Heijunka - The most important prerequisite for JIT production

In the first article of this column, I talked about the issue of Stability in production. We saw that Stability depends on many factors and, obviously, the most important factor is the interaction of people with the system, since they are the most relevant element in implementing and applying lean concepts. In lean, respect for people is the reason for being, and everything is done to make it easier for them to carry out the tasks that truly add value for the customer, whether internal or external.

This time we will reflect on heijunka. But what is heijunka? In quick translation, heijunka, which is a Japanese word, means leveling in plain English. So what is this leveling? And how is it done? What is it for?

Let's see: Heijunka (leveling) means balancing the item and the volume to be produced uniformly (similarly) in the way of producing (sequence and frequency).

The objective is to balance and keep stable the production resources (labor and equipment), to make the type and quantity of day-to-day production as uniform as possible, and to avoid waste, especially inventory.

The manufacture of any part or product is rarely completed in a single process or operation. Usually several processes are needed, linked together in a sequence of operations.

If a given process does not operate correctly, that is, according to takt time, the pull of product from the previous process becomes unstable, causing part shortages and/or inventory between processes. For example, to avoid a part shortage, the previous process will allocate labor and equipment resources that were originally unnecessary, generating waste and, consequently, losses.

In general, people think that producing the same parts consecutively in large quantities is more efficient. Production is done in batches, causing an imbalance in the total quantity of parts across the processes, generating part shortages and/or inventory in the processes and destabilizing production.

In the lean way of producing, production capacity is balanced based on the takt time of each process, and production volume is controlled using kanban.

Here I call attention to the need for the utmost care: if production is not in accordance with takt time, the processes become unbalanced, disrupting production. Therefore, “producing according to takt time” is the most important prerequisite.

Next, the fundamentals of JIT production, which has Heijunka as a prerequisite:

1. Takt Time: know the required volume in detail (what, how much and at what speed it must be produced);
2. Pull Production: a single flow of information (kanban)
3. Flow Production: process in flow (general rule – one-piece flow)

To implement Heijunka, do Kaizen in the following areas:

1. Training employees to make them multiskilled.
2. Small-batch production – drastic reduction in setup time
3. Avoiding scrap and rework (Pokayoke and Jidoka)

And to conclude: The essence of Production is to faithfully meet demand.
Therefore, to implement an efficient Heijunka, pay attention to the following points:

1. Continuously reduce L/T (lead time),
2. Produce in ever smaller batches,
3. Always question and never accept inventory,
4. Adjust and control capacity with mixed production, and
5. Assign a balanced load to the previous processes.

In the next article, we will reflect on Takt Time.