Lean and Six Sigma Make a Good Team

Lean and Six Sigma concepts are not new. In fact, they have both been in use since the 1980s. Both concepts also have proven their value in helping companies improve their processes, with lean initiatives focusing on eliminating waste and Six Sigma on eliminating process variability. Companies approach the introduction of each concept differently. Some will start with lean, as they view it as easier to learn and implement throughout the facility, while others find it more important to get a specific process “under control” and train employees to use Six Sigma tools to make that happen. Regardless of your approach, it is important to recognize that lean concepts and Six Sigma work well together.

If we start using lean tools such as the 5S system of workplace organization, standard work, one-piece flow, quick change-over, pull systems and total productive maintenance (TPM) to eliminate the eight “deadly” wastes (defects, overproduction, waiting, non-value-added processing, transportation, inventory, motion and employee underutilization), we will achieve considerable improvement, as these wastes consume a great deal of time and effort in any company. Lean’s focus on reducing non-value-added time leads to measurable service-level improvements (on-time delivery, lead times, process throughput) and cost savings. Yet the remaining value-added-time—where form, fit and function of a product or service are actually created—may present further opportunity for improvement if the processes employed are not consistent or repeatable. Here is where Six Sigma can augment lean.

Using the generally accepted Six Sigma methodology and appropriate quality management tools, we can improve the processes where value is added. Following this DMAIC methodology, we:

• Define the system. Assure that the needs of the customer are understood, establish metrics, identify desired outcomes. 

• Measure the current process. Determine key aspects of the process, collect relevant data, calculate the “as-is” process capability (its ability to produce outputs within specified limits).

• Analyze the data. Review all factors that contribute to the process, establish dependencies, determine cause-and-effect relationships, discover root causes (not just symptoms).

• Improve the current process. Employ appropriate techniques (design of experiments, mistake proofing, visual/audio controls), create a new process, pilot the new process to establish process capability.

• Control the new process. Ensure any deviations are corrected before they result in defects, initiate corrective action programs, employ control systems (statistical process control, production status boards), continuously monitor the process.

The goal of this effort is to establish a process in which the likelihood of defect-free outcomes is increased substantially. By definition, a Six Sigma process is one that produces no more than 3.4 defects per million opportunities, a yield rate of 99.99966 percent—certainly a lofty goal, but one that has been achieved in numerous industries.

Quality management tools are used to support the Six Sigma methodology’s drive toward defect-free outcomes. Some of the more commonly used tools are:

• Histograms – a bar chart of a frequency distribution (a tabulation of data arranged according to size), ideal for presenting a visual depiction of collected data. The chart may show that the data is normally distributed, where the average result lies in the center of the data points (giving the chart a bell-shaped appearance), or not normally distributed, where the average lies closer to one grouping of the data points (this is often called a “skewed” distribution and is actually more common than a normal distribution). 

• Pareto charts – show the frequency of occurrence of various possible outcomes. 
Pareto is often referred to as the “80/20 rule,” where 20 percent of the input, effort, customers, etc., will yield 80 percent of the output, gain, sales, etc. A Pareto chart helps to separate the “vital few” from the “useful many” and is most useful in prioritizing tasks to be completed.

• “Five Whys” – a technique to assist in arriving at the root cause of a problem and not just a symptom of that problem. This technique involves repeatedly asking “why” questions until the underlying reasons for an occurrence are revealed. This approach can help identify solutions to problems and initiate corrective action.

• Cause and effect diagrams (also known as “fishbone diagrams”) – a graphical technique for analyzing a process problem when there are many possible causes of the problem. The objective is to find the “causes of the causes” and ultimately determine corrective actions or required process changes. This technique can be time-consuming, but offers the benefit of recording all possible factors that contribute to a problem, so they can be discussed, evaluated and prioritized.

Whether your company starts with applying lean techniques, the Six Sigma methodology or a combination of both, you will be on a proven path to continuous improvement.