Heijunka is a Japanese term that refers to production smoothing in which the total volume of parts and assemblies are kept as constant as possible throughout the value stream. A Heijunka box is a visual scheduling mechanism that distributes work into small time increments and ensures level work load.
In a dual kanban system, the heijunka box contains production kanbans or signal cards. How do you compute the numbers of cards in a heijunka box? One example of the use of a heijunka box is in leveling production and shipping. For our purposes, let's assume a box per product produced. It is filled with kanbans. Each production kanban signals the start of a production cycle that pulls a minimum product lot size. A withdrawal kanban from shipping triggers the pull of a production kanban.
The issue is how many kanban cards should be in the heijunka box?
The key factors to consider are:
* Customer demand for product over a given period of time (usually one shift for one line)
* Lead time to produce the product lot size (replenishment rate; use the same unit of time as you used in representing customer demand - e.g., hours)
* Safety stock expressed as a percentage of demand during lead time (if the total demand is 100 units and the safety stock is 10 units, then the safety stock value you should use is .10)
* Production lot size
Here is a formula offered by Professor Herbert Tuttle, University of Kansas.
To compute the number of kanban cards, use the following formula.
Number Cards Needed = [(Customer Demand x Lead Time) x (1+Safety Stock)] / Production Lot Size. If the computation produces a fractional result, then round up.
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I also found this link that should be helpful:
http://www.si.umich.edu/ICOS/Liker04.pdf
This one looks pretty good too:
http://www.bmpcoe.org/bestpractices/pdf/uec.pdf
Heijunka - Looking for a company we can benchmark in heijunka system
Linear Mode
