Production Leveling

What is production leveling?

Production leveling is the balancing or leveling of production over a fixed period of time. Under the Toyota Production System (TPS) this process is referred to as heijunka (the Japanese term). Production leveling is one of the most challenging techniques to master in the pull production, continuous flow and just-in-time manufacturing techniques. Yet it is imperative to the success of these techniques. Without production leveling, all of the before mentioned strategies would not be successful.

Production leveling is a process that can be challenging because it requires the leveling of a world that is never leveled. Leveling as it is described here, is done so that production can match the demands of the customer. As you very well know, these demands are always changing. So instead, a close level match is to be found.

Production leveling is a lean manufacturing technique because its purpose is to reduce waste. Fluctuations in production lead to waste and therefore are to be streamlined and reduced as much as is humanly possible. Production leveling is rarely at a level of perfection and even its creators at the Toyota Corporation realize that they themselves have yet to come up with a perfect production leveling strategy. But they have come close by implementing a production process where first one model of automobile is made, then another model, then yet another. Batches or groupings of like products are made as small as possible in contrast to traditional mass production beliefs that bigger is considered better. Although to many mass production may seem like a more economically sound concept because change-over times are reduced, this process is not necessarily the only way to reduce waste and the method that yields the greater reduction of waste, lean concepts in this case, ought to be the preferred method of production.

Why is effective product leveling so difficult for managers to master?

Effective product leveling is extremely difficult for many manufacturing managers to masters because it goes against many managers' pre-conceived notions that a high product variety and high product demand volatility workplace is ideal. In America especially this mentality that mass production is the better way, goes contrary to many of the Lean Manufacturing techniques that these same manufacturers try to implement.

Managers are often falsely labeled with being resistant or afraid of change. In reality, many managers welcome change and are excited by the prospect of doing something new to take the company to a place of prosperity that they have never been before. So where is the problem? The problem that most managers encounter is an inability to think in a way contrary to how they have always thought. No matter how willing someone may be to change, it is something different entirely to completely change and in some cases reverse their method of thinking of concepts that they have long believed were fundamentally true. For example, many lean manufacturing principles rely heavily on the input of workers on all levels of production. Yet for some managers the need to have a hierarchy of management is so central to their beliefs about what it takes to effectively manage a business, that they dismiss this fundamental aspect of lean implementation all together. Another common mistake that managers would do well to try to prevent them from making is the mistake of demanding that only the right changes be made. There is no right way to make changes. No matter how long you deliberate or plan for a change there will be times when you suffer a loss. Activities of improvement will naturally bring about bumps in the road. There is no avoiding it, only overcoming it.

Some lean manufacturing myths that may hinder the implementation of production leveling

In order to implement production leveling, there are some imperative steps that must be taken to overcome the more common lean manufacturing myths. Just a few such myths are listed below:

• Production leveling implementation ides should come from management - This is a myth. Implementation ideas are often best when they come from those who will actually be the ones putting the implementation ideas into practice. Employees will not only be more excited about change when they are the cause for the change but they will take a more active role in seeing that the changes that they instigated work out because they have a vested interest in their success.

• Vendor relationships lead to volatility and un-predictability because their operations are separate from your own - This myth implies that a vendor could never have a loyal relationship with a manufacturer. This is not true, vendor-manufacturer relationships are mutually beneficial and when the vendor's input is involved in the lean changes being made by the company, they are more likely to develop a loyal relationship with that manufacturer. Your success is their success and they can feel like they have been a part of that change.

• Sales teams will suffer because of the transitional periods where production leveling is on the low side - This is more of a dramatized fear than anything else. Yes, it is true that in this system of production leveling there will be times of higher sales and times when sales are lower, however, it is how the sales team decides to deal with these fluctuations and contribute to the goal of leveling them out that will really make the difference.

• Imprecise measurements will lead to invalid quality and engineering contributions - This myth plays off of our need to have hard material or numerical evidence to support our entire decision making process. It can be difficult for trained accountants, quality assurance employees and engineers to work from measurements that are rounded and processes that are continually improving (or changing as they may see it). There is a different kind of data out there that also has validity in the lean manufacturing world that may not necessarily be comfortable for trained professionals to accept.

What is Heijunka?

Heijunka is a Japanese term that refers to the overall leveling, in the production schedule, of the volume and variety of items produced in given time periods. Heijunka is what most lean companies are working towards as they try to be able to make just what the customer wants in the time or when the customer wants it. In Heijunka the company is trying to do two things. One is to level production by volume and the other is to level the production by product type or mix of products. Heijunka takes the total volume of orders in a period and levels them out so the same amount and mix are being made each day. In short, what you are trying to do is to build a level schedule everyday by taking the actual customer demand, determine the pattern of volume and mix, and building your level schedule.

Production leveling by volume

Production leveling by volume is all about taking a long-term average and working that average into a production process that reduces variability. Say for example that you are a company that produces widgets. Your customer demand for those widgets is usually somewhere between 600 and 1000 units per production period and shipment. What you would want to do is coordinate your frequency of shipment times with your volume of production. In this example with the widgets, you may want to decide to always carry at least 800 widgets in your inventory (enough to cover one shipment) and to produce 200- 300 widgets every week for four weeks to have the minimum required for shipment but the flexibility to control how large the inventory amount becomes. Carrying this amount of inventory is advantageous because it provides stability and flow to the production line by not requiring that they make a different number of widgets ever week or even every day. The smoothing of the production line also helps to reduce process inventories thereby simplifying operations and reducing costs.

Production leveling by product

In the above example of production leveling by volume widgets were used to represent the product that your manufacturing plant may produce. But the fact of the matter is that most manufacturers are not only going to be producing one form of widget. There may be dozens of different kinds of widgets being produced as well as a number of completely different products that must also share the production line. In more realistic cases like these, the costs and time it takes to change over manufacturing materials to make new products is a real issue of time and money. The Toyota Corporation is the example in this area where their approach to production leveling by product resulted in a different discussion where it reduced the time and cost of changeovers so that smaller and smaller batches were not prohibitive and lost production time and quality costs were not significant. In order to simplify leveling of products with different demand levels Toyota created a "related visual scheduling board" known as a heijunka box. As a quick introduction to this method of production leveling by product, the heijunka box is generally a wall mounted schedule that is divided into a grid. This grid contains boxes in rows and columns. Each column of boxes represents a specific period of time, usually in days or weeks. Cards representing individual jobs (called kanban cards) are placed on the heijunka box to provide a visual representation of the production runs sequentially according to when they should take place.