The Difference Between Lean Manufacturing & Kanban
Someone recently wanted me to explain the difference between lean manufacturing and kanban. The difference between lean and kanban according to the Toyota Production System (TPS) architect, Ohno-san, is “….TPS is the production method, and the kanban system is the way it is managed.” To see how kanban fits in, consider the evolution of TPS.
The TPS was created out of necessity, according to Ohno. Following the second world war, Toyota faced the challenge of competing with mass production in the west while having only a small-volume, high-variety domestic market. In addition, Toyota’s president set a goal to match the U.S automobile industry in three years, requiring a ten-fold increase in productivity. The only way to pursue such dramatic results in these circumstances was to eliminate all waste from the system and to make it highly flexible at lo operating cost.
To Ohno’s observant eyes, the wastes that stood in the way of greater productivity were:
- overproduction
- wait time
- transport
- processing
- holding inventory
- movement, and
- making defective products
All of these tied up working capital and/or wasted capacity (employee and machine) or material. Material had to flow, not sit around; and yield had to be 100 percent. Flow-type layouts and diligent application of quality principles and tools emerged. Subsequently, JIT and autonomation emerged as two main pillars of the TPS.
JIT – delivering or producing exactly what is needed, when it is needed, only in the quantity needed – addressed wastes 1,2, and 5. Autonomation, which involves automatic stopping devices on equipment and on manual procedures at aline to stop producing when abnormal process conditions are detected, addresses wastes 1, 5, and 7. Improved layouts (flow-type) and work methods addressed wastes 3,4, and 6.
Flexibility at low operating cost was improved with the creation of multifunctional workers and teams and by reducing set-up/changeover times. The company improved process reliability by preventive (or predictive) maintenance, and smoothed material flows by leveling the final assembly schedule.
Kanban’s initial role was to control the flows and production in TPS (i,e manage the JIT method of production). It accomplished this by signalling to the next stage upstream the identity, exact quantity, and timing of parts/materials needed in final assembly to produce product that would match market demand (rate and mix). By its absence, it also signaled that nothing was to be made or transported. By ripple effect, from stage to stage back through the production system, the entire TPS could be coordinated to flow smoothly at the market rate of use (or lack thereof).
In addition to this control function, kanban had a role in improvement. Kanbans signaled abnormal conditions when their flow was stopped by trouble on the shop floor. Also, by gradually reducing the number of kanbans (and hence, the directly related containers of WIP inventory), the system became leaner, revealing weak areas in the TPS (e.g., bottlenecks and processes with fluctuating capacities or usage). The trouble spots and weak areas became natural focuses for improvement activities.
The TPS isn’t the only lean production system, and kanban isn’t the only way companies signal the identity, quantity, and timing of items needed downstream.