During college, a variety of quality metrics and measures were discussed in the classroom. Once in industry, you quickly learn the key to an effective Quality Management System is determining which apply best to your application and when and where to utilize them. Here are a number I’ve used over the years.
Pareto Chart of Defects: This is a simple but powerful technique of organizing defects by frequency into a bar graph or table. The most common is first, followed by the second, and so on. The method provides insight into cost prioritizing quality improvement efforts. Typically, the higher the number of defects, the greater the cost to the organization. A good primer on how to create a chart can be found here: https://asq.org/quality-resources/pareto
Defect per Unit (DPU): This is the total number of defects divided by the number of units built, tested, or processed through an individual or set of process steps. You can utilize control charts with this metric (U-chart) to gain a higher level of fidelity with your analyses, identifying when an issue is from ‘special cause’ variation or noise. In addition, it provides managers with another way to gauge cost and insight into product yield if not already measured directly with a simple mathematical formula, e -DPU . A rough expectation of First Pass Yield = e -DPU , dependent on how well reality fits statistical model assumptions.
First Pass Yield (FPY): This is simply the percentage of units able to pass to the next step of the process the first time through. It impacts an organization operationally in a multitude of ways. Yield loss requires rework, or worse, results in scrap. At a minimum, low yields result in higher inventories, increased motion, and over-production/processing. This type of waste is at the heart of what LEAN targets for removal from your operational processes.
Defects per Million Opportunities (DPMO): This is the total number of defects divided by every million opportunities for a defect, also referred to as Part Per Million (PPM). DPMO smooths out product-specific differences by summing all failure opportunities (e.g., number of solder joints) into the denominator. Like DPU, it can be control charted. DPMO provides an understanding of your organization’s baseline process quality level and the opportunity to benchmark your company against others since it’s not product-specific. As a result, management can more easily identify capital and other investment opportunities to improve process outcomes and gauge
company performance against peers.
These four are by no means a complete list. Still, effective and targeted utilization of any or all goes a long way to improving quality levels for your organization.
Rob Wilson, Retired engineering professional and fiction novelist
The author holds a BS in Aerospace Engineering, and an MS in Industrial Engineering funded through NASA sponsored Aviation Human Factors research. After college, his career as a Quality and Manufacturing Engineer in the electronics industry, much of it avionics, utilized a wide range of Lean concepts. He also served in a training capacity for production personnel in 5S and ergonomics and is now a military fiction novelist.