There are a number of industrial standards for Six Sigma. ISO 13053 for DMAIC / Six Sigma may be the most familiar to industrial engineers. However, there are other standards such as ASTM E2281-08A for calculating the process capability index, ASTM E2691-11 for determining job productivity and ISO 10006 for applying quality management system principles to individual projects. There are other ISO and ASTM standards for Six Sigma and the DMAIC process improvement cycle. Where are the lean engineering standards in this list?

The short answer is that there are no official “lean” standards as exist for Six Sigma. Six Sigma is numerically based. Each product has an attribute that is measured and captured as a number. These numbers are aggregated into statistics. Six Sigma quality guide posts like the process control limits and process capability index are the result of statistical analysis. The process output may vary with time and quality levels may shift. However, Six Sigma standards are based on a universal set of mathematical equations.

On the other hand, “lean” is a relative concept. Lean in theory is universal. Do more with less. Use fewer materials to make the product. Make a better product that requires less rework on a production line that has fewer rejected final assemblies. Spend less time idling. Perform the same process in fewer steps. Generate less waste. The problem comes into quantification of these goals and their outcomes.

Each “lean” process improvement project is quantifiable. If three tons of waste was generated last month and two tons is generated this month, the process can be considered a success. If the lean engineering project shortens the production cycle or reduces inventory levels, the outcome is measurable. However, each project is different and cannot be directly compared to another.

In contrast, a Six Sigma project that reduces defects from 34 defects per million to 28 per million is universally understood. And the new defect level can be compared to a different production facility with 29 defects per million. It does not matter if the first production facility makes widgets and the second wigs; the final defect rate is the ultimate point of comparison.

In comparison, zero waste is a goal, but it is not possible or practical for many operations. Reorganizing product lines to use less floor space, fewer people and generate fewer delays are all Lean engineering projects. However, it is difficult to compare a project that reduces cycle time to a project that reduces head count or labor inputs.

Zero defects can be a Lean engineering goal as well as a Six Sigma goal. However, lean engineering and Six Sigma are not synonymous. It is quite possible for a leaner production line to have no impact on process quality at all. In fact, lean engineering projects may have an adverse impact on product quality, requiring later Six Sigma projects to reduce the Six Sigma rate. Lean engineering and Six Sigma are not incompatible. Lean Six Sigma attempts to fuse the two concepts, simultaneously reducing waste while improving quality.

The diversity of improvements that fall under the umbrella of “lean” hinders the rise of a universal, statistical measurement for Lean engineering. This in turn makes a “Lean” standard as those that exist for Six Sigma almost impossible.