Lexan fixture with flexible tabs breaking. Is there a better material?
Lexan fixture with flexible tabs breaking. Is there a better material?
(OP)
I just inherited a project to design fixtures for holding PCB’s in a De-ionized water wash machine. All current fixtures were made out of machined Lexan sheets and glued together.
The part of these fixtures that has failed the most is a spring retaining feature. It is machined into a row of tabs, heated, and the tabs are bent to form the part that retains one edge of the PCB’s. I’m told they are heated in a fixture that applies pressure while they are baked in the oven, and then they are cooled slowly while still under pressure.
All of the tabs show cracking at the location where they bend, and many have broken off. Since this fixture is glued together, replacing just the tabs is not an option.
Is Lexan a material that can be used as a spring?
What would a better material be for this?
I can easily change the design to remove heating and bending of the tabs. Would that help the durability of the tabs?
The part of these fixtures that has failed the most is a spring retaining feature. It is machined into a row of tabs, heated, and the tabs are bent to form the part that retains one edge of the PCB’s. I’m told they are heated in a fixture that applies pressure while they are baked in the oven, and then they are cooled slowly while still under pressure.
All of the tabs show cracking at the location where they bend, and many have broken off. Since this fixture is glued together, replacing just the tabs is not an option.
Is Lexan a material that can be used as a spring?
What would a better material be for this?
I can easily change the design to remove heating and bending of the tabs. Would that help the durability of the tabs?






RE: Lexan fixture with flexible tabs breaking. Is there a better material?
Could you replace the broken tabs with a metal (e.g. stainless steel) piece that then attaches to the remaining fixture with screws (or glue)? Or re-make the fixture using polyethylene?
RE: Lexan fixture with flexible tabs breaking. Is there a better material?
As stated above, it is susceptible to attack from hot water, but especially if it is already stressed and also if the water is alkaline.
Many common solvents and chemicals will also stress crack it.
IF, and only if, it is dried, heated to the CORRECT temperature, then slowly cooled, there should be little residual stress after bending, but IF a spring seats on it, the spring will be applying some stress, quite probably enough to make it quite sensitive to solvent stress cracking.
Possible alternatives are many. It really depends on a lot of details you have not provided to date.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Lexan fixture with flexible tabs breaking. Is there a better material?
Yes, I can change the material. Due to a reorg, it's now my project. They told me that they need 12 more fixtures. I found out that they need them since all of the current fixtures have broken. So I'm trying to re-design them before I order them so they don't break as quickly.
I am looking into the chemicals and temperatures that the fixture sees, and I'll post that info later.
Thank you very much.
RE: Lexan fixture with flexible tabs breaking. Is there a better material?
RE: Lexan fixture with flexible tabs breaking. Is there a better material?
The best material for the job depends on a combination of factors, most of which are undisclosed to date.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.