Truck Assembly Line
Truck manufacturers usually design a new model about every five to seven years. The new design incorporates advances in technology and materials, as well as changes desired by the customers. The design team will use a clay model to determine the overall styling. Just before the new truck goes into production, they will build one or more pilot models using actual production parts to spot any last-minute assembly problems.
Here is a typical sequence of operation for the assembly of a heavy-duty truck:
Assembling the frame
1 A pair of frame rails are selected from stock lengths of C-channel. They are laid side-by-side and fed through an automatic drilling machine or punch to make holes for connecting crossmember brackets, engine mounts, and other frame-mounted components. A computer tells the machine the size and location of the required holes along the length of the frame rails.
2 Small threaded studs are spot welded inside the C-section of the frame rails. The air lines for the brakes and the electrical wires for the lights and sensors are placed inside the frame rails and are secured with rubber-cushioned clamps fastened to the studs.
3 The brackets for the frame crossmembers are bolted in place using high-strength bolts or self-clinching fasteners. The left and right frame rails are then positioned opposite each other, and the cross-members are added. The frame now resembles a long ladder with the rails as the sides and the crossmembers as the rungs.
4 Other frame-mounted components—such as engine mounts, suspension brackets, and air tanks—are bolted in place.
Installing the axles and suspensions
5 The front and rear axles are fitted with the proper hubs (the round ends to which the wheels are attached), brakes, and brake drums. The axles are clamped to the suspensions by means of long u-bolts. Some suspensions use long leaf springs while others use inflated rubber air bags.
6 The front and rear axles and suspensions are lifted into place and attached to the suspension brackets on the frame. The shock absorbers are attached between the axles and the frame.
Finishing the frame
· 7 Up until this point the frame assembly is usually moved from station to station either manually or with overhead hoists. The frame is now placed on a moveable support and begins moving down the assembly line. The air tanks and brake chambers are connected to the air lines, and the lights and sensors are connected to the proper wires.
8 If the vehicle is to be a tractor, the fifth wheel is lifted onto the frame and bolted into place. From this point on the frame assembly with the axles, suspensions, and frame-mounted components is referred to as the chassis.
Painting the chassis
9 All components that are not to be painted are covered with masking tape or paper. The chassis then moves into a paint booth where it is painted with compressed air spray guns. Most truck manufacturers require that all component parts be received with a primer coat of paint, so priming is not necessary.
10 After the chassis has been thoroughly painted and visually checked, it moves into a drying oven where a flow of hot air dries the paint. As it emerges from the oven, the masking tape and paper are removed.
Installing the engine and transmission
11 The engine and transmission are brought into the plant alongside the assembly line. Almost all trucks now use diesel engines. The clutch is installed and the transmission is bolted onto the rear of the engine. The fan, altemator, and other engine components are installed and connected with hoses and electrical wiring.
12 The finished engine/transmission package is then hoisted using lifting eyes that are part of the engine and is lowered onto the engine mounts in the chassis, where it is bolted in place. The radiator assembly is bolted onto its brackets ahead of the engine. The fuel lines, air hoses, starter cables, and coolant hoses are connected to the engine.
Finishing the chassis
13 The fuel tanks are secured to their frame brackets and connected to the fuel lines. Batteries are secured in the battery box, but are not connected to prevent accidental sparking.
14 The tires are mounted on the wheels at a workstation adjacent to the assembly line. Aluminum wheels are left natural or may be polished. Steel wheels are painted before the tires are mounted. The tires and wheels are mounted on the axle hubs, and the lug nuts are tightened. At this point, the truck is taken off its moveable supports and sits on its own tires.
Assembling the cob, hood, and sleeper
[Steps 15-23 are performed in a separate area off the assembly line]
15 The cab and sleeper substructures are welded or fastened together in jigs to hold the pieces in place. The substructures give the cab and sleeper their strength and provides fastening points for the outer skin and the inner upholstery and trim.
16 The outer skin pieces are welded or fastened in place. This includes the sides, back, floor, and roof pieces. The joints between pieces are overlapped and sealed to prevent leaks. The cab and sleeper doors are secured to the hinges.
17 The hood is usually a molded plastic piece and is shipped to the plant without any hardware attached. The hood is checked for rough surfaces and is sanded as required.
Painting the cab, hood, and sleeper
18 The cab, hood, and sleeper for each truck are painted at the same time. The surfaces are cleaned and the areas that are not to be painted are masked off with paper or tape. If a paint design such as a different color stripe is specified, the stripe area is painted first, then the stripe is masked off and the main body color is applied on a second pass through the paint booth. After each pass, the cab, hood, and sleeper go through a drying oven. After the final pass, the masking is removed and the paint is visually inspected.
In most plants, the trucks move along an assembly line as components are added by different groups of workers at successive workstations. The truck starts with a frame assembly that acts as the "backbone" of the truck and finishes with the completed, fully operational vehicle being driven off the end of the assembly line under its own power.
Finishing the cab, hood, and sleeper
19 The grille, headlight brackets, hood hinges and latches, and the manufacturer's emblem or name are installed on the hood. The finished hood is then stored alongside the assembly line.
The exterior components of the cab and sleeper—the grab handles, mirrors, visors, etc.—are mounted before any work on the interior begins.
The instrument panel is attached to the dashboard. The gauges, warning lights, and switches are installed and hooked up to the appropriate wires and hoses. The entire dashboard assembly is then installed in the cab along with the cab heater system and steering column.
Pads of foam insulation are placed in the cab and sleeper walls, and the interior upholstery pieces are secured in place on the walls and ceiling. Plastic trim pieces are screwed in place to cover exposed edges and seams. The floor is covered with a rubber mat or fabric carpet laminated to a sound-absorbing pad, and the edges are secured. The seats are installed on top of the floor covering and secured with bolts into the main cab structure.
The windshield and rear windows are carefully pressed into place. A rubber gasket seals the edges between the glass and the cab structure.
Installing the cab, hood, and sleeper
The completed cab is lowered onto the chassis and bolted to its mounts. The sleeper is bolted in place behind the cab. The steering column is connected to the steering box. The transmission shift lever is installed through the floorboard, and the clutch pedal is attached to the clutch linkage.
After all the cab connections are made, the hood is lowered onto the chassis and secured to its pivot point. The bumper is attached to brackets on the frame. Wire connections are made for the headlights and front turn signals.
The engine, radiator, and other reservoirs are filled, and the air conditioning system is charged. A small amount of diesel fuel is added to the tanks to allow a short road test. The steering wheel, which had been left out to give working room in the cab, is now installed, and the batteries are connected. The completed truck is then driven off the end of the assembly line.
Aligning the front and rear axles
To make sure that the front and rear axles are parallel to each other and perpendicular to the centerline of the frame, the truck is placed on a laser alignment machine and the axle positions are adjusted as required. The angle of the wheels is also adjusted. This ensures that the truck will handle properly and have satisfactory tire life.
Testing the completed truck
The truck is driven onto a dynamometer and secured with chains. The rear wheels of the truck sit on rollers set into the ground and connected to the dynamometer. As the truck engine spins the rear wheels on the rollers, the dynamometer measures the engine power to ensure it is operating correctly.
The truck is driven slowly through a water spray booth as the driver checks for cab leaks. The driver then takes the truck out for a short drive to check out the overall operation. If the truck passes all the tests, it is parked on "ready row" to be delivered to the dealer.