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What is the difference between lean and six sigma - Part 1

When I started my career in the electronics manufacturing during early 90s, six sigma was prevalent where every company wanted to achieve 6 sigma qualities at that time.  According to Wikipedia, six sigma approach was pioneered by Motorola engineers in 80s for the purpose of process improvement.  This methodology focus on data collection and statistical analysis of data, using quality tools for root cause identification and action plan to address the root cause thru phase by phase approach.  It is then follow data analysis using statistic to verify if there is significant follow by standardize action plan to sustain the improvement.  It had become a big phenomenon when Jack Welch made six sigma GE business strategy in 1995.  Several American based multinational corporations followed suit and claimed to have huge saving therefore they are making profit and in business the biggest incentive is profit $.  The word is six sigma  became catch phrase for most company top management,  therefore they “force” their organization to establish six sigma projects everywhere irrespective if  it is a suitable approach or not.

When we approach the 21st century, lean concept practice by Toyota caught the attention of the western world when Dr. Womack et al.  release an iconic book about lean (The Machine That Changed the World) in the 90s.  This book was based on their research in MIT about innovative management and production system use in Toyota.  As lean tools are quite simple and easy to adopt, a lot of company start to use the popular tools such as 5s, standard work, poke-yoke (error proof), kaizen etc., with almost immediate results seen. Thus lean slowly take over six sigma as the groundbreaking tool in production and management.

By the time lean become popular, many organizations had already adopted six sigma “culture” religiously.  At the same time most management does not want to lose out to company who embraced lean which had gain a block buster results,  they start to assimilate lean tools and thus the beginning of term lean six sigma.  Most of the training companies start to rid the wave of trend by offering Lean six sigma course.  
Lean six sigma is a very misguided term as both lean and six sigma are entirely different.  Lean is a culture and six sigma is an approach to reduce variation contributed by poor process control.    Six sigma could be part of lean and not vice versa. 
Six sigma is a structured variation reduction methodology.  I found that a lot of engineers who had study or deploy six sigma still do NOT understand the real meaning of variation reduction.  I would like to use the scenario below to illustrate the meaning of variation reduction.    A manufacturing company found that their product could not customer specification for length of 308.50+/-0.30 (308.20-308.80).  Base on the data collected for product length and plotted on the control chart on the left, it seems some data already exceed or below spec.  The company had to reject the product which does mean customer spec.  The quality engineer decided to use six sigma approach to improve the process in order to produce parts which consistently meet customer spec.  After improvement, the quality engineer collect the product length data and plot in control chart (right).  It was found the product length variation had reduced with tighter control limit as compare to the chart on the left.  It also show that the product length can consistently meet customer spec,  Thus variation of the product length had reduced using six sigma approach.


Six sigma phase by phase approach from define, measure, analyze, improve and control is to ensure that variation quality characteristic of the product is reduce or bring to target per customer spec or both.

Six sigma will only meaningful in a process improvement if useful data are collected diligently with big enough sample size to study the current trend and make a statistical conclusion on the population behavior.  Data collection could focus on one or at the most two parameters which are critical to quality identified through mapping customer requirement.  After improvement, data is collected again and analyzed statistically to ensure the trend had improved for overall population.  Therefore it is very statistical based tactical tools to achieve customer requirement be on objective specification of certain critical quality metric and we must be able to measure the quality metric.

Do refer to this video for more details


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