Standards Forum

in Vol. 19 - May Issue - Year 2018
Mandatory Application of SAE J2597 Computer Generated Shot Peening Saturation Curves

A saturation curve produced by SAE J2597 compliant software

Paul Huyton

September 2017 saw the reaffirmation of SAE J2597 Computer Generated Shot Peening Saturation Curves. Standards issued by the SAE committees are reviewed at a five-year frequency; if the relevant committee decides that the standard is still relevant and no changes are required, it is reaffirmed.
The procedures for using the Almen strip test to construct a saturation curve are defined in SAE J443, currently at the August 2017 revision. This standard permits the use of a manual technique in constructing the saturation curve. However, paragraph 3.2 of J443 does state:
"The use of computer-generated saturation curves that comply with SAE J2597 is recommended."
It should be noted that this is a recommendation but not a requirement, so manual techniques may be acceptable. However, it is the expected practice in modern shot peening facilities that software should be used to provide consistent accuracy in determination of the process intensity value using a saturation curve. For some facilities, it is now becoming mandatory.
For Nadcap-approved facilities, if software is used to generate the saturation curve, it must be compliant to J2597. This requirement is already present in the checklist AC7117/2 for Automated Peening. However, the Surface Enhancement Audit Handbook, 9 March 2018, contains this general statement: “For Nadcap the curve solver shall be SAE J2597 compliant.” The general checklist AC7117 rev.C, valid from 17 June 2018, also requires solver software to be J2597 compliant. So compliance to J2597 will be mandatory for all of the peening techniques relevant to Nadcap approval from that date.
So when selecting the software for saturation curve solving, there must be verifiable evidence that it is compliant to SAE J2597. This may be found in a statement from the software supplier on the product or on the supplier’s website. A shot peening facility should be able to provide this evidence in the case of an audit. When compliance to J2597 is a customer requirement or for Nadcap accreditation, a failure to provide this evidence will result in a non-conformance being raised.
Another approach to compliance can be to obtain the standard SAE J2597 and to use the ten datasets it contains to validate an existing software programme (see the next paragraph). This may need to be done if the software is built-in to the shot peening machine control system and not “stand-alone” software. All this data should be retained so that it can be provided to auditors or customers.
The most significant part of SAE J2597 are the ten datasets, which are used to validate the software. Each dataset contains four or six arc heights, their related exposure times or inverse feed-rates and a target intensity value. These arc heights and exposure times must be input to the software and a result obtained for the intensity value. In order to conform to the standard J2597 the output intensity value from the software must conform to the target value ± 0.001 inch (± 0.025mm).
The standard also gives examples of suitable algorithms for the software, applicable in various circumstances:
a) a four data-point curve,
b) for use with French specification NF L 06-832,
c) a curve constructed with more than four data-points.
However, these are example algorithms and others are permitted if they provide results conforming to the target intensity ± 0.001 inch for all of the ten datasets.
It should be noted that using the software is likely to give a slightly different result than that obtained by a manual technique. So if moving from a manual to the computer-generated technique, all the saturation curves should be recalculated with the software and checked for conformance to the customer’s intensity requirements. It is recommended that new Almen strip tests are also undertaken so that the process intensity value is completely validated at that particular date.
The use of computer-generated saturation curves conforming to SAE J2597 provides consistency across the industry and repeatability of the technique to obtain shot peening process intensity. A reputable source for the software should be used and shot peening operators can, if required, validate the output by use of the datasets in SAE J2597 September 2017.

For questions contact paul@mfn.li

Standards Forum
by Paul Huyton,
MFN Course Director World Wide
more information at www.mfn.li/trainers
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