Definitions

• The Kanban system is a type of pull system which uses cards to communicate production requirements between processes.
• A kanban is a signalling 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.

Calculation of number of Kanban

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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