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# Need Help on the method of calculating tube wall Within Part Variation

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#### DZ-Jang

Hello Folks:
very glad to discuss with u all here .
Our product were tubes and one of the charicteristics is wall thickness .when I did the G R&R, I can`t fix the point the appraiser measured on the tube axis ,so the result of the G R&R report is not exactly the same as it did in the plants.
I have seen one way of calculating WIV but only if there were maximum and minimum measured ,this method comes from the 2nd edition of the MSA manual.
And I can`t find any formula in the third edition MSA Referenced Manual except a short explain in words.
Can anyone give any suggestions or the method for calculating With-in part var ? Thank you in advance !

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#### Marc

##### Captain Nice
Staff member
What pages of the MSA Manual are you referring to? Let's start there.

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#### DZ-Jang

Marc .
I d`ont have the English version of the manaul but the Chinese Version .It seems that they r the same . The Manual here of the 2nd edition related r page 64-66. It gives out the formula to calculate the WIV for maximum and minmum value of the characteristic .
thank u

#### Atul Khandekar

##### Quite Involved in Discussions
Not sure if I understood you correctly, but how do they do it in the plant? If they are able to fix the location of measurement in the plant, may you should study the method / fixtures used there and try to replicate it. Or try to design a fixture where you can carefully control the location.

If you are using the 2nd edition format, the operator should obtain measurements of wall thickness at various locations (say, 10) along the circumference and/or length. (rotate the tube if needed.) Then use the maximum, minimum and the range of these 10 readings as one trial for one operator.

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#### DZ-Jang

What is the characteristic this Within-Part Variation G R&R evaluated ?

Atul Khandekar said:
Here is a link to a PDF document I found at the AIAG website:

Quantifying the Effect of Excessive Within-Part variation

Atul:

I had seen the similar documents before and what puzzled me is : for which characteristic this 《Quantifying the Effect of Excessive Within-Part Variation》is evaluating ? The maximum ,the minimum ,or the average ? If it is for the later ? why ?

You once asked the measurement method used in the plants . The truth is ,I did the same way as they did in the plants to do the G R&R . They note down the the maximum and the minimum value of the wall thickness in their register ,but the method or how many points should be measured were not stipulated . The operators just use their own way (e.i. one`s experience) to find the maximum and the minimum . I can see some of them find the point quickly while some of them may use longer time.
And I don`t know whether this kind of Experience can be trust in.

I`m waiting

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#### Atul Khandekar

##### Quite Involved in Discussions
DZ-Jang said:
.... They note down the the maximum and the minimum value of the wall thickness in their register ,but the method or how many points should be measured were not stipulated . The operators just use their own way (e.i. one`s experience) to find the maximum and the minimum . I can see some of them find the point quickly while some of them may use longer time.
And I don`t know whether this kind of Experience can be trust in.
This is why you should develop a standard measurement procedure that all operators must be trained to follow. Also, you should supervise the study being conducted.