×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to define a sheet metal ring? (Flat pattern? Free state? Restrained State?)

How to define a sheet metal ring? (Flat pattern? Free state? Restrained State?)

How to define a sheet metal ring? (Flat pattern? Free state? Restrained State?)

(OP)
Hello, I'm struggling with the best way to define a thin sheet metal part (.010" thk). My part is a fairly simple stamping which is rolled into a "C-shape". The stamping looks like a long-thin strip with some features... you could think of the part as a rolled up Chevrolet logo. The design requires the part to have a given amount of compression when installed, so the free state diameter is important.

Originally, we defined the part formed in its free state, but we got feedback from the manufacturer that the definition would be difficult to produce because the part is so flexible.

I think that it may be more appropriate to describe the cutout as a flat pattern, and then define the formed shape in the free state. However, our PDE group is recommending that we define the part in the as-installed constrained state and add a free-state diameter requirement. I'm wondering which method is more conventional?

In my mind, the relationship between the flat pattern and the installed state is straightforward, and defining a flat pattern would allow the vendor to inspect the cutout after stamping with a comparator, rather than making up some jig to do so. I don't do a ton of work with sheet metal, so any suggestions would be greatly appreciated.

RE: How to define a sheet metal ring? (Flat pattern? Free state? Restrained State?)

flash3780,

I do not show flat patterns unless there is some feature that cannot be shown on the as-formed part.

ASME Y14.5 has a section on how to dimension flexible parts. Your drawing should show how you will fixture the part for inspection. On flat sheet metal parts, I routinely attach a note to my primary datum...

Quote:

DATUM A APPLIES WHEN THE FACE IS CLAMPED TO A FLAT REFERENCE SURFACE.

In your case, this will be a bit more complicated. You may need to make a fixture.

--
JHG

RE: How to define a sheet metal ring? (Flat pattern? Free state? Restrained State?)

(OP)
Thanks for the input. I've read through ASME Y14.5-1994 on the issue and there's not a lot of great examples of flexible parts in there. I was thinking that a separate flat-pattern and a formed shape would be clearer in the case of my part (again, it's a sort-of "Chevy bow-tie" rolled into a 2.5 inch diameter "C" shape). However, it seems like the popular opinion is that it's not the modus operandi for this sort of thing.
Maybe defining the part in the constrained (installed) state and specifying a free-state diameter is the way to go after all. Unfortunately that leaves me defining things with angles rather than linear dimensions. Ahh well, as long as the part gets made the way we need it, it's just semantics, really. There's no difference in the tolerance stackup that I can tell.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources