KANBAN loop size
For an equipment which is producing multiple references, you need for each of them to have enough inventory to satisfy the demand when you are producing the other ones.
Loop: inventory required by the system
Loop Time: the worse case
Imagine the worse case: you just have completed your batch for the reference A and you have on your launcher a batch of all the references that your equipment can produce. On the top of that, your equipment will have to be shut down for scheduled maintenance.
The time between the completion of the batch of reference A and the next time when your first part A will be produced and available for consumption is called the Loop Time.
The consumption during the Loop Time is called the Loop Inventory or Loop.
The Loop time for a part A is equal to the sum of:
- the changeover time plus the batch time of all references in KANBAN, reference A excluded;
- the change over time of the reference A;
- the time to produce and release for consumption the first unit of the reference A;
- the shutdown time of the equipment scheduled for this period.
Loop calculation
Loop with less references
The number of references in KANBAN has a direct impact on the size of the loop... but it is not the only reason.
The loop time as well as the loop inventory is directly linked to:
- the number of references produced by the equipment;
- the value of the period when the customer consumes and the equipment is down.
But in reality this statement is not totally true because the maximum number of batches on the launcher depends also of the demand profile:
- is the demand smoothed?
- is the demand perfectly mixed?
Moreover the demand seen from the equipment managed with a KANBAN can also modified by the way how the customer is pulling the products from the KANBAN stock. These are some extreme cases:
- a removal of all the material needed for a day versus a pull every hour;
- a removal of all the material of the reference A in one shot, followed by all the material of the reference B during the next one;
- a consumption batch higher than the production batch;
- an erratic consumption (consumption in one shot of all the references for a quantity equivalent of the demand for the full period at the end of it ,followed by one at the beginning of the next period);
In all these examples, the loop needs to be increased. Said in another way, if the consumption is perfectly smooth and mixed, your loop will be lower.
Our KANBAN sizing tool calculates the worse case scenario. It is a conservative way to calculate the loop. In order to optimize the loop size, the best way is to observe the maximum number of batches on the launcher. After few day of observation, if you found that the maximum is 5, take just the first 5th longest couples: change over time + batch time that you have for all references in KANBAN. Add these times and consider this total time like your loop time for all your references. This is the best way for sizing a KANBAN loop!
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