Many companies confuse Statistical Process Control with control charts... Control charts are just the tip of the iceberg. They are merely a tool for achieving the objective of bringing the process under control, mastering sources of variability to achieve better quality at a better price.
Here are 5 tips for using control charts in production:
Choosing the right criteria
A part in a workshop usually has many criteria to be monitored. For obvious reasons, and especially when using manual cards, it is unthinkable to place all criteria under control cards. The basic rules for choosing which criteria to monitor are as follows:
- The criterion must be indicative of product quality.
- Control charts should be the only means of controlling the process, and should not be superimposed on any other system. The sampling frequency required by the criterion must therefore be compatible with the filling of control charts.
- The chosen criterion should preferably be controllable, i.e. in the event of drift, the operator should be able to bring the criterion back within acceptable limits.
Automate the filling of control cards
When a control card is set up, it must become the only means of controlling the process. A practical problem arises when the frequency of checks becomes too high, making it difficult to fill in the card manually. In such cases, data capture and processing must be automated.
Using software
Writing on paper retains some of its pedagogical virtues, which it would be unwise to sweep aside with too much computerization. However, with advances in software and access to IT tools in production environments, it would be a shame not to computerize the use of control cards. Here are three objective reasons:
- Card tracking will then be integrated into the overall management of production resources.
- The control frequency required for piloting is too high to be managed manually.
- Too many parameters to monitor.
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Recalculate limits
A problem often encountered when applying control charts concerns the recalculation of limits. As a reminder, the limits depend solely on the short-term dispersion of the process. Thus, a stabilized process whose dispersion does not change over time will always give the same limits. Limits should be recalculated when it is certain that short-term dispersion has changed.
Bringing the Statistical Process Control (SPC) approach to life
Just as easy as it is to set up an approach, it is equally difficult to keep it going for many years without losing effectiveness. Some companies even reach the point where, several years after implementing the approach, they have to start all over again. This cycle of "implementation" then "running out of steam" then "implementation" again is unacceptable, as it is costly for the company. Here are a few tips to help you avoid this process of wear and tear:
- Set up a steering committee and a person dedicated to monitoring the process.
- Train staff not only in MSP tools, but above all in the principles and culture of the underlying process control.
- Respect the method.
- Rigorously monitor capabilities.
- Implement an action plan when capabilities are insufficient.
- Set up an audit system to ensure that there are no drifts over time.
- Publish success stories on a regular basis