Manufacturing Handbook
University of Michigan OM
Professor R. Eugene Goodson

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SUBJECT: Lean Production/ Lean Manufacturing

ALPHANUMERIC IDENTIFIER: Supplied by Instructor (leave space for)

BRIEF DESCRIPTION:

A concept pioneered by Toyoda Kiichiro and Taiichi Ohno at Toyota in Japan, and largely championed by James Womack in the United States, Lean Production a philosophy that involves empowered teams on the production floor, enhanced communication across operations, the vigilant elimination of waste, and tireless continuous improvement. Lean production (as opposed to mass production) is believed to require half the human effort in the factory, half the manufacturing space, half the investment tools, half the engineering hours, and half the product development time (Womack, 1990). Other terminology commonly used to describe lean production include: Lean Manufacturing, Toyota Production System, and Just In Time Manufacturing. This document will use the term "Lean" to describe the overall concept.

KEYWORDS: LEAN PRODUCTION MANUFACTURING TOYOTA TPS JIT

OVERVIEW:

In contrast to statistical process control (SPC), which defines acceptable defect levels, Lean sets absolute, unachievable goals so that improvement must be continual. Edwards (1983) boils the goals down to the "seven zeros", discussed below. Included with each goal are Lean tools which can be used in striving toward the goals. Zero Inventories, the main driver to all the goals, is the relentless crusade to banish muda (or waste), especially waste in the form of inventory.

  • Zero Defects: zero inventories are not possible without zero quality defects, as defects require buffer inventories to avoid disrupting production. Poka-yoke (or foolproofing) processes to prevent human error, visual management to make quality more readily visible, real-time root-cause problem solving (or asking the five whys) by teams of production workers on the floor, andon cord (enabling workers to stop the line for defects), 100 percent check (with workers correcting their own errors) and process control run by line workers, all help approach this goal.
  • Zero (excess) Lot Size (or lot size of one): larger lot sizes require excess inventories. This goal is enabled by working toward the next goal. Since in reality lot size of one is sometimes impossible, kanban (visual card system for managing inventory and production) and pull scheduling set to takt time (or frequency of orders by the customer) aid in reducing lot sizes.
  • Zero Setups: the key to reducing setup times is to separate internal setup (steps which must be done with the machine stopped) from external setup (steps which can be done off-line while the line is still running), and to minimize the internal setup required. Jigs, fixtures, parallel machines, and uniform product design all contribute to reaching this goal.
  • Zero Breakdowns: a zero-WIP system cannot tolerate any machine breakdowns. Preventive maintenance is the main tool involved, along with the Five S’s: Sort (separate out everything unneeded to reduce clutter), Stabilize (clearly identify a place for everything and keep everything in its place), Sweep (keep the workplace clean), Standardize (define an on-going system to institutionalize the first three S’s), and Sustain (instill self-discipline in everyone to adhere to the system).
  • Zero Handling: if parts are made just in time, no extra moves to and from storage can be tolerated. Cross-trained teams in flexible work cells contribute to this goal.
  • Zero Lead Time: this means both cycle times and setup times must be reduced. Kaizen, or continuous improvement, by empowered teams aids this and all the other goals.
  • Zero Surging: to achieve smooth material flow, demand surges must also be smoothed. Final assembly scheduling, which specifies daily or even hourly production schedules requires smoothing aggregate production requirements by working with customers and sequencing final assembly, product by product. Capacity buffers (time between shifts, to accommodate overtime) can help deal with inevitable surges. Mixed model production (producing several products on the same line) also aids in preventing surges in demand on suppliers, as does close, cooperative relationships with the suppliers.

Lean techniques can and should be applied to all operating systems and processes, including manufacturing, product development, and purchasing activities. Lean is not a rigorous manufacturing process or system, but more of a philosophy, or collection of methods and slogans. Actually implementing them requires not simply applying the tools identified above but also making very complex tradeoffs in the overall system, paying excruciating attention to small details that are specific to each process, and being extremely persistent over a very long time.

For example, Toyota reduced some setups from three hours in 1945 to three minutes in 1971 (Ohno, 1988), but only through 25 years of ingenious, incremental improvements, specific to those processes.

As such, a simple Lean implementation instruction manual is impossible to produce.

It is clear that the early pioneers guarded their developments as a competitive advantage. Ohno admits that the Japanese used deliberately confusing terms to describe JIT concepts (Myers, 1990). Successful implementation of Lean requires 1) a never-ending process with deliberate cultural change from Mass to Lean thinking, 2) enduring commitment at all levels of the organization, 3) a leader who can make tough, technical tradeoffs while rallying people around a clear, common vision 4) countless ingenious ideas from everyone in the organization, and 5) an empowering organizational system that maximizes each individual’s potential contributions.

REFERENCES:

  • Monden, Yasuhiro. 1998. Toyota Production System: An Integrated Approach to Just-In-Time. Engineering & Management Press.
  • Cusumano, Michael A.; Nobeoka, Kentaro. 1998. Thinking Beyond Lean : How Multi-Project Management Is Transforming Product Development at Toyota and Other Companies. Simon & Schuster.
  • Womack, James P. 1996. Lean Thinking. Simon & Schuster.
  • Toyota Motor Company. 1995. The Toyota Production System. International Public Affairs Division & Operations Management Consulting Division, October.
  • Mishina, Kazuhiro; & Takeda Kazunori. 1995. Toyota Motor Manufacturing, USA, Inc. Harvard Business School, September.
  • Womack, James P.; Jones, Daniel T.; & Roos, Daniel. 1990. The Machine That Changed the World – The Story of Lean Production. Harper Perennial.
  • Myers, F.S. 1990. "Japan’s Henry Ford." Scientific American 262(5): 98.
  • Ohno, T. 1988. Toyota Production System: Beyond Large-Scale Production. Productivity Press.
  • Imai, Masaaki. 1984. Kaizen – The Key to Japan’s Competitive Success. McGraw-Hill Publishing Company.
  • Edwards, J.N. 1983. "MRP and Kanban – American Style." APICS 26th Conference Proceedings, pp. 586-603.

ACKNOWLEDGEMENT: This is a March 29, 1999 revision by Gene Goodson of an assignment for OM742 contributed by Charlie Choi.


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Copyright � 1999
R. E. Goodson
University of Michigan Business School