latch design in plastic/sheetmetal housing

[amckenna]

Hey all,

I'm in the process of designing a product which has a plastic molded front and a sheetmetal back cover. I'm not a plastics expert, and would like some input on ways to fasten the cover and backing together without using screws. I've been thinking about using snap latches, but I'm wondering if it would be a pain if someone had to open it up after assembly was completed. If anyone has any ideas, it would be greatly appreciated. Please see attached pic.

Thanks all,
Andy

 

[patprimmer]

Screws or snap fits are the way to do it. The alternatives of adhesives or hot staking or outsert moulding will give a permanent joint.

Regards

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.

 

[pierdesign]

Based on image shown this is not an application for snap fits; screw mounting is best, if production is very high volume look at insert molding and screws with lead ins for automation assembly.

Snap fits work when your assembly engages from one direction only. Yours engages from two, the base and back face, perpendicular to each other. A snap fit on one will leave the other loose.

If you are persistent, you could try snap fits on the plastic housing to the sheet metal base plane and mold in vertical grooves for the sheet metal back wall to slide in, thereby capturing it in assembly. This would be tricky assembly requiring pre-alignment.

Snap fits generally never disassemble well. From your image it appears you are early in design stage, and also appears that your product may have some size to it, going by what appears to be a display window on the molded plastic. Again, something this big is not a candidate for snap fits due to the assemblies' weight and probable warpage of molded plastic housing of this design type causing snap fit misaligment.

Another design trick is to mount all or most assemblies to a sheet metal chassis with final assembly step of slipping on your plastic cosmetic cover. Snap fits may be applicable, provided lifting and handling of the device is not compromised.

 

[dwightdixon]

I would design a groove into the plastic so the cover would slide over one side of the plastic and then put two or more screws in from the other direction to hold the sheet metal into the groove.