Every business would like to have a consistent volume over time so there is a consistent and predictable workload. That is an easy sell in concept. But if your sales department does not behave like Toyota Sales by cooperating to avoid spikes in demand, what can you do?
The TPS expert might suggest that a manufacturer hold some finished goods inventory and build at a leveled pace to replenish what the customer takes away in a pull system (discussed in Use “Pull” Systems to Avoid Overproduction). The manufacturer screams, “But we have 15,000 part numbers!” The expert says, “Look for a smaller number of part numbers that are in big demand and perhaps even seasonal, build those when you have fewer real orders, and then keep those in inventory.” That is, use a combination of build-to-stock and build-to-order like the aluminum gutter company in the case study at the end of this chapter. This sounds reasonable to the manufacturer. But then comes the hard sell. The TPS expert says to changeover frequently to level the mix of products built every day. Most manufacturers balk. After all, it is so convenient building in batches, making product A for a while, then retooling, and making product B for a while, and so on. Quick retooling does not seem possible, until an expert shows them how they can do a three-hour changeover in five minutes. Even then, it is difficult for many manufacturers to maintain the discipline of quick changeover. And the real root cause of the problem may be sales promotion strategies that contribute to uneven customer demand. The most sophisticated lean enterprises begin to change their policies in sales to maintain a level customer demand. This requires a deep commitment at the very top of the company, but these organizations quickly find the enormous benefits of heijunka make it a worthwhile investment.
It cannot be overstated. To achieve the lean benefits of continuous flow, you need Principle 4: Level out the workload (Heijunka). Eliminating muda is only one-third of achieving flow. Eliminating muri and smoothing mura are equally important. Principle 4 focuses on muri and mura by leveling your product volume and mix and, most importantly, leveling out the demand on your people, equipment, and suppliers. Standardized work is far easier, cheaper, and faster to manage. It becomes increasingly easy to see the wastes of missing parts or defects. Without leveling, wastes naturally increase as people and equipment are driven to work like mad and then stop and wait, like the hare. Working according to a level schedule applies to all parts of Toyota, including sales. Everyone in the organization works together to achieve it.