Kanban

Kanban is a visual pull-system from the Toyota Production System using cards, bins, boards, or digital signals to authorize production or material withdrawal only when downstream process needs it. In manufacturing, it tells a machine cell, material handler, or supplier what to make, how much, and when to replenish, rather than pushing based on forecasts.

On the CNC shop floor, Kanban operates as a pull signal that triggers production only after downstream consumption. For example, a CNC cell may use kanban cards or bins to authorize the next batch of parts once the assembly area uses the previous lot, preventing overproduction and excess WIP. In millwork, it controls replenishment of sheet goods, hardwood blanks, edgeband rolls, and hardware, ensuring the shop never stops for shortages nor buries the floor in inventory. Lean implementations often display kanban boards showing stages such as raw material prep, CNC machining, assembly, quality check, and packaging, which make bottlenecks visible in real time. This supports just-in-time production by passing information backward through the process about what and how much to produce, aligning output with actual consumption rather than forecasted push scheduling.

• ⚠️Signal-card mismatch or loss: If cards detach from bins, mix between similar part numbers, or are not returned promptly, the shop runs the wrong job or misses replenishment entirely because the kanban signal is the authorization mechanism.
• ⚠️Oversized containers or bad lot sizing: One kanban loop covering too many parts builds hidden WIP and increases lead time; too few parts cause excessive changeovers and material handling, weakening pull system efficiency.
• ⚠️Using kanban without stable process capability: When CNC cycle times, scrap rates, or downstream demand fluctuate heavily, the loop starves or floods because replenishment assumes repeatable consumption and predictable flow.