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
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.