# Snap fit calculations?

Asked by Jonathan_hodgkins (555) January 31st, 2014

I am currently designing something that needs plastic snap fits in order to secure it. I have found several formulas online, but they aren’t intuitive to me. I am trying to figure out how the geometry of the design effects the perpendicular force, the stress and the strain. Can anyone help me by walking me through the process of the calculations and how it was derived? Thanks.

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Here’s the Snapfit by BASF. It is not an intuitive process.

This question is far too vague for anyone to respond positively, I think.

What kinds of forces and stresses do you need the snap to resist? What kind of environment will it operate in? What kinds of materials will it be applied to?

That’s a very interesting site, @Tropical_Willie.

CWOTUS (24133)

We use to use it at a company I worked at for designing Snap-fit. I am not an engineer but have had to do process sheets and operational design. I let the people with the advanced degrees ( rocket scientists ) crunch the numbers.

These are the equations that I have found in regards to snap fit, but I don’t understand the intuition behind them.

http://machinedesign.com/site-files/machinedesign.com/files/archive/machinedesign.com/common/files/images/snap-fit-parameters.preview.jpg

It is not just intuitive, it is is mathematics (trigonometric) and physics. The parameters are engineering, I assume you don’t have an engineering background. Flexural modulus is the ratio of stress and strain for the plastic.

I am actually in school to become a mechanical engineer and so all of the terms make sense to me. I know flexural modulus, stress and strain. I am just wondering about how the calculation was derived.

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