Single Piece Flow
Why mass production isn’t the most efficient way of doing ‘stuff’
Right at the back of the book ‘The Lean Startup’ from Eric Ries, there’s a link to a video in which is demonstrated that ‘single piece flow’ beats the process of ‘large batches’ (or ‘mass production’) with a significant time and efficiency difference.
Imagine you need to mail 10 brochures to customers, by going through the following stages:
- fold 10 brochures
- insert them into envelopes
- seal the envelopes
- stamp the envelopes
Which approach will be better:
- Finish each step completely before you start the next one. This means first folding ALL the brochures, followed by inserting ALL of them into the envelopes, followed by sealing all the envelopes,… and so on, until you complete the last step.
- Fold one brochure, insert it into an envelope, seal the envelope, and stamp it. Continue with the next folder and go through this complete process for every single piece, until all pieces are done.
The majority of the people I’ve spoken too would select the first approach. This approach is called ‘large batching’, or ‘mass production’. It’s the process that you can find in large factories, where large inventories of unfinished parts are piled up, waiting to be finished in the next step of the production process. It’s the process used in most traditional car manufacturing plants, or any other traditional factory where goods are produced.
It will surprise most people when they find out that the second approach is actually the better one (in most situations). This process is called ‘single piece flow’, was first used by Toyota and therefore referred to as an important element of what later became ‘The Toyota way’ of doing things. Today this is referrenced to as ‘Lean manufacturing’.
Why is the second approach more efficient that the first one ?
It’s faster
Watch the video… otherwise you’re not going to believe me.
One of the reasons is that a large batch approach requires you to manage the piles of unfinished goods.
Reduced waiting times
The image below shows the differences between the two process flows for Folding — Inserting — Sealing — Stamping 5 brochures.
The waiting times are much shorter in a single piece flow. The customer can get the first finished product early in the process.
Reduced inventory
Faster shipment results in less inventory being needed. No inventory is required to store unfinished products.
Faster detection of defects
Imagine that the envelopes cannot be sealed because they don’t have any glue applied to them. This would be a total disaster in a large batch factory: unfinished goods will keep on piling up and a lot of time would have been lost.
In a single piece flow approach, you would be able to detect the problem during the completion of the first product.
Increased feedback
Let’s assume that the customer doesn’t like the brochures. Using large batches, you would have to discard not only the brochures, but also all of the envelopes because they can not be reopened without damaging them.
Not only will this result in more waste (throwing away the envelopes as well) but it will also increase the waiting time again because everything will have to be redone before the customer will receive new products.
Conclusion
All of these elements result in the following best practices for almost any production or office environment:
- make sure that the flow of work is clearly visible and tracked, by using a methodology like kanban.
- apply the Andon principle (stop the lines) whenever a critical problem is detected.
- apply WIP limits to reduce the work in progress.
These are the basics of Lean Thinking.
Stefan Luyten
For more information: http://www.triton-consulting.be
