KANBAN Sizing
Sizing a KANBAN means:
- define batch sizes, which are the fixed quantities to produce for each reference or family of references when the Kanban triggers production;
- define loops size which are the maximum inventory allowed by the system for a reference or a family of references.
The KANBAN sizing has to be done at the same frequency than the MPS. In fact this task has to be part of the output of the MPS process. Of course you are not going to review all your sizing figures but a quick check of the KANBAN data consistency is necessary to avoid issues.
Capacity check
Capacity check
Each Master Production Schedule, a simple capacity check has to be done: Kanban does not work if you do not have enough capacity!
First you have to check if your production line will be able to produce the demand. From the opening time, you have to subtract pauses and average breakdown times in order to find the remaining time to be consumed for changeovers. A quick capacity check consists to consider one batch of each references which has to be produced to cover the demand during the period (do not forget to remove the references already covered by an inventory). If the total time obtained is not lower than the operating time, you must reconsider your opening time.
This point will be reviewed in the chapter KANBAN batch size but you can easily understand that higher the difference between the operating time and the sum of the single batch of each references will be, more it will be possible to increase the number of changeovers.
Scope definition
It is very important to understand that KANBAN is a replenishment system. It means that it replenishes the production based on an inventory consumption. If you are using this method for a reference which has to be produced only one time, you are going to create an inventory of it with no immediate usage. Indeed, just after the consumption of this reference, the system is going to ask you to produce it again in order to reach its KANBAN loop and this quantity will be no used.
Before launching a KANBAN it is necessary to define which references or families of references you want to control under this process. Choose only references regularly consumed during a period covering at least 2 or 3 MPS process (if you have a weekly MPS, take at least 2 to 3 weeks of horizon).
Later in the sizing process, when you are going to get the batch size for a reference, check always if this size covers more than this horizon. If it is the case, consider if it is possible to remove this reference from the KANBAN process and produce only its net demand in order to reduce inventory and then, re-do the sizing calculations.
If you do not apply KANBAN to all the references produced, you need to allocate a period of time dedicated to the production of references not managed with KANBAN.
This time has to be at least equal to the sum of the production time to satisfy the demand for all references chosen:
Change Over Time + Round-up to the packaging size of (Demand * (1+ scrap rate in %)) * real Cycle Time
A and B references are not managed in KANBAN. Operating time for KANBAN references has to be reduced consequently.
This time has to be subtracted of the operating time of the line for the next MPS period.
Of course you can chose to produce this type of reference with more than one batch. In this case you are going to consume more changeover times which will reduce the time allocated to produce references in KANBAN but reduce also your inventory if the demand consumes a batch before the next one is produced.
You have defined which references will be produced in KANBAN and what is the operating time allocated for KANBAN references. Now you can size your KANBAN parameters!
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