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1+1 = Zero Defects
Reduce defects, partner your control plan with PFMEA
by Chris Hermenitt
A control plan is a document that helps you plan and allows you to control the products you make and the processes used during the creation of those products. It consists of the product description and the process characteristics necessary to ensure the quality of the final product.
This information is an important addition to the detection and prevention controls listed in the process failure mode and effects analysis (PFMEA), and the two documents are meant to be used together. Because it is a supplement to the PFMEA and not a replacement, everything on the control plan must be shown on the PFMEA: It explains the why and what of the process and product controls, while the control plan explains how they should be implemented, how often, how many and the what if analysis.
Consider an example of the relationship between the PFMEA and the control plan. Specifically, the process of molding and injecting the plastic for a simple transparent ruler. The overall size of the ruler is important for the customer. If the ruler is too small or too large, it will be inaccurate. If you look at the PFMEA for the ruler, it will list various failure modes with the effects of the failures and their causes, and it will list the prevention controls and the detection controls.
Process and results
Prevention controls focus on the process and detection controls focus on the processes’s results. In this example, we consider a prevention control, monitoring the machine settings, and a detection control, measuring the size of the ruler.
The control plan would provide more information and connect the controls to the process and product itself. On the control plan, the machine settings would be a process characteristic, and the thickness of the ruler would be a product characteristic. The control plan includes the process and product specifications (shot size—5 grams, ruler thickness—3 millimeters), measurement techniques (machine display, calipers) and the sample sizes and inspection frequencies (once per shift, five pieces per hour).
The control methods (machine setting check sheet and statistical process control chart) and reaction plans also are included in the control plan. The reaction plans give instructions regarding how to react to a failure (quarantine the product since the last inspection and notify the supervisor).
The control plan gives detailed instructions to the employees about how to implement the controls defined in the PFMEA, ensuring alignment between the PFMEA, the shop floor and proper execution of the controls.
Because product quality is only an output of the process, controlling the process characteristics is more important than controlling the product characteristics. This is how pairing the control plan with the PFMEA can save an organization money: They identify the prevention controls and implement them by monitoring the process itself.
This is completely different from isolating your focus on the process results (product quality). In this example, if the relationships between the machine settings, other process inputs and the product characteristics were completely understood, any defective products could be avoided. This is a method to reach zero defects and reduce costs.
Control plans, in conjunction with PFMEA, can be used to prevent problems and save organizations money by identifying prevention controls and ensuring their successful implementation.
Chris Hermenitt is the vice president of quality North America for Henkel Adhesive Technologies in Madison Heights, MI. He is a doctoral candidate at Northcentral University in Prescott Valley, AZ, and he earned his master’s degree in engineering management from Eastern Michigan University in Ypsilanti. He is a senior member of ASQ and an ASQ-certified quality technician.