TIG
WELDING for
AUTOMOTIVE FABRICATION
metal
at the point of fusion and produces a narrow heat affected zone. This
reduces
stress, cracking and distortion in the finished weld. Spatter is
not produced by this process, leaving the weld and surrounding metal
clean.
Because of the lack of spatter and flux smoke, the TIG process allows
the
operator a clear view of the weld puddle. The torch body in most
cases is small enough that the operator can hold it in the same manner
as he would hold a pencil allowing easier manipulation. The power
source is constant current, either AC, DC, or combination AC/DC. Type
of
metal determines which type is used. DC (direct current) is
most normally used for TIG welding of stainless steels and mild and low
alloy steels. AC (Alternating current) is used for TIG welding of
aluminum. Surface oxidation is automatically removed by the
action
of the arc each time the electrode becomes positive, (60 times per.
second).
Because AC crosses over the zero volt point 120 times per second (once
going positive and once going negative each cycle), the arc shuts off
120
times per second. To keep the arc going when using AC, a high
frequency
"arc stabilizer" is used. The high frequency also allows the
start
of an arc in DC mode without having to "strike" an arc, thereby
reducing
the possibility of tungsten contamination. If the electrode
accidentally
touches the weld pool, it becomes contaminated and must be cleaned
immediately
to 
prevent
weld
contamination. TIG requires an extremely clean surface to weld
successfully
and is a fairly slow operation. On the plus side, TIG produces
high
quality work and does not generate slag or spatter. The welder can
adjust
the heat input while welding by using foot or hand amperage controls.
MIG (Metal Inert Gas), also referred to as wire
feed
welding, utilizes a consumable arc. The process generates heat
from
an electric arc maintained between a consumable wire feed electrode and
the part being welded. This process produces spatter making it
difficult
for the operator to see the weld and causing damage to nearby surfaces
and objects from the hot particles thrown off. Flux cored
"gasless"
welders produce smoke from the flux, and pose a cleanup problem.
Because of the higher welding speeds of the MIG process, the chance of
producing porosity is higher. A common mistake with novice
welders
utilizing the MIG process is the possibility of producing a good
looking
weld with little penetration. A MIG can produce an arc into the
puddle,
allowing one to create a nice 
looking
weld while the base metal underneath is not being properly
melted.
This cannot be detected before failure without either destructive or
non-destructive
testing. In the TIG process, the base metal is melted to produce
a puddle before any filler is introduced into the weld. This
allows
the operator to see the penetration during the welding process.
Another
drawback in MIG welding in restoration of automobiles is the
workability
of the weld. The wire used in MIG cools harder than in TIG
welding,
making it harder to hammer and dolly the weld afterwards. Because
MIG welding uses a constant fed wire to produce the arc, some buildup
of
material usually occurs that has to be ground off. This also
generates
heat in the panel that can cause warpage. With TIG, filler is
only
added when needed, and the thickness of the filler can be changed by
picking
up a different size rod. This reduces post weld finishing.
While TIG welding requires greater skill, the results are far better
than
other welding methods. Welders of both types are available from
many
sources, such as Eastwood, Daytona
Mig, and Professional sources such as Miller
Electric. A source that I have found to be particularly
helpful
and has excellent prices is RAM
Sales.
If you are looking for a welder, I recommend staying away from Flux
cored
units. They are messy and many do not have the power required to
do most welding you will get into. Small 110 volt welders are
available
that will do a good job with practice, but go with gas for MIG (MIG by
definition is metal INERT GAS, not flux) Flux cored units are
advertised
as "wire feed", Don't assume that they are MIG welders. If you
are
looking for a TIG, there are also several nice small units available,
but
consider it only if it has "high frequency" and AC if you don't want to
mess with striking an arc and there is a remote possibility that you
may
want to weld Aluminum someday.
Be careful when welding parts
that are possibly plated! Welding of these materials is not for
the
average person, as special precautions must be taken! can be given off when welding
various platings that can cause serious medical problems orFor an update of this problem and
to visit a company interested in your safety, see
Borgeson Universal Co.
Any welding of suspension,
steering,
or safety critical component should be done by a qualified
welder.
Any weld that could cause an accident if it failed should be inspected
by non-destructive means. Most local machine shops can perform
magnaflux
inspections at a reasonable price. Don't take chances - if in
doubt,
ask a professional.
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