Just-In-Time (JIT) Production
Produce only what is needed, when it is needed, in the amount needed to eliminate waste and approach zero inventory
Just-In-Time is one of the two pillars of the Toyota Production System. In a JIT flow process, the right parts needed in assembly reach the assembly line at the time they are needed and only in the amount needed. Rather than pushing materials from earlier processes to later ones based on forecasts, JIT reverses the flow: a later process goes to an earlier process to pick up only the right part in the quantity needed at the exact time needed. The earlier process then produces only the number of parts withdrawn. This pull-based approach, inspired by how American supermarkets restock shelves based on what customers take, connects every link in the production chain through synchronized demand signals. When established throughout an organization, JIT approaches zero inventory while dramatically reducing the timeline from customer order to cash collection.
- The later process goes to the earlier process to pick up only what is needed, when it is needed, in the quantity needed
- The earlier process produces only the quantity just withdrawn by the later process
- Production quantity must equal the required number based on actual market demand, never more
- The flow of production is reversed: start from the final assembly line and work backward to the earliest material-forming department
- A company establishing JIT flow throughout can approach zero inventory
- The slower but consistent tortoise causes less waste than the speedy hare who races ahead and then stops to doze
- Speed is meaningless without continuity; high-speed machines that produce more than demand are not truly high-performance
- Conventional management methods that push materials forward do not work for JIT; the entire production system must be rebuilt around pull
- Establish Production FlowRearrange machines from function-based clusters (all lathes together, all drills together) into the actual sequence of manufacturing processes. This creates a continuous flow where one operator can oversee multiple machines across different process types, shifting from single-skilled to multi-skilled workers. This eliminates the waste of storing parts between departments and is the foundational prerequisite for JIT.Pro tipStart within your own sphere of authority. Ohno began with the machine shop he managed, arranging machines in parallel lines or L-shapes so one worker could operate three or four machines along the processing route.WarningExpect resistance from workers who are accustomed to single-function roles. Be patient rather than forcing quick, drastic changes.
- Implement Production LevelingSpread production evenly throughout the workday and across product types. If 10,000 units are needed over 20 days, produce 500 per day rather than batching. On the assembly line, alternate between models (sedan, hardtop, sedan, wagon) rather than running all of one type, then all of another. This prevents the peaks and valleys that cascade through earlier processes and require excess capacity.Pro tipLeveling requires reducing setup times dramatically. Toyota cut die changes from two to three hours in the 1940s to three minutes by the late 1960s. Start by eliminating adjustments and having everyone contribute ideas for faster changeovers.WarningDo not attempt to implement JIT across your supply chain until you have leveled production internally first. Asking suppliers to deliver just-in-time while your own production fluctuates wildly will cause chaos.
- Reverse the Material Flow with Pull SignalsInstead of each process pushing output to the next, have the final assembly line pull from earlier processes. When parts are consumed at assembly, a signal goes to the preceding process to produce the exact quantity withdrawn. This signal cascades backward through every process. The production plan goes only to the final assembly line; all other processes produce based on what the next process withdraws.Pro tipUse simple visual signals rather than complex computer systems. Toyota found that providing information only when needed, at the point where it is needed, is more effective than flooding every process with detailed schedules.WarningThis rule requires top management commitment and courage. It reverses the conventional flow of production, transfer, and delivery, and will meet significant resistance.
- Synchronize Internal and External ProcessesExtend the pull system to cooperating firms and suppliers. This should happen only after internal processes have been thoroughly converted and problems exhausted within the company. Bring suppliers in to observe the system in action at your plant, then guide them through implementation process by process.Pro tipToyota took nearly 20 years (from 1950 to the early 1960s) to implement JIT company-wide before extending to external suppliers in 1963. Do not rush this step; suppliers need to see the system working before they can understand it.WarningNever demand JIT delivery from suppliers without first helping them transform their own production methods. Using JIT as a way to push inventory costs onto suppliers without changing their underlying processes makes the system a dangerous weapon rather than a tool.
- Continuously Reduce the TimelineLook at the entire time line from when the customer places an order to when cash is collected. Systematically remove every non-value-added activity along this timeline. Reduce lot sizes further, shorten setup times more, eliminate waiting and transport waste, and keep driving toward the ideal state where production quantity exactly equals required numbers with zero excess.Pro tipWhen Ohno was asked what Toyota was doing at the pinnacle of their improvement journey, his answer was simple: reducing the timeline from order to cash collection by removing non-value-added wastes. This clarity of focus should guide all improvement efforts.
In 1953, Toyota applied the American supermarket concept to its machine shop. Just as a supermarket restocks shelves based on what customers take, earlier production processes began producing only what later processes withdrew. Cards listing part numbers and machining information circulated between processes as withdrawal and production signals.
Toyota's Tsutsumi plant leveled production of Corona, Carina, and Celica models on two assembly lines. Rather than batching all Coronas in the morning and Carinas in the afternoon, models alternated on the line. For 10,000 monthly Coronas (5,000 sedans, 2,500 hardtops, 2,500 wagons), the daily sequence was arranged as one sedan, one hardtop, one sedan, one wagon, and so on.
After World War II, Toyota faced a challenge that American automakers did not: producing small quantities of many car varieties under conditions of low demand. Toyoda Kiichiro declared Toyota must catch up with America in three years, but mass production was not viable for the Japanese market. Ohno calculated that American workers appeared nine times more productive than Japanese workers and concluded the gap was not physical effort but waste. He began thinking about the problem in reverse: what if a later process went to an earlier process to pick up only what was needed? The idea crystallized when Ohno connected automobile production to the American supermarket, where customers get what they need, when they need it, in the amount they need it. In 1953, Toyota applied this supermarket method in its machine shop, and over the next decade refined it into the JIT system that would eventually transform global manufacturing.