Incoming Quality Control ( IQC )

Incoming Quality Control ( IQC )

Incoming quality control is the process used to validate the quality of a supplied lot of parts or components. The outcome of this process is simply to determine if the lot is “compliant” or not? If yes, accept the lot, and if no, return it to the supplier.

This ‘incoming quality control’ process is extremely important:

1. If we reject a lot and our production system is ‘just in time’, It will de-stabilise the production schedule and could cause other knock-on issues in the workshop (material or component shortages)
2. If we accept a ‘bad’ lot,” It will have a direct effect on the quality of future processes and cause manufacturing or assembly problems.

Either way, the effects are immediate… Given the important nature of this decision there are international standard defining the process, statistical methods and rules. These are found under the term “Incoming Quality Control” and the standards are ISO2859 or ISO3951.

Incoming Quality Control Principle

The principle is to validate a lot by checking a sample of pieces (we can’t check 100% of the parts!). Based on the risk that we decide to accept (depending on the critical nature of the products), we will decide the precise number of parts to be tested (sample size) and the acceptance criteria (e.g. out of a batch of 1000 pieces, we check 20, and if there are 2 or more that are non-compliant, we refuse the lot)

On a practical level, the terms used are:

1. AQL: Acceptable Quality Level – or –
2. NQT: Quality Level Tolerated

There are 2 types of risk:

1. Accept a bad lot  (which is a risk to the consumer)
2. Reject a good  (risk to the producer/supplier)