Statistical Quality Control (SQC) SQC also known as SPC(statistical process control) is a mathematical technique to graphically display the probability of defects occurring. SQC charting can tell you if a process is producing product within tolerance or not - hence it can be used to decide if a process is capable. Mathematical capability analysis is a tool in the six sigma methodology
The Shingo System Shigeo Shingo, the co-developer of the Toyota production system, has argued that SQC methods do not prevent defects. Although they provide information to tell us probabilistically when a defect will occur, they are after the fact. The way to prevent defects from coming out at the end of a process is to introduce controls within the process. Shingo develops the concepts of source inspection and Poke Yoke to achieve zero defects. Another key contribution from Shingo is SMED - single minute exchange of dies. Originally developed for large presses, this methodology can be used for any process where there is a set up before production can begin. The methodology helps people reduce set up times from hours down to less than 10 minutes.
Two Systems for Improvement
Both the Lean and the Six Sigma methodologies have proven that it is possible to achieve dramatic improvements in cost, quality and time by focusing on process performance. Whereas Six Sigma focuses on reducing variation and improving process yield by following a problem-solving approach using statistical tools, Lean is primarily concerned with eliminating waste and improving flow by following the Lean principles and a defined approach to implement each of these principles. However, using either one of them alone has limitations: Six Sigma will eliminate defects but it will not address the question of how to optimize process flow; and the Lean principles exclude the advanced statistical tools often required to achieve the process capabilities needed to be truly 'lean'. Most companies embarking on Lean and Six Sigma create their own combination - picking and choosing which elements to emphasize. However, all companies must embrace the basic methodology of each system.
Six Sigma (6σ)
"This big myth is that Six Sigma is about quality control and statistics. It is that - but it's much more. Ultimately, it drives leadership to be better by providing tools to think through tough issues. At Six Sigma's core is an idea that can turn a company inside out, focusing the organization outward on the customer." - (Jack Welch, Straight from the Gut, New York: Warner Business Books, 2001). Under Jack Welch GE spent over a billion dollars training its professional workforce in the concepts of Six Sigma. Now, virtually every professional in the organization is qualified in Six Sigma techniques.
A process that is in Six Sigma control will produce no more than two defects out of every billion units. Six Sigma uses many statistical tools but applies them in a clear 5 stage project oriented cycle: Define, Measure, Analyze, Improve, Control (DMAIC). Tools used in the Six Sigma approach include Flow charts, Run charts, Pareto charts, Check sheets, Cause and effect diagrams, Opportunity flow diagrams, Control charts, Failure mode and effect analysis, Design of experiments
In post World War 2 Japan, Taichii Ohno and Shigeo Shingo were sent by Toyota to study the Henry Ford car production system. The two Toyota Motor Company executives picked apart the Ford Motor Company's production system, honing in on Ford's shortcomings and making adjustments. One of their improvements was to design an assembly line that could accommodate new products, something they believed Henry Ford had overlooked. Accordingly, Toyota incorporated equipment changeovers into its process and got timing down to a fine science, reducing set up times from hours to minutes and seconds. This allowed for the production of smaller batches and eliminated excess inventories. The buzz phrases "just-in-time" and "lean manufacturing" were born.
Lean is aimed at the elimination of waste in every area of production including customer relations, product design, supplier networks and factory management. Its goal is to incorporate less human effort, less inventory, less time to develop products, and less space to become highly responsive to customer demand while producing top quality products in the most efficient and economical manner possible. The keys to Lean are understanding where the value in your process lies, iIdentifying all non value adding activities as waste and devising plans to remove the waste from the process. Flowcharting is a core tool of Lean - as flowcharting provides a visual image of a process enabling waste identification to take place. This flowcharting is known as value stream mapping. Lean considers that there are 7 wastes - Defects, Overproduction, Transportation, Waiting, Inventory, Motion, Processing (DOTWIMP). The worst of all the 7 wastes is overproduction because it includes in essence all others and was the main driving force for the Toyota JIT system Ohno and Shingo were smart enough to tackle this one to eliminate the rest.