Flow is the movement of a product or service through a process in a continuous stream of value. A process might have several steps, for example:
One goal of Lean thinking is to move towards continuous flow in a process. Perfect flow is achieved when only value is added, the work between process steps is balanced, and work in progress (WIP) is eliminated. Any mistakes and process issues become obvious in a process designed to flow, and therefore fixed quickly (ideally to root cause, so the issue does not resurface).
The counter-intuitive benefit of Flow
Perfect flow is rarely achieved, even with the best-designed processes in the world, and attempting continuous flow in a poorly designed process leads to many stoppages and an out-of-balance condition. It is therefore typical to use WIP and other buffers in a process to soften the impact of these wastes. Even Toyota does this – they split their assembly lines into sections and build small buffers of WIP before and after each section to deal with minor stoppages.
Attempting to flow makes process wastes visible – so the wastes can be addressed and improved. A process with large buffers (often represented by WIP or inventory) minimizes the true effect of the wastes in the process. Large buffers due to batching work or inventory is akin to raising the level of water in the stream. The buffers not only hide the other problems but they are a form of waste themselves. Only by lowering the buffer will the wastes become visible so they can be eliminated.
This short video does an excellent job showing the benefits of one-piece flow. Changing the batch size does not change the work completed, but with one-piece flow the work is completed more quickly, feedback is immediate, and WIP is eliminated.
Our continuous improvement workshops include several simulations that demonstrate the difference between Flow and Batch. Click on the link to sign-up for a workshop today!