Home Forums General Discussion Shot Peening Process, Intensity, Coverage arc height verification

Hi all;
Drwaing requires the part should be peened at 0.004"~0.006"A.

My curve(only one strip location):2.8(1passes)~4.0(2passes)~4.7(4passes)~5.3(8passes),the curve saturated at 3.08passes,intensity 4.65A.

While the customer specification requires "the arc height shall not exceed ±0.001" of the target arc height and above the drawing minimum intensity when routine verification", I defined the routine verification range as [4.0~5.7,at 4passes] in our internal work instruction.

If our operator gained an arc height of 4.0 at 4passes during routine verification some day, it it permissible to start production peening as 4.0 is inside the verification range.However,in this case,there is a high possibility that the true-intensity lies below drawing requirements.
so,what's your opinoin? it seems to be a contradiction.
And,for PVT with multiple strip locations, the situation will be more complicated i think.

"Target arc height" is a relatively-new concept and is now embodied in SAE J443. Verification is to be carried out to confirm an arc height predicted by the saturation curve - rather than one of the measured points. For your data the target height at four passes would be 4.9, with SAE J443 specifying that a single-strip verification test must give a deflection within +/- 0.0015". Your customer has reduced this to +/- 0.001" to give a range of 3.9-5.9 for your example and added a further restriction that the minimum value should exceed the drawing minimum specification of 4. That leaves you with having a range of 4> to 5.9. Personally I believe that the allowed range should be reduced considerably but meanwhile we 'play by the rules' even though, as you correctly point out, the true intensity at verification would probably be below the drawing requirements. "Target arc heights" are very useful for multiple strip locations.
TSP articles (Fall 2015 and Summer 2016) cover this topic in detail.

I recently posted the following message at the SAE ASEC web site. The term "Arc Height Verification" has an interesting meaning. See below:
===============================================
For General Discussion:
1. Intensity determination is performed using four or more test strips and evaluation of a saturation curve using T and 2T and the 10% rule.
2. Process consistency is performed by subjecting a test coupon to the blast stream for a selected time (or equivalent) and charting its repeatability. Note: a single test coupon does not display intensity because intensity is the interpretation of a saturation curve.
3. Intensity Confirmation would involve four test strips and a saturation curve.
4. New saturation curve is required when:
media size / shape violation occurs
equipment modification (hose, nozzle, etc)
within (12) months of the previous saturation curve

Terminology such as the following should be avoided:
1. Peening for Coverage and Saturation
2. Exposure time shall be longer of saturation or coverage
3. Both T and 2T must be within the peening tolerance band


Please think about these issues for discussion at our next meeting May 16-17 in Troy.
Jack Champaigne