Why I don’t like the concept of AQL – A lean manufacturing view

I believe many of you in the manufacturing industry are aware of the concept of AQL or the Accepted Quality Level. This is a statistical method of quality checking. Here how this operates. A random sample is taken from a lot. This sample size is dependent on the lot size and the quality level we expect and determined with a mathematical formula. Then the sample is tested. If the check is positive, that is the number of quality defects found is less than the threshold set by the AQL procedure, then the check is passed. If not it is failed and then the necessary action is taken to rectify the quality defects.

For me as a lean thinker this is little confusing. Fist of all think as a customer. If you are going to buy clothes or some electronic items, you are not going to buy hundreds of pieces. You will buy only one. If you found that piece is damaged then what will be the reaction of yours as a customer. You are not interested on the 99 pieces which might be good. But the product you bought must be up to the quality standards you want. Therefore for you the quality you get is either 100% or 0%.

From the manufacturer’s point of view how this will affect them. How many loyal customers have turned to other brands because they have got one bad product? They say it will take years to make a loyal customer, but minutes to loose them. On the other hand this is an end of the pipe system of quality improvement. That is the quality is not inbuilt to the system. It is imparted by picking the good quality products from an average rest. This can eat up your resources and obviously incur huge costs in to your manufacturing process.

We will calculate the net effect of this concept on your organization in a later post. Remember good quality products are easy to be manufactured and cost less than the bad quality once.