Forum for Sampling Practices

Anyone know if after you establish a sample size, would an inspection plan, describing what to inspect and how be a requirement for a sound system?

At places I have worked in the past usual plan was a folder with characteristics listed, sometimes by the QC person sometimes by the ME, QE, or manager.

Seems to me if I was an auditor after asking how to get a sample size, I might want to know what you are going to inspect and how.

Right now I see a hole in our system because it does address critical characteristics and designating them on drawings, but no mention how to proceed with minor things.

Is this flawed??

PS: Thanks in advance for you opinion.

Tumbleweed Tim wrote:Anyone know if after you establish a sample size, would an inspection plan, describing what to inspect and how be a requirement for a sound system?

At places I have worked in the past usual plan was a folder with characteristics listed, sometimes by the QC person sometimes by the ME, QE, or manager.

I think the documentation should include everything necessary to disposition the inspected material. In my opinion it should describe (off the top of my head):

• the product,
• the procedure and/or test method,
• the personnel requirements,
• the quality characteristics and their classifications,
• sample size, frequency, acceptance number or decision limits.
• the definition of a lot,
• what to do with a lot when accepted and if rejected (rework, scrap, etc.),
• and what records are kept of the inspection.

I also think the decision properties of the sampling plan should be documented:

• Acceptable Quality Level (AQL)
• Rejectable Quality Level (RQL)
• Producer's Risk (Alpha)
• Consumer's Risk (Beta)
• the Operating Characteristic Curve (OC Curve)
• the within-lot standard deviation for variables plans
• the source of the sampling plan.

Seems to me if I was an auditor after asking how to get a sample size, I might want to know what you are going to inspect and how.

If I were the auditor I would be suspicious that the plan might not be a reality if I did not see that documented.

Thanks Stan,
I just don't think the current documentation that instructs you to select a sample from a lot is near enough to achieve any high level of certification within our corporation.
Example: Lot of turbine blades come in. Inspector selects sample based on the C=0 plan we use. Probably always 6 parts. Then they do what? Inspect what is convenient? Inspect what you feel like? Inspect per direction of wind blowing.
???
All Characteristics would be the class 4 minor, but I still think you need some documented criteria selected from the drawing based on something other than ones personal experience.
We have a ways to go to get there, but I am sure we will arrive eventually.
Tim