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A new Honda Motor Co., Ltd. plant in Prachinburi, Thailand, is unlike any other in the world. In operation since March 2016, the factory currently turns out a mix of four models: the Jazz (also sold as the Fit), the City (also sold as the Grace), and four-door and hatchback versions of the Civic.

What sets the plant apart is not its products but the revolutionary system that Honda has installed there for the final assembly process, when parts are attached to the car after the body has been welded together and painted.

Normally, vehicles are assembled on a moving line, and individual workers are responsible for attaching only a few parts to the body of a car as it moves past them along a conveyor belt.

But at the Prachinburi plant, all the parts for a single car are attached by a small team of workers who ride along the line together with the vehicle they are responsible for.

The concept is based on the assembly method known as “cell production,” but it is so revolutionary for the automotive industry that Honda saw fit to name the new assembly line the Assembly Revolution Cell, or ARC, line.

“The Prachinburi plant, with its ARC line, is the only automotive plant in the world using cell production for the mass production of cars,” said Nobuhiro Kozasa of Honda Engineering Co., Ltd.

According to Honda, the ARC line boosts productivity by 10 percent, but this official estimate is likely modest. The actual improvement may well be much higher.

The ARC system brings flowing cell production to the assembly of cars.

SIZE MATTERS
Cell production is a well-established method for assembling consumer appliances and relatively small items of industrial equipment. Because the equipment investment is low and the system can be applied to high-mix, low-volume production, cell production has helped to greatly reduce costs and shorten lead times at factories. For some products, cell production has boosted productivity by more than 30 percent.

The advantages are obvious, so why hasn’t cell production been used in automaking before?

According to Kozasa, one reason is size.

Normally, with cell production, workers do not need to move around very much to perform their tasks, which translates to less loss. But because car bodies are so big, workers have to make large movements and travel relatively long distances just to reach the parts or tools they need. All of these so-called incidental movements cancel out the advantages of cell production.

Honda’s breakthrough was to figure out a way to reduce incidental movements so that cell production could be used even for assembling large products.

LOOP OF CELLS
The ARC line is composed of a number of ARC units, moving platforms on which teams assemble the cars.

Each ARC unit is composed of two work areas: one round platform and one rectangular platform with concave sides that match the arc of the round platform. The ARC units are lined up end to end, with the rectangular platforms of one unit fitted against the round platform of the previous unit. The car body sits between two round platforms, with work areas on all four sides providing room for tools and parts.

A team of four workers boards the ARC unit and moves with the car body around the ARC line. Each worker is tasked with assembling all the parts on one of the four sides of the car—right, left, front, or rear. The parts for each of these areas are all available right on the platform, helping to minimize incidental movements.

If the ARC units were simply lined up on a nonmoving production line—as in conventional cell production—then supplying car bodies and parts to ARC units further down the line would entail traveling significant distances.

Honda’s answer was to move the units in a loop. The entire ARC line is akin to a slowly moving string of beads. When an ARC unit reaches a certain place in the loop, the car body and the parts are placed on the platform, and the four workers climb aboard to begin their tasks.

Increased productivity is not the only advantage that Honda expects to reap from the ARC line system.

By adding or removing ARC units, the automaker can also flexibly respond to changes in production volume.

Automotive technology is advancing rapidly. By adding units and extending the loop, Honda will be able to handle the increased parts count that new technologies such as advanced driver-assistance and self-driving systems will require.

One challenge with the ARC line system is that it requires skilled workers who can take responsibility for assembling many kinds of parts. To secure such workers, Honda plans to train people “offline” so they can learn at their own pace without disrupting the moving production line.

Originally published in Nikkei Monozukuri, July 2017

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For some products, cell production has boosted productivity by more than 30 percent.