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Making the Monsters


Building the big stuff takes special talent

By Robert B. Aronson
Senior Editor


Micro and nano manufacturing are the current buzzwords, but many of our industries rely on massive machines. The manufacture of mining trucks, tunnel boring units, and military vehicles, to name just a few, takes special machinery and requires specialized manufacturing techniques.

The manufacturing philosophy for most of this type of equipment is at the opposite end of the scale from most of today's production. Where the automotive industry measures production in minutes, for the "monster makers" production time is often a matter of months per unit. Many are one-off units, often hand-built in segments with minimal fixturing by a highly talented workforce.       

Here's a look at a few of the more impressive examples.

The size of a dragline is determined by how much overburden must be removed and how fast. One of the biggest ever made had a 225 yd3 scoop (172 m3). Because of construction and maintenance issues, this machine was never duplicated. Initial cost and maintenance issues made smaller units more practical. Today, the largest dragline has about a 160 yd3 scoop (122 m3) and a 400' (121-m) boom.

"Design and planning are essential because you have to make it right the first time," says Neil Massey, chief engineer, P&H Mining (Milwaukee). "Dragline manufacture is a little like house building. You build a big metal frame over the base, then add machinery, a propulsion system, and finally wiring.

"We make some of the smaller weldments here, but final assembly is always in the field. Welding is the most common method of fabrication, and welding segments 8 to 12" [203 - 305-mm] thick are common. With the manufacture of draglines and larger shovels, welding is the only way to do the job. Because of the size and low volume, few fixtures are used, so clamp and weld is a common assembly practice.

"One of the key elements in the manufacturing cycle is the planetary drives that rotate the machine. They have to carry a lot of power, and that power has to be evenly distributed through the drive system, so machining accuracy is important. The four planetary units on every dragline each measure 8' (2.4-m) high and 4' [1.2 m] in diam.

"All our draglines are electrically powered with each machine drawing about 7200 V. Except for small shovels we do not use diesel power. Commonly a dragline has motors that deliver a total of 800 hp (600 kW). Electricity is used because diesel power can't handle it. Each machine would need its own pipeline to supply diesel fuel. Plus, diesel power is more expensive.

"Maintenance is very important. We work in a very hostile environment and machine failures that lose production time can be extremely costly. We like to maintain the machine ourselves and sell that service as an aftermarket maintenance contract. With that contract we can monitor all performance data from Milwaukee, and more easily see problems coming. We have systems that monitor machine functions such as temperatures, pressures, and vibration signatures.       

"Crawlers are not practical for machines this big. Crawlers that could move that kind of mass and not sink in the ground would be too big to be practical. Instead, we walk the machine from place to place. In normal operation, the machine sits on a flat base on the ground. To move, "feet" extend down, lift the entire machine, then transition a few yards and retract. This cycle continues until the machine is in its new position.

"We have a highly talented workforce, but it is aging, and that is influencing our design and manufacture. Parts have to be lighter and easier to move, and there is much more concern for personal safety and health."

Locomotives. The Union Pacific Railroad's "Challenger" No. 3985 is the world's largest operating steam locomotive. Although no longer used in commercial service, it's retained as a tourist attraction and for public affairs activities. But keeping this monster rolling is a challenge to modern manufacturing techniques. The engine needs constant maintenance performed by a five-person staff of machining experts in a shop located in Cheyenne, WY. In its prime, the shop had 5000 employees.

"A steam engine has three operating conditions: on, off, and full power," says Steve Lee manager, train operating practices. "So when the engine is moving there are a lot of pressures and stresses on all the elements. And as a result, a lot of maintenance is needed."

The 61-year-old locomotive is an articulated design; a "hinged" frame allows it to negotiate curves. It's 122' (37-m) long, weighs more than 1,000,000 lb (453.6 t), has 6' (1.8-m)-diam drive wheels, and can reach a top speed of 70 mph (84 km/h). No. 3985 was built in 1943 for fast freight service and was retired in 1959. In 1981, it was restored to running condition for special service by Union Pacific volunteers.

It is one of the Challenger class of locomotives with a 4-6-6-4 wheel arrangement. Originally it burned coal and pulled a tender with a 32-ton (29-t) capacity. In 1990, it was converted to use oil.

The steam engine could not beat the efficiency of diesel power. Although steam engines were as powerful as diesels and often faster, their huge appetite for fuel and water, and the need for labor-intensive maintenance, spelled their doom.

Since no one makes locomotive parts anymore, that job requires a lot of resourceful engineering and machining. This task is made a bit more challenging because the shop has no modern CNC equipment.

"In our shop, the machine tools are as old as the engines," says Lee. "Management is not going to pay for the latest five-axis CNC unit to keep these trains running. We rely heavily on the special talents of our machinists rather than the latest equipment. We have, however, been able to take advantage of some advanced software, particularly when we need to copy parts.

"Typical of the work we do is the remanufacture of bolts. About 4000 are used in the locomotive frame. They frequently break because of the heavy loads imposed by the locomotive's motion. They are a particular problem because each was originally custom-made to a different size and length. Each replacement, therefore, requires a lot of measurements and manual work."

Stretch limousines have two unique features: their length and a plush interior. Some manufacturers convert vehicles customers supply; others work with models of Lincolns and Cadillacs that have been designed for conversion. There are also two different philosophies. Some manufacturers go for the tourists and special-event market (proms, weddings), and concentrate more on the vehicle's internal glitz. They may offer special seats, sound systems, strobe and laser lighting, disco balls, electric fireplaces, hardwood floors, and multiple TV sets. For this market, the number of conveniences and gadgets a limo maker can offer is usually the key to profitability. Other builders are after a more conservative market such as government officials and CEOs of large corporations. Their designs are more concerned with vehicle durability.

In the limo industry, vehicle size is given in the number of inches the builder adds to the vehicle so a 200" (5080 mm) limo is one in which 200" or almost 17' (5 m) have been added to the vehicle's original length.

One of the oldest limousine builders, LCW Automotive Corp. (San Antonio, TX), builds certified limousines from specially supplied Cadillac and Lincoln base vehicles. "The certification means our vehicles are built to meet or exceed specifications established by Lincoln and Cadillac," says Ken Boyar, company president. "We build about 250 vehicles per year, and that includes special funeral, utility, and armored vehicles in addition to the limousines."

The vehicles they offer are from 6 to 130" (152 - 3302 mm) longer than the initial body. The longest finished Cadillac is 130" (3.3 m), and the longest Lincoln is 120" (3 m).

In the manufacturing operation, the vehicle is first placed in a jig and cut in two sections. Then new sections are added that can range from 6 to 140" (152 - 3556-mm) long with an accuracy of 1/16" (1.6 mm).       

The elements of the added areas are a combination of GM or Ford parts plus those that LCM fabricates from metal stampings, aluminum extrusions, and hand-laid-up composites.

The greatest effort goes into the interior elements. Customers can choose from a long list of special features for comfort and entertainment. LCW stays with more conventional features such as bars, sound systems, and TVs, because its customers are often corporate or private owners. Their prices range from $75,000 to $150,000 for the top of the line.

Tunneling Machines. Tunneling is another task where monster machines are required. Robbins Inc. (Solon, OH) builds some of the largest tunnel boring machines (TBMs) in the world. Each machine is a custom-built unit that produces tunnels from 2 to 40' (0.6 - 12.2 m) in diam.

If the work situation involves hard rock or mixed face geology, an open type gripper machine with minimal shielding is required because of the rock's stability. In more fragile rock, a shielded type machine is necessary to support the ground and protect the operators and machinery until proper support can be installed.

The primary difference between an "open gripper" TBM and a "shielded" TBM is geology to be bored and the ground support that is required to support the excavated geology. With an open machine rock bolts and wire mesh or shotcrete are used to support the tunnel, this is called the primary support. Once the primary support is installed the contractor will then line the complete tunnel with concrete after the TBM completes the tunnel. The then concrete fully lined tunnel is the completed construction and forms the final support and allows the tunnel to then be put into operation. With a shielded machine, in most cases, pre-cast concrete segments are used to support the ground and line the tunnel. The then segmented tunnel forms the final construction for the tunnel.

The TBM is designed using hydraulically operated grippers that act as crawlers and has a single cutting head mounted on a movable shaft. This head is a wheel the diameter of the finished tunnel and is studded with cutting teeth called disk cutters. In the cutting operation, gripper plates are first extended from the sides of the cutting machine under hydraulic power. They anchor the machine to the tunnel wall.

Then the main cutting head is pushed forward using hydraulic cylinders that are connected to the grippers and the cutting wheel. The stroke or forward movement of the cutting head may extend up 6' (2 m) on a large machine prior to being reset for another "bite" into the rock. A 6' bore stroke is made and the machine grippers are reset. The hydraulic pressure pushes the cutterhead forward and the disk cutters or cutter teeth fracture the rock and broken pieces are collected in a hopper at the cutting head center.

Robbins tunneling machines are electrically powered because of the problems of handling diesel exhaust and supplying fuel. On their largest TBM machine ten 450-hp (337.5-kW) electric motors drive the cutter wheel. Each motor transmits power through a two-stage set of planetary gears to a bull gear which is connected to the cutterhead.

"The machine frame is made of welded segments that are bolted together," explains chief engineer Dennis Ofiaria. "A new machine is first assembled at the plant and tested, then disassembled for shipment and reassembled at the job site. How many parts the machine is made from is determined chiefly by the size of the tunnel and logistics of getting the elements to the work site."

"As with most machinery, customers are constantly demanding more versatile designs. That is, machines that can handle a variety of rock conditions.

"Failure of the cutting teeth is a big concern. If one tooth breaks and does not get carried away, but stays at the cutting face, it can do serious damage to other teeth and the head itself. Operators must be aware of changes in cutting volume."

Mining trucks are among the more commonly seen of the monster vehicles.

Terex (Memphis, TN) a manufacturer of construction and mining equipment, offers a number of trucks for the mining industry. The largest is the TR 100 truck. They make about 90 a year.

Factors that go into what truck to use for a given job include weight of the material to be moved, size of the loading tool, and production rate (tons/hr) to be met.

"Power assists are a big factor in truck operation particularly for steering and braking," explains Bryan Flanigan, product manager - RIGID Haulers, Terex Construction America.

"The brakes on the TR 100 use a 2500-psi [1.7-MPa] system operating through accumulators with a safety backup system. Steering is full hydraulic and hydrostatic steering systems with cushioned valving so the steering effort is smooth.

"You also need to customize your drive system. Do you want your truck to have a high ground speed or be able to handle grades? A truck that can easily take a 10% grade may have a lower flat ground speed.       

"At Terex all trucks up to 100 tons [907-t] capacity are diesel powered. Larger trucks are diesel electric. That is, a diesel engine powers an alternator that supplies power to electric drive motors in the wheels. With the new AC diesel-electric you can easily do 40 mph [64 km/h]," explains Flanigan.

The reason for this 100-ton break point is that the larger trucks are made in lower volume and it may not be economically practical to design and manufacture a separate mechanical transmission for them. Maintenance is also a factor. A diesel drive system typically needs maintenance every 12,000 - 15,000 hr while a diesel-electric drive has maintenance about every 24,000 - 30,000 hr. An operator with 24/7 operation would probably go for diesel-electric, while a contractor who worked about 2000 hr a year would go diesel.

The designs feature welded structures with high-tensile-strength resistance to impact and wear.

"A key feature that helps maintain high productivity, longer truck life and operator safety is an on-board weighing system," says Flanigan. "There are three lights [red, yellow, and green] on the truck's cab. Load cells register the truck's load and control the signals. The green light shows when the truck load is well below rated capacity. The yellow light comes on when the load is near capacity. The loader knows at that point the truck can safely take about one more load or scoop. The red light warns that capacity has been exceeded, or met.

"Manufacturing these vehicles has a long manufacturing time because of the lower volume and specialized, high-cost components," Flanigan explains. "No one builds these parts on spec. This requires very accurate forecasting.

"Because the machine tools needed to make our parts are generally larger and more specialized, you tend to stay with a limited number of suppliers, if you don't have your own machine tools. This is unlike the auto industry where there are a large number of first and second-tier suppliers to work with."

There is legislation coming into effect that will influence truck manufacture and design. First is a change in emission law that will force a redesign of some types of engines.

Two others involve worker protection. One limits the vibration a driver experiences. The other requires an enclosed, clean, dust-free cab, where before most cabs were open. As a result of the quiet cabs, drivers now want radios and stereos.

One of the largest trucks now in operation is the Liebherr T282B made by Liebherr Mining Equipment (Newport News, VA). Its GVW is 1,305,000 lb and it can carry 400 tons. The truck is powered by a Cummins 3659-hp engine, with a Siemens AC electric drive. The dump body can carry 290 yd3 (221 m3). Tires are Bridgestone 55/80 R63 or Michelin 56/80R63. Basic dimensions are 48.5' long, 29.1' wide and 21' high (14.8 X 9 X 6.4 m). To date, 60 of these king-size trucks have been built and, according to the company, they are presently building two per month.

"In determining the load a truck is designed to take, the tires are a big factor, but mine depth, ground conditions, power, and maintenance all enter into the equation," explains Francis Bartley, R&D engineering manager. Initially a truck is designed to a set of specifications, but after a model is introduced, its capacity can be stretched. But there is a limit to how far this can be expanded.

"Ease of operation is a big factor. There are many power assists. For example, on the company's diesel-electric trucks there is a selector switch for forward, neutral or reverse. No other gear shifting is required."

Because of the large size and the specialized nature of each vehicle, they are assembled in one location, as opposed to on an assembly line. Initially the frame is put in place, then subassemblies are added.

After final assembly and testing, the truck is partially disassembled for shipment.

"In the manufacturing operation welding is a critical factor," says Bartley. "Welding is used extensively because the large elements involved can't be formed like automotive frame components. Consequently, we need a number of highly trained welders."

Some of the latest developments are in the truck's on-board computer systems. One monitors and controls the engine, one checks the drive system, and some smaller units control other functions. There is a display system that warns the operator of problems or potential failures.


This article was first published in the November 2004 edition of Manufacturing Engineering magazine. 

Published Date : 11/1/2004

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