ing is still sometimes used. MIG,
clips, screw clamps, and various Cleco
to be pretty bulky and cumbersome.
TIG, and resistance (spot) welding are
devices. Each of these represents a
Beyond that reach, other methods of
the main approaches covered here.
class of fixturing devices, and each
fixturing must be employed.
comes in a great variety of styles, sizes,
Edge clips are limited to holding
Stick Welding
and configurations. Each also has
the edges of panels and patches, but
This method was once used to
application to most types of seams—
have the advantages of being quick
join autobody panel metal, both in
butt, lap, and offset lap.
to apply and to remove, and of offer-
production and for repair. This prac-
Locking pliers are often referred to
ing very little obstruction to or inter-
tice involved using small-diameter,
by the name given to this tool by the
ference with adjacent parts.
coated welding rods that were
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
73
CHAPTE R 8
years, car manufacturers sometimes
supplement spot welds with adhe-
sives and anti-corrosion treatments to
add bonding strength, and to protect
joints that are welded this way.
Some of the spot welders used in
repair and restoration do not squeeze
the weld area between two elec-
trodes, but apply spot welding force
and heat to one piece of metal that is
grounded through the other piece to
be joined to it. These devices are par-
ticularly handy where access to both
sides of a spot weld area are difficult
or impossible to achieve. There are
Spot welds are not very strong individually, but in numbers they gain strength.
also numerous attachments for MIG
The key to making good spot welds is getting the welding duration right, so as
welders that mimic the strength,
to not under-weld weak attachments or burn through with excessive weld
appearance, and configuration of
times. Clean contact and mating surfaces are also critical.
resistance welds.
Another technique for duplicat-
specifically designed for sheetmetal
and considerable squeezing pressure
ing the appearance and function of
work. Both AC and DC formats were
on the two outer surfaces of the weld
spot welds is button hole welding.
employed. Stick welding sheetmetal
area by the welding electrodes, melts
This technique employs torch, MIG,
required
considerable
skill,
and
the spot into a fusion weld. Spot
or even TIG welding to join two sec-
yielded results that were often less
welds are quick and easy to make, and
tions together, one on top of the
than great. The main problem was
reasonably neat and strong. Modern
other, by welding through the top
that when stick welding was per-
light vehicles depend on as many as
thickness of metal and into the sur-
formed with the machines commonly
3,000 or 4,000 spot welds to hold
face of the metal under it. This must
associated with it, the process pro-
their structures together. In recent
be accomplished without overheat-
duced excessive heat for thin-section
ing the whole area, and ending up
jointure, resulting in excessive drop-
with an unsightly and embarrassing
out and distortion. The time required
hole through both pieces. One trick
to finish stick welds in sheetmetal was
to avoid this is to do a pseudo-
excessive, by today’s standards. This
button-hole weld by drilling a hole
practice is obsolete.
through the top section, and weld-
ing its rim to the metal under it.
Resistance or Spot Welding
Spot welds are often vulnerable
This has been a mainstay of auto-
to corrosion because the places
motive construction since the 1930s.
It uses no flux or filler, and is accom-
attracting moisture between the
plished by applying a concentrated
joined pieces of metal through capil-
short circuit, and strong physical pres-
lary action. This problem is made
sure, to a small spot on as many as
This type of spot welder allows you to
worse by the fact that spot welding
three thicknesses of body metal to be
make welds from one side of a panel.
tends to vaporize many of the steel
joined. A combination of intense
This can greatly ease access
treatments, like galvanizing, that are
heat, created by maintaining a very-
problems. It takes high electrode
employed to protect sheetmetal. This
high-amperage short circuit at the
pressure and clean metal for this type
problem is mitigated by using a
point of the weld for a short interval,
of weld to work well.
weld-through primer between pieces
74
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
W E LDI NG BODY M ETAL
Applying a good weld-through primer
to the surfaces between spot welds
goes a long way to protecting them
from corrosion. This technique can
also be used with MIG and TIG
Today, MIG welding is the mainstay of most autobody welding. It is relatively
welding, but is less effective in those
easy to learn this technique. It is being used here to fill weak spots in a
cases than with spot welding.
sheetmetal floor.
that are spot welded. Such primers
reason than that everyone uses and
the short circuit. However, it is
contain a very high percentage of
understands them.
quickly reestablished, as more wire is
zinc in their solids. This makes them
In the MIG process, a welding
fed into the puddle, creating the
conductive, and thus able to carry
wire is continuously fed into the
short arc cycle that is the basis of
spot welding currents, and protects
weld area—the puddle—as it is
MIG welding. This all occurs at about
finished welds with ions from the
drawn along the weld seam. The wire
100 to 150 cycles/second, and pro-
zinc particles in the coating after a
carries current, and is surrounded at
duces the famously characteristic fry-
weld is made.
the weld, by an inert shielding gas
ing egg sound that is associated with
that is fed there through the welding
MIG welding.
MIG Welding
h
ose and gun, along with the wire.
The most-often botched aspect
This has become the most com-
C-25 is the most common gas used
of MIG welding is fit-up, the distance
mon type of repair and custom auto-
for sheetmetal welding, in a 25-
between the edges of the metal
body welding. Its name derives from
percent CO2 and 75-percent argon
pieces that are being joined. In lap
the term metal inert gas, which is
mixture. The gas acts like the heat-
and offset lap joints, fit-up is not an
really a misnomer. After all, so-called
vaporized rod coating in stick weld-
issue because the joints are overlaps.
TIG welding (for tungsten inert gas)
ing. It shields the weld puddle and
But in butt welding, it is critical to
is also a metal-inert-gas welding
the cooling weld from most of the
leave
adequate
fit-up
distance
process. Properly, what is called MIG
oxidation corrosion that would
between butted edges. This space is
should be called—according to the
occur if the weld was made and
consistently in the range between
American Welding Society (AWS)—
cooled in a normal air environment.
the thickness of a dime and a nickel.
GMAW for gas metal arc welding.
The actual MIG process involves
It may sound more difficult to carry
TIG is properly designated as GTAW,
a cycle. As the mechanically fed wire
a weld puddle down such a gap than
for gas tungsten arc welding. I’m
contacts the puddle, it creates a
down two more closely fitted edges.
glad to get all of that sorted out,
direct
short
circuit
with
the
However, this is not the case.
thank you. Now, please forgive me,
grounded work piece. The heat gen-
What is beyond difficult, in fact all
while I continue to use the vernacu-
erated by the short melts off the
but impossible, is to get a good MIG
lar terms, MIG and TIG, for no better
wire’s end, into the puddle, ending
butt weld when edges are fitted up too
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
75
CHAPTE R 8
These welds, with their fronts shown on the left and their backs on the right, represent (top to bottom: 1) a finished
weld done with alternate tacking and grinding, 2) a bead, welded with trigger on/off segments, and 3) a weld bead
comprised of automatically stitch-timed segments.
closely or in actual contact with each
Amperage is set by setting the wire
ting wire speed and voltage properly
other. This is because the expansion
feed speed. Different wires and differ-
for MIG welding. Some machines set
from welding heat inevitably distorts
ent thicknesses of metal require dif-
one, or even both, of these variables
too-closely-fitted metal edges so badly
ferent speeds. Manufacturers supply
automatically. While many welds do
that it is very hard to weld them. It is
recommendations for this setting
not allow for practice, some do. If
also very difficult to straighten out
with their machines. It is, however,
you can duplicate the conditions of a
panels welded that way.
rough data, and you should plan to
difficult weld with scrap metal that is
There are several issues to master
modify it for your own situations and
similar to the material in the sections
in order to do good MIG welding. You
according to your own experience.
that you will be welding, and prac-
need to figure out ideal gas flow for
Voltage settings are also critical.
tice your difficult weld, it would be
your work. This is set with a regulator
The best MIG machines have contin-
to your advantage to do so.
as the volume of shielding gas deliv-
uous voltage settings, while less-
Some MIG welding machines
ered. Try to use a two-stage regulator
expensive ones rely on step settings.
have fine controls for things like
that employs a volume indicator in its
In either case, the voltage setting in
stitch welding, that is, weld time on
second stage. About 10 to 20 CFM (at
MIG welding is somewhat analogous
and time off, and burnback control,
atmospheric pressure) is a good range
to how long an arc you hold in stick
which is the time that the wire elec-
in which to work when you are weld-
welding. It controls the format of the
trode remains energized after the
ing body metal with .023- to .025-inch
weld bead and thus its height, shape,
gun trigger is released. These are
wire. Practice and experimentation are
and, to some degree, its penetration.
handy features that can improve the
your best guides in this matter.
Somewhere between your gen-
convenience and quality of work,
Amperage settings are critical
eral experience and getting frequent
but they are not essential to doing
when MIG welding sheetmetal.
practice, you will get the hang of set-
good MIG welding.
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AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
W E LDI NG BODY M ETAL
One thing that is essential is to
use good wire. MIG welding wire
varies in quality. Some wires are
junk, barely good enough to weld
with, while others are a pleasure to
use. Today, most of the major wire
brands perform well. Still, different
wires often have different features
and advantages. For example, one
wire may produce welds that are eas-
ier to grind, while another may lay
down more uniform beads. Again,
these are things with which you
should experiment.
Other
variables,
like
torch
approach (forehand or backhand),
distance from work, position, and
angle, are best dealt with in manuals
and other sources that are specifi-
cally devoted to MIG welding
instruction.
TIG Welding
TIG welding is probably the most difficult welding technology to master.
This is probably the most skill-
However, it pays the reward of being the best way to join sheetmetal pieces
intensive type of welding, but pre-
and panels, when quality is the prime objective.
sents an odd dichotomy. It can be
understood in very complex and
nology, but knew how to weld with
sus thumb wheels, and so forth, are
technical terms, but it can be per-
it, instinctively and superbly.
hot topics. Also, there is specializa-
formed beautifully with little knowl-
The point is: You can interpret
tion in TIG welding particular metals
edge of its technical aspects.
TIG welding in many ways and at
and alloys.
Here is an example: Back in the
many levels, comprehending and
Unfortunately, is not possible to
age when TIG welders did not have
mastering as much or as little of the
offer instruction in TIG welding in
the modern sophistication of solid-
underlying technical issues as the
this book. However, if you are inter-
state-generated square-wave forms
spirit grabs you. Some people revel in
ested in doing ultimate-quality weld-
and slope control, they relied on car-
the complexities of TIG waveforms
ing work on a variety of metals, from
bon bundle frequency generators for
and the possible adjustments to them.
stainless and common steel to alu-
superimposed high-frequency cur-
Others are greatly concerned with the
minum, TIG welding provides the
rents to keep their arcs from stalling
shape of the TIG electrode and/or of
best results. It takes some consider-
at the AC wave turnover point. I
its ceramic. Others almost intuitively
able commitments of money for
knew a man who operated one of
know or remember how to make the
equipment and of time to learn to use
those primitive TIG machines. He
best choices in these matters.
it, but you should at least consider
would not have understood much of
TIG is the most individualistic
making those commitments if ulti-
the technical sentence above, but
welding format that exists. Some
mate welding quality is your objec-
with the equipment of that period,
operators prefer air-cooled torches;
tive.
Don’t
let
the
imposing
he could deposit a uniform and well-
others prefer liquid-cooled units. The
technicalities of TIG welding scare
penetrated weld bead on the business
merits of each are often debated for
you off if you are interested in this
edge of a razor blade. It was no small
jobs that involve the same materials
format. You do not have to under-
feat. He understood little of TIG tech-
and similar welds. Foot controls ver-
stand it in technical detail to make
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77