That fixture commonly encountered in the modern restroom: the electric hand dryer. At the Honda Suzuka Plant, what passes through this appliance is not human hands, but rather gears—gears held by robot hands, to be exact. Equivalent to its bathroom counterpart in both appearance and function, the hand dryer is a strange sight to behold on the production line.
This hand dryer is being used in gear finishing and washing carried out by the Transmission Machining Department. Its job in these processes is to remove cutting oil from the gears after polishing: the oil-drenched gears are inserted into the opening of the dryer, and fast-moving air blasts the oil off.
This unique method of removing oil arose from the consolidation of production processes to increase efficiency. The Suzuka Plant produces the N Series, a line of mini-vehicles that continues to be popular in Japan, with cumulative sales topping 1.5 million units in November 2016.* To meet this demand, the entire plant has had to run at full capacity while streamlining its operations. Gears are no exception: daily production volume for these parts has had to increase too.
Among the various steps involved in making gears, two are relevant here: a finishing process that polishes the gear teeth, and a washing process that removes the oil used for polishing. Before line consolidation, these two processing lines were separate; freshly polished gears were collected and, when they reached a certain number, carried to another line with a large washing machine. The consolidation project combined these two lines. Gears are now promptly washed, thereby increasing both work efficiency and production volume. At the same time, however, this also created a problem.
Yuichiro Takezaki, who managed process consolidation as project leader, explains the problem.
"Since consolidation, we’ve had to feed more cutting oil into the polishing machine used in the finishing process and also replace the washing fluid in the washing process more often, which also increased the amount of fluid waste. As it turns out, the reason was because the gears were moving to the washing step without enough of the cutting oil removed."
The previous setup allowed adequate time to remove the oil between finishing and washing. Oil dripped off by its own weight as the gears waited for collection and were carted over for washing. The process even incorporated a means of collecting and reusing that oil. But the newly consolidated line allowed only 10 seconds for oil removal—not enough to remove oil properly as before. Consequently, gears were carried to the washing machine along with large amounts of oil.
The consolidated gear finishing process. One robot performs all steps from polishing through washing.
Yuichiro Takezaki, Senior Staff, Transmission Machining Department, Suzuka Plant, Transmission Factory, Production Operations
Work flow before and after consolidation of the gear processing lines
Oil on gears means oil not collected. Line workers compensated for this drop in reusable oil by adding fresh oil, increasing its consumption. Naturally, the large amount of oil carried into the washing machine also degrades washing fluid more quickly. The result was replacing the washing fluid more often, and using more of it.
"Consolidating the lines provided huge benefits to the plant overall. That's why I strongly felt the need to resolve this problem quickly," says Takezaki. "My first priority was to improve the frequency of washing fluid replacement, which was a burden to our staff."
Takezaki set a goal to prolong the replacement time from once every few days to once a month. Doing that would require reducing the amount of oil left on the polished gears before washing by about 80 percent. To hit that target, Takezaki began exploring new methods to remove the oil.
Jun Yoshihara, Staff Engineer, Transmission Machining Department, Suzuka Plant, Transmission Factory, Production Operations
Air nozzles were mounted inside the polishing machine in an attempt to remove oil by compressed air and centrifugal force
The bathroom hand dryer actually used to test dry a wet gear
Yasunao Oi, Staff Engineer, Transmission Machining Department, Suzuka Plant, Transmission Factory, Production Operations
Takezaki brainstormed potential solutions. "The first method I thought of was to use the polishing machine," he says. "Since the machine spins the gears when polishing, I thought we would keeping them spinning after and remove the oil by centrifugal force."
However, a test run removed only small amount of oil—far from the 80-percent target. Takezaki consulted his colleague Jun Yoshihara, a staff engineer in charge of equipment maintenance.
"We had to perform the entire oil removal step within the line, but space was limited, so we couldn't add any large machinery. And we had to do it in ten seconds or less. I thought, those are some tough conditions," reflects Yoshihara.
Yoshihara first tried installing air nozzles inside the polishing machine. The idea was to blow air on the spinning gears to eject the oil.
"It had an effect, but still only about half the oil we wanted came off. We started to try to think of a method that would take off more."
Deep in thought, Yoshihara watched absent-mindedly as the robot moved its arm about, polishing gear after gear. Looks like something I know. And in that moment, a decisive idea flashed in Yoshihara's mind.
"The robot looked like a human hand carrying a plate. If the plate were wet, how would the person dry it off? How does someone dry off their hands when wet? Wipe them with a towel? With a paper towel? A series of images scrolled through my mind, like I was playing some word association game. Eventually I came to the image of a hand dryer blowing the water off."
"My honest thoughts were, 'You’ve got to be joking! That’s how?" Takezaki admits. "Yoshihara even suggested installing a commercial hand dryer right on the line. I was skeptical, but immediately went to a nearby restroom to test it out."
The hand dryer matched the gear size perfectly, as if custom built for the purpose. Figuring it's worth a shot, Takezaki doused the gear in water and inserted it into the hand dryer. Pulling it out ten seconds later, it was surprisingly dry.
This just might work, thought Takezaki. He shared news of the potential solution with Yasunao Oi, who worked as unit leader of the finishing process.
"Takezaki came over with a bright, confident look on his face," laughs Oi. "The idea was outlandish but it made sense. After all, Honda has a culture of independent thinking and bold creativity, so it was wonderful that both Takezaki and Yoshihara were approaching the problem with these kinds of ideas. As unit leader, I proposed to our supervisor that we implement the idea as an environmental improvement."
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