metal stretchyness for clip design

[safiredesignengineers]

hi group

please see enclosed rough picture of a clip, is it possible to use inventor 2014 professional to design a clip like this so that when a rod or ball is pushed into the round hole at the top the clip stretches a bit wider to let it in and then returns to the initial point to retain the rod or ball?

i can play with the design with slot length, slot width or material removal at the bottom of the slot but up to now i use trial and error by making the part to see what i get (time consuminig!!), is it possible to work out the best design in inventor so that the design will spring open just enough without deforming?

regards Adrian

[JDMather]

Attach the file here.

In FEA

Add Fixed Constraints with an offset at guessed distance. (or if your rod or ball is already known - use that distance)

Run FEA and check Safety Factor (SF>1 the part will return to original dimension, that is, only elastic deformation, no plastic deformation).  Check digital solution against actual experiment.

You can experiment with the slot length/width to increase/decrease SF.

You can set this up as a Parametric Analysis to semi-automate the analysis of different slot widths/lengths.

What book are you using to learn FEA?

[safiredesignengineers]

Hi Jd

im glad it is possible, i will look into the fea to see i can find.

please find the file enclosed. i have wasims 2011 book.

regards Adrian

[JDMather]

If you set the x,-x distance on the part - this is how far it would have to open for the pin to clear.

Then run FEA and check the SF.

You can also right click on the constraints to check the resultant forces that would be required to clip the parts.

If you name the dimensions it is easy to set up a Parametric analysis for different sizes of the dimensions.

(I think I would move the hole down some or make the fillets smaller.  Also consider that perfect parts cannot be manufactured - so the pin would probably have a max allowable diameter a little smaller than min allowable dia for the hole.  It might be best to consider the manufacturing tolerances  If the hole encloses the pin more than it does now, you wouldn't necessarily have to have clearance.

[safiredesignengineers]

Hi JD

ok so i have played a little see enclosed piccie.

I read in a help file tat a SF of 2- 4 is acceptable but i guess i am aiming for a green colour as much as possible?

so as in this picture the optimun would be a SF of 6 - 8.

I assume from this i keep playing with the design until I get mainly green over the design, is this correct?

regards Adrian

[LT.Rusty]

To make this a little easier to and interpret, here's a few things you can do.

1.  Change Smooth Shading to Contour Shading instead.  This will establish a banded display of colors, rather than a cloudy pattern.  It's less precise, but it allows you to rapidly see patterns and gradients more clearly than Smooth Shading does.

2.  Adjusted x1 exaggerates the distortion of your part.  If you turn that back to x0.5 or even set it to Actual, you don't get distracted by things that look like potato chips and don't really look like what you're working with.

3.  Adjust your color bar settings.  If you open it up, it'll be set to MIN and MAX by default.  You can change these settings to compress or expand the display of color.  If, for instance, you don't care about anything with a safety factor of >1, you could set the max to 1 and the min to 0, and everything >1 would be blue, and you'd see the spikes where it was lower and identify the weak points. 

It is, of course, up to you.  This is how I usually do it when I'm running FEA, though.  Makes it easier / quicker for me to see what I'm doing.

[JDMather]

Something isn't right with your file.

Attach it here again with the FEA set-up.

[safiredesignengineers]

Hi Lt Rusty,  that all makes sense, thanks.

Hi JD, i have been messing around with the design to see what happens, i think in that picture i had the fixed constraints set at +/- 0.25 or +/- 0.5 which might of made it look a lot worse as it was quite a bit of movement?

I have been playing with settings and design to see the changes to the simulation, (please see enclosed piccie of a version), what i would like to know is what is acceptable elastic movement and what is deformation?

I guess:

blue: is no elastic movement

green: is acceptable elastic movement

red: is deformation?

With other colors in between as a progression to elastic movement / deformation

obviously the colors relate to the numeric UL value, but is there a chart or a given accepted range that i can work to? do need to make my design work between 1 and 2 which is green?

on my enclosed picture i guess the tips of the entry will wear and the bottom circular relief's will deform, is this correct?

Regards Adrian

[safiredesignengineers]

Hi Jd

I have the simulation 2011 book, by wasim, but I got to admit due to lack of time I have not read it too much, I find these types of books are not an easy or fun read unless the actual projects relate to what I am doing in a good way.
I find the best way to learn is to practise on a project that will give real life results as it is more rewarding.

however I do refer to the book when I am playing like this.

can I ask if the later versions of wasims book have a lot of changes in them or do they just have basic additions to the original print?

i.e are they all pretty much the same or does each book offer different and mixed content?

regards Adrian

[LT.Rusty]

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@safiredesignengineers wrote:

Hi Lt Rusty,  that all makes sense, thanks.

Hi JD, i have been messing around with the design to see what happens, i think in that picture i had the fixed constraints set at +/- 0.25 or +/- 0.5 which might of made it look a lot worse as it was quite a bit of movement?

I have been playing with settings and design to see the changes to the simulation, (please see enclosed piccie of a version), what i would like to know is what is acceptable elastic movement and what is deformation?

I guess:

blue: is no elastic movement

green: is acceptable elastic movement

red: is deformation?

With other colors in between as a progression to elastic movement / deformation

obviously the colors relate to the numeric UL value, but is there a chart or a given accepted range that i can work to? do need to make my design work between 1 and 2 which is green?

on my enclosed picture i guess the tips of the entry will wear and the bottom circular relief's will deform, is this correct?

Regards Adrian

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There's more to it than just looking at the safety factor.  Safety factor can be a useful tool IF your material properties are set correctly.  If the material properties are not accurate, however, then it will not be particularly useful to you.

What you really need to do is carefully look at the stress / strain curves for the material that you're using, but even that will just give you a set of reference numbers that don't necessarily mean anything.  In general though, when I'm looking at something like this I check the yield strength of the part that I'm simulating and compare that to the Von Mises stress that the simulation shows.  If the VM stress is lower than the material's yield strength, then it will probably spring back.  If you go past the yield strength, then it will probably not spring back so well, and your deformation will be permanent.  This, of course, assumes that the published yield strength for your material is in fact consistent through the batch that you've got, and there's other factors that should be considered as well.  Inventor's simulation tools are not a substitute for making actual prototypes and testing them.  They just help you minimize the number of prototypes and tests that are required.

What I would probably do in the case you've presented here is set up a dynamic simulation of the clip functioning, and then I'd export individual frames to the stress analysis module and examine the stress and safety factor over the range of motion.

 Something else that you can do, if you don't know the exact properties of the material you'll be working with, is to model out a design that you know works, through actual physical testing, and assign both the known-good part and your digital prototype the same material.  You won't get real-world-applicable numbers out of it, but you'll be able to compare the simulated performance of the new design against the simulated performance of the known-good design, and if your materials are the same, you'll get some information that will help you refine your design further.