Levelized Production (Heijunka)
Levelized production, simply put, is a method in which the same amount of product is built everyday. In a lean manufacturing facility, this type of standardization is very important. A pull system is required along with the use of kanbans in order to properly implement this aspect of lean manufacturing.
Your customer orders will most likely fluctuate from day-to-day. One day they will want 10 black and 5 red parts, the next day could be 12 red and 7 black. The obvious problem in this scenario is that one day the customer will order 15 parts and the next day they require 19. On the third day they may only require 13 parts. Whatever the numbers, they will vary.
Levelized production is used to smooth out that variance. Using the above example, if the level volume is set at 15 parts per day, production would replenish the 15 parts that were ordered. On the second day, as the order is 19 parts (4 parts higher than our levelized production volume) they would still build 15 parts and the shipping area would take 4 parts from an inventory called "Fluctuation stock". On the third day, the order was 13 parts, which is two less than our heijunka volume, two parts can be rebuilt and put back into fluctuation stock.
This is a very basic idea of how the concept works.
In order to set the level volume for production, you will need a good forecast and a good record of shipping history. The forecasts will be the driving force for setting the volume but the history of customer orders will let you understand the level of fluctuation you can expect from any one of your customers.
This fluctuation is key to setting your fluctuation stock levels. If a customer can vary 30% a day for 3 days, then you will need to be prepared to carry 90% of a day in fluctuation stock. If it can not be replenished throughout the week, it should be rebuilt over the weekend if time allows. This may seem contradictory to the
waste of inventory
principle, but this is controlled stock (through the use of kanbans). There is also a huge benefit in other areas that will off-set this inventory.
Benefits of Heijunka
The biggest beneift you should see when implementing heijunka will be the stability of your manpower and reduction of unnecessary overtime. Depending on your current situation, a reduction in inventory levels is also likely due to the control you will be able to maintain through the use of kanbans.
Consumption of raw materials should also improve as you are only building that which is required, when it is required. Building up too much of one product and consuming components that are needed for another should be a thing of the past.
Another major benefit you should see is a reduction of stress levels in the production area. The production schedule should no longer be a guessing game as they will know each day how much product is expected of them and be able to plan accordingly. This can go a long way towards improving morale.
One word of caution; as with most things in life there will be many who will resist the change at first. Be sure to stick with it and point out the benefits. In time, their attitude towards levelized production