The C in DMAIC is about controlling the “vital few” variables, typically the top two or three, that we identified in the Analyze and Improve phases of the project.
Permanent product or process design changes typically require no ongoing human intervention, and are the best types of improvements to consider. For example, if a radius is added to a molded component to reduce stress and prevent cracking, we know that the radius will remain in the mold tooling for the life of the tool, and will need no ongoing monitoring. Similarly, if a software change adds an error-proofing feature to a customer service system, the change will be inherent in the software and will not need to be monitored. These are two examples of fundamental product or process redesigns that require no ongoing audits or maintenance.
In situations where permanent process or product changes cannot be made, error-proofing should be implemented wherever possible, and error-proofing device functionality must be monitored as part of the quality system for the long run. For example, if an adhesive curing process takes place in an oven, and new temperature settings were identified in the Improve phase, temperature alarms could be installed on the oven to alert the operator the temperature drifts outside acceptable limits.
It is very helpful to run a PFMEA (Process Failure Modes and Effects Analysis) on each critical process step, thinking through all possible failures and developing countermeasures where risks are unacceptably high. PFMEA’s are one of the strongest, prevention-based DMAIC tools.
Lastly, the control plan is a key document that fully describes all in-process inspection and control points, and is considered a basic element of the quality system.