Evolution of the Toyota Production System

Throughout our lives we are slaves to time. Our every working moment is scheduled and controlled by the inexorable ticking of the clock.

In manufacturing, under the auspices of Lean manufacturing and its champion, Toyota Production System (TPS), it is even more demanding with the actual speed of the production line exactly balanced to meet the demands of the customer. This speed or tempo of manufacturing is called takt time.

Takt time is Toyota's adaptation of the German word taktzeit, originally meaning 'clock cycle'. Toyota's meaning is slightly different in that it is the pace of production. For a given product line this pace is determined by dividing the allowable time in the production shift (for example eight hours, or 28,800 seconds) by the average production volume (for example 500 cars).

Takt time, or the rate of production, for the day becomes 57.6 seconds. Work at each operation is planned to be as close as possible to this. Anything faster is over production and slower is under production.

JIT's pillars

It is part of Toyota's overall Just-in-Time (JIT) pillar of production. A Mitsubishi aircraft plant applied the takt time concept in Japan, apparently having learned it from the Germans. Toyota combined takt time with flow production, pull system and level production to form the basis for its JIT System.

The phrase 'Just in Time' was coined by Kiichiro Toyota around 1937. The element of takt time was not really formalised in Toyota manufacturing until after World War Two. It took a while to iron out the details in Taiichi Ohno's manufacturing shops where he experimented with these concepts.

One man who understands the importance of takt time to the TPS is Art Smalley, the author of the Lean Enterprise Institute (LEI) workbook 'Creating Level Pull: a lean production system improvement guide for production control, operations, and engineering professionals', which received a 2005 Shingo Research Prize.

Smalley learned about lean manufacturing while living, studying, and working in Japan for ten years as one of the first foreign nationals to work for Toyota. He spent the majority of his Toyota career helping the company transfer its production, engineering, and management systems to facilities around the world.

After leaving Toyota, Smalley became director of lean production operations at Donnelly Corporation, (now part of Magna Inc), a tier one auto--motive supplier with more than 15 plants in North America and Europe. Smalley subsequently joined McKinsey & Company, where he was the firm's leading expert in lean manufacturing. He currently aids companies implementing lean through Art of Lean.

Limiting wasted work

"Takt time limits over or under production," he says. "It attempts to synchronise processes so that there are no delays or build up of excess inventories in terms of scheduling. In terms of productivity, it seeks to maximise the productivity of the employee so that no seconds are wasted during the day."

Takt time is one of three elements for standardised work, the other two being work sequence and standard work in process. "Standardised work is a work analysis tool that centres upon human motion," he continues. "Workers are tasked with work elements that reflect takt time so their available time is used effectively. Using takt time in conjunction with time and motion studies Toyota teams analyse their jobs and make small incremental improvements every month."

At Toyota they attempt to keep takt time steady for a month at a time. However, volume changes in the market place over time (let's ignore mix for the moment). As inventory increases and sales fall, Toyota adjusts takt time from 57.6 seconds to a slower number to reflect the decline in demand. This will continue as needed each month. When inventory falls (sales pick up), they will increase takt time to a faster rate (such as 48 seconds) and, of course, potentially add more workers to the line. Month by month, Toyota does this type of adjustment and moves people to where they are needed the most to reflect demand conditions.

The use of takt time is not suitable for all types of manufacturing. It works best in discrete part examples like automotive manufacturing with some volume. In a slow build environment like satellites it is somewhat less useful.

At least the concepts need to be played with a little. "For example, if a company makes one satellite in two years the takt time is two years and it does not really help me then," Smalley explains. "I need a more detailed breakdown of the work to see if I am staying on track day by day and week by week."

Similar work content

Takt time also works best when the products going down the line have similar work content. If type A has 30 per cent more work content than type B and they come back to back, then there is some difficulty. You wind up having to take a weighted average cycle time for the different products.

Takt time is also important in terms of determining if things are ahead or behind in production during the shift. "If things are ahead of schedule then there may be residual play in the line [improvement potential].

"If things are consistently behind then problems are occurring and these stoppages have to be identified and then become the focus of improvement projects. Takt time does not solve problems, however, it relentlessly exposes problems and weak points which then have to be improved."

To implement takt time changes successfully requires some ability to move the workforce around on a monthly basis. When takt time changes, the staffing on the production line changes as well (up or down). Usually when one line is busy another line is slow. When everything is slow workers are taken off line and put to work on improvement projects for a defined period of time.

In tough economic times like this current global downturn, however, things are pretty abnormal. Toyota has taken to idling plants for short periods of time, perhaps the most extreme takt time adjustment you can make.