design_lean_sysm - Massachusetts Institute of Technology...

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Massachusetts Institute of Technology Leaders for Manufacturing Program Use of a Queueing Model to Design a Lean System Prepared as a basis for class discussion by Jamie Flinchbaugh 1 . Toyota has evolved the design of their vehicle assembly plants for 50 years. Much of the work coincided with the development of the Toyota Production System 2 and has evolved through periods of trial and error. In this case, with the corresponding model found in lean_factory.xls , you have the opportunity to use a queueing model to explore the relationship that Toyota discovered when developing the Toyota Production System. A brief explanation of the factory dynamics In a factory using the andon process 3 , buffers are used to create independence among departments attempting to push decision making further down in the hierarchy and create mini-companies within the factory. This is attained by physically promoting significantly more independent departments or line segments than a traditional assembly plant would have, as depicted in the figure. A line segment may consist of somewhere between 20- 40 workstations. Separating each line segment is an accumulating buffer that can hold several work cycles of product. The buffers allow each of the teams to make decisions regarding stopping the line to fix problems. The buffers also increase the independence in operating metrics. These buffers seem to violate the principle that inventory is waste and should be eliminated; instead these buffers de-couple one line segment from another, and thus prevent downtime at one segment from shutting down downstream segments on account of no inventory. 1 Jamie Flinchbaugh is a Fellow in the Leaders for Manufacturing Program, Class of 1998, and is sponsored by Chrysler Corporation. This case is extracted from Implementing Lean Manufacturing Through Factory Design , an MIT Thesis by Jamie Flinchbaugh, 1998. 2 This case requires a working knowledge of the Toyota Production System. An adequate understanding can be reached by reviewing Harvard Business School case study Toyota Motor Manufacturing, U.S.A., Inc. (case number 9-693-019, September 5, 1995, prepared by Kazuhiro Mishina). 3 The andon process: each line worker can signal for help from the team leader if there is a quality problem. The team leader makes a decision on whether or not to stop the line, but if at all possible, will make sure that the quality problem is fixed before leaving the workstation. This results in problem solving closer to the problem and very little rework, resulting in a better quality product.
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