Nadcap (AC7107/7 C, paragraph 6.1.b) NCR - Machining Tensile Specimens

[Kevin H]

After joining a new employer in August of this year, we had a Nadcap audit for the internal testing lab last week. One of the identified nonconformances is confusing me, we sought additional informatin during the audit and didn't succeed in getting anything more than "that is the requirement". We machine round tensile specimens from various size bars and billets to ASTM E8 dimensions. Blank specimens are cut from raw samples using water soluble oil cooled bandsaws. Tensile specimens are turned on CNC lathes, again with water soluble oil cooling, and as one continuous process, from blank to final size. We 100% check the final dimensions on all turned specimens.

The checklist cited was AC7107/7 C, paragraph 6.1.b Paragraph 6.1 states " Blanking is performed by methods which do not distort the material or produce surface sffects deeper than would be removed by final finishing." Subsection b states " A minimum of 0.010" (0.25mm) remains on rough machined surfaces for final finishing operations."

The expectation of the auditor was that we should stop the CNC lathe operation 0.010" shy of final dimensions, check the that a minimum of 0.010" remains, record that dimension, and then resume machining.

My opinion is that blanking is what we do when we cut the rough sample specimen from the mill sample, or when we rough machine a tensile specimen prior to heat treating it (we leave more than 0.010" to machine in this case), not stopping midway through machining to verify that we still have 0.010" left. Our final cut for the reduced section of tensile specimens is significantly less than 0.010" so that we can generate an adequate surface finish.

I'm a little bit lost here as most prior experience was either automotive related (ISO/TS) or ISO 17025 related for testing labs. Does anyone have any experience with an interpreted requirement such as the one cited, or any suggestions in dealing with it? Thanks for any words of wisdom.

 

[dsanabria]

After joining a new employer in August of this year, we had a Nadcap audit for the internal testing lab last week. One of the identified nonconformances is confusing me, we sought additional informatin during the audit and didn't succeed in getting anything more than "that is the requirement". We machine round tensile specimens from various size bars and billets to ASTM E8 dimensions. Blank specimens are cut from raw samples using water soluble oil cooled bandsaws. Tensile specimens are turned on CNC lathes, again with water soluble oil cooling, and as one continuous process, from blank to final size. We 100% check the final dimensions on all turned specimens.

The checklist cited was AC7107/7 C, paragraph 6.1.b Paragraph 6.1 states " Blanking is performed by methods which do not distort the material or produce surface sffects deeper than would be removed by final finishing." Subsection b states " A minimum of 0.010" (0.25mm) remains on rough machined surfaces for final finishing operations."

The expectation of the auditor was that we should stop the CNC lathe operation 0.010" shy of final dimensions, check the that a minimum of 0.010" remains, record that dimension, and then resume machining.

My opinion is that blanking is what we do when we cut the rough sample specimen from the mill sample, or when we rough machine a tensile specimen prior to heat treating it (we leave more than 0.010" to machine in this case), not stopping midway through machining to verify that we still have 0.010" left. Our final cut for the reduced section of tensile specimens is significantly less than 0.010" so that we can generate an adequate surface finish.

I'm a little bit lost here as most prior experience was either automotive related (ISO/TS) or ISO 17025 related for testing labs. Does anyone have any experience with an interpreted requirement such as the one cited, or any suggestions in dealing with it? Thanks for any words of wisdom.

Get clarification from the auditor or cal NADCAP Technical adviser for additional clarifications and expectations.

 

[Kevin H]

Clarifying through the auditor will not work - this is an auditor with whom we had an extended argument regarding temperature control during tensile testing. The room is temperature controlled with a traceable instument indicating room temp, room tempearture at time of test is manually recorded on each printed test report. The work instruction states to not test if room temperature is outside acceptable range and defines the range. He was bound and determined that the only way we could meet Nadcap temperature monitoring requirements was to have a log book. It took intervention from PRI to stop that one, also about 2 people on our side and 3 hours of time. Most of the nonconformances identified were legitimate, and in my opinion some were missed that should have been written. The one mentioned abpve just doesn't make sense to me.

 

[andygr]

Once the audit is done the auditor is not involved.
You are best served by contacting the assigned staff enginer who is reviewing the audit.
While I would try and get it voided the justificaion would be the same for answereing: I would clearly state that at the point the sample blank is placed in CNC it is compliance with the requirement, the blank at this point has more than the req min stock required. Supply the objective evidance supporting that the blank you insert into the CNC is in compliance with the requirement as backup to your argument.
There is no checklist or guidance that requires an inprocess check of the sample once machining has started in the way that your indicat your process works.