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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 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 | 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. |
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. |