What factors might make kanban inappropriate for controlling material flow through a job shop, that is, a system with many, possibly changing, routings with fluctuating volumes?

Kanban is a just-in-time (JIT) inventory control method that uses visual signals (cards or boards) to track production flow. It is designed to reduce waste, minimize work-in-process (WIP) inventory, and improve process efficiency. However, it works best in environments with a stable and predictable production flow and demand levels.

Job shops often have varying and unpredictable routings for products. Kanban systems work best with a fixed and predictable production flow. The changing routings in a job shop might make it difficult for the kanban system to accurately track and manage material flow, leading to inefficiencies, delays, and potential production errors.

Kanban assumes a relatively stable and consistent demand for products, allowing for accurate estimation of required inventory levels. However, in a job shop scenario, production volumes and demand levels might fluctuate significantly. This fluctuation makes it difficult to establish the right number of kanban cards, potentially leading to excess inventory or stock shortages.

The complexity of operations in a job shop can make it challenging to implement a kanban system. The numerous routings, processes, and products require a significant amount of coordination and planning. The kanban system may struggle to accommodate the complex nature of the job shop and might not provide the desired results in terms of efficiency and inventory control.

Resource constraints in a job shop, such as a limited number of machines, operators, or other production resources, might interfere with the smooth functioning of a kanban system. Kanban relies on continuous flow and requires resources to be available when needed. Resource constraints, particularly in a constantly changing job shop environment, might disrupt the flow and lead to inefficiencies. In conclusion, kanban might be inappropriate for controlling material flow in a job shop due to changing routings, fluctuating volumes, operational complexity, and resource constraints. These factors make it difficult to achieve the desired efficiency, inventory control, and continuous flow that kanban systems strive for in more stable and predictable environments.