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 removalBody Steels
Hot rolledthickness ranges 2-8 mmgenerally used for full frames, sub frames (unibody) and crossmembersCold rolledhot rolled, acid rinsed, cold rolled thin, then annealedbetter surface qualitygood workabilitymost unibody panels are cold rolled steelstamping process increases strengthCold Rolling Mill to Stampings
Grain Structures of Steel
HSLA
Mild Steel
Properties of Steel
Mild Steel HSS HSLAUHSSAHSSup to 30,000 psi yield strength
30 - 70,000 psi yield strength
75 - 100,000 psi yield strength
100- 160,000 psi yield strength
110 180,000 psi yield strength
HSS
Gets its initial strength during the heating/cooling treatment from the steel manufacturerIs used mainly for load bearing components in the body structure, however more commonplace today throughout entire body structureMay be repaired cold or with controlled heatMore difficult to repair than mild steelYield 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 applicationFound in areas such as:Door intrusion beamsBumper reinforcementsLock pillarsFront and rear frame railsHinge pillars (A,B,C)Yield strength up to 110,000 psi.UHSS/AHSS
The strongest of the structural steels found in today's automobilesOften referred to as Boron, Martensitic, Dual phase steelsFound in these areas:Front and rear bumper reinforcementsintrusion beamsA,B,C pillars (some vehicles)No heat whatsoever is to be applied to any component of this designation!These steels are generally not repairableRequire special considerations when removing/sectioningIdentification of Steels
Location and application of HSS steels vary widely from manufacturer to manufacturerSources of information include:OEM body repair manualsInternet 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 apartCompressiona load that forces parts straight into one anotherShearA load that pulls sidewaysCleavagea load that pulls parts away from each other at an anglePeela load that pulls parts straight away from one anotherLoads present during a collision
Terminology
Yield strength: The minimum amount of force any piece of metal can resist without bending or deforming permanentlyYield Point: The amount of force that a piece ofmetal can resist without tearing or breaking
Tensile strengthis measured as the maximum force per unit of area that causes a complete fracture of breakTerminology
Work HardeningIs the upper limit of plastic deformation, causing the metal to become hard in the bent areaMalleabilityis the property which allows deformation under compression or upsetting (shrinking)Elasticityis the ability of the metal to be bent or stretched and spring back to its original shapeTerminology
Plasticity: The property that permits metal to change shape when sufficient force is applied to itPlastic 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 stateTerminology
Torsional strengthis the property of a material to withstand a twisting forceShear Strengthis a measure of how well a material can withstand forces acting to cut or slice it apartCompressive Strengthis the property of a material to withstand being crushedMetal Strength Terminology
Elastic Deformation
Plastic Deformation
Terminology
Rigidity: Opposite of plasticity. example: Cast iron will not bend or deform, it will only break under loadDuctility:ability of a metal to plastically deform without breaking or fracturing, with the cohesion between the molecules remaining sufficient to hold them togetherHeat and Sheet Metal
The point at which Steel melts is 2600 Degrees FWe 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 FLow Crown
High Crown
Reverse Crown
Buckles
Buckles occur when metal has been bent past its elastic limitWork hardening has occurred and a new shape is formedThe buckles found in indirect damage are as follows:simple hingecollapsed hingesimple rolledcollapsed rolledDirect 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
simple hinge buckle
two types of rolled buckles
Collapsed 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
HammersDolliesSpoonsDent pullersBody picksOxy-Acetylene Body filesBody 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 adolly in hard to reach
areas
When used withdue care, can be
used for leverage
Great tool fordispersing the force
of a hammer blow
Body Picks
Body Puller Set
(Slide Hammer)
Pull Rods
Other Body Working Tools
Pry BarsSuction CupsStud WeldersPorta-spot Dent PullersBody FilesSlap FilesHydraulic Porta-PowerDent 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
VisuallyPhysicallyMechanicallyUse 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 distanceHammer on Dolly
Hammer off Dolly
Metal Fundamentals
Properties of steel Working the metal Heat ShrinkingDetecting an Oil Can or stretched area
Time to Shrink!
Shrinking
Shrinking Procedure
- 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
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 filePanel shrinking Removal of small dents and bulges Filling with body filler Filing, sanding, and priming the fill area Rustproofing the back side of panelsCompletion of repairsEnd of Metal Repair Fundamentals