Flow (One Piece Flow)

In a Lean manufacturing setting, products are ideally “pulled” through the value stream, one piece at a time, continually. There might be times when batches greater than one are necessary. But, the goal with Lean is to find ways to reduce batch sizes in a way that improves flow without harming quality. Each step is ideally adding value, without waste, when the customer requests it (although there might be some “necessary waste.”) It is a similar process when performing a service for a client. 

Think of a value stream as a relay race. When the gun goes off (initiation of the value stream), each of the four runners advances one baton in a predetermined order (using standardized work). Each runner runs his leg of the race quickly and skillfully (adding value), and the hand-offs (pull) occur smoothly and without delay (waste), just at the right time (JIT) when the next runner signals his readiness (kanban). The result is, hopefully, a flawless (perfect) execution, in record time resulting in a first place medal (satisfied clients). The runners are ecstatic and proud (confident and engaged). The fans go wild (positive word of mouth advertising)!

This is opposed to “batch and queue” production where batches of product are produced at one time and then stored before going on to the next step. This results in much “hurry up and wait,” a lot of work in process (WIP) inventory, large amounts of warehousing space, and longer lead times.

For example, a product requires three steps to produce. Each step requires 10 minutes. In “batch and queue” mode, 10 units are produced at one time. The first step requires 10 units × 10 minutes = 100 minutes. The second step requires 10 units ×10 minutes = 100 minutes. The third step requires 10 units × 10 minutes = 100 minutes for the entire batch. However, the first unit is off the line in step 3 after 10 minutes. Therefore, it requires a total of 210 minutes (the lead time) for the first unit to be available to the consumer, and 300 minutes for the entire batch to be ready. This is not considering any waiting time between the batch processing steps (which tends to occur any time we have batching). 

Compare this with one-piece flow, where the first unit is through step 1 in 10 minutes. It then progresses straight through step 2 in 10 minutes and, finally, straight through step 3 in 10 minutes. The total elapsed time until the consumer receives his product is 30 minutes, plus any delays between steps. One-piece flow results in a savings of 180 minutes and is 85.7% faster.

In a multi-doctor hospital, four 10:00 am appointments arrive at the same time. Each client requires ten minutes to get the primary complaint, update the client information, pull the file, write the date and reason for the visit in the medical records, weigh the pet, and enter that data into the medical records.

The receptionist checks in all four clients before signaling to the techs that clients are ready to be seen.  This means that the first client is not seen until 40 minutes after his/her arrival.

In one-piece flow, the first client could be seen within ten minutes of arrival (and probably be checked out and on the way home before the fourth client gets into an exam room).

Or, techs draw all of the morning blood samples of hospitalized patients before centrifuging and running any of the tests. This keeps the doctor from being able to formulate any treatment orders as quickly as he could if blood samples were run as they were drawn.

Flow is the result of good value streams, JIT, kanban systems and standardized work. Flow equals value to the client. What’s also unintuitive is that reducing batch sizes can improve productivity. People often think working in batches in faster. Sometimes this is true, but not always. It depends on the work and the setting. We do know that working in batches creates a lot of waste -- sorting, moving, inspecting batches, logging them in computer systems, etc. -- work that wouldn’t be required if we had better flow. 

Improving flow in healthcare settings often requires changes to the process, such as the physical layout of a department or clinic. In the Lean mindset, we’d challenge ourselves to ask why we have batching or a particular office layout. “It’s always been that way” doesn’t mean it has to be that way in the future. If it is not adding value for the client or pet, it's probably muda and needs to be removed from the system.