A Quality Management system is often focused on a few key areas: CAPA to identify, correct and prevent the reoccurrence of non-conformances; auditing to ensure processes are using the quality systems effectively; and continuous improvement of the quality system itself. The system encompasses the full supply chain from your suppliers through to customers, as well as training of staff on the systems and processes. Process control is very important to the successful execution of a Quality Management System because it shifts focus from the quality of the end product to the Quality of the process producing the end product. That a particular product is good does not necessarily mean that the process that produced the product is good. This is where process control relates to quality management system.
With respect to CAPA, when non conformances are observed in the quality of the end product, the ideal thing to do is to identify the cause of this non conformance, correct it and then adopt preventive measures to forestall a repeat of the non conformance. This can be done by thoroughly inspecting the quality attributes of the end products. Well, this is true for a process that generates only a few end products in a day. The same cannot apply to a process that generates thousands of end products per hour. For such a process, there is no way all the end products can be individually inspected for non conformance.
Let’s look at a scenario to drive this point home. A universal packaging machine running at a speed of 35 takes less than a minute to fill 25 pouches of 70gm tomato paste. You can do the math to find out how many sachets the machine will generate in an 11 hour shift. Having done that, please imagine the possibility of inspecting all the sachets for non conformances. You can agree that it’s impossible. You cannot inspect your way out of the problem. This is because even the few sachets you inspect cannot be said to be a representative sample of the entire sachets produced. You can only use representative sampling for a process you are sure is under control.
A process that is under control is a process that is stable. A stable process is one which has variations that are in agreement with the upper and lower control limits. To determine the stability of a process control limits must be set and then the process monitored over time and data generated. Analysis of this data determines whether the process is under control or not.
The fact is, without evidence of process control, you have to apply 100% inspection of all the sachets in the scenario mentioned above. This inspection-focused approach is actually a very costly method for preventative action . And it is really not preventative at all! At best, it is reactive, at least when a process is out of control. Even for a process that is in-control, it shows poor foresight, in that we could predict for the in-control process the percent of product exceeding requirements. Failing to address those issues before shipment is simply a poor quality system.
The bottom line is that using such preventative approach increases the cost of production as more and more line inspectors have to be employed so as to achieve uniform quality in all end products. This approach will fail woefully when cost-benefit analysis is applied.
The economic approach to preventative action is process improvement to prevent the occurrence of the nonconformance. This creates the need for a control chart to achieve process improvement, since only a control chart can differentiate between a common cause of process variation, which is built into the process, and a special cause of variation. Reacting to a common cause variation as if it were a special cause increases process variation. The point is that you cannot do meaningful process improvement without a control chart. Failing to recognize that is one of the reasons non-conformances reoccur at some organizations, and their quality department is constantly fighting fires!
Finally, when you talk about improvements to the quality system itself, you focus on internal KPVs (key process Variables) that estimate the system responsiveness to problems. Here again, you need Process Control to differentiate between the expected common cause variation in response and the special causes, since the special causes often provide insight into the dynamics of your systems, and thus the potential for improvement.
You cannot genuinely achieve a continuous improvement in your Quality Management System without employing Process Control.
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