11 Replies Latest reply on Jan 18, 2015 2:30 PM by Deepak Gupta

    OT: 3D Printing - Which is better design

    Deepak Gupta

      Anyone who is using 3D printing on regular basis and using those parts for sample testing. Can you please check the attached part (SW 2014 file) and suggest which would be better in terms of strength; the one with the grooves OR no grooves. OR can you suggest some ways to improve strength for a simple cylindrical part.

       

      I believe the one with grooves should be better compared to one with no grooves but still open to any suggestion/advice. Thanks in advance for any help/advice.

       

      3d Printing.PNG

        • Re: OT: 3D Printing - Which is better design
          Dwight Livingston

          Deepak

           

          Depends on a lot. How is it going to be loaded? Also, will it be printed solid or skinned?

           

          If skinned and hollow-walled, the grooves might help connect inner and our walls, improving strength.

           

          If solid, and the major dimensions are the same for both, then the one with more material will be stronger. Then again, if you are talking about strength-to-weight efficiency or some other definition of  "better", then the grooves may be an improvement.

           

          Dwight

            • Re: OT: 3D Printing - Which is better design
              Deepak Gupta

              Thanks Dwight for your reply. They would be printed like shown (dimensions may vary) i.e. solid wall.

               

              But as you said

              if you are talking about strength-to-weight efficiency

              Yes I'm talking about strength vs weight and looking for improvement. The initial design is solid wall with no grooves but I believe that one with grooves should perform better.

                • Re: OT: 3D Printing - Which is better design
                  Kelvin Lamport

                  Can you not run simulations on both designs & compare results?

                   

                  I understand how using less material could optimise the strength to weight ratio, but removing material will never make something stronger.

                  • Re: OT: 3D Printing - Which is better design
                    Dwight Livingston

                    I'll make some comments on a strength-to-weight efficiency. These are my best guesses, not definitive, just opinions.

                     

                    To make it easier, I will compare the slotted version you show above to an unslotted cylinder that has an equal volume of material (same weight) and a slightly thinner wall. That way, one need only compare strengths in order to compare efficiency.

                     

                    I'll assume a compression load from the top, as if your cylinder rested on a stiff horizontal surface (oriented as shown) and large stiff mass were placed on top of it.

                     

                    • If the load is perfectly constrained to move only downwards, then cross-section area matters most. In the slotted version, the smaller cross section and lack of hoop strength at the slots will make it less efficient. I'd expect the ribs to bow out and collapse.

                     

                    • If your load is allowed to translate sideways as well as move down, and it is not perfectly centered, then the thicker wall of the slotted version might make it stronger. That or the slots will be a weakness (beats me).

                     

                    • If your load is allowed to turn on the cylinder axis (twist), then the slots really look like a weakness.

                     

                    I would be tempted to try round holes (each on a radial axis to the cylinder) in a hexagon pattern. You'd want enough to increase the wall thickness significantly.

                     

                    It might be better to not pierce the wall, but do make ribs that run the full height. Or perhaps better to corrugate the wall.

                     

                    I'd be more tempted to take advantage of an FDM printer to make a stiffer wall using the same amount of material. Our FDM printer has the option of making a 1-mm shell with a sparse interior. If your cylinder has, say, a 5-mm-thick wall, then having 1-mm inside and outside shells filled with sparse fill between would probably make a very weight efficient structure.

                     

                    Dwight

                      • Re: OT: 3D Printing - Which is better design
                        Jesse Robbers

                        What type of printer and material will you use? For example, a FDM ABS would limit you a lot for the actual strength of the part due to the layers coming apart depending on the orientation the part is printed in and the direction(s) of force it would receive while in use. For different printing types, like SLA (ObJet24 with Styrene type material), there are still layers of material but they are bonded together much better than FDM (is air/water tight and a much finer resolution). So the SLA part breaks more typical to how a manufactured plastic part would fail.

                          • Re: OT: 3D Printing - Which is better design
                            Deepak Gupta

                            Thanks for the reply.

                             

                            It is going to be FDM ABS. The actual part is a metal part but we're looking to replace it with plastic. So trying a 3d printed version first instead of making a mold.

                              • Re: OT: 3D Printing - Which is better design
                                Dwight Livingston

                                Notes on an injection molded plastic version:

                                 

                                The slots as shown will require many side pulls, which are expensive and reduce repeatability. The fillets on the inside edges of the slots are especially difficult, requiring some sort of collapsing core.

                                 

                                Depending on how many you are making, you might want to look at an extrusion, instead of injection molded, to save on mold costs.

                                 

                                If an injection mold is wanted, I'd first look at a mold split half way along its axis. A plain cylinder would probably be best, with suitable draft. Perhaps a fully ribbed or corrugated designs may save weight.

                                 

                                Much depends on how it is attached at each end, and again on how it will be loaded.

                                 

                                Dwight

                                • Re: OT: 3D Printing - Which is better design
                                  Kelvin Lamport

                                  So you're looking to replace a solid metal cylinder with a slotted FDM ABS cylinder?

                                   

                                  What axial & radial loads are involved?

                                  How many load cycles are involved?

                                  Have you considered using an acetone vapour bath to make the exposed surfaces more homogenous?

                                   

                                  Just as a matter of interest, which printer would be used?

                                  In one of my company's products, we recently replaced several metal parts with ABS using a Makerbot Replicator 2X.