Controlling Thickness

[HvyB]

I have a plastic part which is injection molded, then subsequently R.F. Welded. One area of the part has fairly thin sections which is where the welding will eventually occur.

We call out a nominal thickness of .030" +/- .005"

The welding operation is not tolerant of SUDDEN changes in thickess (i.e. .005" thickness change in any .250" x .250" area). This can happen from sinking, or other molding abberations. Sudden changes cause "Bridging" in the welding process. This thin section is subject to warpage of up to 1/8", but that does not make a "Bad" part as the welding process will readily flatten this "warp". I don't want to throw away good parts.

I want to define the part so the nominal thickness may float from .025" to .035", yet limit any "sudden" changes to .005" in any .250" x .250" area. Flatness won't work as the warpage blows away the "delta" in the surface.

I can simply "write a book" on the face of the drawing and spell out what I've desribed above, but would rather use GD&T. What do you think?

Thanks

HvyB

 

[PaulJackson]

There is no way in ASME Y14.5 or ISO that I know of to control material thickness variation as a refinement of size.

I think that you are stuck with writing that note.

Paul

 

[LizardmanDan]

I know this is an old thread, but I stumbled upon it and decided to respond anyway...

I think the answer to your problem is shown on as a Tec-ease example.

http://www.tec-ease.com/gdt-tips-view.php?q=112

take a look and see if this helps.

Hopefully you get an email notifaction that your thread has risen from the grave.

 

[Belanger]

That tip shows per-unit profile but just to control form. I don't know if it would help the OP.

I was almost going to suggest the new "I" modifier, but that too wouldn't help with the per-unit thickness idea; it would only divorce size from form.

Guess we're back to a note..?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[pmarc]

I believe flatness per unit could work here. It is mentioned in para. 5.4.2.2 of Y14.5-2009 standard.

 

[LizardmanDan]

PMarc's comment makes sense. It would make sense to use some sort of control "applied on a unit basis"

I checked the OP's history and this is the only thread he has made or replied to so I doubt we will find out if he ever found an answer to his problem.

 

[HvyB]

Hi Fellas,

I went with the note, mainly because the Inspectors at my supplier, as well as my incoming at my factory are not very savvy on the subtleties.

THICKNESS VARIATION NOT
TO EXCEED .005" IN ANY
.250" X .250" AREA

This has been the case many times before, making the translation to the "real" world often means NOT using GD&T. Engineer to Engineer these terms make sense, but all too often, the inspectors (on my incoming) won't understand a concept or symbol, and will just skip it......

I've used this forum over the years under another logon, but forgot what it was.. thanks.