Compression Spring, Equation Driven, in SolidWorks
Not sure this is a tutorial, or just the description of my process for building a printable compression spring. There are equations in the excel documents not just for a printable spring, but also designing custom metal.
Designing the spring and Using the model loaded here:
Compression Spring, Equation Driven
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Step 1: Model Description
This model is a "Closed and Ground" Compression Spring that I wanted to print. The model is equation driven with the following Variables.
D_Mean: Centerline of the Coil.
d: Diameter of the Wire
H_Free: Free Length of the Spring
N_Total: Total Number of Coils
N_e: Number of End Coils (Should be 1, Don't worry about this)
Na: Number of active Coils.
the rest of the variables are calculated and used to drive the model and won't be discussed.
Fig 1.1: Equation Manager in SolidWorks
Printing Support:
The Slicer printing support was a mess. So, I included a Quick Extrusion that can be toggled on and off in the tree.
Fig 1.2: Without Support
Fig 1.3: With Printing Support
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Step 2: Excell Calculator Introduction
This Calculator is based on the designs given in Shigley's Mechanical Engineering Design, Ninth Ed. Chapter 10, Mechanical Springs. For Further information and reading please reference source.
This was not originally for this model. It can be used for other designs. Various materials are programed in. I would advise to take great care with both stainless and Phosphor-Bronze as their material properties change greatly with wire diameter.
Fig 2.1: Calc Page of Excel Sheet.
Choices: some of these choices will change the design, other will be asked when sending the spring out for a quote.
Spring Constraint: Self explanatory. If it will be in a hole, or around a bar this can help with rigidity.
Pre-set: can be used to increase the strength on the spring.
End conditions: for this model we'll be using closed and ground. In the real world this can add unneeded expense to the design.
Material: Since this is about the Printed Spring. It'll be set to experimental. Other materials are charted for use.
Chose two to define: Two of the three; Pitch, Free Length, and Number of Coils; are required. Ther other will be calculated.
Inputs: These will drive the design:
Mean Diameter: This is the centerline of the coil.
Wire Diameter: this is the Diameter on the wire, in the real world check with manufactures for available wire diameters to keep costs low.
Working Load: This will check the use on the spring. Not needed for basic calculations.
Free Length: This is the length of the spring with no load.
Number of Coils: This is the Total Number of coils, active and end coils
Experimental Only: these values need to be included if not using standard materials. in our case they'll be used.
The Rest of the calculator is Calculations, outputs and checks. So they don't need to be messed with.
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Step 3: Printing 2 Springs
I printed two springs that were close with the following properties.
Fig 3.1: Two printed Springs.
I then weighed the amount of mass it would take to fully close spring 1 to solid length. it was approximately 410 grams (sorry in advance for the unit swapping that will be happening). I converted this to 0.90 lbm.
Fig 3.1: Spring 1 to solid length
Putting this into the calculator. I used a What-if Analysis to goal seek the "Force to Solid". I chose to change the "Expected G", it came up with 89,877 psi.
Fig 3.2: Goal Seek.
To check this. I took the second spring and put it through the calculator. It said it should take .254 lbf to solid length. Converting this to grams, it comes out to 115 grams. Applying this load to spring 2, it looks pretty close, maybe a tad low.
Fig 3.3: Spring two with 120 grams applied.
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Step 4: TBD
These steps are yet to come. More testing and tweaking is required, but it might be on the right path. Let me know if you try similar experiments and get results.
