers in my office, one cost $30,000 and the other $160,000
    the injection molder in my garage cost me about $500. There are options for both printers and molders that fall everywhere in between and some that go even higher.