6 Replies Latest reply on Jan 2, 2013 5:28 PM by Roland Schwarz

    Help with a part made of spring steel?

    Rick Donnellon

      I need to design a part from spring steel to exert a approximate force at a specific deflection. Attached is a PDF trying to demonstrate requirements.

       

      • The spring part is held in place on a pivot shaft and a pin at one end (not shown) is inserted in a hole in another part (part B).
      • A force is applied at the other end of the spring part moving the one end about 2.5MM and trying to rotate around the pivot.
      • Since the pin is in the hole in part "B" and can't move the spring part flexes exerting a force on the hole in part "B".
      • The force I am looking for is about 440N

       

      I am thinking If I can set up a SolidWorks Simulation, I can play with the cross section of the spring part until I get the required force at the required deflection? I don't have a material picked out yet, I am hoping to get some help with that. I am working with a spring manufacture, trying spec a material and get the required mechanical properties. Can anyone tell me which of the following properties are required to run a simulation like this?

       

      Elastic Modulus

      Poissons Ratio

      Shear Modulus

      Density

      Tensile Strength

      Compressive Strength in X

      Yield Strength

      Thermal Expansion Coefficient

      Thermal Conductivity

      Specific Heat

      Material Damping Ratio

       

      Also

      I only have SolidWorks Premium 2012 SP5 so I only have SimulationXpress ( I think) and the first thing I noticed it it only offers "Fixed Holes" for fixtures. I think I may need like a hinged type of connection to solve this? Can anyone confirm this?

       

      Can anyone suggest a material?

       

      I am not a spring steel expert and have only done a couple very simple Simulations so any help and/of feedback will be greatly appreciated.

       

      I have also attached a SolidWorks file of the spring part if anyone wants to play with it.

       

      Thanks in advance

      Rick

        • Re: Help with a part made of spring steel?
          Billy Wight

          Hi Rick,

           

               You're definitely going to want to use (at the very least) the actual simulation module, which you should have access to if you have a license for SolidWorks Premium.  Check under Tools - Add-Ins and check the box for simulation, it should load it in.  This will give you the ability to use the appropriate constraints and run a linear static study (and you will therefore need only elastic modulus, Poisson's ratio, and density if you're adding gravity to run the analysis).

           

               Ideally, for what you're trying to achieve, you would run an optimization run for size/shape to iterate through and get the exact reaction force you're looking to achieve.  Also, you will want to verify that your final solution agrees with the results of the same analysis as a non-linear solution (geometric non-linearity).  Just quickly looking at the dimensions, it should be close, but it's hard to say without actually running the non-linear solution.

           

               Finally, be sure you have mesh solution convergence.  I would recommend at least three elements across the flexure thickness.  Typically the default element size will be too coarse which can throw off your results. 

           

               As far as the materials are concerned, I would start running the analysis with a basic steel and see where you have to go from there.  You may find that the cross section changes necessary are too drastic and a different material modulus will be required.  From there, I would consult with your spring supplier to find their recommended material that matches your necessary modulus and geometry.

          • Re: Help with a part made of spring steel?
            Mike Pogue

            Rick,

             

            I would find a starting point by approximating this as a cantilever beam with the length and cross section of the thin section, i.e., assume the thicker sections are rigid. Wikipedia will give you the simple formula for the spring constant, which you can solve for the force. Once you have an expression for the force, you can use the height, width and Young's modulus as knobs to turn to get the correct force.

             

            If you begin by iterating FEA models in the dark, I think you will burn up a lot of time unnecessarily.

             

            Also, it is important to know the acceptable error in the force, and to look at the sensitivity to error in height, width, length, movement,  and Young's modulus. Springs typically have very sloppy responses. And spring constants are not as linear as your math teacher wants you to believe.

             

            http://en.wikipedia.org/wiki/Cantilever