Production Leveling: Extended Entry
What is Heijunka?
Starting with production leveling, Toyota's view is that production systems vary in the muri and mura and the capacity of a machine is forced in some time periods. Muri or overburden is considered to be all the unreasonable work that management assigns upon workers and machines due to poor organization. Some examples of muri are carrying heavy weights, dangerous tasks (behavior-based safety issues), and working at a significantly faster than normal pace. Muri defines this work as pushing a person or machine to a pace beyond their normal limits. Muri is associated with the preparation or planning phase of the production process. Mura or inconsistency focuses on the implementation and elimination of fluctuation of scheduling. This usually falls to the operations level to schedule the quality and volume of the production process.
The approach Toyota uses to combat muri and mura is to manufacture at a long-term average demand and carry a level amount of inventory to keep up with a variable demand. This means they will have a stable production process and will reduce the frequency of shipments.
Leveling the production by product type is a little different. Most companies produce a mix of products and the quantities of specific products is uneven. Again, the solution Toyota used was to reduce the time and cost of the production changeovers so that smaller batches of products were produced and the lost production time was minimal. This leveled out the demand for certain components and reduced the total inventory that was not used. Toyota uses a heijunka box to achieve the heijunka style efficiencies; this is basically a visual scheduling board that shows the different demand levels for certain products.
Implementing heijunka helped Toyota reduce vehicle production time and inventory. Toyota is known for creating lean manufacturing or the Toyota Production System, as they call it. Several successful companies have looked to their approach to reduce excess waste at their organization and increase overall productivity.
How does Production Leveling work?
Production leveling works by trying to keep these fluctuations to a minimum or a zero. Toyota implemented production leveling and their strategy is to never assemble the same automobile model in a batch. There production is leveled by making a single automobile, then another, and so on. Production leveling focuses on making smaller batches as compared to mass production where more is considered to be better. The final assembly process assembles the car in a small batch, just like all the earlier processes.
In the past long changeover times have meant that it was smarter to produce as many parts as possible. Now, the Toyota Production System has proven that die changes can be made quickly and can be improved with more practice. To give you a good perspective of how changeovers have improved it has been stated that "in the 1940's it took two to three hours, in the 1950's it dropped from one hour to 15 minutes, and now it takes three minutes." This is a significant improvement from the old methods of mass production.
Toyota is continuing to work on the final stage of production leveling to ensure all their processes are level. Single piece flow is the intended result of production leveling and so far, it is in the intermediate stage. Toyota is a large advocate of single piece flow because you can determine where adjustments and adaptations need to be made in the production stage. This will help your business because you will avoid major issues in the future.
Why should my company implement production leveling?
Ideally, you should not have any work in progress apart from the parts that are being processed in the work areas. Unfortunately it is very difficult to run your business after this manner. There are so many constrictions that prevent this from happening such as: machine capacity requirements, technical requirements of machinery, and human limitations. Equipping your facility to handle the peak requirements all the time will create a cost with a non-added value. This is simply because during off-peak periods, your machine will be running as though it is a peak period. Hence, this is why you need to implement production leveling to obtain a smooth, consistent balance all the time.
Production leveling will prevent overloading the machinery and people during the peak seasons. If your demand fluctuations are predictable, then this is the easiest way to see how production leveling will help. By understanding the fluctuations, you can collect good data and analyze the mechanisms to gain a proper evaluation. Production leveling initially requires some work from you in the beginning, but it depends upon the predictions rather than the actual demand. Leveling out the production load will reduce the cost of operation and will reduce the stress on your machines and your employees. Another great benefit to production leveling is that it will create value to the customer. To put it simple, production leveling will make your internal processes stable during the fluctuating external demands of your customers.
By putting your products on a repetitive production cycle, you will find that it is unnecessary to change this cycle for extended periods of time. By accomplishing this stabilization, you are gaining a benefit in the form of "economy of repetition." This basically means that when you run the same sequence every time for the same amount of time for each product, your production team is more capable to reduce setup time, deal with maintenance and material issues, adhere to a standard of work, and run lengths for each product that is varying.
As your business learns to master production leveling, it will be possible to incorporate more and more products into this new steady sequence, until your entire process is leveled. The frequency of your products will also increase from a monthly to a daily process. The more you practice production leveling, the more your production team will be able to gain experience and monitor the varying volumes.
Eliminating waste is essential to watch your company grow. Unnecessary steps, unnecessary handoffs, and other factors can be completely eliminated with implementing lean manufacturing and production leveling. While many think the concept of production leveling combats lean manufacturing, it really is an additional tool to include in lean manufacturing. It is important for those in the production industry to implement lean manufacturing or at least adopt production leveling (heijunka). This will ensure you that every process at your company will be leveled by volume and mix. This creates a smoother working environment for everyone at the facility and will create a better experience for your customers. If you are giving your customers their products on the date promised, your customer satisfaction levels will increase and this in turn causes your overall profit margin to increase. It has long been stated that word-of-mouth is one of the best marketing tools businesses have, by implementing production leveling; you are saving on a marketing cost as well. The customers are happy and you are satisfied because you have saved money and reduced muda, muri and mura. Plus, your employee satisfaction levels will increase because they are not feeling overburdened by their workload.