To be able to effectively manage a large family, we run on a pretty strict routine — I didn’t say “schedule” here because our family operation is also very flexible and agile. But, we have a routine and we, for the most part, stick to it. One routine is that I make the kids’ lunches everynight for school the next day.
During one late evening last week while making peanut butter and jelly sandwiches (PB & J), I noticed that this was an opportunity to test batch-and-queue versus one-piece flow.
One-Piece Flow comes from the Toyota Production System, anglicized in the United States as Lean Manufacturing. One-Piece Flow is also known by various other names such as the following:
- One-piece Flow
- Make-one, Move-one
- Single-piece Flow
- Continuous Flow
- Flow Manufacturing
TPS emphasizes right-sizing your batches because batches that aren’t the right size leads to queues, which leads to waiting time, which leads to poor space or resource utilization, increased Work-in-Process (WIP) or Things-in-Process (TIP), longer cycle times, which are all forms of wastes or muda.
On the other hand, the Batch-and-Queue approach teaches us to build stuff, let it queue in front of the next step, all throughout the system. Batch-and-Queue systems lead to poor space utilization because of the batches of work waiting to be served that take up space on the production floor, longer cycle times, a higher probability of defects because you build stuff and let it sit and, lower morale because batch-and-queue leads to large sizes of work-in-process, not finished goods — the psychological message is that you’ve created a bunch of unfinished stuff, further burdening the team with thoughts of “man, we have so much more to do.”
Peanut Butter Sandwiches, One-Piece Flow
There are two ways to build sandwiches — the Batch-and-Queue method or the One-Piece Flow method.
- Batch-and-Queue: To build sandwiches the Batch-and-Queue style I would take 3 pieces of bread (3 lunches to make) and place peanut butter on it. Then, let the 3 pieces of bread with peanut butter sit, while I take 3 pieces of bread and place jelly on it. Then, I’d marry the two sides of the bread and be done with 3 sandwiches.
- Single-Piece Flow: For Single-Piece Flow, I’d take one piece of bread place peanut butter on it, then take one piece of bread and place jelly on it, and then marry them. I would do this 3 times.
Single-Piece Flow approach is much better because there’s no waiting involved, cycle time is shorter because I’m completing sandwiches at each motion, and I feel better because I can visually see what I have completed.
One-Piece Flow and Other Processes
One-Piece Flow can be applied to many other processes. Here are a few examples:
- Software: Most software is built modularly — that is, in small modules, where one class can consumes or uses the services of another module. Ideally, modular code is of the right size such that the engineer can build each module to completion including dependent modules, instead of building several modules in parallel, leading to task-switching, which is a waste.
- Software Requirements: Requirements documents are historically chubby, batchy documents. a one-piece flow approach is to follow the Agile method by creating user stories, sizing them by effort and prioritizing them, then unpacking each story into atomic units we call “tasks” with time attached to it. Each tasks represents the take-one put-one approach and forces continuous flow in software development. Joel (Joelprah) talks about task-switching for software and simulated the huge negative impact it has on productivity. The one-piece flow approach embraces iterative development and rejects the Waterfall approach, which is akin to Batch-and-Queue.
- Order Fulfillment: At Amazon it was mandatory to complete an order at a time, instead of several orders at a time. The associates had a difficult time understanding this concept until we showed them that the batch-and-queue approach leads to “switcheroos” — that is, mistakenly putting an item in the wrong order. The one-piece flow approach avoided this defect altogether and led to shorter cycle times, enabling the order to meet shipping deadlines.
There are many, many other processes where you can employ the principle of One-Piece Flow. A few things to keep in mind before employing One-piece flow:
- Process must be highly capable of consistently producing high-quality product. If there are serious and consistent quality issues, then one-piece flow will be difficult to implement.
- Process must be repeatable.
- Where equipment is involved, uptime should be close to 100%, otherwise interruptions will disrupt flow.
Today, take a look at the processes around you. In what ways can you implement one-piece flow in your environment?