Feb 1 2015
Origin of One-Piece Flow at Toyota | Chip Chapados | LinkedIn
According to Chip Chapados, the concept of one-piece flow emerged from the need to rapidly detect defects in engine castings when Kiichiro Toyoda was reverse-engineering a Chevrolet engine in 1934, and it was originally called “one-by-one confirmation.”
In the TPS Principles and Practice discussion group on LinkedIn, he gave the following explanation to the origin of one-piece flow at Toyota:
Let’s revisit the origins and reasons for one piece flow. According to Mikio Kitano, former President of Toyota U.S., one piece flow was originally called one by one confirmation. In 1934 Toyota was trying to duplicate the Chevrolet six cylinder engine. They were having difficulty with casting the heads. After they thought that they had refined their processes adequately they made a batch of approximately 300 castings which were then sent for machining. After the parts were machined and engines built it was discovered that many of the engines performed poorly. Investigation showed that there were significant defects in many of the castings.
The head of the team, Kiichiro Toyoda (son of the founder of the company), decided that continuing batch production as they were doing it was too costly, so he put in place a process where each casting as it was made would be sent to the next step (machining). Machining workers would carefully inspected, and if it failed to pass, it would be sent back to casting. In short, machining would “confirm” that the casting was good before they put in additional time machining. Soon, the entire production line was set up using one by one confirmation.
The people who would start assembling after machining would check the machined parts to make sure they met specifications, and if they didn’t they would return them to machining, and so on down the entire line. One piece flow has always had at its heart the idea that only “good” parts should be worked on at the next work station. What was soon realized that by doing one by one confirmation lots of other benefits besides quality occurred. The overall cycle time for production was shortened, inventory was reduced, customization could be inserted without great difficulty, One by one confirmation became known as one piece flow. Usually, because the history of one piece flow isn’t known, people don’t tie quality into process as was originally intended.
The Toyota UK company blog gives the following additional information about the Toyota 1934 engine:
Eighty years ago to this day, development of Toyota’s first engine, a prototype 3.4-litre straight-six called the Model A, was completed and signed off for production.
Based on the design of a contemporary Chevrolet unit, Toyota manufactured its own cast parts such as the cylinder head, cylinder block and pistons, while employing off-the-shelf Chevrolet components for the crankshaft, camshaft, valves, plugs and electrical components.
Toyota had re-engineered the cylinder block’s water jacket using inspiration from an efficient oil cooler design, while the cylinder head benefited from a redesigned swirl combustion chamber. These modifications allowed the Model A to outperform the Chevrolet engine, reaching an output of 65bhp at 3,000rpm.
February 1, 2015 @ 12:42 pm
I find it hard to belief the explanation that the origins of one piece flow came from the attempt to produce one piece supply from a foundry to a machine shop and then from machine shop to assembly in the 1930’s. My own understanding is that it came from the desire to produce products Just in Time. Over the years the batch size was then progressively reduced. The quality element is covered by Jidoka, which is essential to the success of one piece flow. JIT and Jidoka are the two main pillars of TPS. —
When lean thinking was being extracted from TPS not enough emphasis was given to Shigeo Shingo’s original thinking on the structure of productive activities. This created a serious flaw in lean thinking. —
In 1989 I had a one hour session by myself with Shingo and his interpreter. The major part of the time was Shingo explaining his concept that the production mechanism should be seen as a network of two flows; Processes and Operations. My reason for asking him about this subject was the fact that the same two pages on this subject appear in all his books. When I asked him how important this concept was he said it was fundamental that these concepts and their relationships were understood in order to make effective improvements in productive activities. The comments below are based on the notes I took at the time and my subsequent experiences. —-
He explained; Production is a network of two activity flows. Processes and Operations. —-
Processes. These are the sequence/flow of events that products and services pass through on their journey from raw material/information to being finished items. —
I.e. Storage —Transportation — Storage/delay —transformation — storage/delay —- transportation. Repeat —
Within the process flow there are two types of storage/delay; Lot Delay and Process Delay. —
Lot Delay. An item is delayed while the rest of the lot/batch is produced.
Solution —One piece flow. —
Process Delay. An item is delayed while it waits for previous items to be processed through the next machine/activity. Solution — Synchronise cycle times. —-
Operations This is the sequence/flow of activities conducted by people, machinery and systems on the raw materials/information and products at each process stage. —-
I.e. Set-up — Essential motion — Auxiliary motion — Marginal allowances. Repeat—S.E.A.M
(Essential motions are those that produce what the customer requires; are valuable to them. i.e. P.S.E. P — Product- the physical item. S — Service to support the product. E — Experiences the customer enjoys acquiring, using and maintaining the product/service). —-
If you see processes as the vertical flow and the operational one as a horizontal flow along from each process stage you can see his network. —-
What then becomes obvious is that only the essential step of the transformation process is valuable to the customer, everything else is waste and is a candidate for elimination. —
The fundamental rule is to improve the process before the operation. Don’t improve transportation eliminate it. —
The ultimate goal is one piece flow with synchronised cycle times that represent customer demand rate. —-
When you see all these elements you can appreciate Shingo’s genius for simplicity. They should be the basic principles for all lean thinking and waste elimination activities. —
When you understand Shingo’s network, which I understand came from his work with and studies of the activities at Toyota Motors, it becomes easy to see the waste in any system.