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.