The content of the QA matrix
The QA matrix (see example below) is broken down into 3 parts described below.
1-the list of defects related to the product
This list includes all the defects known to date, from the most minor to the most critical. The designation of each defect must use standard terminology to the company that everyone understands.
2-quality criteria quantified and classified
Faults are classified in function of their criticality. This criticality depends on the company and the sector of activity but here is an example:
- Minor faults: faults that do not require a line stop. The problem can be treated without stopping the machine if it is not necessary. This type of defect does not cause customer claims.
- Major faults: faults which require a stop of the machine until the problem is resolved but do not require a blockage of the production batch .
- Critical faults: faults that require a line stop and a blockage of the batch being produced. This class of defects corresponds to any anomaly of the finished product likely to generate a customer claim.
3-locating the origin of the defect
Each column header corresponds to equipment or subsets of the equipment. The challenge is to cut them in the most logical and simple way to facilitate maintenance and interventions.
For each of the faults, markers are placed in the boxes corresponding to the sets or sub-assemblies where a failure generating the defect can occur.
In order to refine the diagnosis given by the tool, different markers can be used to differentiate the probability of occurrence or origin of the defect. Two, three benchmarks (low, medium, Strong…), or more, but be careful to be limited to a number that allows to differentiate them clearly without risk of creating confusion or misunderstanding.
Building the QA matrix
Building the quality matrix is a long and ” never ending ” process. Throughout the life of the equipment, defects are removed but new ones appear. So we have to live the matrix so that it reflects the reality of the facts and all can rely on it to intervene.
The first version of the matrix is built in the following way:
- Make an inventory of all the characteristics qualities required for the product. From the original specifications as well as from the product history. These elements are expressed with measurements, measurement system, ranges of tolerances…
- From the mapping of the process, we will determine the phase or phases of the process which influence these characteristics by specifying the possibility of detection of the anomaly on the process or the equipment and the level of prevention of the defect put in place.
- Train staff to the QA matrix and set it up in a visual way on the line.
- To live the matrix as the problems eradicated and the new problems.
R. Lindqvist, L. Mattisson, N. Josefsson, J. Salmela (2011) – Implementation of the quality assurance matrix and methodology