Snap Lock

The question needs much more detail.

The average small plastic case would deform severely, if not break when dropped from that height.

permanent non releasable

Why not just glue it shut?

Del

Thanks for you reply.

but it is to be used in automotive industry and it will have to withstand a vibration test and impact test too. i have a enclosure with me with a snap lock(trap type) but it does not withstand drop test. is it impossible to design a snap lock for drop test?

is it impossible to design a snap lock for drop test?

Probably... first you need to understand how the current snaplock fails.

You don't answer the question...why not use an adhesive?

Del

sorry the adhesive might be ineffective in a vibrating environemt with a temperature fluctuation of -30 deg C to +80 deg C. i cannot make out how the current snap fails. probably the impact of drop releases the lock.

Try filling the inside faces of the box with plasticine or similar (play doh). Repeat the drop test...examine the plasticine, it may show where the deformation is occurring.

Solving problems is easy...the hard part is find out what the actual problem is.

Del

that is a good idea but still i didnot get my answer on whether a snap lock can be designed for a drop test. i will try that.

i didnot get my answer on whether a snap lock can be designed for a drop test

Arrrggghhhhh!!! The answer is yes and no...

If it is just the snap lock itself that is failing then, the snap lock can be designed to survive.

If however the problem lies with the box flexing due to bad design, then it maybe that the box rather than the snap needs re-designing.
I would have thought that my previous replies would have made this obvious.

Bear in mind I cannot see the parts! Do you think I am psychic???

Del

I am sorry for the silly question. yes ofcourse you cannot see the case it is a small case of size 3" X 1" and typical wall thickness of 0.1". any how thanks for the suggestions. Any idea on how to do a anlaysis of snap lock mechnism in ansys.

I would say analysis is probably worth nothing (I'm sure others will object to this statement) ...

Look at the assembly, flex the parts, feel it, look carefully at how it snaps together and how the parts deform. Understand it.

By how much do the engaging parts engage? Assuming your 0.1" wall thickness, any snaps should engage by at least the full 0.1 if you want it really strong, I expect your snaps are engaging by a just few thou.....

Does it snap together easilly? If so, it will probably snap appart easilly. Are any 'fingers' solid enough? Once engaged do the parts lock together to prevent any fingers flexing back again?

Show us a sketch or a photo....

Del

thanks for your interest in this. yes you are right actually i too think that the snap is not getting engaged properly and the also flexes when i press it from sides. what i could make out from the drawing i have tried to put it in a picture as attached. Can this lock be made non releasable. also withstand drop test. please find the picture below.The picture is my assumption this may be true actually, this is just show how the snap looks like.

I suggest you mold in some vertical ridges on the lower section, these can extend up slightly above the join line as short fingers, this will a) Stiffen the bottom section. b) Stop the top section flexing outwards.

Also the depth of snap on the top section could be increased hugely for short sections every 1/2" or so such that it virtually penetrates the wall of the lower section.

Hope this gives you some ideas.

Del

A lot of questions have been asked only one not how do you perform the test :

with an empty box or with the contend? what is in ? which mass does it have?

As your drawing looks it could be possible that your upper part is already heavily loaded at assembly and thus looses part of its holding capability.

As a general comment a snap can be designed to resist such a test but it depends from many factors as among others the kind of plastic you use, how it will fall, where the contact will give the highest load on the parts, and so on...

As Del wrote try first to understand why it fails and then it will be easier to define the solution.

As usual in the frame of the discussion ther are few comments answering the question and more comments and suggestions for other solutions. It could be perhaps better to assume that if a question is asked there are reasons and first we have to try to find an answer and after it suggest an other way. For many reasons in automotive boxes are based on snap systems among other reasons the easy change of content in case of maintenance.

Thanks a lot for spending time with me on this. it was a learning experience. once agin thanks and bye.

How about a hinged lid that is extended to folds over the opposite edge and held in place with a strip of velcros, should work better than glue?

Regards JD.

maybe try molding both faces of lock with saw teeth that inter lock onto them selfs?

as pic shows slight deformation is this really happening on pcs? causing to un-latch?

Back that puppy up with a cable tie - that should work. The specification of a "permanent non-releaseable" closure makes the type of lock somewhat redundant, does it not?

Sonic welding would make it permanent and eliminate any intricate molding. Using various types of tabs may lock the tab and mating surface permanently, but fatigue may eventually cause a breakage of the tab itself. Keep the connection simple and durable and weld it.

Cable ties work great and are strong. Might incorporate these into the design

Rusty