A recent celebration at the Robert Bosch Corp. plant in Anderson, South Carolina, caught a few employees by surprise.
The plant had shipped more than 2 million of its new planar oxygen sensors with zero defects. That's zero, as in none. Plant management thought a little recognition was in order, but some employees wondered what all the fuss was about.
'On the planar team we have about two-thirds veteran Bosch people and people brought in from the outside to man the project. Some of the new people didn't understand what we were celebrating,' said Michael McCormick, director of manufacturing operations and engineering for oxygen sensors at the Anderson plant. 'They said, 'Of course there are no defects; why would we want to make a defect?' From the outside it seemed so obvious that this was really some accomplishment, but for some of the people it was just what they do for a living and they didn't understand all the hoopla.'
Bosch's Anderson plant has produced oxygen sensors since 1988. The thimble, or finger, oxygen sensor was the first new product introduced in the complex, which Bosch purchased in 1985. Anderson began manufacturing the sensors, which originally were produced in Germany, to supply the growing North American market.
In the past 12 years, the Anderson plant has produced more than 75 million sensors. Most go to the original-equipment market, but the aftermarket is a growing segment of the company's business.
Before 1996, oxygen sensors performed one function: providing feedback in a vehicle's fuel-injection system.
The sensor analyzes the gases from the combustion process, looking for the residual oxygen level in the exhaust stream. It then signals the control unit to indicate whether the proper mixture of gasoline and air is being fed to the cylinder. Based on that signal, the control unit then extends or reduces the injection time to assure the proper mixture.
With the advent of the onboard diagnostic system used by all makers, vehicles built after 1996 required a second oxygen sensor in the catalytic converter. This downstream sensor performs a policing function to ensure that the entire emission-control system is within parameters.
Most vehicles are equipped with two sensors, McCormick said, but some have four.
The major difference between the planar oxygen sensor and the thimble sensor is in the ceramic sensing element. The thimble sensors are manufactured using powder that is pressed into shape and coated.
The planar sensors are produced using thick film ceramics. The ceramic film is screen printed and fired in an oven.
'This changed the entire design of the product,' said McCormick. 'It had to be built around the new sensing element. Although our customers perceive it as an almost direct substitution, the technology is all new. It required a new manufacturing process and, in a lot of cases, new suppliers.'
The planar sensor provides feedback to the control center much faster than the thimble sensor because the heating element is combined with the sensing element. This allows the sensor to reach an operational temperature more quickly.
'Customers always want products that are faster, lighter and cheaper,' said Daniel Hyman, the Anderson plant's vice president of manufacturing. 'And really, the one thing that is critical for an oxygen sensor is for it to look at that exhaust gas instantaneously and say whether the mixture is correct.'
Work on bringing the new sensor into the plant began about three years ago. A sister plant in Germany already was producing the planar sensor, which gave the Anderson complex a jump-start.
'We were able to go over and look at their processes and their assembly line and learn what they knew, both good and bad,' Hyman said. 'We were able to bring our people in to learn the systems station by station and operation by operation. It was a very good opportunity for us to see what they had done and make improvements as required.'
Bosch invested $12 million for tooling and infrastructure in the Anderson plant to produce the planar sensor. The highly automated assembly line was tested in Germany, then torn down, packed and shipped to Anderson in December 1998. The planar sensor was launched in March 1999.
Fifteen components are brought together to produce the planar sensor, and the assembly line performs 27 steps. The sensors are heated twice along the way to eliminate any contamination, and two tests are performed - one to check for leaks and one to evaluate performance. The plant cranks out about 20,000 of the sensors daily.
Because it was a new process manufacturing a new product, McCormick said, people were more than just a little tense.
'This is an emissions-control component, and there is a much higher level of conservatism on the side of the OEMs who apply these products,' he said. 'Not only could you have an unhappy customer if something were to go wrong with this new technology; you could also have an unhappy Environmental Protection Agency. And the EPA has wide-ranging authorities, as does the California (Air) Resources Board, to make your life miserable.'
To keep everybody happy, the Anderson plant had a lofty goal: zero defective parts per million. To hit their target, plant officials left nothing to chance.
The line was double-checked to eliminate potential problems upfront. The model provided a systematic checklist for the new process and looked at everything from manufacturing planning to training to machine capability studies, Hyman said.
Even with the machinery in perfect sync, there was still one variable: the human element. Despite the extensive training, humans are still, well, human.
'There is a real team focus,' Hyman said. 'On each and every shift, each and every associate is thinking, 'Have I done everything I can today to make this product good?' That kind of consciousness about no quality spills makes a big difference.'
The magnitude of shipping 2 million parts without a defect wasn't lost on Zavone Bonney. He had previously worked on the thimble sensor line and was on the startup team for the planar sensor.
'It was huge,' Bonney said. 'We put a lot of work into it to achieve that. Now we're sitting back looking at our process to continue on and keep the ppm low.'
While the achievement is a source of pride for the employees, it's also good for business. Ford and Nissan are two of Bosch's biggest customers, and the company is looking to expand that base.
'We want our product to be in every car in North America,' Hyman said. 'To do that, the new technology had to be perfect, as perfect as we could make it. We wanted a perfect product so we can go to the Chryslers of the world or the Toyotas of the world and say look, here's a brand new technology. It's faster, it's cheaper, it's lighter and, oh, by the way, it's zero ppm. That's a perfect marketing strategy.'