JUST down the street from the new $39-million Thomas Built Buses plant in High Point, North Carolina, it is still possible to get pulled pork sandwiches and hush puppies. But the view inside the facility more closely resembles places where such Southern cuisine is less common and where automobile production is prominent.
Detroit, Portland, and Stuttgart have brought new technologies to the North Carolina school bus manufacturer. These three cities are homes of Thomas Built's commercial vehicle and automotive-oriented parent companies — Freightliner LLC and ultimately DaimlerChrysler. Their techniques and procedures are reflected from one end of the assembly process to the other.
The plant, which opened for business in August, was designed to build the Saf-T-Liner C2, Thomas Built's next-generation school bus. Like the plant that produces it, the new school bus reflects a lot of current automotive techniques, including the use of more stamped (as opposed to fabricated) structural members and a significant increase in the use of structural adhesives.
And to produce that design, the company has adopted a fair number of manufacturing techniques pioneered in the auto industry, including automated application of structural and windshield adhesives, robotic paint application, and even the use of automated guided vehicles (AGVs) to make unmanned deliveries.
Being owned by DaimlerChrysler gives the school bus manufacturer access to resources the company never had when it was family owned. That includes production engineering, product engineering, along with testing and validation. The school bus manufacturer also does business with some of the parent company's suppliers — including Utica Enterprises of Shelby Township, Michigan. Utica, which has produced assembly fixtures for DaimlerChrysler, built and installed the fixtures Thomas Built uses on its assembly line. The company produced the fixtures at its Detroit area facility and shipped them to High Point for installation.
“We use a lot of prepunched material,” says Allan Haggai, manager of marketing and sales support. “Doing that saves time and improves quality. But to be successful assembling buses with prepunched parts, we needed very precise fixtures. As part of DaimlerChrysler, we see the wisdom of investing in tooling.”
And being a subsidiary of Freightliner LLC has enabled Thomas Built to conduct road-simulator testing of the design without having to farm the job out to a third party.
Adhesives play an increased role in the production of Thomas Built school buses.
“As a bus travels over irregular surfaces, the racking that is produced can eventually lead to leak paths along the rivet holes,” Haggai says. “One of our goals in designing the C2 was to reduce as many potential leak paths as possible. We have been able to do that with a combination of rivets and structural adhesives.”
Before deciding to use adhesives for joining body panels of the new bus, Thomas Built tested riveted and bonded sheets. Sample joints demonstrated nearly twice the strength of riveted joints in standardized FMVSS 221 compliance tests. Riveted joints with a four-inch overlap, Haggai says, were tested to about 8,500 pounds before they failed. Two sheets with a two-inch overlap were bonded and tested to more than 13,000 pounds. At that point, the metal failed.
“The combination of adhesives and rivets results in fewer fasteners,” Haggai says. “That gives us fewer potential leak points and substantially stronger joints. When the side panels are bonded to a structure of welded floor, rafters, and stringers, we get a unitized body that provides stability and durability. Tests we have done indicate that adhesive joints can maintain a higher percentage of integrity throughout the life of the bus when compared to rivet-only joints.”
The self-piercing fasteners that Thomas Built uses do not fully penetrate the structural member to which the sheet is fastened. Instead, the gun is equipped with a special die to drive the fastener through the outside sheet and into — but not through — the structural piece. The result is an upset fastener that secures the sheet without giving moisture a direct route to the inside of the bus.
The 275,000-sq-ft plant has a 3/4 — mile-long assembly line with 75 workstations. At full production it will be able to produce 22 buses per shift.
An electronically-controlled conveyor system moves the buses through the assembly line. Each bus is assembled on a cart that carries it through the line until the body is ready for mounting. At the end of the trip, body is removed, and the empty cart is loaded onto an AGV to be taken back to the start of the line.
The AGV does not use a rail for guidance. Instead, it has been programmed to take a specific path along the open floor of the plant. Even without tracks, the AGV has an excellent driving record. That's because electronic sensors guide the vehicle and stop it if people, forklifts, or other intruders get in the way. An alarm protests the obstruction, but if the path remains blocked, the AGV simply waits.
The movement of buses also is tracked electronically. The work order for each bus is placed in a clear plastic bag that includes a transponder. The transponder produces a signal that tells management the location of the bus throughout the manufacturing process.
Knowing exactly the status of production is mandatory. Like many manufacturers, Thomas Built is using a just-in-time system that leaves little margin for error. Materials are delivered on custom carts to specific assembly points to ensure maximum efficiency in the production process. When the ramp-up phase is complete, management expects to keep no more material in inventory than what will be required for eight hours of production.
Hard-working robots
Thomas Built has put robots to work in a number of applications. Some of the jobs they perform:
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Painting. Quality paint coatings are applied by robotic equipment in a state-of-the-art facility that features downdraft ventilation and environmentally-sensitive air filtration.
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Welding. This includes MIG and spot welding.
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Adhesive application for structural body joints and stationary glass
The planning stage
The Saf-T-Liner C2 project started with preliminary planning and product development in 1999 and by mid-2000, the project was approved. Thomas Built held a groundbreaking celebration in October 2002 to launch preparations of the 90-acre site.
Nine different major contractors built the structure and installed production systems. The team had an aggressive construction schedule. In spite of some severe weather during construction, the building was ready for occupancy in November 2003.
Nearly 290,000 square yards of asphalt were used to pave bus parking areas at the site. The factory floor alone required 6,800 cubic yards of concrete, with another 4,500 cubic yards used for the surrounding areas.
The upfitting of the plant interior, employee training, and the building of a small volume of buses were done during the first half of 2004.
“We built 60 units that will never transport children,” Haggai says. “We built them as test units, as demos for our dealers, and for training purposes.”
In March 2004, two of those pre-production units began a national ride-and-drive tour. More than 230 industry leaders were given an opportunity to test drive the new model school bus produced by the new plant.
With the new plant, Thomas's corporate headquarters and manufacturing plants span more than a million square feet — a far cry from a former streetcar manufacturer founded in 1916.
Today, a different kind of car is influencing the High Point company. This time the influence is from the automotive industry, and the result is a higher quality, more efficient way to build buses.
What the new plant produces
Thomas Built designed its new plant specifically to produce its new Saf-T-Liner C2 conventional-style school bus.
“The Saf-T-Liner C2 doesn't look like any other bus on the market today because we started with a clean sheet of paper,” said John O'Leary, president of Thomas Built Buses, when introducing the bus in November. “We held focus groups and developed a group of nearly 1,000 industry professionals to survey. We listened to what school transportation directors, technicians, and drivers told us they wanted in a school bus. We combined those ideas with advanced technologies to create an all-new, Type C school bus — the Saf-T-Liner C2.”
Among the features that Thomas Built incorporated from the research:
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Increased visibility. The company redesigned the cowl area to provide a substantially larger windshield — 2,700 square inches. In addition, the sloping hood of the Freightliner chassis enhances the view of what is immediately in front of the bus. A standard power-operated entrance door and front “A” pillar windows increase sight lines for children getting into and out of the bus. Large side windows create a better view all around.
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Improved ergonomics for the driver.
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A choice of Mercedes-Benz MBE 900 series engines or Caterpillar C7 diesel engines. The C2 is built on a Freightliner chassis that is designed for school bus applications and interfaces easily with the Thomas Built school bus body.
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Recessed warning lights. Lights mounted above the surface of the bus are more subject to damage from impacts. Recessing the front and rear lights at the roofline reduces their exposure to impacts while still meeting federal lighting requirements. Lexan lenses further resist impact.
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Bulbs can be changed from the inside of the bus via built-in service areas. The entire fixture no longer must be removed.
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Multiplexed wiring system shared by the body and chassis. Multiplexed electrical systems reduce the amount of wiring and relays, eliminate connectors and make it easy to add switches and accessories without reprogramming. Downtime and repair costs are further reduced by more accurate diagnostic capabilities provided by the multiplex system's electronic control unit.
“There are huge electrical loads on school buses,” Haggai says. “Multiplexing is proving to provide a number of advantages, including the ability to program switches to the locations that individual drivers prefer. We can also program the system to accommodate pre-trip inspections. The system is timed so that the lights are sequenced to come on as the driver walks around the vehicle. Plus, states have different requirements about the order in which safety equipment begins to operate. Multiplexing makes it easy for us to comply with each state's requirements.”
“The C2 changes forever what passengers, drivers, operators, and technicians think about school buses,” O'Leary says. “The ride to school is no longer a history lesson, because we have designed a bus with proven automotive technology for improved performance, life cycle cost, and safety.”
Look, Ma, no hands
Using an automated guided vehicle to move material
IT'S almost a mile from the beginning of the assembly line to the end at the new Thomas Built bus plant in High Point, North Carolina.
For the first trip these newly assembled bus bodies take, they are passengers on a steel cart. The cart provides a square, rigid platform on which the bodies can be assembled.
Transported by the plant's conveyor line, the cart carries the bodies from the initial assembly station through body assembly, the paint shop, and the trim shop. That portion of the trip is more than a half mile.
When the school buses are trimmed, the line takes a 90° turn. There the bodies are mounted, windshields installed, final details applied, and the vehicle inspected.
At this turn, the carts are no longer needed. As a result of a series of turns that the assembly line makes, the cart is less than 100 yards from the beginning of the line. Even so, the cart must be returned to the beginning of the assembly line. Thomas Built used to do the job manually. But in the new plant, an automated guided vehicle (AGV) obtained from Transbotics Corporation of Charlotte, North Carolina, makes the delivery.
With the cart raised, the AGV is placed beneath it. The battery-powered vehicle backs up, makes a 90° turn, moves forward, makes another 90° turn, and returns the cart to the beginning of the line.