Our customer never wants to know what, when, and how much they will want. They are such a being that, the moment they cannot find even the smallest thing, they become very upset and their satisfaction falls at once. They never forget the difficulty they experienced, and every time we have to negotiate on price they set what they went through in front of us, one by one. And, inevitably, we have to give a discount.
Production always wants to know what, when, and how much it will produce. It has such constraints that, with the smallest change, its efficiency falls, and it takes a long time to reach its former efficiency again. Meanwhile, we too have to work overtime. Costs get out of hand.
Under these conditions, producing, selling product, and giving a delivery date is a miracle; even so, if we are able to sell product, we owe this only to the sales team. Well, in that case, nothing we do for them is enough. So that they can easily find what they want, when they want it, we rent separate warehouses and fill them with stock.
Do you think this situation describes a utopian company?
This situation does not describe a utopian company. If you work at a company that insists on producing to sales forecasts, holding stock has become normal for you and has now entered among the indispensable conditions of the work. If you work at a company that tries to produce the customer's order, arguing about delivery dates with the customer and with production every day has become normal for you.
Heijunka is a Lean Production System practice built on the pull system and designed to produce the product the customer has purchased.
The goal of the Heijunka practice
The basic goal of the Heijunka practice is to eliminate completely, or to reduce to a minimum, the negative effects on production of sudden changes in customer demand. In this way, with balanced, regular, rhythmic production back upstream from production, it is to raise efficiency to the highest levels and increase added value.
The beginning
When starting Heijunka practices, the first thing that must be known is that the company's material, product, and information flow has to be examined on site and in detail. Data taken from inside the computer should not be trusted, and, by moving the Kaizen group along with the material, the whole team should be enabled to understand thoroughly the system, the problems, and people's thoughts. Heijunka is a system that must be considered over the long term. Instant adaptations generally cause problems to arise.
For Heijunka practices to be sound, the company must have passed a certain stage in its lean production system practices. For example, it must have shortened model changeover times and absorbed Kanban practices. In this way, by balancing its production, the company can eliminate the losses that will arise in production, in logistics, and at its suppliers because of sudden jumps and stops, and can bring stock levels down from days to hours.
Classification of the products
Every company's products can be classified as fast sellers, infrequent sellers, and very infrequent sellers. Even if the company works to order, this classification can be made through joint work with the customer. In this way, the products are divided into groups by a standard ABC analysis.
As a result of this grouping, it will generally be seen that 80% of turnover is provided by 20% of the products. In this case, it is appropriate for the infrequently selling products to be sold without holding stock. In this way, orders can be met immediately and the time taken to receive payment can be shortened.
Takt Time
Customers do not consume the products they buy immediately. Instead, they buy product for a certain period. Takt Time is the name given to the time it takes for a product to be sold. For example, it is obtained by dividing the total working time within a year by the total quantity of product sold in that year. For a company that sells 1 million refrigerators and produces on 3 shifts, this time is 26 seconds. This means that one refrigerator is sold every 26 seconds. Of course, refrigerator models are not taken into account here. When Takt Time calculations are made, products produced on the same line are calculated together.
Daily average production quantity
As a result of examining sales realized in the past, or sales forecasts to be realized in the future, the daily average sales quantity is calculated for each product item. The point to note here is that, among the products identified by the ABC analysis above, the A products are sold every day.
It will be seen, however, that companies generally order several models of product together in one order, rather than taking only one model. This means that the producer, too, must produce these products in similar groups. For example, suppose that X: 500, Y: 350, and Z: 250 units are being sold; in this case these quantities need to be produced every day. Otherwise, production reaches a state in which it cannot meet sales.
Production periods
Above, we spoke of calculating the daily average quantities and of the need for these quantities to be produced regularly every day. During this production, a certain balancing must be carried out as a principle. If this balancing is absent, material consumption concentrates on one material, so the quantities consumed at one time increase. Consequently, the supply quantity and the lead time increase. In this way, quantitative stock uncertainty and the stock level increase in every area.
For the example above, the periods can be set as X: 100, Y: 70, and Z: 50. In this way, production can be carried out 5 times a day, in the same sequence, within this period. This means that the materials used for these products can also be replenished 5 times a day. In this way, the milk run (milk - run) practice can easily be applied. Heijunka planning boards are used to eliminate the loss of time in setting these production periods and to make planning easier visually.
As can also be understood easily from the picture beside it, these boards, which make production planning considerably easier, place the company's 3 products in the fast-selling product group, and the other products in the infrequently selling product group, in the column that represents the hour of the day at which they need to be produced. The production line concerned thus knows exactly which production it will do at which hour. Here the period is in the form 1213213. In addition, as many group B products as needed have been interspersed within this period.
Value stream analysis
Value stream analysis is a study that must be carried out before Heijunka work is started. In this way, the improvements that need to be made in the company's processes, and what kind of flow the processes will have in the future, will have been determined. To learn how value stream analysis is done, click here.
The importance of information flow
Information is also one of the most important elements whose flow must be provided in the production environment. The employee must know exactly what, how much, and when to produce. Otherwise, production slows down and stops. We can compare the movement of production to racing dogs chasing a mechanical rabbit. As long as the rabbit runs ahead, the dog will chase after it. The moment the rabbit stops and falls behind, speed drops; if the rabbit is too fast, the dog gives up the chase. Starting from this, it becomes clear that information must flow a little ahead of production, and only as fast as needed.
Starting the Heijunka practice
The Heijunka practice can be started on a line that is less complex than the other lines. In this way, employees are shown how much this process eases the work. At the start of the application, the team records all the data it has gathered on a large board and expresses the current flow visually. In this way, it decides where on the flow, and what improvements, need to be made. The target flow plan is drawn. The flow also includes all movements of information, product, and people.
The team rearranges the production line in line with the target plan, and, by trying the application out on site, possible problems are reviewed again and the necessary corrections are made.