BACK TO BASICS
The Forgotten “C” in DMAIC
by Phillip L. Rybarczyk
When using Six Sigma’s define, measure, analyze, improve, control (DMAIC) approach in an improvement project, quality practitioners often either neglect or poorly execute the control stage, jeopardizing the sustainability of any improvements acquired from the project.
In a manufacturing environment, it is important to create or revise a process’ SOPs to incorporate the changes that contributed to the improvement. More importantly, once the SOPs have been created or revised, all personnel affected by the procedural changes must be trained or retrained, and the training needs to be validated for understanding. Some type of testing should also be performed to determine whether the procedural training has been effective and the content is understood.
To maintain consistency in the process and sustain the improvements, changes to the actual process, such as tooling requirements, cycle times, materials or suppliers, must be documented on the process routings, work orders, engineering drawings, approved supplier listing and other related documents.
A process control plan (PCP) must also be developed, implemented and used. And if one already exists, it must be updated. Either way, the PCP should document the controls to be implemented, from the receipt of incoming raw material to the final shipment of the completed product.
Table 1 shows a standard, formal PCP for XYZ Co., a widget manufacturer. Such plans always list:
- Which quality characteristics to control.
- Which tolerances to maintain.
- The frequency of inspection.
- Which sample sizes to take.
- Which instruments and analysis methods to use.
on what to do if nonconformances are detected.
This standard PCP can then be modified based on what is most effective for the manufacturing or service organization. As the process is continually improved, the PCP should also be updated to incorporate the process changes needed to sustain the improvements.
A PCP is a formal document that can be used to control critical characteristics of a process to sustain a continuous improvement effort, maintain conformity of a product and ensure the “C” in the DMAIC quality improvement approach has integrity and meaning.
- Juran, J.M., and Frank M. Gryna (editor), Juran’s Quality Control Handbook, fourth edition, McGraw-Hill, 1988.
PHILLIP L. RYBARCZYK is a quality engineer at Static Control Components, Sanford, NC. He is a Senior Member of ASQ and an ASQ certified quality engineer and manager and a Six Sigma Black Belt.