SPC is one of the oldest tools in quality management and one of the most used. Unfortunately we have to say very often misused and therefor not bringing all potential benefits. As long as a process is not statistically stable it is not predictable so by definition not controlled. With the help of control charts we can detect instabilities, find the causes and remove them.
Once this has been achieved we can use the control chart to keep the process stable. Only now can we work on process improvement (reducing variation) and increase process capability.
in our courses on SPC and capability we emphasize some requirements for successful implementation. The problem with SPC is not the theory but the correct use of the method. Important attention points are:
- SPC can only be successful if the organization is willing to react immediately to signals form the control chart.
- SPC is extremely preventive if process parameters are followed up and controlled with a control chart. Integrate with DOE – Design Of Experiments.
- Pay enough attention to statistical stability. Only then the calculated control limits and the attached capability have predictive value.
- Use control chart signals also for other purposes (for instance to perform condition based maintenance).
- There are different types of control charts: use the right one at the right time, but don't make matters unnecessarily complicated.