If some problem occurs in one-piece flow manufacturing then the whole production line stops. In this sense it is a very bad system of manufacturing. But on the other hand, when production stops everyone is forced to solve the problem immediately. So team members have to think, and through thinking team members grow and become better team members and people.
Teruyuki Minoura, former President, Toyota Motor Manufacturing, North America
Continuous flow means that when your customer places an order, it triggers the process of obtaining the required raw material, just for that specific order. Then, the raw material flows immediately to the supplier plants, where the workers also immediately complete the order, flowing the completed order to the customer without any delay. The entire process should take a few hours or days, rather than a few weeks or months.
Of course, the ideal of one-piece flow is not reality, yet, and Toyota is anchored in reality. This is why you will not see Toyota bringing machines and suppliers together, forcing the one-piece flow where it does not fit. Taiichi Ohno wrote that achieving flow takes time and patience. Inventories are used judiciously where continuous flow is not possible today. But the ideal of flow provides a clear direction. At Toyota, this means using small lots, having the processes laid out as close as possible and keeping the material moving through the processes without interruption.This is much better than producing large batches and having them “sit and wait”.
Toyota managers and engineers do not have to do a detailed cost-benefit analysis every time they want to implement something that is going to improve flow. Cost is obviously a factor, but the plan is to create flow wherever possible and continually improve towards a better flow. Click To TweetEven though Toyota installs inventory in places where continuous flow is not possible, the objective is to go on reducing inventory all the time to improve flow. In fact, inventories put in the right place can actually allow for better overall flow throughout the company.
One of the comforting aspects of traditional mass production thinking (as opposed to Lean Management) is that if one of the processes stops producing, because it takes a long time to changeover a machine for a new process or because a person is out of work or the equipment broke down, all other operations in the process, which are “separated”, can continue to work because there is a large amounts of inventory. If operations are joined in a one-piece flow, the entire cell will slow down if only one piece of equipment should fail. You sink or swim together, as a unit.
In that sense, why not having some inventory to make life a little more comfortable? Because if there is a lot of physical material or virtual information waiting to be processed, inventory hides problems and inefficiencies. Inventory allows for the bad habit of not having to deal with problems. If you do not solve your problems, you will not improve the systems that enable you to achieve the results. Continuous flow and continuous improvement (kaizen) go hand in hand! Click To Tweet As Minoura, former president of Toyota Motor Manufacturing, North America, and Taiichi Ohno’s disciple explains:
The purest form of pull is one-piece flow. When we run one-piece production, we can’t get the amount we want, so we get frustrated and don’t know what to do. But then, within that, we have to find a way to think: what is the way to get the required quantity. This is the true essence of the Toyota Way, and, in that sense, we create confusion, so we have to do something different in the way we attack this problem.