The power of one piece flow

I remember when my teacher in Japan tried to explain to me that we should stop the batch and queue manufacturing and build in one piece flow. I looked at him like he was crazy. All of my industrial engineering school told me to calculate economic order quantities, and ideal transfer batch sized to keep cost as low as possible. The lesson went like this.

We must produce one piece at a time!

NO, it can’t be better to build one at a time.

Look it produces parts faster, with fewer defects.

Not possible, the text book says we need to calculate the economic batch size, and that math says we need to be producing in batches of at least 10, 100 would be better.

Frustrated my teacher walked away, he returned 5 minutes later with a box of BIC click pens.

He poured them out on the table and began to take them apart. The different parts were segregated into piles. Out came the stop watch. I was asked to assemble the pens in the batch process that I thought was better. At the end of my assembly time I was told how long it took get the first pen assembled and how long it took to assemble all of the pens.

My teacher then took the pens apart again, and segregated the parts. My turn to time him. He built each pen one at a time until the entire box was assembled again. I marked down the time for one pen and then the whole box. He was faster, not only the first pen but the entire box.

Me being the difficult student that I am, I said, well then I need a bigger batch size to make up for the extra motion. So he left again. This time he returned with a stack of paper a stapler and a stack of envelopes.

The new process was to sign and date the paper fold it in 3, staple closed, and stuff in the envelope.

I picked a batch size of 10. Sensei picked one. He beat me. I picked a batch size of 20 sensei picked 1, he beat me by a greater margin. I picked a batch size of 5 he beat me again.

OK you have proven the point that batch size of one is better now can you tell me why?

He wrote this formula

Lead Time = cycle Time X WIP

In Lean we are trying to get to the lowest possible lead time to have the least amount of waste in the process.

Since this learning I have repeated these experiments many times to explain the importance of one piece flow. When working in the electronics business, I started with the implementation of one piece flow through the assembly process. Going from batch and queue or Stall build to one piece flow was easy to do, but difficult to convince the leadership team it was a good thing. The fear of losing control was holding them back. The truth was they had no control at that point. The Result was a lead time reduction form weeks to hours. My Manager wanted to understand how this improvement was possible. I showed him the formula.

When I joined the school bus industry the first improvement project was creating a one piece flow assembly for the window assembly department. From there one piece flow expanded through the business until the entire build of the school bus was in one piece flow changing the WIP from 1200 buses to 48 buses, the lead time to build a bus went from 8 weeks to 3 days. The results were incredible.

Now in the auto industry the concept of one piece flow is the most difficult concept to get embraced. Most leaders I meet are afraid to remove the inventory between work centres for the fear of what happens if the machine stops working, How do I protect the customer from disruption of supply? I though the auto industry was supposed to be ahead of the rest of the world leading the charge of lean. I am finding that the auto industry has fallen so far behind the current lean thinking, I am scared for our future.

So please if you are working on any multi step process, look to how you can apply one piece flow. Whether you are making a product for sale, or writing your Christmas cards, try one piece flow. You will be amazed at how much effort it takes to change your habits, and how much better the process is.

#LeanManufacturing #onepeiceflow