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Kanban - Describing a Pull System
Definitions - The Kanban system is a type of pull system which uses cards to communicate production requirements between processes. - A kanban is a signaling device that gives authorization and instructions for the production or withdrawal (conveyance) of items in a pull system - Cards - Triangular metal plates - Colored balls - Electronic signals - Any other device that can convey the needed information while preventing the introduction of erroneous instructions Withdrawal System advantages: - Reduction of cost processing information - Rapid and precise acquisition of facts - Limiting surplus capacity of preceding processes Supermarket: - The location where a predetermined standard inventory is kept to supply downstream processes. - Located near the supplying process to help that process see customer usage and requirements - Each item in a supermarket has a specific location from which a material handler withdraws products in the precise amounts needed by a downstream process - As an item is removed, a signal to make more (such as a kanban card or an empty bin) is taken by the material handler to the supplying process System description: - Conveyance/withdrawal card Used when the part is removed from the stock point (the worker places it on the container) - Production card Used when the part is removed from the stock point (the worker takes it from the container to make a new part to replenish the stock) - Production and withdrawal cards must work together to create a pull system Example - At a downstream process, an operator removes a withdrawal card when using the first item in a container. - This card goes in a nearby collection box and is picked up by a material handler. - When the material handler returns to the upstream supermarket, the withdrawal card is placed on a new container of parts for delivery to the downstream process. - As this container is taken from the supermarket, the production card on the container is removed and placed in another collection box. - The material handler, serving the upstream process, returns this card to that process, where it signals the need to produce an additional container of parts.
No of cards = A x B x (1+C) / D Where: A – the average daily demand for the item B – the round trip conveyance lead time C – safety stock maintained for the item D – capacity of the container Example A = 1200 pieces per day B = 2hrs/8 hr shift = 0.250 lead time C = 2hrs/8 hrs = 0.250 safety stock D = 25 pieces/container # of cards = 15 cards - Customer processes order goods in the precise amounts specified on the card - Supplier processes produce goods in the precise amounts and sequence specified by the card - No items are made or moved without a card - All parts and materials always have a card attached - Defective parts or incorrect amounts are never sent to the next process - The number of cards is reduced carefully to lower inventories and reveal problems
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