Lean_forward___back - Lean Thinking: A Look Back And A Look...

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Lean Thinking: A Look Back And A Look Forward By James P. Womack It's now been fifteen years since the term lean was given its modern meaning, and more than a decade since my MIT colleagues and I published the book The Machine That Changed the World in an effort to describe lean production to a mass audience. What were we trying to say? What has happened in the interim? And what are the logical next steps? Let's start with what we mean by lean . What does lean mean? Although there are instances of rigorous process thinking in manufacturing all the way back to the Arsenal in Venice in the 1450s, the first person to truly integrate an entire production process was Henry Ford. At Highland Park, MI in 1913 he married consistently interchangeable parts with standard work and moving conveyance to create what he called flow production. The public grasped this in the dramatic form of the moving assembly line, but from the standpoint of the manufacturing engineer the breakthroughs actually went much further. Ford lined up fabrication steps in process sequence wherever possible using special- purpose machines and go/no-go gages to fabricate and assemble the components going into the vehicle within a few minutes, and deliver perfectly fitting components directly to line-side. This was a truly revolutionary break from the shop practices of the American System that consisted of general-purpose machines grouped by process, which made parts that eventually found their way into finished products after a good bit of tinkering (fitting) in subassembly and final assembly. The problem with Ford's system was not the flow: He was able to turn the inventories of the entire company every few days. Rather it was his inability to provide variety. The Model T was not just limited to one color. It was also limited to one specification so that all Model T chassis were essentially identical up through the end of production in 1926. (The customer did have a choice of four or five body styles, a drop-on feature from outside suppliers added at the very end of the production line.) Indeed, it appears that practically every machine in the Ford Motor Company worked on a single part number, and there were essentially no changeovers. When the world wanted variety, including model cycles shorter than the 19 years for the Model T, Ford seemed to lose his way. Other automakers responded to the need for many models, each with many options, but with production systems whose design and fabrication steps regressed toward process areas with much longer throughput times. Over time they populated their fabrication shops with larger and larger machines that ran faster and faster, apparently lowering costs per process step, but continually increasing throughput times and inventories except in the rare case--like engine machining lines--where all of the process steps could be linked and automated. Even worse, the long time lags between process steps and the complex part routings required ever more sophisticated information management systems culminating in computerized
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This note was uploaded on 02/20/2012 for the course MIST 5750 taught by Professor Bostrom during the Spring '09 term at University of Georgia Athens.

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Lean_forward___back - Lean Thinking: A Look Back And A Look...

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