Cleaning up automotive manufacturing
10/01/2003
Automakers continue an innovative, steady drive toward contamination-free manufacturing
By Sheila Galatowitsch
There are likely a million contamination control stories in Motor City, and this month, CleanRooms brings you three.
Automakers are among the key new user groups of clean manufacturing technologies, with automotive paint spray operations at the forefront. Consumer demand for high-quality paint finishes and rock-solid reliability continue to drive automotive manufacturers toward cleaner processes.
Their approaches might seem primitive to semiconductor and pharmaceutical cleanroom pros—many automotive applications don't adhere to the ISO cleanroom classifications because their particles of concern are on the order of 5 to 10 microns (µm) and larger. But automakers are justifiably proud of how they are cleaning up their manufacturing processes by thinking outside traditional cleanroom concepts.
Two stories prove that point. In one, Delphi Delco Electronics Systems (Kokomo, Ind.) uses an unconventional contamination control approach to manufacture vehicle "black box" components. In the other, General Motors Corp. (Detroit, Mich.) focuses on controlling sediment in its automatic transmission assembly rooms—a task made ever more difficult by the increasing complexity of automatic transmissions.
Back in the paint spray booth, engineers at Ford Motor Company (Dearborn, Mich.) have found a way to continue using solvent-based paints, which provide a high-quality paint finish but release dangerous fumes into the air. Instead of burning these fumes, Ford is turning them into clean electric power. Its patented "Fumes-to-Fuel" system is generating interest not only from other automakers but also from the pollution control industry.
The key application for contamination control technology in automotive manufacturing is also the most energy-hungry. The paint shop uses the majority of energy in the process of building a car, which is why engineers at Ford were determined to transform an energy-wasting process into an energy producer. Their solution came from an unlikely source: The volatile organic compounds (VOCs) emitted when solvent-based paints are used.
Ford's fuel cell innovation
In automotive paint shops everywhere, VOCs are routinely incinerated in a natural gas-fired furnace. The traditional automotive abatement technique involves extracting VOC emissions from the paint spray booth air and routing them to an on-site abatement center for incineration. While this approach protects air quality in the paint shop, it is costly, hogs energy and emits nitrogen oxides and carbon dioxide during the incineration process.
Always searching for greater energy efficiency, Ford has a partnership with its local power utility, Detroit Edison, which employs a team of nine energy engineers to work exclusively for Ford. It was from this partnership that the idea of turning VOCs into electricity emerged.
Detroit Edison had originally developed the concept, and together with Ford, the companies spent several years refining the "Fumes-to-Fuel" system. Here's how it works:
- The system captures the VOCs in paint fumes and concentrates them into a rich mixture of hydrocarbons, which are a source of fuel.
- The mixture is fed into a reformer that turns it into a hydrogen-rich gas.
- From there, the gas is fed into a stack of solid oxide fuel cells, where a chemical reaction between hydrogen and oxygen creates electricity, water vapor and an insignificant amount of carbon dioxide.
When the paint shop operations are down and VOCs are not being produced, the solid oxide fuel cell uses natural gas to generate electricity. This dual-fuel capability was designed specifically for the system because solid oxide fuel cells run better when they run continuously, says Mark Wherrett, the Fumes-to-Fuel system project leader and principal environmental engineer, Ford Environmental Quality Office.
In a pilot test at the Ford Rouge Center Paint Shop in Dearborn, the system is generating 5,000 watts of electricity—enough to power an average home. It's also cleaning paint exhaust better than the traditional incinerator-based system, says Wherrett.
And it has other benefits, including the potential to save Ford millions of dollars by reducing the cost of incinerating paint fumes in natural gas-fired furnaces.
Plus, it cuts carbon dioxide emissions by a factor of seven and allows for the continued use of solvent-based paints over water-based paints. While water-based paint has a very low VOC level, solvent-based paint provides a higher quality paint finish and a wider temperature and humidity operating window.
Other than the equipment installation, no changes were required at the paint shop to accommodate the system, says Wherrett. The Ford Rouge Center Paint Shop is a three-level facility with a footprint of 450,000 square feet and 800,000 square feet of floor space. It currently produces Mustangs, but is capable of producing any size unit from the Focus up to the F-Series pickups. As Ford's most environmentally advanced paint shop, Rouge Center uses water-based primer and basecoat paints, followed by the solvent-based clearcoat paint.
"The rest of the paint shop operates as normal," says Wherrett, "and since this is a pilot test, we are handling only a small portion of the total controlled air—roughly 5,000 cubic feet per minute of the total controlled air."
The 5,000 watts of electricity generated by the pilot Fumes-to-Fuel system is the energy source for the lights in the bay where the fuel cell is located. After the pilot test concludes in December, Ford plans to scale up to a permanent system next year that will handle 100 percent of the controlled air stream and generate more than 100,000 watts of energy that will be dumped into the plant electrical grid and used in other locations throughout the plant.
Ford is exploring using the fuel cell technology at additional plant sites, and it has also contracted with Climate Technologies (Northville, Mich.) to market it to automotive and non-automotive industries. Both Detroit Edison and Ford hold patents on the system.
"We've even had interest from traditional pollution control companies, and we are trying to work with them," says Wherrett. "There are lots of possibilities—some we haven't yet discovered."
Unconventional thinking at Delphi Delco
As automotive electronics keep shrinking, the particle sizes of concern keep getting smaller, too. Component manufacturers are controlling contaminants, such as metal, fibers, skin flakes and spittle, ranging from 80 to 120 µm on the high end to 40 to 60 µm on the low end. While their goal is the same as mainstream cleanroom users—preventing visual or electronic defects in the product—their methods are unconventional.
"Cleanroom classifications don't apply here," says John Weaver, manager of contamination control at Delphi Delco, a manufacturer of vehicle electronics and computerized advanced engine control systems. "Particles in the 80 to 120 micrometer range fall like baseballs. Gravity is the biggest source of transport."
To control these types of contaminants, Delphi Delco uses a "non-conventional clean manufacturing facility;" a semi-open plant environment where the air is kept clean but complete barriers to air movement within the plant are unnecessary.
While cleanrooms focus on airborne contaminants, non-conventional clean manufacturing facilities target non-aerosol contaminants. "In these facilities, particles tend not to float in the air, but they still need to be controlled," says Weaver. "It requires a different way of thinking, but it's still contamination-control thinking." Contaminants under 60 µm, however, can become airborne depending on the circumstances. The non-conventional approach totally encloses areas where these contaminants pose a threat, while 80-µm particles and above are generally contained via a 10-foot high wall.
The first goal in non-conventional facilities, as in conventional cleanrooms, is to "prevent the particle from being generated," says Weaver. "If you can't do that, then prevent the transport of the particle generated to critical areas. And if you cannot eliminate contamination of critical areas, then thoroughly clean those areas."
For example, plant operators control hard particles by following three principles. First, they seek to change the equipment surface material to reduce the friction, thereby minimizing particle generation. In some cases, a Teflon plate may be used between two surfaces.
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If that's not possible, they install a barrier around the surfaces to prevent particles from reaching critical areas. "We've even done some unconventional things like put a magnet in place to act as a getter, attracting and holding metallic particles," says Weaver.
If the process design is such that barriers or getters can't be put in place, operators institute a cleaning step, using a product-specific wipe-down or ionized air blow-off and vacuum, often coupled with final assembly in a clean facility.
Meanwhile, "soft" human-borne contaminants are controlled in a similar approach, starting with the use of protective garments, such as gloves to contain oils on hands, and caps and gowns for human-borne organic particles.
Non-conventional facilities monitor incoming air cleanliness and seek to avoid strong lateral air currents (like a strong wind blowing through an open door) that could make airborne those particles that aren't normally in the air. And materials entering the facility, especially those that are shipped via over-the-road truck, have to go though elaborate cleaning procedures before they can enter the plant.
The unconventional approach is pervasive among Delphi Delco's 200-plus manufacturing sites, which also house traditional cleanrooms for components (semiconductors and sensors, for example) impacted by aerosol particles and non-particle aerosol contaminants, such as airborne molecular contaminants. "Sometimes, devices can be designed in a more robust fashion that would make contamination control unnecessary," says Weaver, "but that is rare. The overall trend is moving toward more and more stringent controls."
GM controls sediment contamination
That trend toward more stringent control has been quietly obvious to transmission manufacturers for the past 15 years. The increasing complexity of automatic transmissions has led to a corresponding rise in assembly room cleanliness.
The automatic transmission in your vehicle has some 900 components, including electro-hydraulic parts, solenoids, pulse-width modulating valves, shift valves and sensors. Openings and clearances between the valves and moving parts can measure from 10 µm to as low as 1 µm, making the system extremely sensitive to sediment particles above 10 µm (such as plastic debris, metal and coolant oils).
"Contamination in the air or in the system during the assembly process can result in parts not performing in the field for the customer," says James B. Lewis, director of manufacturing engineering for transmissions at General Motors Corp. "We worry about sediments sticking to those valves, so we pay close attention to the cleanliness of the parts and the assembly room."
All parts entering the assembly room are first subjected to cleaning with high-pressure water and ultrasonic washers. Then personnel test the parts for sediment using a solvent wash, which is filtered through 44-µm and 10-µm filtration paper and weighed. Once the parts are sufficiently clean, they are nested in clean plastic packaging to ensure they remain contamination-free during transfer into the assembly room.
GM has seven automatic transmission assembly rooms and is investing approximately $300 million in a plant in Ypsilanti, Mich., to produce a six-speed, rear-wheel-drive automatic transmission. This new plant will include an assembly room modeled after its other state-of-the-art rooms.
The rooms measure roughly 85,000 square feet and are completely enclosed, with special ceilings, glass walls, sealed floors and pressurized, humidity-controlled air. Access is limited, and personnel use lint-free wipes and wear low-sediment gloves along with their standard assembly uniforms.
"Grease and lubricants are carefully controlled and applied," says Lewis. "We don't allow any extra people, no outside equipment at all, and we monitor movement of hoses and anything that could generate particles." Once assembled, the transmissions are sealed and leave the assembly room with no special protective treatment.
The assembly rooms are not designed to ISO cleanroom classification, and they do not use HEPA filtration—not yet anyway. But as engineers add more electrical and computerized components to new transmission designs, can ISO Class 8 assembly rooms be far behind?
"I think we will continue to get cleaner," says Lewis. "Over the next decade, we will migrate toward the semiconductor manufacturing model and away from the heavy steel industry."
SHEILA GALATOWITSCH, a special correspondent to CleanRooms magazine, is based in Denver, Colo. She can be reached at: [email protected]