Body Materials, Trim and Mechanisms

Learning
Objective
At the end of this chapter completion the students must know:
 Steel sheet,
 timber,
 plastic,
 Properties of Materials: (Corrosion and Anticorrosion methods)
 Saltation of paint and painting process
 body trim items
 Body mechanisms
 Introduction
• The main materials used for making cars, parts and components, along with future
trends, are steel, aluminum, magnesium, copper, plastics and carbon fiber.

• The main factors for selecting the material automobile body, are numerous and include
• Thermal resistance
• Chemical or mechanical resistance
• Easy manufacturing and
• Durability

• Affordability is an important issue in vehicle manufacturing, which includes factoring in

the costs associated with a car’s complete life–cycle, including manufacturing, operating
and disposal costs.
Cont
…
• Composite materials may have big advantages over steel
• Because it is lighter, better concerning stiffness and strength,
safer, rust resistance (non corrode) and more fuel efficient vehicles.
• Significantly it increase vehicle fuel economy by reducing vehicle
weight.
• But it is high materials than steel.
• Steel form the critical elements of the structure for the vast
majority of vehicles, and are low cost materials.
• The prime reason for using steel in the body structure is its inherent
capability to absorb impact energy in a crash situation.
 Aluminum
• Aluminum usage in automotive industry .
• Due to its low density and high specific energy absorption performance and
good specific strength that can potentially reduce the weight of the vehicle
body.
• Aluminum is used for body structures, closures and exterior
attachments such as crossbeams, doors or bonnets

Magnesium
• Magnesium is another light metal that is becoming increasingly common in
automotive engineering.
• It is 33% lighter than aluminum and 75% lighter than steel/cast iron
components.
• Magnesium alloys have distinct advantages over aluminum that include better
manufacturability longer die life and faster solidification.
Properties of steel, cast Iron Mg-alloy and Al-
alloy

CFRP (Carbon fiber reinforced polymer/plastics)

Titanium
Titanium has been mainly used in high temperatures zones, and high
strength requirement areas, such as exhaust systems, suspension
springs, valve springs, valves and connecting rods.
 Steel sheet:
• The vehicle body building industry uses many different types of steel.
• Low carbon steel is used for general construction members.
• High tensile steels are used for bolts and nuts which will be subjected to heavy load.
• The steel sheet thickness various from 0.08mm to 1.5mm.
• This type of sheet metal is mostly used in vehicle body construction.

Timber
Before the introduction of plastics, timber was used in vehicle body
construction, because it is readily available, easily worked and economically
competitive, so far as the smaller manufacturer.
 Plastic:
• The applications of CFRP (Carbon fiber reinforced polymer/plastics) includes
Passenger cell, Roof compartment cover, trunk lid, Wheel rims, Cabin, floor, roof,
pillars, hood, Front and rear bumpers, Instrument panel, inner door modules & etc.
• Additionally dashboard, gauges, dials, switches, air conditioner vents, door handles,
floor mats, seat belts, airbags and many other parts are all made from different types
of plastics.
• In addition to the dashboard parts, many of the tiny parts inside the engine,
such as the handle on the oil dipstick, are also made of plastic.
• Because of their lightweight nature, plastics are being increasingly used in body
structures and in engines during automotive manufacturing.
• The other material used in automotive is glass.

• Obviously, its primary use is to create windshields to see properly

while remaining safe from any airborne objects.

• It's also used to create rear and side-view mirrors to boost a view of
what's around while driving.

• In modern cars glasses can be used to create navigation screens and

lenses for back-up cameras to allow drivers to have an even better view
of what's behind them.
 Properties of Materials
Corrosion and Anti-corrosion:
• A vehicle body exposed to corrosion throughout its life and because of the load
carrying structure determines the service life of the vehicle, it is essential that it
should be properly protected against such effects.

There are three types of vehicle body corrosion.

1. Chemical corrosion
Chemical corrosion refers to the gradual destruction of a metal's surface due to the
reaction of the surface with substances in its external environment.
It is often characterized by the oxidation of a metal with an acid
to form oxides.
It occurs whenever a gas or liquid chemically attacks an exposed surface, often a metal
, and is accelerated by warm temperatures and by acids and salts.
Cont..
Chemical reaction
Corrosion happens when a metal continues to oxidize. The metal becomes weaker over time, and
eventually all of it may become metal oxide.
Rusting
Rusting occurs when iron or steel reacts with oxygen and water. The overall reaction is:
iron + oxygen + water → hydrated iron(III) oxide
Hydrated iron(III) oxide is the orange-brown substance seen on the surface of rusty objects.
Rusting is a complex process. The example below show why both water and oxygen are needed
for rusting to occur. They are interesting examples of oxidation, reduction and the use of half
equations:
1. iron loses electrons and is oxidized to iron(II) ions: Fe → Fe2+ + 2e-
2. oxygen gains electrons in the presence of water and is reduced: ½O2 + 2e- + H2O → 2OH-
3. iron(II) ions lose electrons and are oxidized to iron(III) ions by oxygen: 2Fe2+ + ½O2 → 2Fe3+ + O2-

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2. Electro chemical corrosion
• Electrochemical corrosion occurs when two dissimilar metals are present in an electrolytic medium.
• Electrochemical corrosion of metals occurs when electrons from atoms at the surface of the metal are
transferred to a suitable electron acceptor or depolarizer.
• Water must be present to serve as a medium for the transport of ions.
• Because the electrons flow through the metallic object itself, the anodic and cathodic regions (the two
halves of the electrochemical cell) can be at widely separated locations.
• Anodic regions tend to develop at locations where the metal is stressed or is protected from
oxygen.
• Contact with a different kind of metal, either direct or indirect, can lead to corrosion of the more active
one.
3. Fretting corrosion
• Fretting corrosion is the deterioration of material that occurs at the
interface of two contacting surfaces due to small oscillatory movements
or rubbing action arising.
• Fretting is gradual wear by means of rubbing or gnawing action between
two surfaces. Fretting corrosion is a combined action of fretting as well as
corrosion, which involves corrosion at points where two metal surfaces
make contact by means of a rubbing action.
Anticorrosion methods
Anti-Corrosion treatment
Corrosion can be prevented by three basic methods
1. Improve materials.
2. Protective coating.
3. Correct design.
Coating type
Barrier coatings
Barrier coatings aim to prohibit water, oxygen and other chemicals from making contact with the substrate. In
reality, it’s taken for granted that some water and oxygen will reach the surface that barrier coatings protect.
Thermal barrier coatings are one of the most commonly used examples of this type of corrosion protection.
Inhibitive coatings
inhibitive coatings are made up of pigments that actively impede chemical reactions. These coatings were
designed to keep corrosion from ever starting. Red lead is a well-known example of an inhibitive coating
Sacrificial coatings
Sacrificial coatings (also sometimes called “cathodic protection”) must be applied directly to a ferrous metal,
such as steel. Galvanized steel is an example of sacrificial coating.
Selection of paint:
• The colors for finishing the vehicle should be based on scientific principles of
coloring, which can be briefly outlined as follows,
• All shades are based on three colors i.e. Blue, yellow and red.
• The basic concepts of color technology are as follows,
TONE/ HUE : (the name of a color)
The tone of color can be defined by its position in the spectrum. i.e. Wave length
VALUE:
Value can be measured by the mixture of a natural grey, value corresponds to the concept
of lightness or darkness of colors

TONE
VALUE

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 INTENSITY:
• Intensity is defined by the mixture of white in the colors, where full color
has no white mixed with it.
#What is the difference between hue/ tone, intensity, and value?
Precisely, HUE is the name of a color. VALUE is the lightness or darkness of a
color. INTENSITY is the strength or purity of a color.
Your eyes will see three things in each color: • What color (its hue or
name), • Its lightness (reflectance) or darkness (its value), and • Its
brightness(luminance) or dullness (its intensity).
 Modern Automotive Coating Processes
• Modern automotive coating methods consist of five main steps. They include the
following:
 Pretreatment: removes and cleans excess metal and forms an appropriate
surface structure enabling bonding of a corrosion protection layer.
 Electrodeposition (ED) of the anti-corrosion or rust prevention layer.
 Applying Poly Vinyl Chloride (PVC) for anti-corrosion, elimination of
water leaks, and minimization of chipping and vibrational noise.
 A primer applied to promote adhesion between the surface and the
basecoat; it also imparts a smoother surface for subsequent layers and has
anti-chipping properties.

• Finally, the topcoats that include a

basecoat and clearcoat are applied;
they provide surface properties that
are sought after, including color,
appearance, gloss, smoothness, and
weather resistance.
 Pretreatment
• Pretreatment means surface preparation. Here by pretreatment, we mean
metal pretreatment as the powder coating is predominantly applied to metals.
Surface preparation includes: Cleaning – mechanical or chemical. Mechanical
cleaning includes methods like scratch brushing and sand blasting.
• When the automobile body sheet metal components are welded together, the
resulting structure is referred to as the body-in-white (BIW).

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Cont..
Pretreatment consists of cleaning the body surface to remove remaining oils from the
stamping process and welding residues through three primary liquid dip processes of
degreasing, conditioning, and phosphating.
An additional pretreatment cleaning that employs ~pH 9 hot water can also be used.
A phosphate treatment applies an inert layer of metal phosphate, providing resistance to
corrosion spread .
The degreasing solution is composed of alkaline, salts and surfactants and can include
caustic soda, trisodium phosphate, and sodium carbonate.

The degreasing zone typically consists of at least two sequences, including a spray stage
known as knock-off-degrease (KOD) and a dip sequence. The advantage of using these two is
that a significant portion of the oil and dirt will be removed by the high-pressure spray,
thereby leaving a relatively lower load for the dip sequence to clean.
Pretreatment process

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Electrodeposition (ED)
The metal underbody and frames of automobiles are coated to prevent corrosion,
whereas other areas like the roof are not rust-proofed.
When not coated to prevent corrosion, the structural metals (or other materials) are
primed before applying additional coatings.
Since then the use of E-coat has grown at a rapid pace. By 1970, 10% of all cars
were electrocoated and by 1990, 90% of all cars were electrocoated.
Today, it is the most conventional coating process used in vehicle manufacturing.
• The E-coat solution consists of a mixture of resin, binder, a paste containing the
pigments, and a solvent.
• During anodic electrodeposition, metal parts are positively charged while the paint
is negatively charged; because small amounts of metal ions migrate into the paint
film, it limits the performance properties of the coating.
• Hence, anodic coatings are mainly used for interiors and offer excellent color and
gloss control.
 Electrodeposition

• In cathodic electrodeposition, the metal part is negatively charged while the paint is
positively charged. \
• In contrast to the anodic process, the cathodic process reduces the amount of iron that
can enter into the paint film.
• The E-coat process is considered to be relatively environmentally friendly; it uses only a
0.5% solvent solution. 22
Pigment
• Pigments are granular solids incorporated in the paint to contribute color.
• The pigments impart toughness, texture to give the paint special properties.
• It does not allow the main vehicle to loosen the paint particles.
• Titanium dioxide is used as pigment in most paints Silica, Alumina
,Zirconium are also used as pigments .These materials give better exterior
durability or better hiding performance.
Enamel
• The enamel portion of paint is mixed with vehicle and pigment to give
it glazing appearance.
• Drier
• The drier in the paint allows the paint to dry as fast as possible so that the paint may not slip
down from the body of the automobile to give it a uniform appearance at all parts of the body.
• Driers are oxygen carrying catalysts.
• They accelerate the drying of the oil film by oxidation , polymerization and condensation.
• Most effective driers used are resinates, linoleates , tungstates and naphthalenes of copper,
manganese, lead and zinc.
• Thinners
• The thinner in the paint is used to make it thin while mixing the vehicle, pigments and drier .
• It enables the paint to spread easily and also to be sprayed as the case may be.
• It is a volatile substance.
• Therefore evaporates after the paint has been applied.
• Popularly used thinners are turpentines , mineral, spirits, benzene, dipentene,
napthalene, xylot, kerosene, methylated naphthalene etc.
Methods of Painting
• Different types of painting methods are being applied
for painting of automobiles
 Brushing
 Dipping
 Roller coating
 Spraying
 Tumbling
 Brushing
• In automobiles some of the inner parts which can not be in reach of spray
gun, can be painted by brushing with automobiles paints using paint
brush.

 Dipping
• The parts of irregular shape and small in size can either be sprayed nor
brushed.
• Such parts can be removed from the vehicle and dipped in a drum
filled with paint.

 Roller Coating
• In automobiles the parts which are in sheet shaped can be painted by roller
coating
• The sheet shaped articles are passed though the rollers which are dipped in
paint.
• By rotating the rollers on the sheets, the paint will be applied uniformly.
 Spraying
• The entire outer surface of the vehicle body is painted by means by spraying
the paint with spray gun.
• In this method the paint is atomized by the force of compressed air or by the
action of high pressure compression of paint and turning of paint into small
particles which travel to the article to be painted.
 Tumbling
• Small sized articles are painted by this method.
• They are put in a rotating barrel containing properly mixed paint .
• The barrel is closed and rotated for a suitable amount of time.
• Articles get coated with paint and after taking out, they will be finally dried.
 Painting Procedure
• Automotive manufacturers have developed several different techniques for body painting that yield
effective, reliable results.
• The process is completely automated and works mainly through sealed chambers built onto the
assembly line
 Step 1: Electrocoating

• E-coating is an immersion wet paint finishing process that uses electrical current to
attract the paint product to a metal surface. This process is also referred to as paint
deposition.

• E-coat is a type of finishing that involves covering the components with protective
paint. Sometimes known as Electrocoating or EPD, the process is usually completed by
submerging the components into the paint to allow maximum coverage
• Step 2: Primer
• Once the anti-corrosive layer has been electroplated on, primer is applied to
add smoothness and allow a top paint layer to stick to the body.
• First, the body is lowered off the chains to rest on a floor
apparatus attached to a track.
• To apply the primer, the body moves down the track into a special sealed
room called a “flow chamber”.
• The flow chamber features a constant flow of air that takes vaporized
primer particles from openings in the ceiling where they gently deposit on
the exterior for a uniform thickness.
• Meanwhile, the bottom of the chamber has several outlet openings attached
to a vacuum, removing excess primer to be collected and reused.
• After about 10 minutes, the body is moved down the track to another
drying room.
• Step 3: Base Coat
• Once the primer has dried, the body moves into another flow chamber for
the application of the base coat.
• The base coat constitutes the actual “color” of the car, including textural
details
like aluminum flakes for a sparkle effect.
• Like the primer, the base coat’s application involves the continual flow of
vaporized paint across the body for about 10 minutes, followed by a trip to
a drying room.
• Step 4: Clear Coat
• Just as the electrocoating protects metal from corrosion, the clear coat protects
the base coat against light scratches, organic solvents, water and UV sun
damage.
• As the name suggests, it is transparent, showcasing the base coat like glass does
a picture.
• Typically, a flow chamber applies the clear coat as well.
 Body trim items
• Trim is anything the manufacturer applies to the car to enhance its
style and appearance.
• Decorative and functional strips around the vehicle are an integral
part of vehicle design.
• Common exterior trim items include radiator grills, window frames,
light rings, door handles, emblems and antennas.
• Interior car trims are all of the parts of the vehicle that are more
decorative than functional. Its primary purpose is to make the inside
of the car into a comfortable and warm environment.
• Examples of trim may include a leather steering wheel, door lining,
car roof lining decorations, seat trim, or a sun visor mirror.
Body mechanisms
1. Door locking mechanisms
2. Window winding mechanism
3. Seat adjustment mechanism

Door locking mechanisms

• Like many parts of the vehicles, the doors are an integral safety
system, providing protection for passengers and security from
thieves.
• Car doors need to open, remain closed when shut and lock on
demand to protect precious cargo.
• The door locking mechanism currently available in two.
 Mechanical (Latch mechanism)
 Power door locking mechanism
 Latch Mechanism
• A latch mechanism is the cylinder that is driven through the edge of the door.
• This is often also called a tubular latch mechanism.
• The mechanism has a spring loaded latch that retracts to open the door and upon
release of the door knob or lever, protrudes to keep the door closed.
• A tubular latch mechanism for an exterior door often comes with an attached
mortise plate, and requires mortising, or some chiseling to be done on the edge of
the door for the plate to rest correctly recessed in the door.

 Power locking mechanism

Power door locks (also known as electric door locks or central
locking) allow the driver or front passenger to simultaneously lock or
unlock all the doors of an automobile or truck, by pressing a button
or flipping a switch.
• In this car, the power-door-lock actuator is positioned below the
latch. A rod connects the actuator to the latch, and another rod
connects the latch to the knob that sticks up out of the top of the
door.
• When the actuator moves the latch up, it connects the outside door
handle to the opening mechanism. When the latch is down, the
outside door handle is disconnected from the mechanism so that it
cannot be opened.
• To unlock the door, the body controller supplies power to the door-
lock actuator for a timed interval.
• Door handles
• Door handles are located on the inside and outside of a car door.
• When you pull on the inside or operate an outside door handle, they
either extend a metal rod (or other linkage) or pull a cable that
disengages the door latch from the anchor.
• A binding or jammed door handle or linkage will leave the door stuck
in the open position. Leave replacing a malfunctioning door handle,
door latch release linkage or a broken latch release cable to the pros.
• A car (or truck) door is made up of many parts that need to
operate together to work properly.
• The main component is the latching mechanism.
• Located inside the door assembly, it engages a door anchor,
or striker, that is attached to the body of the vehicle, to keep
the door closed.
• Operating the inside or outside door handle releases the
latch from the anchor, allowing the door to open.
• Other parts include the door assembly itself, door hinges,
door lock, door latch linkage or cables and, if equipped,
electrical actuators and switches that lock or unlock a door.
 Window winding mechanism
• A mechanism for opening and shutting the windows in a motor
vehicle; especially one by which a side window in a car can be
manually wound up and down using a handle below the window.
Manual Window winding mechanism

Window
Window track

Gear arm Rectangular arm

Manual drive handle Rectangular truck
 Power
• TheWindows
windows on cars which can be opened or shut with the
help of buttons, are called power windows.
• Power windows are controlled by switches and wires and
are powered by battery or electricity.
• Power windows do not function if the ignition of the car is
not turned on.
• Unlike the traditional windows, power windows do not
have
manual handles.
• They do not work manually.
• The basic power windows generally have control of all the
four windows and can be controlled by the driver.
• When the switch pressed the window electric motor start
rotating and turn window gear drive.
• The gear drive turn geared which move the linkage that
 Seat adjustment mechanism
• An adjustment mechanism for a car seat provides multiple vertical
and horizontal locking positions for adjusting the seat to
comfortable position.
• The car seat has a base with forward and rear support walls each
having a key way matching the profile of the stem portion of a locking
plunger.

seating adjustments can be carried out in

several ways as follows :
(a) Fore and aft seat setting,
(6) Vertical seat-height setting,
(c) Seat squab tilt, and
(d) Seat cushion rake.