Background
After the Second World War, Japan's car market was small and varied, so Ford-style mass production could not simply be copied. Toyota's Taiichi Ohno, inspired by American supermarkets that restock shelves only as goods are sold, refined a system that minimized inventory and waste during the 1950s–1970s. It drew attention when Toyota recovered faster than rivals from the 1973 oil crisis, and Ohno described it in a 1978 book (English edition 1988). Producing many models in small volumes, it adds flexibility to repetitive line production among the types of production process.
The two pillars
- Just-in-time (JIT): supply the parts needed, when needed, in the amount needed, minimizing inventory. Downstream processes withdraw only what they use from upstream ones in a pull system, signaled by kanban cards (Sugimori et al., 1977).
- Jidoka (autonomation): "automation with a human touch." When a defect or abnormality occurs, the machine stops itself or a worker pulls the andon cord to halt the line, and production resumes after the cause is fixed. It traces back to founder Sakichi Toyoda's automatic loom.
The seven wastes
Ohno treated every activity that adds no customer value as waste (muda) and named seven kinds: (1) overproduction, (2) waiting, (3) transport, (4) overprocessing, (5) inventory, (6) motion, and (7) defects. He called overproduction the worst because it hides the others. A well-known metaphor: lowering the "water" of inventory exposes the "rocks" of problems.
Kaizen and shop-floor tools
- Kaizen: continuous small improvements by frontline workers. Imai (1986) presented it as the core of Japanese competitiveness, in contrast to large leaps of innovation. Asking "why" five times to find root causes is a typical method.
- Heijunka: leveling production by evenly mixing models and volumes.
- Poka-yoke: mistake-proofing devices that prevent errors from occurring.
- 5S: sort, set in order, shine, standardize and sustain, so waste becomes visible.
- Standardized work: takt time, work sequence and standard work-in-process as the baseline for improvement.
Spread as lean production, and limits
Womack, Jones and Roos (1990) of MIT's International Motor Vehicle Program named TPS "lean production," reporting that it achieved higher quality with half the labor, space and inventory of mass production. Lean then spread beyond manufacturing to hospitals, software (lean startup, agile) and services, and combined with Six Sigma and TQM as "Lean Six Sigma." But JIT presumes close, trusting supplier relationships, and its fragility showed when supply chains broke in earthquakes, the pandemic and chip shortages. Critics also say it shifts inventory burdens onto suppliers and intensifies work. After the 2011 Great East Japan Earthquake, Toyota adjusted by holding more stock of critical parts.
See also: Scientific Management (Taylorism)
References
- Ohno, T. (1988). Toyota Production System: Beyond Large-Scale Production. Cambridge, MA: Productivity Press.
- Sugimori, Y., Kusunoki, K., Cho, F., & Uchikawa, S. (1977). Toyota production system and Kanban system: Materialization of just-in-time and respect-for-human system. International Journal of Production Research, 15(6), 553–564.
- Imai, M. (1986). Kaizen: The Key to Japan's Competitive Success. New York: Random House.
- Womack, J. P., Jones, D. T., & Roos, D. (1990). The Machine That Changed the World. New York: Rawson Associates.