How just-in-time works
JIT rests on three mechanisms:
- Takt time sets the pace at which the customer consumes product, so every process runs to the same rhythm.
- Continuous flow moves work one piece or one small batch at a time between steps, rather than building stock between them.
- Pull means a process only produces when the downstream process signals demand, usually with a kanban card or an empty container.
Together they replace the push system, in which each step produces to a schedule and the output waits for the next step.
What it requires
JIT exposes problems that inventory used to hide, so it only works on a stable base:
- Short changeovers (SMED), so small batches are economic.
- Reliable equipment (TPM), because there is no buffer to cover breakdowns.
- Built-in quality (jidoka), because a defect stops the line rather than being picked out of stock later.
- Levelled demand (heijunka), so the rhythm does not swing shift to shift.
- Capable suppliers delivering in small frequent lots.
Benefits and risks
Lower inventory and working capital, shorter lead time, faster detection of defects and a plant that is easier to see and manage. The risk is fragility: a supply disruption or an unreliable machine stops production quickly. Toyota's answer is not to add stock but to make the problem visible and solve it, while holding deliberate buffers where supply genuinely cannot be stabilised.
JIT and daily management
JIT depends on abnormalities being seen and acted on the same day. The tier meeting, with delivery, inventory and downtime measures on the board, is where a missed pull signal or a late supplier becomes an action rather than a reason to build safety stock.