1st Year Apprenticeship
Metal Work
In this block you will learn about:
•
•
•
•
•
Metals and their properties
Deformation effects after impact
Tools used for effective repair
Stretching and shrinking
Paintless dent removal
Body Steels
• Hot rolled
– thickness ranges 2-8
mm
– generally used for
full frames, sub
frames (unibody)
and crossmembers
• Cold rolled
– hot rolled, acid
rinsed, cold rolled
thin, then annealed
– better surface quality
– good workability
– most unibody panels
are cold rolled steel
– stamping process
increases strength
Cold Rolling Mill to Stampings
Grain Structures of Steel
HSLA
Mild Steel
Properties of Steel
•
•
•
•
•
Mild Steel
HSS
HSLA
UHSS
AHSS
up to 30,000
30 - 70,000
75 - 100,000
100- 160,000
110 – 180,000
psi
psi
psi
psi
psi
yield
yield
yield
yield
yield
strength
strength
strength
strength
strength
HSS
• Gets its initial strength
during the
heating/cooling
treatment from the
steel manufacturer
• Is used mainly for load
bearing components in
the body structure,
however more
commonplace today
throughout entire body
structure
• May be repaired cold or
with controlled heat
• More difficult to repair
than mild steel
• Yield strength of up to
70,000 psi.
• Lack of available
identification for HSS
means treat all steel as
HSS!
HSLA
• Like HSS except varying
alloying elements
(chemicals) are added
during the
manufacturing process
to increase its strength
(yield and tensile)
• May be reworked cold
or with controlled heat
application
• Found in areas such as:
–
–
–
–
–
Door intrusion beams
Bumper reinforcements
Lock pillars
Front and rear frame rails
Hinge pillars (A,B,C)
• Yield strength up to
110,000 psi.
UHSS/AHSS
• The strongest of the
structural steels found
in today's automobiles
• Often referred to as
Boron, Martensitic, Dual
phase steels
• Found in these areas:
– Front and rear bumper
reinforcements
– intrusion beams
– A,B,C pillars (some
vehicles)
• No heat whatsoever
is to be applied to
any component of
this designation!
• These steels are
generally not repairable
• Require special
considerations when
removing/sectioning
Identification of Steels
• Location and application of HSS steels vary
widely from manufacturer to manufacturer
• Sources of information include:
– OEM body repair manuals
– Internet sources (OEM approved)
– Mitchell manuals (estimating manuals)
• If you cannot positively identify the makeup
of a component, you must treat it as HSS!
HSS Locations
Part Loading
• Tension:
• a load that tries to pull parts straight apart
• Compression
• a load that forces parts straight into one another
• Shear
• A load that pulls sideways
• Cleavage
• a load that pulls parts away from each other at an angle
• Peel
• a load that pulls parts straight away from one another
Loads present during a
collision
Terminology
• Yield strength:
– The minimum amount of force any piece of metal
can resist without bending or deforming
permanently
• Yield Point:
– The amount of force that a piece of
metal can resist without tearing or breaking
• Tensile strength
– is measured as the maximum force per unit of
area that causes a complete fracture of break
Terminology
• Work Hardening
– Is the upper limit of plastic deformation, causing
the metal to become hard in the bent area
• Malleability
– is the property which allows deformation under
compression or upsetting (shrinking)
• Elasticity
– is the ability of the metal to be bent or stretched
and spring back to its original shape
Terminology
• Plasticity:
– The property that permits metal to change shape
when sufficient force is applied to it
• Plastic Deformation:
– The ability of the metal to be bent or formed into
different shapes ( bent beyond its elastic limit)
• Elastic Deformation:
– The ability of the metal to be stretched or bent
and return to its original state
Terminology
• Torsional strength
• is the property of a material to withstand a
twisting force
• Shear Strength
• is a measure of how well a material can
withstand forces acting to cut or slice it apart
• Compressive Strength
• is the property of a material to withstand being
crushed
Metal Strength Terminology
Plastic Deformation
Elastic Deformation
Terminology
• Rigidity:
– Opposite of plasticity.
• example: Cast iron will not bend or deform, it will only
break under load
• Ductility:
– ability of a metal to plastically deform without
breaking or fracturing, with the cohesion between
the molecules remaining sufficient to hold them
together
Heat and Sheet Metal
• The point at which Steel melts is 2600
Degrees F
• We should know the effects of the
temperature change between 400 - 1600
degrees F.
• Three Effects:
• scaling
• changes in grain structure
• expansion and contraction
Temperature and Colour Change
• Light film of scale (iron oxide) 430 F
• Pale yellow / Straw / Brown / Purple / Light Blue
• Dark Blue / 600 degrees F
• Reddish Glow / 900 degrees F
• Blood Red / Dark Cherry 1200 F
• Cherry Red 1550 degrees F
• Critical Point 1600 degrees F
Low Crown
High Crown
Reverse Crown
Buckles
• Buckles occur when metal has been bent past
it’s elastic limit
• Work hardening has occurred and a new
shape is formed
• The buckles found in indirect damage are as
follows:
–
–
–
–
simple hinge
collapsed hinge
simple rolled
collapsed rolled
Direct and Indirect Damage
Impact effect on a High Crown
Effect of damage on a Low Crown Panel
Effect of impact on a combination High / Low
Crowned Panel
Tension can only be removed by “unlocking” the
pressure areas
Combination of Buckles
two types
of rolled
buckles
Collapsed hinge
buckle
simple
hinge
buckle
Steps in Unlocking Damage
First in last out
“Collapsed Roll Buckle”
What happens to the Steel upon impact?
In this case, the damage (Hinged Buckle) has
caused severe damage to the molecular structure
Hammering helps the atoms to ‘vibrate’ back
into shape, or order
Tools
•
•
•
•
•
•
•
Hammers
Dollies
Spoons
Dent pullers
Body picks
Oxy-Acetylene
Body files
Body Hammers
Hammers
Holding the Body
Hammer
Dollies
Holding the Dolly
Using the Corner of the Dolly
Using the Edge of the Dolly
Using the Dolly as
a tool for bumping
Spoons
Uses of the Body Spoon
• Can be used as a
dolly in hard to reach
areas
• When used with
due care, can be
used for leverage
• Great tool for
dispersing the force
of a hammer blow
Body Picks
Body Puller Set
(Slide Hammer)
Pull Rods
Other Body Working Tools
•
•
•
•
•
•
•
Pry Bars
Suction Cups
Stud Welders
Porta-spot Dent Pullers
Body Files
Slap Files
Hydraulic Porta-Power
Dent Removal Tools
Dent Removal Systems
Hammer Maintenance
Depending on the
condition of your
hammer, several
steps may need to
be taken to restore
the ‘mirror’ finish
to the surface on
the face of the
hammer.
From filing to
wet sanding and
polishing.
Locating Damage
• Visually
• Physically
• Mechanically
Use your sense
of sight and the
reflection of a
light source as a
means of damage
identification
If a visual reference
is not possible, feeling
for damage will be
more than satisfactory
Mechanical Methods
Hammer and Dolly
Variables:
• Force of hammer blow
• Force of Dolly rebound
• Shape of Dolly
• Working distance
Hammer on Dolly
Hammer off Dolly
Metal Fundamentals
• Properties of steel
• Working the metal
• Heat Shrinking
Detecting an ‘Oil Can’ or stretched area
Time to Shrink!
- Hold torch
at right angle
to panel
- heat metal
to desired
degree
- place dolly
behind area
to be shrunk
- hammer area
from centre out
- quench
immediately with
wet sponge
Shrinking
Shrinking
Procedure
Cold Shrinking
Using a Carbon Rod for heat shrinking
Repair Plan
•
•
•
•
Determine the extent of
the damage
Removal of moulding,
emblems, or sound
deadening materials
from behind panels
Roughing out dents
with hammer, puller, or
pry bar
Metal finishing with
hammer, dolly and
body file
•
•
•
•
•
•
Panel shrinking
Removal of small
dents and bulges
Filling with body filler
Filing, sanding, and
priming the fill area
Rustproofing the back
side of panels
Completion of repairs
End of Metal Repair Fundamentals