13 Replies Latest reply on Jul 17, 2018 12:35 PM by Frederick Law

    Hollowing out for 3D Printing for Investment Casting

    Dennis Dohogne

      I am doing some work with some pretty complicated geometry that will be investment cast.  I want to 3D print the parts using some of the new castable SLA resins.  Formlabs just introduced one with 20% wax that is supposed to yield much better results for surface finish and burnout.  Since the printed part only needs to be strong enough to survive the ceramic coating process the part can be printed pretty well hollowed out.  This would shorten the print time and save on resin, but would also make the burnout much easier.

       

      Supposedly, some of the 3D printer software handles this, but the folks I have been dealing with do not give me a lot of confidence.  They seem to only be interested in using the castable resin for jewelry and dental castings, which are very small and do not need to be hollowed out.  My parts are on the order of 50 X 50 X 125mm with wall thicknesses at least 3mm.  So there would be a lot of benefit if I can hollow out these parts.  No, shelling will not work.  Since I don't have a printer and am relying on someone else I would like to send them a file that is already hollowed out.

       

      Some of you have 3D printers.  Does the software do a good job of hollowing out the parts like I want?  I know they can do some things to create a less-than-solid-fill, but since I don't have any direct experience with this I don't know if that itself is suitable.  I think there is still a lot of internal lattice with that and more than what my prints will need.  Really, what I'd like to have is akin to the exterior surfaces being offset by a minimal shell thickness of 1mm (or less if the resulting print is strong enough), and only where there appears to be a big internal void would I consider adding in some support.  But I don't know if that is the best approach, or even how to achieve it so I am turning to the helpful forum for advice.

        • Re: Hollowing out for 3D Printing for Investment Casting
          J. Mather

          Lets say that you were able to Shell this part.

          The 3D printing software would still build an internal lattice as there must be a "platform" on which to lay down a layer of material - cannot lay material in air.

           

          With the printer software that I use I can set wall thickness and sparse or dense lattice.

           

          Some of the printers that I have can build the support lattice with water-soluble material.

          For these machines it makes sense to Shell or other means remove void material in the CAD software.

          The printer software then builds the void lattice with the soluble support material.

           

          If it is a machine that uses only one material - just let the printer software build the lattice.

          • Re: Hollowing out for 3D Printing for Investment Casting
            Frederick Law

            That's call infill in most 3D printer slicer.

            Download Cura from Ultimaker.

            Basically most if not all 3D printer slicer create hollow part.  That's why they need infill to support the "roof".

            Share your model.  I can slice or even print it for you.  50x50x125 is not that big.

            • Re: Hollowing out for 3D Printing for Investment Casting
              Dan Pihlaja

              Designing for 3D printing something that will be hollow must either rely entirely on the 3D printer software and the 3D printer people to build in the supports that will "hold up" the material while it is curing and soft, OR you can design in your own supports.  That way, you can get what you want.  Maybe some hollows with "pillars" to hold up the material while it is being printed.  I would find out from the 3D printers what the maximum distance (for this specific material) you can travel with the printer head over a cavity before you need supports.   With PLA material, it is about 1 inch (possible a little less) (you can build a 1"  hollow cube with no supports).

              Once you have this number, then put "pillars" at spacing set below this number.

              If you do this right, then you can specify to the printers that you don't want support material printed and see what they say about it.

              • Re: Hollowing out for 3D Printing for Investment Casting
                Dan Pihlaja

                Another Option:

                Create your part with the hollows.

                Then create bodies that fill the hollows completely and color them, say...blue.

                Send the entire thing to the 3D printer people and tell them that everything blue needs 5% infill and the rest is solid.

                 

                This could be an easy way to provide the support that you need without sacrificing a lot of design time and resin.

                • Re: Hollowing out for 3D Printing for Investment Casting
                  Richard Doyle

                  Dennis,

                  Have you looked at some of the powder-based systems? (little to no supports required).

                   

                  Richard

                  • Re: Hollowing out for 3D Printing for Investment Casting
                    Dennis Dohogne

                    Thanks for all the ideas.  Instead of replying to them individually I'll just address them all here.

                     

                    The application is explicitly printing a part that will later be burned out of a ceramic shell.  The print material is liquid resin for a stereolithography machine.  When SLA parts are made with infill (not solid) the uncured resin is given a path to some drain holes.  Support for the part is not a problem and eliminating the excess liquid is not either.  The problem I am pondering is the vendor I am talking to is used to dealing with castable prints, but only for very small items likes rings and dental crowns.  Those parts are printed pretty solid just because there isn't much interior cross section.  However, my part is huge by comparison and the geometry is totally unworkable for the shell command.  I cannot recreate the part with hollows as it would take too long.  I was considering doing something like a core/cavity function and offsetting the exterior surfaces and subtracting the resulting void, but I don't mess with surfacing enough to have confidence in that technique.  Besides, I doubt that it would would work anyway.

                     

                    Due to the proprietary nature I cannot upload the part, but below is an image with a cross section.  The part has been changed enough to show here.  The part is roughly 2" diameter and about 5" long.  You can see the geometry is complex.  Shelling fails.

                    I am really looking for either a) a clever and simple technique in SWX to achieve this hollowing, or b) the confidence and the help with the correct terminology to speak more knowledgeably with the printer service to help them get where I need them.  I think pursuing the settings with the printer software is likely to be the best bet.

                    • Re: Hollowing out for 3D Printing for Investment Casting
                      M. D.

                      So I guess your problem is that you want to hollow the part out due to cost of printing material and time, but you need it to be solid to prevent the liquid from leaking through drain holes.

                       

                      It sounds like you can either 1. Make it with a medium amount of infill that is the same material as the rest of the part and hope that the liquid doesn't drain out. 2. Figure out how to remodel the part so that you can put solid areas where you need them and the rest can be minimally infilled. (Ahem maybe send part to Paul Salvador with an NDA ) 3. Just go for solid part and eat the extra costs.

                       

                      Good luck.

                        • Re: Hollowing out for 3D Printing for Investment Casting
                          Kevin Chandler

                          Marcus Dimarco wrote:

                           

                          So I guess your problem is that you want to hollow the part out due to cost of printing material and time, but you need it to be solid to prevent the liquid from leaking through drain holes.

                           

                          It sounds like you can either 1. Make it with a medium amount of infill that is the same material as the rest of the part and hope that the liquid doesn't drain out. 2. Figure out how to remodel the part so that you can put solid areas where you need them and the rest can be minimally infilled. (Ahem maybe send part to Paul Salvador with an NDA ) 3. Just go for solid part and eat the extra costs.

                           

                          Good luck.

                          Hello,

                           

                          Actually, I believe it's the opposite, you must have at least one drain hole so any unzapped resin isn't trapped within.

                          Also, part orientation on the print platen must be such that drainage happens by gravity alone.

                           

                          Cheers,

                           

                          Kevin

                        • Re: Hollowing out for 3D Printing for Investment Casting
                          Frederick Law

                          B9Creator_2017-10-09_17-05-41_large.png

                          Looks like you either pay for solid model or pay for support on hollow model for draining.