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Lean & 6-Sigma


  1. LSS: Peanut Butter & Jelly
  2. 6-Sigma Summary
  3. Lean vs. 6-Sigma
  4. When to Use Lean? When to Use 6-Sigma?

LSS: Peanut Butter & Jelly

Lean & 6-Sigma are two very different - but complimentary - disciplines that go together like peanut butter & jelly. Often abbreviated as "Lean Six Sigma" or "LSS", they are frequently taught as a single discipline. A Lean practitioner will often use 6-sigma tools, and vice-versa.

Lean is a series of tools focused on finding and eliminating waste. It typically emphasizes simple things that can make major improvements to an operation. It stresses visual controls and very low-tech solutions to problems. 6-Sigma is a statistical science that tries to identify and eliminate variation. While variation is often a cause of waste, Lean takes a more expansive view than 6-Sigma. Lean is the "macro" approach, while 6-sigma is the "micro" approach.

6-Sigma Summary

6-Sigma is a set of tools that helps to reduce variation in a process. The name derives from the term for statistical standard deviation, and our desire to have a process run with +/- 6 standard deviations of the specification limits. So, for example, assume we are making automobile pistons, and our specification is +/- 0.0002 inches on the diameter. A 6-sigma capable process for grinding the cylinder diameter would ensure that no more than 3.4 cylinders in every million are outside this tolerance (when under "normal" manufacturing processes).

6-Sigma methodology, abbreviated by the acronym DMAIC (Define, Measure, Analyze, Improve, and Control) is a fairly rigid framework for identifying, analyzing, and improving the process to reduce variation. It utilizes a large number of sophisticated statistical tools to determine what creates variation, and this allows us to then development countermeasures to reduce it.

Lean vs. 6-Sigma

How do Lean and 6-Sigma differ? How are they similar?

Lean 6-Sigma Comparison Comments
Eliminate Waste Eliminate variation Variation is often a cause of waste. Lean looks more broadly at waste, while 6-Sigma looks more narrowly
Improve the Flow of materials along the entire Value Stream Improve the Processes that constitute the Value Stream Lean is mostly concerned with what happens between operations, while 6-Sigma is concerned with the operations themselves.
Make disruptions to Flow "self correcting" Make the process more tolerant of variation In a Lean world, the flow is constant and any disruption to that flow is obvious, and therefore likely to be easily fixed. In a 6-Sigma world, the individual processes produce a consistent output, despite changes in the input.
Standardize Procedures & processes through 5S & visual controls Standardize Procedures and Processes through documentation Both have the objective of improving standardization.
Visual Mathematical Lean is easier than 6-Sigma.
Simplify everything Potentially make things more complex Both Lean and 6-Sigma would prefer things simplified, but 6-Sigma is generally more willing to allow for complexity if it helps reduce variation.
Use the skills, experience, and common sense of people doing the operation Leverage the skills and experience of people doing the operations with highly trained experts Lean is very easy to do. 6-Sigma takes extensive training.
Compress Time None Unique to Lean.
Reduce Inventory None Unique to Lean.

When to Use Lean?
When to Use 6-Sigma?

Lean and 6-Sigma are tools. Like all tools, some are useful in some situations, and some in others. Here's are chart showing which types of problems are best attacked with Lean, and which with 6-Sigma.

Problem Lean Tools 6-Sigma Tools
Associates spend too much time looking for special tooling when an unusual product has to be run. 5S. Establish standard locations for all tooling. None
A molding process always creates scrap for the first 10 minutes of production until the molds are warm. Standard Work instructions to preheat the mold before use. Design of Experiments (DOE) to determine the optimal molding parameters with the widest temperature range so the process is tolerant of temperature changes.
Delivery lead time is longer than desired. Value Stream Map the process and develop measures to improve Flow and reduce Work In Process (WIP) None
A turning process produces up to 10% scrap, which varies with the skill of the operator. Create visual work instructions, with emphasis on how and when to make adjustments. Use Statistical Process Control (SPC) charting and Out of Control Action Plans (OCAPs) to determine when to make process adjustments.
Production schedules need to be revised several times per day for each of several departments. Use FIFO lanes and continuous flow so that only a single point has to be scheduled. Build a Kan Ban system to eliminate that schedule. None
Different inspectors measure the same parts and make different determinations about whether a particular lot of product is within specifications. Create Work Instructions to show how to make measurements. Ensure all inspectors are using the same gages and same methods. Conduct a formal Gage study to determine if the gages are capable of making the measurements. Identify variation caused by the inspector. Potentially develop a better gaging system.