Six Sigma and Lean Manufacturing

by: Thomas Pyzdek

Topic: Six Sigma Lean Manufacturing

2/17/00

Six Sigma and Lean Production

Thomas Pyzdek

January 2000

I am sometimes asked to explain the difference between Lean Production and Six Sigma. The question is usually phrased something like "Should I use Six Sigma or Lean Production methods to improve my operations?" Before I tell you my answer to this, let me provide a brief background on these two approaches to process improvement.

Lean Production is based on the Toyota Production System (TPS). It usually includes the elements shown in figure 1. When properly implemented, a Lean Production system can dramatically improve productivity compared with traditional batch-and-queue production systems, in some cases by 95%.

Figure 1: Elements of Lean Production[1]

Lean Production's origins date back to the post-WW II era in Japan. It was developed by Taiichi Ohno, a Toyota production executive, in response to a number of problems that plagued Japanese industry. The main problem was that of high-variety production required to serve the domestic Japanese market. Mass production techniques, which were developed by Henry Ford to economically produce long runs of identical product, were ill-suited to the situation faced by Toyota. The Lean approach (the term Lean was coined in the early 1990's by MIT researchers) systematically minimizes waste--called muda--in the value stream. Muda includes all types of defective work, not just defective products. Wasted time, motion, and materials are also muda.

Ok, so how does this relate to Six Sigma? To make a valid comparison we need a new definition of quality itself. I propose the following definition:

Quality is a measure of value added by a productive endeavor. Potential quality is the maximum possible value added per unit of input. Actual quality is the current value added per unit of input. The difference between potential and actual quality is muda.

By defining quality in terms of value rather than in terms of defects we can see that Six Sigma quality involves a search for ways to reduce muda. Six Sigma is:

A general approach to reducing muda in any environment.
A collection of simple and sophisticated methods for analysis of complex cause-and-effect relationships
A means of discovering opportunities for improvement

Lean offers a set of solutions to muda in a high-variety production environment. Six Sigma applies to the problems addressed by Lean, but it also seeks other problems. However, since both Six Sigma and Lean address the problem of muda, there is a great deal of overlap. The two approaches should be viewed as complementing one another. Some examples of this synergism are shown in Table 1.

Table 1: The Synergy of Six Sigma and Lean

LEAN	6σ CONTRIBUTION
Established methodology for improvements	Policy Deployment Methodology
Focus on customer value stream	Customer requirements measurement, Cross-functional management
Project-based implementation	Project management skills
Understanding Current conditions	Knowledge Discovery
Collect product & production data	Data collection and analysis tools
Document current layout and flow	Process mapping and flowcharting
Time the process	Data collection tools and techniques, SPC
Calculate process capacity and Takt time	Data collection tools and techniques, SPC
Create standard work combination sheets	Process control planning
Evaluate the options	Cause-and-effect, FMEA
Plan new layouts	Team skills, project management
Test to confirm improvement	Statistical methods for valid comparison, SPC
Reduce cycle times, product defects, changeover time, equipment failures, etc.	7M, 7 QC, DOE

In my opinion, if you are facing a situation where Lean solutions can be used (high variety production), you should not hesitate to implement Lean. Lean offers proven solutions to known problems. Six Sigma methods will help you with Lean, and they will help you continue to improve when it is time to move into administrative and other non-production areas.

Thomas Pyzdek is author of The Complete Guide to Six Sigma (www.qualityamerica.com) and a consultant in Six Sigma. Visit his web site at www.pyzdek.com for more information on Six Sigma.

[1]Adapted from JIT Factory Revolution, Hiroyuki Hirano, Editor-in-Chief, 1988, Productivity Press