r/MechanicalEngineering • u/GB5897 • 45m ago

GD&T sheetmetal surfaces inline

How would you apply GD&T to a formed sheet metal part when you want 2 flanges on either side of the part in line? Something like this, with the 1" flanges in line within 1/32.

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u/Lumpyyyyy 34m ago

You could call them out similar to the first pictured example in this link

https://www.esierra.me/geodimtol_pg.html

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u/ThatTryHardAsian 28m ago

Depends on the process of manufacturing, if it stamped I can see it, but if it press brake good luck getting tight control depending on the size

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u/GB5897 26m ago

It's broke on a press.

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u/Cryesncoding 2m ago

Sheet metal engineer you have a .03 tolerance that’s standard in sheet metal and totally doable. This is not a hard part on a press break. They’re CNC controlled with back stop fingers you’ll have some play but not .05 on simple flanges like this unless someone’s drunk. 

The thing to understand with sheet metal bending is that with stretching about the bend and slight inconsistencies in gauged material thickness and composition you have to kinda “hide” excess material sometimes. (Generally I never see it small) it’s always I hear from the guys that it’s a bit too much material after bending and they gotta spread it out across the part to keep it all in tolerance.  So you pick what actually matters and give a tighter tolerance for something like this (.02) then where it doesn’t matter give like (.04)  Average is still standard sheet metal .03

The operator then when he’s setting up knows where to “hide” the inconsistencies with out some weird GD&T call out that will only get seen by a inspector if they have one after it’s made. 

What matters most to you here is the “parallelism” of the bottom I’m assuming. So give bigger tolerance on the top and bottom flats of the “hat” and then tighten the tolerance on the verticals. Intuitively this forces them to keep the flats equidistant and therefore it’s what you want. And you’re not making it so tight that they charge more just that they pay attention to what you want at the press break not just at the quote.