An example to illustrate the Kanban process is assuming the case of an assembler who is drawing a particular component from a pallet which, when full, contains 100 pieces. As the last piece is drawn, the assembler takes an identifying card from the empty pallet and sends it back down the line to the earlier work centre where that part (among others) is made. On receiving the Kanban card, the work centre responsible for supplying the component makes a new batch of 100 and sends it to the assembly post ( so that the assembler isn’t kept waiting, there will probably be an extra pallet in the system to maintain the supply while the new batch is being made). This means that there is a minimum of paperwork, and the order cycle is generated on a ‘pull’ basis, the components only being made when there is an immediate need for them, thus keeping work-in-progress to a minimum.
A number of variants are present for implementation of the Kanban system, the above example is of the, 1 card Kanban. Other types of Kanban are
- The 2 card Kanban – It is the original Toyota method, developed at a time when replenishment supplies were routed through a component or parts store. The card released by the user authorizes the stores to ‘move’ a replenishment supply to the user. When they do so, a second card, which is found on the pallet they are about to supply, is removed and sent to the component supplier as authority to ‘produce’ another standard quantity.
- The 1 card Kanban – It s similar to the 2-card system, but a single card acts as both ‘move’ and ‘produce’ authority. This method is typically used where the supply point is close to the user point, so that the supply and user operatives move the empty and full pallets between the two work centers themselves without the intervention of a stores function. It is also commonly used where the movement of pallets is automated.
- The container-based Kanban – In this system, there are a predetermined number of containers or pallets in the system, all uniquely identified to a particular part number or component – if the maker of the component has an empty container waiting he or she fills it; if there is no empty container waiting, then the operator must stop production of that component and switch to some other task. This procedure is often used when special-purpose containers or pallets are provided, so that there is no doubt as to which components have to go into them.
- The shelf-space Kanban – It is similar to a motorway cafeteria method. At the cafeteria counter a range of dishes is provided to the customer via a display/dispensing cabinet, which is subdivided into a number of ‘pigeon-holes’, each providing one compartment for each type of dish. The instructions to the kitchen staff are ‘ensure that there is always at least one and not more than three of each type of dish available in the cabinet. If there are three dishes available of all types of dish, stop producing and find something else to do (like cleaning equipment)’. The same principle, applied to the factory, takes the form of shelf spaces marked up with the part number/description of different parts. Someone is given the task of making sure that empty shelf places are filled. When all spaces are filled, production of the item stops.
- The floor grid Kanban – It is same as shelf-space Kanban, but used for bulky or heavy components which are unsuitable for putting on shelves.
In all the above examples of Kanban, the number of containers is systematically reduced till supply is kept just in balance with the rate of use, so that the replenishment supply arrive ‘just-in-time’ for the user. The usual way of doing this is to keep taking away one more container each day (or week) until reaching the point where production is interrupted because the next full container doesn’t arrive in time or it’s ‘just-too-late’, replacing one container should then bring the supply back into balance with the rate of use.
A ‘simulation’ model can also be used to test the effects of different demand levels and a different mix of production with a high degree of confidence.