Geometric control of long thin walled tube with varying cross sections

[lwealing]

I wanted to get a few opinions on how to control the features on a specific type of part.

Imagine a complex surface of revolution, much like a bowling pin or a coke bottle. The features along the part are circular in nature, but not all features are cylindrical. Now imagine the same bowling pin, but instead of being solid, it is a thin walled part where wall thickness variation is important and the wall thickness is varying in cross section along the length of the part. Confused yet??

One additional piece of information. Due to the manufacturing process (injection molding), the part is subject to free state variation which results in deviation in each circular cross section (wants to become ovalized) as well as "bowing" or warping along the length of the part.

The function of the part (to use the bowling pin as the example) is to be held by a cylindrical feature at one end (think the base of the bowling pin) and clear a clearance hole at the other end (at the tip of the bowling pin). There are other organically shaped features in between both ends.

Wanted to get a few opinions on how you would control the following:
Size (for the features of size)
Form of features at each circular cross section (perpendicular to the part's DML)
Form along the length of the part (to limit "bowing")
Wall thickness of part, especially as nominal wall thickness and feature shape change along the length of the part

I have some ideas, but wanted to get your opinions before proceeding.

 

[3DDave]

Knowing what to do depends on what difference each variation makes. Controlling just for having controls is a waste of money.

 

[AndrewTT]

What features do you plan on measuring in the free state? What features do you plan on measuring in a restrained state?

 

[Belanger]

You'll get the most bang for your buck with profile of a surface or profile of a line -- but as mentioned, it depends on many factors.

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

 

[lwealing]

What features do you plan on measuring in the free state? What features do you plan on measuring in a restrained state?

One of the challenges here is measuring every feature in the free state. I have already suggested to use a restraint condition when first consulted, but that idea was dismissed early on. The challenge here is if we can define these features in the free state or not.

You'll get the most bang for your buck with profile of a surface or profile of a line -- but as mentioned, it depends on many factors.

Kind of along the lines I was thinking. I attached a cross section view of the part. It is held by the short cylindrical diameter on the right side of the part. The cylindrical diameter on the left side of the part is meant to clear a hole.

 

[mkcski]

My first thoughts are profile too. Will the material allow Ultrasonic Testing to confirm wall thickness. If yes, use profile on the OD and check the wall thickness with UT. Maybe?

Certified Sr. GD&T Professional