3D Printing molds for Molded Fiber is something we have been interested in for a long time. Why, you might ask? Simple molds can cost 7-15K and have a 10-12 month lead time, far to high for short run products.
In contrast, an open source 3D printed paper pulp molding process will allow small batch / maker movement to test paper pulp with their product. Later leading to more demand for higher production runs and high production companies. Everybody wins.
Understanding The Process
part Design Considerations
I drew my part in Fusion 360. It’s an easy to learn CAD package that is free for makers that that are a member of a maker space and earn less than 100K from their product sales.
The part will need to be desinged in a similar way that injection molded parts are designed. You can see some design considerations near the bottom of this page.
I am still playing with exact dimensions and I will update this blog as I find out more. But if you copy the draft angles, corner radii, wall thickness, and other geometry from an egg carton you should be able to mold your part.
Draw The Molds
I made a fairly large port for the vacuum. I also 3D printed a couple plate adapters could hook the mold up to different vacuums. At first I thought I would use a vacuum pump, but a shop vac worked really well. The shop vac also gives the water some place to go.
We are still working on the paper pulp recipe. there seems to be very little documentation about how to make an industrial grade paper pulp slurry. I have mine below, but it needs work see below.
I drew four guide pins on the cavity side of the mold that up with four holes on the core side so the two halves of the mold fit correctly and keep dimensional tolerances. Proper GD&T goes far here. Ames Web GT&T Resource.
I used an RC7 Free running fit and that worked great. Too bad this calculator is in English units. If anyone has a reference that is in SI units, please post it below.
Mold Infill Density
To pull an even vacuum, you will need to have different infill densities in different parts of your mold. The infill should be open on the back side and fairly tight on the side that will contact the paper pulp. The tight infill will lead to a good surface finish of the final part.
You can do this by changing Infill density in a specific section of your part. This guide will show you how to do this. At the end, you will be left with a few bodies (parts) that you manually stack in Cura. You can set the infill density for each part individually in Cura.
"Cutting" The Molds
So far I have found that it works best to cut the mold into at least three pieces.
The first one will be the outer layer. This offset will of the outermost 5mm or so of your mold, on the side that contacts the part. I have had good luck with a fine square mesh. A fine mesh make for a nice surface finish and helps when getting parts out of the mold.
The next layer in is another offset, meaning that the cut follows the contours of your mold. Like a nesting doll. This will have less infill so more vacuum can pass through.
The third layer goes all the way to wherever the the vacuum enters the mold. It will have the least amount of infill.
You may also want to make a section that will just be a smooth wall and have mesh for the vacuum around it. Think about how your part will suck up on to the mold, be transferred from one mold to another and eventually blown out of the mold core.
How to Slice Mold in Cura
- Turn off collision detection
- Turn off adhere all parts to build plate
- Top Layers – 0
- Bottom Layers – 0
- Wall thickness – 0
What we are doing here is basically stacking all of the parts in the center of the build plate and adjusting the Top, Bottom, and Wall thickness to zero for any part that will have vacuum pass through it. Then we will set the infill density to greater and greater infill densities the closer those parts are to the actual part.
Placing & Slicing The Parts
tart by bringing in the base of your mold and place that on the bed at position 0, 0, 0.
Then bring in the next part that is closest to the bottom. You will need to offset this part in the +z-direction so it sits right where it should within the base of the mold. Set bottom layers, top layers, and wall thickness to zero. Set the infill density. This layer goes all the way to where the vacuum port. This is where the shop vac hose attaches to the mold. So this one can have very wide infill. There just needs to be enough infill to support the print and give the mold rigidity. I have found triangles let more vacuum pass through the bottom layers.
You now have a section vacuum can pass through your mold! Repeat this for the other parts.
The next layer for the middle layer the infill density can be 3-5 times larger than the outermost surface finish later layer.
The final layer works well with a fine square mesh. There may need to add a final layer that can have a wall thickness. I make the walls of my transfer mold like this so it would not blow the walls of my part inward.
— This is still in an experimental phase. If you take this farther, be fair in the spirit of open source and post your solutions below! —
Molded Fiber Recipe
I have been told making molded fiber parts is more of art than a science but this is what I have so far.
- 480 grams of water (a little more than 2 cups)
- 40 grams of shredded newspaper
0. See the needed improvements section, this is what I have tried so far, but there are problems. It seems 3x to 4x water is needed.
1. Combine the water and shredded newspaper in an old pot (that will only be used for industrial processes after this)
2. Heat on medium low for 20 minutes. You can use a (candy) thermometer to check the temperature. I have found good results with 65C (150F). I have tried higher temperatures but it did not seem to be much of an improvement. Plus it shrank my PLA molds! Ooops!
3. I use an old blender to blend the material. I blend quite a bit. I have read that the paper pulp should looks something like oatmeal, but this has been proving difficult to mold.
I 3D printed a coupler that attaches to a shop vac hose and stick on to the back side of the mold. A small shop vac seems to work perfect for drawing the fibers on to the mold.
See the video above and here for more about the molding process.
The molded fiber is too sticky and thick. It pulls up on the mold core and turns into a thick layer that I cannot squish into the transfer mold. Adding more water seems to be the obvious solution. Im thinking for a next batch I might do 3x or 4x times the water to try to get a positive result. I need to get a bigger pot, I never thought I would need so much water.
Currently I have my wall thickness drawn at 2mm. The thick slurry does not work at all with that think of a wall thickness. Hopefully a more watery slurry will work better.