66 Section 1 Introduction to Collision Repair
On many full-frame vehicles, only a portion of the frame,
such as the front section, is hydroformed. The rest of the
frame is made of stamped steel. The stamped steel sections
and the hydroformed sections are welded together. Certain
portions of a frame may be made from stronger steel than
other portions of the same frame.
Once the unibody vehicle is welded together or
the cab or body is mounted on the full-frame vehicle, the
bolt-on parts can be installed. Bolt-on parts include the
hood, fenders, doors, deck lid, and bumpers.
The vehicle panels must be protected from corro-
sion. One way to protect is to use galvanized steel in
areas subject to corrosion, such as the rocker panels.
Additional protection is added during the manufacturing
process. The vehicle is dipped in corrosion-resistant
primer. The seams where panels join are filled with a
sealer to keep out contaminants. The entire vehicle is
sprayed with a durable paint finish, Figure 3-23.
After the vehicle is painted, the interior, drive train,
electrical wiring, and glass are installed. See Figure 3-24.
Some vehicles have rigid or structural foam inside body
cavities such as the rocker panels, unirails, and center
pillars. Structural foam is molded to the internal shape of
the cavity. The structural foam transfers some energy in
a collision, adding strength and stiffening the part. Rigid
foam also stiffens the part but does not contribute to the
overall strength of the vehicle. Stiffening of the parts with
internal cavities makes the vehicle feel more solid and ride
better without making the vehicle significantly heavier.
Vehicle Safety Rating
A vehicle safety rating is a measure of a vehicle’s g
crashworthiness. It is determined by measuring the amount
of damage a vehicle sustains and the potential for occupant
injury that occurs when the vehicle is subjected to stan-
dardized tests. There are four basic types of safety ratings:
frontal impact, side impact, roof strength, and rear impact.
To arrive at the frontal impact rating, the two stan-
dardized collision tests are performed: the full-width
frontal test and the frontal offset test. The full-width frontal
test is the standard in the United States, while the frontal
offset test is the standard in other countries, such as
Japan and Australia. In the full-width frontal test, two test
dummies are positioned in the front seat or seats of a
vehicle and the vehicle is propelled into an unmovable
barrier at 35 mph. The entire front of the vehicle hits the
barrier. The movement of each dummy is measured to
determine the potential for injury to the head, chest, and
legs. If the dummies have less than a 10% chance of
sustaining a life threatening injury, the vehicle receives a
5-star front impact safety rating.
In the frontal offset test, only 40% of the driver’s side
of the front of the vehicle, which is moving at 40 mph,
hits the barrier. The barrier is not totally rigid. Instead,
the vehicle impacts a deformable aluminum face on
the barrier. The amount of deformation in the vehicle’s
passenger compartment, overall damage to the vehicle,
and the movement of the dummies are evaluated. The
vehicle safety rating of good, acceptable, marginal, or
poor is calculated by factoring in many criteria such as
whether the test dummies heads were partially ejected
from the vehicle, if the test dummies chests hit the dash-
board, if the fuel system leaks, if the floor moves back
Figure 3-22. After a vehicle’s body panels are stamped
at the factory, they are assembled and welded together
as shown here. (Ford)
Figure 3-23. After a vehicle’s body has been
assembled, it is primed and painted to help prevent rust
and corrosion. (Ford)