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How to Create a Smarter Snap-Fit Design Using FEA

snap fit header 2

Snap-fits are everywhere you look! Remeber your indestructible Nokia 1200? It made use of a very well designed snap-mechanism to ensure the device safety through repeated falls (it also survived the acid attacks inside a fish, but that’s a completely different story). The Lego toys that you loved playing with as a child? Snap-fit mechanism. Your belt buckles? You food cans? Be it camera covers, production of cars, a simple battery case for a remote, or even a huge rocket, everywhere we look we are surrounded by this marvel of engineering.

The question in everyone’s mind now is, why does this omnipresent mechanism break so easily on some bodies, and lasts decades in others? How can you, as a designer or an entrepreneur, ensure customer happiness by using a better snap-fit design?

The answer lies in FEA.

This 3rd of August, we discuss how to make better snap-fit designs. How to ensure that the least possible material is used, and the longest life-cycle achieved. What goes on behind the scenes for ensuring a snap-fit will last forever or break right after the warranty runs out. 

Join us on this journey to find out how an extraordinary engineering marvel can still be improved with an on-the-cloud simulation, and how it can help you become a better designer!

What Engineering Simulation Brings

Product design is a highly complex process, with multiple objectives, requirements, and constraints, all of which need to be satisfied for the final product to be successful. The important factors that the designer has to keep in mind include aesthetics, functionality, cost-efficiency, durability, safety — and the list goes on. And while the aesthetic appeal of a product is not quantifiable, the other design aspects are and can be accurately tested.

In the traditional design process, your initial design is derived from best practices and past experience — which limits your creativity and leaves little room for radical innovation. Coming up with a truly new, innovative design, without relying on best practices, however, is risky and can lead to poor performance. The only way to ensure the durability of such a product is to perform a high number of design iterations until all criteria are met. Traditionally that means a high number of physical prototypes and a time-consuming and expensive physical testing phase.

Product design process

Of course, physical testing cannot (and should not) be eliminated from the product design process entirely. However multiple prototype building cycles, which account for the bulk of financial and time costs, can be easily avoided by integrating virtual simulation into your workflow. With Computer-Aided Engineering (CAE) you still have an iterative design process, but the days, weeks or months of physical testing are replaced with hours or sometimes even minutes of a simulation run.

When You Should Simulate

Product design cost escalation

Employing simulation at the right stage of the product development is another important decision for the designer.

It is important to keep in mind that the closer you get to the product launch, the more costly design alterations become, due to the increasing number of dependencies in the design. At some point implementing minor changes and improvements is simply no longer cost-efficient. With simulation, on the other hand, these design changes can be implemented even before the first prototype is built, allowing you to iterate on your design from the very beginning of the development process. This can potentially result in lower costs, minimized failure risks, lighter design, improved performance and user experience, increased product lifetime and more.

So Why Isn’t CAE an Industry Standard Yet?

Despite all the advantages mentioned above, several barriers have been preventing more engineers and designers from integrating simulation into their design process. Here’s how SimScale is aiming to change this:

  • Accessibility (upfront investment). Traditional software needs to be installed locally and needs a significant amount of computing power. That means highly expensive hardware, that stands idle while the simulations are running. With SimScale all computations are done in the cloud, no local installation — just a standard web browser.
  • Operating costs. High licensing costs for standard commercial tools put them out of reach for many designers — SimScale starts with a free Comunity plan with an option to upgrade to an affordable Professional subscription.
  • Know-how. Current CAE tools are not too user-friendly and are designed for CAE experts. This expertise gap can be minimized with intuitive UI, large public template project library, live support chat, and free training material. Any of the public projects in the SimScale Library can be imported into your workspace, so you can simply exchange the CAD model, reassign the boundary conditions and run it without having to know too much about simulation upfront. 

SimScale simulation workflow.

Example Study: Smarter Snap-Fit Design Using FEA

The snap-fit design depends on the expected use and life, and can hence vary substantially. Cantilever snap designs are known to be the most common, and the “U” or “L” shape snaps are very popular as well. The design factors to be kept in mind include the shape of the snap, the thickness of the beam, and the ratio of the thickness to the beam length. Optimizing the design of a snap body is a challenging process, and a lot of information about the stresses on the body can be obtained from simulations. One can use the information obtained to determine the life cycle of the snap, how much load it can sustain, and under what conditions. This knowledge can be used to determine the expected lifecycle of the part, the different stress concentration regions, and even be used to determine the manufacturing process itself.

Traditionally engineers have relied on experiments and physical testing to ensure the reliability of their snap-fits — yet in addition to being expensive and time-consuming, identifying all stress points through experimentation is highly challenging and the designer risks missing critical information. Simulation simplifies the data analysis necessary to make informed design decisions while saving time and money, and as a result delivering a more reliable product to the market faster.

To illustrate the benefits of employing FEA for a better snap-fit design, we are  hosting a free live 30-minute demo session on 3 August 2017 — register below even if you cannot attend, the recording and all relevant materials will be sent to you via email:

Project Overview

The project we will be using in the demo session is publicly available in our simulation project library — feel free to copy and modify it: Smarter Snap Fit Design using FEA.

Snap-fits come in a wide variety of shapes, sizes, and materials. There is no one-design-suits-all — how well our snap-fit design will perform in real life depends heavily on the intended application. Therefore, in order to approach the problem of optimizing its design, we first need to determine the following design parameters:

    • Material
    • Cross section shape
      • ConstantSnap-fit design CAD model
      • Varying
    • Cross section type
      • Cantilever snap joints
      • U-shaped snap joints
      • Torsion snap joint
      • Annular snap joints
    • Taper radius

One we have all the information we need, we can proceed with the simulation setup. We will use the results to validate the solver for snap-fit design simulations by comparing it to the experimental data presented in the Bayer Material Science paper [1].

After setting up our CAD model, we move on to meshing — the mesh defines the accuracy of the result. It should only be fine at the areas of interest: initially, it can be coarse all over, afterward, you can provide refinements to the areas of interest based on the results.

Snap-fit design simulation - meshing and boundary conditions.

The snap shall be given a displacement boundary condition. The small box against which the body deforms shall be given a fixed boundary condition. Using symmetry conditions allows us to decrease the number of nodes, increase the convergence speed and reduce the size of the model.

Simulation Results

123[Conflict]Areas undergoing the highest stress are clearly visible in the simulation results — the snap deforms and snaps into place. This CAD model is already fairly well-designed, with the snap end being tapered, and hence the strain on the final body is not excessive. Without this taper, however, the strain on the snap would be much higher, causing an earlier breakdown and hence limiting the lifetime of the snap.

For comparison, the initial (points) and the final (solid) positions of the snap body can be seen in the image to the right.

Snap-fit design - simulation results compared to experimental values.

Now, if we compare these results to the ones presented in the paper, we can see that the mating force and the maximum deflection of the snap seen in the simulation closely match the experimental values. The little difference in results can be attributed to the meshing grade and can be fine-tuned later.

Conclusion

Looking at the results of this simulation, it becomes evident that a proper snap-fit design is essential for ensuring low-stress concentration at points of contact, taper points and at the deflecting face. A snap-fit has significantly more stress near the deflecting face (head) than on the tail of the deflecting snap. Most importantly, we discover that compared to the snap-fit design with constant cross section, a tapered snap has lower stress values (can undergo more cycles), longer life (increased durability) and uses less material (cost saving).

In this case, we investigated leveraging FEA to design smarter snap-fit mechanisms — but this is just one example of how designers and engineers can apply simulation tools in the product development process. The SimScale Public Projects library has a wide selection of templates simulating various product use conditions across multiple industries, including automotiveaerospacemachineryelectronicsHVAC and more.

Explore it by creating a free Community account or discover the perks of our Professional Plan by signing up for the 14-day trial.


Want to read about other applications of FEA? This case study shows a stress analysis of a wheel loader arm performed with the SimScale simulation platform.


References

[1] Snap-Fit Joints for Plastics, Bayer Material Science:
http://fab.cba.mit.edu/classes/S62.12/people/vernelle.noel/Plastic_Snap_fit_design.pdf

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