One Piece Flow is one of the lean tools developed at Toyota, and is sometimes referred to under different names like Single Piece Flow, Continuous Flow or Flow Manufacturing.
It is in some way opposite to traditional manufacturing which is done in large batches that are moved from process step to process step. One Piece Flow has a smooth flow of product through the process without build-up of material along the way.
One Piece Flow vs. Series Production
In a traditional factory with series production, it is easy to see how producing in a larger volume is more economical. Below is a simple example that illustrates this.
If a phone manufactures monthly labour cost is £20.000 and it produce 1000 phones a month, the cost to produce each phone is £20 plus material, if on the other hand demand increase to 2000 a month, the price to produce each phone is only £10 plus material.
Now for both One Piece Production and Series Production, selling more will always increase profit. The difference between them is the actual cost of producing the product.
Below is a comparison of the two types of productions, when producing exactly the same product. To keep it simple and easy with the purpose of showing the idea behind the two types of manufacturing, I have used a product most people are familiar with. In the example, the two factories will produce a pencil as seen on the picture below.
An order of 4000 pencils a month for 6 month is send to each factory, which both have the four people (Ben, Mike, Sara and Donna) available to do the job.
Series Production Factory (SPF)
- Every month SPF order
- 4000 pencils
- Material to produce 4000 ferrules
- Rubber Material to cut 4000 erasers.
- Ben machines the end of the pencils preparing them to have the ferrule added. As he finishes them, he places them in a box until he has around 100. He then walks over to Sara with the box and returns to start fill another one.
- Mike creates the ferule from the material ordered. He also place them in a box until it reaches around 100, then he walks over to Sara with the box and returns to start fill another one.
- Donna cut the rubber material into erasers. She also place them in a box until it reaches around 100, then she walks over to Sara with the box and returns to start fill another one.
- Sara assemble the three parts (pencil, ferule and eraser) together to the finished product and put them in a box.
- Every week the produced pencils (around 1000) are picked up from Sara and shipped to the costumer.
Now the same people walk over to the One Piece Flow Factory (OPFF) to produce the exact same product.
One Piece Flow Factory (OPFF)
- Two times a week OPPF order
- 500 pencils
- Material to produce 500 ferrules
- Rubber Material to cut 500 erasers.
- Ben sees that the marked area between him and Mike is empty and create a ferule to place it there.
- While Ben does that, Mike cut an eraser from the rubber material and put it into the ferule and places the assembly in the marked area between her and Sara.
- At the same time Sara machine a pencil and then pick up the assembly from Mike and put it on to finish the product. The finished product is placed into a box
- Every day the produced pencils (around 200) are picked up from Sara and shipped to the costumer.
Now in the One Piece Flow Factory Donna was not needed to produce the order, so she got a role doing continuous improvement in other areas of the factory.
If looking at some of the waste that is seen with Series Production compared to One Piece Flow in above example.
Inventory: The Series Production has much more inventory than the One Piece Flow. E.g. Materials for up to 4000 pencils compared to 500 pencils. Also there is always 100 work in progress (WIP) pencils with Series Production compared to less than 5 with One Piece Flow.
Issue: if a defect is found or a designer introduce a change, much more material and WIP pencils are affected and have to be scrapped.
Defects: If the machine that produces ferules start producing defective parts, it is seen much later with the Serial Production compared to One Piece Flow due to all WIP.
Issue: In Serial Production you could end up with a machine that produce defective parts for a long time resulting in huge amount of scrap, with One Piece Flow it would be detected right away and no further scrap produced.
Implementing One Piece Flow
With all the advantages, then you might ask why One Piece Flow is not implemented everywhere. Well in order for a production to qualify for or be able to take advantage of One Piece Flow, it must fulfil following criteria’s.
- The process must be capable to continuously produce good products. If there are a lot of quality issues, it is not possible to implement One Piece Flow.
- When equipment is used, it needs to have an uptime close to 100%.
- Process times must be repeatable; One Piece Flow is not possible with too much variation in process times between the steps.
One Piece Flow is one of the lean tools, if you found it interesting then our 5S Training might be of interest to you. It is usually the first step to take when starting out with lean, as it creates the foundation for further improvements to be implemented.
Alternatively you can continue to our Quality Training page to see some of the other types of training we provide.Go to Quality Training