I had this idea for bulky parts for just printing the shell (PLA) then pouring in some kind of filler in to make up the bulk/strength.

Printing bulk .2mm at a time line by line is slow and subject to warping!

So I though precision print a shell and fill it with 'something' - has this been done by anyone? What is a good something to use?

Yours hopefully!

  • $\begingroup$ What are your requirements? There are many materials you could fill a container with that would give you a variety of properties. $\endgroup$ – tjb1 Apr 19 '17 at 16:34
  • $\begingroup$ @tjb1 by default PLA :-) -- my current print is a chainwheel for a belt on an electric bike... the 3d print for teeth is important, but the bulk could be anything (instead of 8 hours of warping bulk!) $\endgroup$ – pperrin Apr 19 '17 at 16:59

I've looked into doing something similar to this before and love the idea, never had the chance to follow through on it yet. This is sort of a hybrid method between cast molding and 3D printing.

The accepted answer to a question I had a while back had some very good points by fred_dot_u

Post processing FDM for strengrh

Short version, Epoxy is a good option but you may have to consider heat generated from it. Urethane is another really good option (cast urethane is a pretty standard process). Chem-Eng isn't my area of expertise but there is a huge range of material options out there that can be mixed as two parts. I think there are enough options out there right now that you can choose your material properties you need and then select the material from there.

You could also consider going the chopped-fiber composite route. (carbon, glass, etc) and then combine with whatever the appropriate resin is for those materials.

I see the most difficult part of this is getting the shells to print properly. When I had looked into doing this, I considered modeling my part then hollowing it out completely. Then going back into the hollow part and designing in minimal internal structures for the purpose of supporting the thin-walled shell model. Printing that, and then drilling and filling the part after the fact. This approach I see as being a good option however the location of the drill points would be critical otherwise you could get voids as your fill material is injected in. And, the additional modeling time wouldn't be insignificant, however the saving I expected would come from having a ridiculously strong part, with complex geometry and be significantly cheaper than even a cast-urethane part.

If you get some good results, please post a link to them! This is a huge interest of mine!

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  • $\begingroup$ I was aiming for really simple, having no infill so leaving 'ponds' to have filler poured in to self level and set. Or minimal infill and stop the print before the cap is printed, leaving a load of wells. I have not played much with settings - I have 1.75 walls and 20% infill by default. The plastic is strong enough, I just want to avoid the time/trouble of printing the bulk! I will look at the urethane... $\endgroup$ – pperrin Apr 20 '17 at 16:32
  • $\begingroup$ You can reliably go less than 20% for sure. For aesthetic parts, or when I'm just checking geometry I usually only do 10%, sometimes I've gone as low as 5% (hex pattern infill). In Solidworks, there is a feature "shell" that will hollow a part out for you to a desired wall thickness. depending on your CAD software I'm sure there's an option for you. Stopping the print short will make your part a little stumpy is all. Good luck! $\endgroup$ – Diesel Apr 20 '17 at 17:50
  • $\begingroup$ I now have some polyurethane on order (it should arrive real quick, as it is classed as 'hazardous' so comes via very specialist couriers!). I couldn't trick Cura into doing anything useful with the original design, so have done a new one with specific 'walls' to handle the casting... fingers crossed! $\endgroup$ – pperrin Apr 22 '17 at 0:51
  • $\begingroup$ Instead of polyurethane one could consider special foam adhesive tapes placed between two 3d printed edge bonded fixed thin shells and allow it to foam into the cavity by heating the assembly. It forms a very rigid sandwich shell after cooling. $\endgroup$ – Narasimham Jun 13 '17 at 23:20

Or you could use a second head to do low-density infill with very thick layers, like a 1.5mm nozzle and 1.2mm layers.

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  • $\begingroup$ Cheers, a possible compromise, but in my case my printer was 'flat pack' rather than a real 'kit' so I am not competent to add a 2nd head... $\endgroup$ – pperrin Apr 20 '17 at 16:26

Not exactly the same, but MakerBot Industries is making improvements to their programs by allowing users to do away with standard infill practices (patterned infill). Their approach is to treat infill similarly to how they treat outer support structures, the "infill" only exists in the interest of supporting roofs.

Check out MakerBot's article about it.

This method achieves the same time-savings that you describe in your question, but will not necessarily provide as much structural integrity, depending on your approach.

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  • $\begingroup$ Could be part of the solution - leaving maximum volume to be filled with the filler... $\endgroup$ – pperrin Apr 20 '17 at 16:46
  • $\begingroup$ I design in FreeCad and then process in Cura - I tried loads of options to get 0% in fill but support and no top/bottom shell but a 'raft' -- couldn't get what I was after... But I think it should have worked! $\endgroup$ – pperrin Apr 22 '17 at 0:47

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