The AQL lot acceptance sampling plans are in place to screen out nonconforming material. While it is better to work upstream to improve processes to reduce the opportunities for nonconforming material, we work with the processes as they exist and must therefore have some mechanism to manage the risk of nonconforming material.
The Lot Acceptance Sampling schemes (AQL sampling plans) have several purposes:
They were developed to allow the use of sampling inspection as an alternative to constant 100% screening, but in a way that manages the probability of making a wrong decision regarding acceptance or rejection of a lot. Resources and Risk are balanced in a quantitative way.
They are built to protect the customer from receiving a lot/batch with unacceptably high levels of nonconforming product.
They also protect the supplier from the possibility of unnecessarily rejecting a lot/batch with acceptable levels of conforming material.
They provide an economic incentive to improve conformance ('quality') of upstream processes to reduce the opportunities for defective/nonconforming material.
The O-C curves provide a measure that provides the mechanism to quantitatively balance risk and resources.
The sampling scheme switching rules either tighten or reduce the inspection burden based on increases or decreases in nonconforming material. SHOULD BE USING THE SWITCHING RULES, WHICH WILL REQUIRED TIGHTENED INSPECTION IF 'QUALITY' (CONFORMANCE) BECOMES POOR
Need to adhere to the sampling plans that were agreed and specified, and that are documented in procedures. If do not adhere to a sampling plan, at all points in their value stream, then that lot should not be allowed to ship until it has been properly screened using the full, agreed sampling plan.
If a lot/batch of finished product is not subjected to the agreed, full sampling plan, then it should not be allowed to ship until it has done so.
If any batch of material, components, or sub-assemblies have not been screened with the full, agreed AQL sampling plan then they should not be released for production until this has happened.
If we allow a lot to ship without passing the full and agreed sampling plan, then we impose risk on ourselves and our customers. If we allow our own team to make up for the deficit in a suppliers resources that are needed to accomplish inspections, then we have substituted our resources for their own. In either case, what is the incentive to improve the upstream processes?
The Lot Acceptance Sampling schemes exist to protect a company from receiving nonconforming material and they provide an economic incentive to improve the quality/conformance of product and materials upstream in the value chain. Allowing them to be altered or circumvented reduces the incentive to improve and increases our exposure and risk.