13 Replies Latest reply on Mar 24, 2014 6:38 PM by Daniel Bergqvist

    Problem with etched sheet metal

    Daniel Bergqvist

      I'm building waggons for a model railroad. I etches a sheet of brass so I get partial cuts in the sheet and I then bend the sheet at these cuts. The depth and width of the cut is half the thickness of the sheet and the bend is 90 degrees.


      I need to be able to unfold the sheet to get the drawing for etching. But I cannot figure out how to solve this in SolidWorks.


      I can either do a bend but no unfold, or I can do an unfold but not a correct bend. I think the problem is that my sheet of brass has different thicknesses and I don't know how to get SolidWorks to accept that.



        • Re: Problem with etched sheet metal
          Daniel Bergqvist

          One correction: The width of the cut is the same as the thickness of the sheet. The depth of the cut is half the thickness of the sheet.




          • Re: Problem with etched sheet metal
            Anna Wood

            SolidWorks Sheet Metal requires constant material thickness.


            What you want to do is build your formed part first without the cut.  Then flatten and add the cut after.





            • Re: Problem with etched sheet metal
              R. Nair

              Curious if you ever worked this out?  I'll tell you my recent experience:


              We have a series of duct nozzles made from .018" thick stainless sheet with half-etched bending channels .025" wide for 90 deg and .050" for 180 deg, for hand-bending and spot welding.  Whenever we needed to make custom dimension nozzles I used to manually alter Autocad drawings, such a waste of time....I decided to finally make a SW model.


              Unfortunately these etched channels are on both sides of the sheet, so I could not use a half-thickness sheet and then add half-thickness extrusions to the flat pattern.  So I ended up using full thickness sheet, then sketched bends at the centerline of the channels, with a bend radius equal to the 1/8 of the sheet thickness and a K-Factor of .25, this is for 90 deg and 180 deg bends.  I think this corresponds to a neutral line halfway down the (non-existent) etched channel (ie 1/4 of the sheet thickness). 


              And then add cut-extrudes to the flat pattern for the etched channels. 


              So this allows me to get a folded model that corresponds to the correct flat pattern. Haven't had time to try in the opposite direction yet.

                • Re: Problem with etched sheet metal
                  Daniel Bergqvist

                  A friend gave me the solution:


                  If I have a part that I want to bend, I create two different parts. The original part (which only exists in my head) is split at the middle of the bend. I then create an assembly which has two "configurations" to combine the two parts into one assemby. One configuration is bend, the other is straight. See attached example.


                  The downside of this is that I get a lot of small parts and many assemblies, but I haven't found any better solution that actually works for me.


                  Kind regards,


                    • Re: Problem with etched sheet metal
                      R. Nair

                      Right, I see.  Take a look at the part I have attached. Here I have take a piece of the original Autocad drawing and extruded to the full sheet thickness (I removed most of the folds to make it clearer). Then using the Bend Radius = T/8 and K=.25, when I fold the two tabs tab over twice, I get the correct folded geometry (at least in the sense that the two holes line up and the total folded thickness is correct).

                        • Re: Problem with etched sheet metal
                          Daniel Bergqvist

                          I was not able to open the part. I has SolidWorks 2012 and maybe it's too old version?




                            • Re: Problem with etched sheet metal
                              Kelvin Lamport

                              OK, step by step;


                              Create a flat sheet metal part, half the final thickness required.

                              Add material (half the final thickness) to create the "etched" line recess.

                              Use a Sketch Bend to form the bend.


                              The trick here is to make the recess  wide enough to avoid the edges contacting each other when formed.

                                • Re: Problem with etched sheet metal
                                  R. Nair

                                  Kelvin, I think Daniel and I both require the inside corners to actually touch when bent.  Also I need etches on both sides of the sheet so I don't think the half-thickness works.


                                  Previous engineers here (long gone unfortunately) figured out the correct bend allowances for stainless steel thickness T=.018" with half-depth etched bend channels:


                                  For sheet thickness T=.018", Bend Radius R = 0 they use:


                                  Bend Angle A = 90 deg use Bend Allowance BA = .025"
                                  Bend Angle A = 180deg use Bend Allowance BA = .050"


                                  So calculate K-Factor = [(1/PI)*(180/A)*(BA-R)]/T = 1/(20*PI*T)


                                              =.88419 (T=.018")


                                  Thickness T     0.018       
                                  Inside Radius     0       
                                  K-Factor    0.88419       
                                          Bend Angle A    Bend Allowance
                                          5                        0.001
                                          10                       0.003
                                          15                       0.004
                                          30                       0.008
                                          45                       0.012
                                          60                       0.017
                                          75                       0.021
                                          90                       0.025
                                          105                     0.029
                                          120                     0.033
                                          135                     0.037
                                          150                     0.042
                                          165                     0.046
                                          180                     0.050


                                  If I use this K-factor with R=0 for Daniel's 0.30mm thick sheet, I get these allowances:


                                  Thickness T     0.3       
                                  Inside Radius     0       
                                  K-Factor    0.88419       
                                          Bend Angle A(deg)    Bend Allowance (mm)
                                          5                                0.023
                                          10                              0.046
                                          15                              0.069
                                          30                              0.139
                                          45                              0.208
                                          60                              0.278
                                          75                              0.347
                                          90                              0.417
                                          105                            0.486
                                          120                            0.556
                                          135                            0.625
                                          150                            0.694
                                          165                            0.764
                                          180                            0.833


                                  Daniel, I attached a SW2012 file with a 90 deg and 75 deg bends on opposite sides, K=.88419, (Inner Virtual Sharp, BendOutside). Sketch6 on the flat pattern shows the etch widths match the table allowances. Do these allowances come close to the etched channel widths that you use? If not I think you could adjust the K-Factor until you get a match.


                                  That's all I can do on this for the moment unfortunately, got to move on....

                                    • Re: Problem with etched sheet metal
                                      Daniel Bergqvist

                                      Thanks for your help. I can open your last example.


                                      I'm new to etching and I got the solution to the problem by an experienced constructor which has developed several train models with this technique, so I will stick to it. It's not perfect, but it works for him. (I haven't yet had sent my sheet for etching). But I hadn't got his answer at the time I asked the original question here.


                                      The good thing with my solution is that I have control. I can add new holes for example, without adding extra trouble.