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What Is Lean Manufacturing?

Excerpted from the book "THE MACHINE THAT CHANGED THE WORLD" Authors James P. Womack, Daniel T. Jones and Daniel Roos - reproduced with permission from Macmillan Publishing Company.

Our next stop was the Toyota assembly plant at Takaoka in Toyota -City. Like Framingham (built in 1948), this is a middle-aged facility (from 1966). It had a much larger number of welding and painting robots in 1986 but was hardly a high-tech facility of the sort General Motors was then building for its new GM-b models, in which computer-guided carriers replaced the final assembly line.

The differences between Takaoka and Framingham are striking to anyone who understands the logic of lean production. For a start, hardly anyone was in the aisles. The armies of indirect workers so visible at GM were missing, and practically every worker in sight was actually adding value to the car. This fact was even more apparent because Takaoka's aisles are so narrow.

Toyota's philosophy about the amount of plant space needed for a given production volume is just the opposite of GM's at Framingham: Toyota believes in having as little space as possible so that face-to-face communication among workers is easier, and there is no room to store inventories. GM, by contrast, has believed that extra space is necessary to work on vehicles needing repairs and to store the large inventories needed to ensure smooth production.

The final assembly line revealed further differences. Less than an hour's worth of inventory was next to each worker at Takaoka. The parts went on more smoothly and the work tasks were better balanced, so that every worker worked at about the same pace. When a worker found a defective part, he-there are no women working in Toyota plants in Japan-carefully tagged it and sent it to the quality-control area in order to obtain a replacement part. Once in quality control, employees subjected the part to what Toyota calls 'the five why's", the reason for the defect is traced back to its ultimate cause so that it will not recur.

As we noted, each worker along the line can pull a cord just above the work station to stop the line if any problem is found; at GM only senior managers can stop the line for any reason other than safety-but it stops frequently due to problems with machinery or materials delivery. At Takaoka, every worker can stop the line but the line is almost never stopped, because problems are solved in advance and the same problem never occurs twice. Clearly, paying relentless attention to preventing defects has removed most of the reasons for the line to stop.

At the end of the line, the difference between lean and mass production was even more striking. At Takaoka, we observed almost no rework area at all. Almost every car was driven directly from the line to the boat or the trucks taking cars to the buyer.

On the way back through the plant, we observed yet other differences between this plant and Framingham. There were practically no buffers between the welding shop and paint booth and between paint and final assembly. And there were no parts warehouses at all. Instead parts were delivered directly to the tine at hourly intervals from the supplier plants where they had just been made. (Indeed, our initial plant survey form asked how many days of inventory were in the plant. A Toyota manager politely asked whether there was an error in translation. Surely we meant minutes of inventory.)

A final and striking difference with Framingham was the morale of the work force. The work pace was clearly harder at Takaoka, and yet there was a sense of purposefulness, not simply of workers going through the motions with their minds elsewhere under the watchful eye of the foreman. No doubt this was in considerable part due to the fact that all of the Takaoka workers were lifetime employees of Toyota, with fully secure jobs in return for a full commitment to their work.¹

A BOX SCORE: MASS PRODUCTION VERSUS LEAN

When the team had surveyed both plants, we began to construct a simple box score to tell us how productive and accurate each plant was ('accurate' here means the number of assembly defects in cars as subsequently reported by buyers).² It was easy to calculate a gross productivity comparison, dividing the number of hours worked by all plant employees by the number of vehicles produced, as shown in the top line of Figure 4.l

However, we had to make sure that each plant was performing exactly the same tasks. Otherwise, we wouldn't he comparing apples with apples, So we devised a list of standard activities for both plants- welding of all body panels, application of three coats of paint, installation of all parts, final inspection, and rework-and noted

any task one plant was doing that the other wasn't. For example, Framingham did only half its own welding and obtained many prewelded assemblies from outside contractors. We made an adjustment to reflect this fact.

We also knew it would make little sense to compare plants assembling vehicles of grossly different sizes and with differing amounts of optional equipment, so we adjusted the amount of effort in each plant as if a standard vehicle of a specified size and option content were being assembled.⁴

When our task was completed, an extraordinary finding emerged, as shown in Figure 4.1. Takaoka was almost twice as productive and three times as accurate as Framingham in performing the same set of standard activities on our standard car. In terms of manufacturing space, it was 40 percent more efficient, and its inventories were a tiny fraction of those at Framingham. You might wonder whether this leap in performance from classic mass production, as practiced by GM, to classic lean production, as performed by Toyota, really deserves the term revolution. After all, Ford managed to reduce direct assembly effort by a factor of nine at Highland Park.

In fact, Takaoka is in some ways an even more impressive achievement than Ford's at Highland Park, because it represents an advance on so many dimensions. Not only is effort cut in half and defects reduced by a factor of three, Takaoka also slashes inventories and manufacturing space. (That is, it is both capital-and labor-saving compared with Framingham-style mass production.) What's more, Takaoka is able to change over in a few days from one type of vehicle to the next generation of product while Highland Park, with its vast array of dedicated tools, was closed for months in 1927 when Ford switched from the Model T to the new Model A. Mass-production plants continue to close for months while switching to new products.

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