13 Replies Latest reply on Nov 19, 2017 5:14 AM by Majd Al Mohtar

    URGENT How can I find the right force to mount two blocks together?

    Majd Al Mohtar

      I want to know that two blocks are fully mounted together (or two pipes) without any welding or connections only by squeezing them into each other, how can I find via solidworks the right force to do this?

        • Re: URGENT How can I find the right force to mount two blocks together?
          Bill McEachern

          Just figure out the acceleration, then you will know the forces needed to resist it.

            • Re: URGENT How can I find the right force to mount two blocks together?
              Majd Al Mohtar

              Hello, my application is to mount two blocks onto each other, or two pipes without any welding only by fitting them into each other so they become mounted, how does acceleration come in hand here? I want to figure out the force needed to perfectly squeeze two parts into each other.

                • Re: URGENT How can I find the right force to mount two blocks together?
                  Jim Steinmeyer

                  You might need to use a lot of acceleration when bringing them together so that the heat generated will weld them together.

                   

                  No Seriously, a little more information might be helpful. From your question I envision one block sitting on top of another and you want to know what force is needed to keep them together, without any acceleration the force of gravity will probably do it. You want to hold two pipes together, end to end? side by side? one slip fit inside the other? how big are these pipes, the resulting weight would make a big difference in how much force is required.

                   

                  As it stands your question is kind of like asking "how big is a house?"

                    • Re: URGENT How can I find the right force to mount two blocks together?
                      Majd Al Mohtar

                      Yes I see your point, imagine they are something similar to lego blocks, but on a larger scale, and two pvc pipes of a small diameter as well. I want to simulate that if a person himself wants to mount these blocks and pipes by squeezing them into each other and I want them to be mounted, the shapes are already studied but I want to know how much force the individual will need to mount them. Thank you and I am sorry for the previous vague explanation.

                        • Re: URGENT How can I find the right force to mount two blocks together?
                          Jim Steinmeyer

                          The answer would then depend on the material used and the amount of "interference" between the two parts. Take the lego blocks for example. If they are made of plastic and the pins were .025 inches in diameter with the receivers being .02499" in diameter having a wall thickness of say .005 inches. the force would be "x" for example. Now make the wall .5 inches thick and the plastic is much more resistant to deforming so the force would be x*y maybe. But if the pins are .025" in diameter and the receivers are .245" in diameter with a wall thickness of .005" The force will be x³ *y. Now you have to consider the number of pins that are involved and multiply the initial force required by the number of pins. Add to all of this ambiguity that maybe the blocks can be made of rubber that will easily deform to allow the pin into the receiver, or it could be made of steel which is much less likely to deform and allow the press fit.

                          Follow this with the question of are the pins chamfered to allow the insertion to be gradually guided and the material to force into the receiver? or is the end of the pin flat requiring the material to be moved more drastically?

                          Then you can take into account the relative temperatures of the materials. In a previous job we needed to mount hubs on steel shafts for a press fit application. We could get a several ton press to use forcing the hub onto the shaft, or we could let the thermal elasticy of the material work for us. We heated the hubs with a torch and ran liquid nitrogen over the shafts so they shrank. Then we used the previously mentioned velocity to easily slide the two parts together before the temperatures normalized and the items were stuck together so there was no taking them apart.

                          Now knowing that the shapes are already studied maybe you should take some time and study the material properties to determine how resistant they will be to the deformation required to introduce the interference fit that you are looking for. That will go a long way in determining how much force little Johnny will need to exert in assembling his lego blocks.

                           

                          I know this text may sound mean spirited but I am assuming you are a student who is attempting to rapidly gather information for a project. Now you can see why there are several classes and a lot of studying required to obtain an engineering degree. These answers aren't just laying around to be picked up off our desks.There are many variables that need to be considered and factored in.

                            • Re: URGENT How can I find the right force to mount two blocks together?
                              Majd Al Mohtar

                              I fully know what you mean. I am aware of the constraints and the variables I have. The thing is being a student, I cannot test the actual material since its manufacturing requires injection molding and is costly, so I want to simulate it on solidworks. I was thinking of finding the stiffness of the plastic material, if possible, and considering that when the lego pin goes into its receiver we need to create some preload with displacement x (a design value) and then I could estimate the force needed to reach such a displacement? Or is this not possible? Now this means that if I need to remove the block, the force required would be k(x). As for heating, if little Johnny mounted his lego blocks by thermal elasticity he would be stuck to the same lego building his entire life, which is not recommended. I hope you advice me regarding my idea and how can I build from it, and your efforts are much appreciated.

                                • Re: URGENT How can I find the right force to mount two blocks together?
                                  Jim Steinmeyer

                                  OK,

                                  So I thought you were asking for a value like 3kN.

                                       If I were looking to simulate this, and I have never run something like this so I am sure someone will have more complete ideas, I would fix the bottom block in a given location. I would then locate the top block above it placing roller/slider constraints on the sides to direct it straight down onto the  bottom block. Then I would place " no penetration" constraints between the bottom surface of the top block and the top surface of the bottom block. I would then also put a "no penetration" constraint between the pin and the receiver.  Here is the part where I am sure someone else might have a better idea, but I would then place a small force perpendicular to the top surface of the top block pushing the blocks together and run the simulation. If the material properties of the blocks are correct the blocks will either stop because the pins and receivers do not deform enough to allow the blocks to mate, or the blocks will mate. You can the run iterations raising or lowering the applied force until the blocks just deform enough to mate.

                                       That is how I would approach it though I would assume someone will have a much more elegant method of finding the correct force.

                      • Re: URGENT How can I find the right force to mount two blocks together?
                        Christian Chu
                        only by squeezing them into each other

                        Can you make it more clear?