Popularized in the 1920s and used heavily ever since, the bulldozer,
commonly termed a dozer, is a clear offspring of the crawler tractor. Used
in conjunction with other earthmoving vehicles, the bulldozer is a
powerful and necessary tool utilized in almost every construction site in
Primarily manufactured in the United States by Caterpillar, John Deere,
and Case Tractor Company, the bulldozer provides for many industrial
applications such as construction, waste management, and farming.
Bulldozers and crawlers, characterized for their immense blade and
versatile track, are comprised of many structural, hydraulic, and engine
assemblies. The core body of the bulldozer, consisting of the mainframe
and undercarriage, is primarily fabricated from low carbon structural
steel plates and a giant casting. The cab contains many glass, rubber, and
plastic components which enhance the ergonomic feel of the machine.
Supplying the power for the dozer and its various systems, the engine
contains many high strength steel parts, which endure high operating
temperatures. The other necessary components, the blade, power train, and
various systems components, are formed from structural and high carbon
steel. The track, which is fashioned from many standard grade steel links,
adds to the already tremendous weight of this mostly steel machine. Once
the dozer is filled with fuel, hydraulic fluid, coolant, oil, and other
types of fluids, its weight increases by several hundred pounds.
Decorative trim, decals, and paint complete the dozer's aesthetics
and add distinctive appeal.
Two distinct features characterize the bulldozer, the long, vertical steel
blade in the front of the vehicle and the rotating twin tracks, which
facilitate the bulldozer movement. The blade, which can weigh up to 16,000
lb (7,264 kg), is useful for pushing material from one spot to another.
Perpendicular to the ground, the curved blade is attached to the frame by
a long lever arm that can tilt and move up and down under hydraulic power.
The familiar flexible track of a bulldozer is widely utilized in
industrial machinery equipment and military tanks. In fact, some farming
tractors are considered to be cousins to the bulldozer, since they also
utilize the flexible track instead of standard wheels. Steel links,
sometimes more than 2 ft (61 cm) in length, are connected with lubricated
pins to provide for fluid motion and stability. Moreover, many bulldozers
have incorporated an elevated sprocket design which suspends the power
train, and thereby, improves its reactivity to the terrain. The diesel
engine of the bulldozer can generate anywhere from 50-700 horsepower, so
rough terrain and steep slopes are not a problem for this machine.
Mounted above the flexible track, the operator cabin contains the complex
hydraulic mechanisms, which power the blade in a limited vertical range.
The cabin design has seen many improvements in operator comfort and
ergonomics and has provided for many improved automotive features, such as
air conditioning, AM/FM radio,
automatic seat adjustments, electronic controls, and systems-monitoring
equipment. In these areas of dozer design, the engineering and research
that precedes the manufacturing mimic the automotive industry in many
The power train includes the transmission, differential, and gears that
rotate the track. Coupled to the engine crankshaft, the power train will
transmit power from the engine to the elevated sprocket gear. Many new
bulldozers have independent steering, which allows each sprocket to rotate
at full power even while one is rotating slower as the dozer is in a turn.
Other innovations in recent years include differential steering, hydraulic
power, and planetary gear transmissions.
The bulldozer, a seemingly endless network of bulky steel components,
complex systems, and intricate assemblies, begins its manufacturing
process on an assembly line. Prior to final assembly, much machining,
fabrication, and sub-assembly must take place. Manufacturing begins with
engineering prints and drawings taken from a computer-aided drafting (CAD)
program that outlines the method of construction for each component part.
Some of these programs can be used to set up machines for which most of
the manufacturing will take place, that is, in fabrication cells, large
machining centers, and sub-assembly lines. This is called computer-aided
manufacturing (CAM) and is used to produce the components and assemblies
that join together on the main line. Some of these components will then
undergo heat treating, annealing, or painting after their respective
fabrication cell, sub-assembly line, or machining center step. An overhead
conveyor system will then transport the pieces through the rough paint or
powder coating operation and lift them to the main assembly line, where
they arrive in time to be assembled. These pieces may also be transported
by lift truck, hand cart, or floor conveyor to arrive at the staging area
before they are assembled to the bulldozer.
1 The mainframe core, which forms the rigid inner body, is cut from
steel plate and structural shaped, so that it easily resists high impact
shock loads and torsional forces normally incurred by the dozer. The
main structural skeleton, formed through the welding of steel plates to
machined casting, is comprised of two boxed-in rail sections connected
to the main casing. The fabrication is normally performed in a
fabrication cell, where the burned plate arrives ready to be mounted
into fixtures and manually or robotically welded to the stationary
central casting. Far too massive to be lifted by hand, the frames are
then transported by overhead crane to different stations, where steel
mounting blocks and trunions, or cross members, are welded on as a
support for the other components of the bulldozer. Once completed, the
frame is rotary sanded on all plated surfaces and sent to the paint
booth and the main assembly line.
Diesel engine and transmission
2 At the assembly line, the independently manufactured diesel engine and
transmission join the mainframe. The engine is usually purchased
completely assembled as it is a complex system with machined components
that can be used in many different vehicular applications. In fact, the
engine (which has been subjected to various performance tests) is
certified to operate on arrival. The engine mounts in the front of the
bulldozer; however, it is connected to the transmission, which sits in
the back. The two are connected by a long shaft and supported by
couplings and bearings. The transmission is then connected to a series
of gears and differentials to comprise the rest of the power train. By
mounting on pads previously welded to the frame, the engine/transmission
assembly can be bolted directly to the base on the main assembly line.
Radiator and additional assemblies
3 On the front of the bulldozer, an engine casing is mounted to support
the radiator and hydraulic lifting cylinders. The radiator, another
finished assembly, will then sit between the engine casing and mount to
the front drive shaft. Connections can then be made to attach water
lines from the engine to the radiator. Additional assemblies for the
hydraulic, lubrication, cooling, and fuel systems are also constructed
at other locations and purchased as a finished assembly
ready to be fastened directly to the engine or base. These include
hydraulic lines composed of tubes, hoses, and fittings pre-assembled and
mounted on the engine or frame and connected to pumps, valves, tanks,
and cylinders, each of which can be brought to the main assembly line as
a finished component. Fuel, exhaust, hydraulic, and coolant lines also
arrive ready for assembly and mate to other finished components. Many of
these components and sub-assemblies must be inspected and approved
for dimensional compliance at an incoming inspection station prior to
Two distinct features characterize the bulldozer, the long,
vertical steel blade in the front of the vehicle and the rotating
twin tracks, which facilitate the bulldozer movement. The blade,
which can weigh up to 16,000 lb (7,264 kg), is useful for pushing
material from one spot to another.
Large component assembly
As the entire assembly of the frame, engine, transmission, and line groups
move along the main production line, larger assemblies and components are
brought in by overhead cranes, overhead conveyors, automatic guided
vehicles (AGV), or lift trucks. These components include the cab, larger
hydraulic cylinders, undercarriage components, and the front blade.
4 The cab, which can also be purchased as a finished assembly, is
usually manufactured at a different facility and shipped for assembly.
Usually complete in its array of electronics and controls, the cab will
be mounted on steel blocks or pads located on the dozer frame. After
mounting, connections will be made to the various controls, and power
can supplied to the fully functioning cab.
5 Concurrent with the engine/transmission mounting, the undercarriage,
composed of tubular roller frames, drive sprockets, and bogey
independent suspension rollers, will be mounted on the frame and
assembled to the drive train. The axle assembly will turn the outer
sprockets that rotate the track, allowing the vehicle to maneuver. The
sprockets, typically 2 ft (61 cm) in diameter, will fit into the track
with case hardened teeth, which move the track as they rotate. In many
manufacturing operations, the undercarriage can be machined, assembled,
and painted in the same facility as the main assembly line, but various
smaller components like bearings and lubrication bushings need to be
outsourced to other facilities or outside contractors. The track, which
is often pre-assembled from machined steel links, can be fitted around
the drive sprockets, rollers, and front/back guide gears only after the
engine/transmission and undercarriage components are in place. The
exhaust stack, attached directly to the engine, is supported by brackets
and flanges at its base.
6 After the cab controls are connected to the engine and hydraulic
systems, prefabricated cowlings or body panels are mounted directly on
the base frame to cover the engine, transmission, radiator, and fluid
lines. The body panels are designed to fold back, making the inside of
the dozer easily accessible for regular maintenance. They are assembled
into hinges already fastened to structural supports. Tooling and storage
compartments may also be built into the dozer once the lines have all
been connected. Deck plates lie around the cabin and are welded to
7 The front blade is attached to hydraulic cylinders, which can position
the blade at different angles of tilt. The cylinders, each comprised of
a hardened steel piston inside a honed cylinder, are attached at one end
to engine casing in the front of the bulldozer to move the blade
vertically. Initially in the assembly process, the cylinders are left
unattached at the one end until the roll formed steel blade is
assembled, and then hydraulic lines can be fitted and tightened. The
lower end of the blade is attached at two joints with large steel pins
which rotate and tilt the blade with two more cylinders. Arms extending
from the undercarriage are attached to the blade and then are assembled
along with the other undercarriage components.
8 Once the dozer has been outfitted with its primary components, more
hoses, electrical lines, and fluid lines are attached at fitted
connections. Items such as the batteries, which are connected to the
starter on the engine, lie underneath a cowling in a compartment located
near the engine. Lights, one of the last items installed on the dozer,
will be placed in a number of different areas and connected to their
power source. In addition, hand or guard rails and foot pegs are bolted
on the frame which complete main line assembly.
9 At Caterpillar's Track-Type Tractor (TTT) division located in
Peoria, Illinois, Caterpillar bulldozers and crawlers use the same paint
and final prep lines as many other tracked vehicles. Applied manually
with spray guns, the final paint booth will deliver paint to any area
not blocked off with paper or plastic wrapping. The paint dries quickly
and the bulldozer will
move to the next station where decals and trim are applied by hand
10 Various fluids are added, and the vehicle is then sent to a testing
station where the operation of all systems is mechanically verified and
recorded. The vehicle is transported from the manufacturing site to a
staging area for customization and shipping. The completed bulldozer is
shipped on a flat bed trailer and is ready for field operation upon
Waste produced by the manufacturing operations may include machining
coolants, oils, parts-cleaning detergents, paint, and diesel fuel. The
United States Environmental Protection Agency (EPA) places strict
regulations on manufacturers to mandate that these potentially harmful
liquids are disposed of in a proper manner. Companies contract a waste
removal firm to recycle most of the liquid waste. Metal chips and shavings
are recycled and sold to scrap dealers in an effort to reduce waste.
Bulldozers consistently undergo component design modernization efforts,
and innovations appear inevitable. Improvements in cab comfort and diesel
engine efficiency will probably be the driving force for many of these
changes, while design and operational changes will be limited to
individual components. In spite of the fact these enhancements in both the
manufacturing process and streamlining of material flow will probably not
change the face of bulldozers, costs may improve. Therefore, as a useful
member of any earth-moving team, the bulldozer will continue to serve a
unique purpose in building construction, waste management, and many
Where to Learn More
D7R Track-Type Tractor Specifications.
D9R Track-Type Tractor Specifications.
DllR Track-Type Tractor Specifications.