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Leveling tool, the Heijunka Box is positioned between the customer order table and the production lines. She’s doing the leveling.

Introduction

The leveling box, called Heijunka box, is the intermediate tool between the Logistic Box (Firm controls) and the sequencer or batch Building Box (What will be produced in the near future).

The Leveling box retrieves the customer data (Kanban) of the Logistic box and translated into production order. So, from a weekly mesh, we move to a daily mesh see schedule. It will allow to give the rhythm of production and represents in a visual and pragmatic way the Takt Time.

Sizing of the Leveling box

Located near the line replenishment area (starting from the Mizusumashi Tour), we find:

  • In column, the hourly mesh (from a few minutes to several hours)
  • Online, product references to be manufactured

Called Rece, every Part every Interval, it allows to calculate the frequency of rotation of the products and helps to pass the stages of the leveling. Through this calculation, the following questions are answered:

  • How often can we produce our product families? Once a week, once a month…
  • What is the optimum batch size?

The calculation process is as follows:

1-Identify our capacity

We’re going to measure our possible production time. Depending on whether one is in one team, two or another, the time will differ. Be careful to remove the pause times. This reference time can be taken to the week, to the month, to the day… It all depends on the level at which we are. For steps 0 to 2, we will be on a monthly basis, while for steps 3 to 5, we will be on a daily basis.

2-Calculate our production time required

The time required for production is calculated over the period of time considered. This time is equal to:

Tprod = Nb Part * Tp cycle

To stick as close to reality, and especially if we have a lot of difficulty producing (time required < 50%), the following formula will be used:

Tprod = Nb Part * Tp cycle/time required

3-Deduct the available time of change of series

With the previous data, we will deduct the time we have available to make series changes. The formula is as follows:

TpdS = Capacity – Tprod

For example, our monthly capacity is 8400 mn, our average monthly demand is 5000 pieces for a cycle time of 1mn, our production time is therefore 5000 mn. This gives us a time to change the series from 3400 mn per month.

4 – Calculate the EPEI

At this point, we will calculate the rece, which represents our frequency of optimum series change in our current conditions and the time interval considered. The formula is as follows:

EPEI = GST/TpdS

With:

  • GST: Sum of the series Change times
  • TpdS: Serial Change time available
Always in a Lean logic, the formulas of calculation allow us to have a first approach to design our box of leveling. It will be the implementation and continuous improvement of its functioning that will allow us to improve our performance.
For recall, the calculated EPEI must correspond to the rotational frequency of the Mizusumashi.

5-Deduct the optimum batch Size

By multiplying the EPEI by the need over the time considered, we will get the optimum batch size.

6 – Build the Leveling box

With the previous data, we build the leveling box. The value of the EPEI corresponds to the hourly increment of our columns, and the batch sizes corresponding to the number of Kanban cards that we need to put at each interval.

Example

We have an opening time on the day of 420 minutes (a day of 8hr minus the 1hr of pause). The table below gives the information on the production.

Note: We note that for product D, we produce a lot of waste, and we are only 90% of the time required.

With this data, we calculate all the data allowing us to build our leveling box.

In terms of results, we can conclude:

  • Between each loop of Mizusumashi, we have a time of 105 mn.
  • In a production day, we have four production cycles.
  • Our Kanban cards are sized to take into account technical constraints.

We get the following leveling box:

Once the box is built, we implement it and test its operation. With experiments and new simulations, we can improve it and pass the different levels of levelling.

Source

T. Luyster, D. Tapping (2006) – Creating your Lean Future State

A. Smalley (2009) – Creating level Pull

D. Sarkar (2008)-Lean for service organizations and offices

A. N. Bin Adnan (2013) – Implementation of Just in Time production through Kanban system

L. F. De Araujo, A. A. De Queiroz (2009) – A Framework for production levelling implementation batch Manufacturing

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