What is Kanban?
Kanban systems are an interim step to be used until a breakthrough in process flexibility occurs, or right sized equipment is developed enabling in-lining of processes. The basic definition of a pull system is - what is consumed is produced or replenished. Kanbans are used as an interim step when process capabilities do not allow processes to be connected or when right sized equipment is not available to connect with downstream processes. A kanban system is a minimized quantity of material established between processes. There are three types of kanbans – material delivery, WIP, and supplier.- Material delivery kanbans are used for parts delivered to assembly areas via tugger cart systems. Each assembly station has a small inventory usually 1-8 hours that needs to be replenished in 1, 2, or 4 hour replenishment cycles. As the material handler delivers material, they will pick up the kanbans pulled since the last delivery and deliver material from their current run.
- WIP kanbans are for large amounts of WIP between two process. As the subsequent process pulls from inventory, the kanban is pulled and sent to the upstream process for kanban manufacturing replenishment. Then the material is produced and replaced into the WIP inventory. WIP kanbans can also be used for finished goods inventory. As the customers pull material from finished goods the kanban is sent to the upstream process for replenishment.
- Supplier kanbans are located on the raw material inventory in the receiving area. Supplier kanban sizes are determined by delivery frequency, consumption rates, and supplier reliability. Efforts should be made to group suppliers in common geographic areas and coordinate a combined shipment from all suppliers on a daily/weekly basis to increase delivery frequency by each supplier without increasing logistics costs. When possible, containers from the vendor should be designed in a way that the container can be delivered via a tugger directly to the operator’s fingertips.
Management
The discipline around managing a kanban system is critical to success. The following rules need to be followed to avoid material outages and overproduction:1. Only produce what is consumed 2. Produce only good quality parts 3. Material handlers should only pull the material needed 4. Efforts should be made to minimize inventory over time 5. Kanban systems should be designed to adapt to small fluctuations in demand 6. The amount of parts on the kanban card should equal the number of parts in the container, 7. The kanban system needs to be kept full 8. Material handlers need to pull from one container at a time 9. Kanban systems should be audited to verify there is the correct number of cards in the system and that the rules above are being followed