J. R. Casey Bralla
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Essential for Survival!
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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.
|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.|