What is Leveling - Heijunka
Introduction
Heijunka means sequencing or smoothing of production. It is defined as “the distribution of production volume and mix evenly over time”.
The objective of Heijunka is to absorb
sudden fluctuations in market demand by producing several
different models in small batches on the same line.
The practice of Heijunka also allows mudas to be eliminated by making it easier to standardise work. Good sequencing practice reduces the need for line side labour.
Difference between Traditional Production and Leveled Production
A traditional production process focuses on manufacturing in large-sized lots. The idea is to manufacture the maximum number of products in one lot. A lean production process focuses on producing as the latest market demand.
Figure below gives an example of traditional unleveled production. The line makes a product in three different dimensions (small, medium and large), indicated respectively with A,B,C.
This typical unleveled method creates four problems:
Customers usually do not buy products predictably. If the customer decides to buy the large product early in the week the plant is in trouble.
The risk of unsold goods that must be kept in inventory.
The use of resources is unbalanced.
There is an uneven demand on upstream processes.
Following figure represents an example of mixed-model leveled production. By reducing the changeover time and employing other lean methods, the plant is able to build the products in any order it wants to on its mixed-model assembly line.
The four benefits of leveling the schedule are:
Flexibility to make what the customer wants when they want it.
Reduced risk of unsold goods.
Balanced use of labor and machines.
Smoothed demand on the upstream processes and suppliers
An Example of leveling is shown below:
Benefits of Heijunka
Specific advantages to be derived from this type of system are much more than just about reducing waste. The most specific advantage has to be the flexibility that this system invokes within the company, ensuring that the customer can get exactly what they want, at a specific time that they need it. This ensures that the customer is kept satisfied and therefore ensures the longer-term financial stability of the company. Due to the fact that there is no over or indeed under production, there is no risk that such a surplus of items will be made that will never be sold, so general efficiency is promoted.
therefore, the correct implementation of the system provides predictability by leveling demand, flexibility by decreasing changeover time and stability by averaging production volume and type over the long term.
Implentation of Heijunka
One way to achieve leveled production is by implementing takt time, which means basing the production rate on an estimate of how many units per units of time must be processed at each work center in order to meet market demand.
Takt time sets the pace of production to match the rate of customer demand, and becomes the heartbeat of any lean production system. As the "pacemaker" of a lean system, takt time is essential to the smooth flow of work through production cells, and is a key factor in planning and scheduling work.
By using takt time, production can be leveled to either a set level or to between a minimum and maximum level. These levels can be set in a computer system for any date and any period length, from a day upwards. Leveled production results in a steady demand pattern, which ensures a predictable, smooth schedule and avoids capacity bottlenecks.
This simplifies planning and control (since every day in the plan within the leveled period is basically the same), creates stability in production, and gives operators a far better understanding of what they have to do each day and how they are performing against goals and targets. It also makes life easier for upstream suppliers who can be passed stable schedules.
