Our company is engaged in sorting and verifying parts. We perform 100% check, just as we are articled, and statistical inspection towards this check, according to the internal method, which is statisticaly attested method of effective check; this process provides greater guarantees and is more effective than 100% check.
Statistical inspection allows inspection of large production batches, using statistical tables, without need of passing 100% check again. It could seem, that 100% check is more effective and gives more guarantee. The opposite is true. Especially by large quantity of checked products or goods, there may be major risk, that 100% check will not be 100% effective.
The worker, who inspects large production batch is checking piece by piece and this work is very monotonous. After some period of time his concentration decrease, other side increase risk of fault. Therefore is suitable engage statistical inspection on 100% checked parts, when is checked relatively small sample of batch, but with enhanced accuracy. Size of the sample is affected by statistical tables, size of batch and by range of guarantee that we provide. Statistical tables are issued according statistical inspection technical standarts.
Maximum possible value of guarantee, when using statistical inspection is 99.96%. There is a question: Why use statistical inspection, when there is no 100% guarantee? It is evident, there can not be 100% guarantee as well as there can not be a unsinkable ship, unshootable plane and so on. Top foreign companies are giving usually 1ppm (one part per milion is deffective) or 2 ppb (one part per bilion is deffective) guarantee.
An example from practice:
Let’s imagine an usuall car, which is consisting from 20,000 pieces. Every piece has 10 critical possible faults, which can occur. By 1 ppm guarantee, there is a deffective piece in every 5th car!!
The 1 ppm or 1 ppb can be guaranteed only when statistical process regulation is implemented directly in the production. When re-check of arrived parts or production batch which has leaved production process is needed, there is no applicable statistical method, that provides more guarantees, than statistical inspection.