In addition to setting the AQL, the buyer should choose inspection levels.
The difference between the inspection levels listed below is the number of samples to inspect.
The different inspection levels
Normal inspection (or level-II inspection): It is the default level, and it is chosen for 90%+ of inspections.
ISO 2859 definition for “normal inspection”:
“Normal inspection is used when there is no reason to suspect that the [quality level] differs from an acceptable level.”
“Unless otherwise specified, level II shall be used. Level I may be used when less discrimination is needed or level III when greater discrimination is required.”
Tightened inspection (or level-III inspection): more samples are checked. This inspection level is used for suppliers that recently had severe quality problems, or for high-value products.
ISO 2859 definition for “tightened inspection”:
“Use of a sampling plan with an acceptance criterion that is tighter than that for the corresponding plan for normal inspection.”
Reduced inspection (or level-I inspection): fewer samples are inspected. This inspection level is appropriate when the client is confident that the quality of the products is acceptable.
Note: it is never appropriate for a re-inspection following a refusal.
ISO 2859 definition for “reduced inspection”:
“The discriminatory ability under reduced inspection is less than under normal inspection.”
There are also four other “special” inspection levels. They are used in cases where the inspector can only check very few samples. However, the risk of accepting products of bad quality is higher.
For example: if the inspector has to do a very particular checking that takes him a long time per product (e.g. dismantling a radio system to see all the components, check the welding…).
Another example: if a particular test ends up in the destruction of the product (e.g. undoing the stitching of a garment to check the cut pieces against the client’s patterns).
ISO 2859 definition for “special inspection”:
“Four additional special levels, S-1, S-2, S-3 and S-4 […] may be used where relatively small sample sizes are necessary and larger sampling risks can be tolerated.”
Sofeast’s Supplier Quality Engineers and Technicians Consulting can help you to use the right levels in your product inspections and reduce quality risks in many other ways besides.