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Source: Adapted from The Procedure Handbook
of Arc Welding.
The Lincoln Electric Company, 1994.
In arc welding, an
arc is established from the electrode to the workpiece. To do this, a
smooth flow of electricity needs to complete the electrical circuit, hence
the need for good electrical connections. Not only will good work lead
connections, commonly incorrectly called ground connections, affect the
welding arc and the quality of the finished weld, having good work lead
connections are important to minimize electrical shock hazards. This article
will explain some of the ways to achieve a good work lead connection.
Attaching the Work
Lead to the Workpiece
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A high
production automotive part may benefit
from more than one connection
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To be effective, the
work lead must make good electrical contact with the workpiece. This is
usually performed by using a work lead clamp (also, commonly incorrectly
called ground clamp), or through copper-graphite brushes, or sliding or
rotating shoes. Also, keep in mind that aluminum is poorly suited for this
purpose, as it quickly forms an oxide that is poor conductor of welding
current.
A work lead clamp
is perhaps the common method to connect the work lead cable to the workpiece.
The work lead clamp is bolted to the lug at the end of the work lead cable
and has brass or copper jaws to ensure good electrical contact to the
workpiece. The work lead clamp may be attached directly to the workpiece
or to the fixture holding the workpiece. Remember that the work lead cables
or cables should be neatly organized, not strung about haphazardly.
The work lead connection
may vary with the welding process, amperage, or application. Automatic
welding installations commonly use a permanent stationary connection.
Automatic circumferential welds usually use a work lead connection of
brushes or rotating or sliding shoes with an electrically conductive lubricant.
When grounding is
through a sliding shoe, two or more shoes should always be used. This
will prevent interruptions of current in case one shoe loses contact by
an unexpected surface protrusion, such as the reinforcement of another
weld, a piece of weld spatter, or granular flux.
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Be careful not to allow the welding
current to flow through sensitive
electronic components.
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An improvement on
sliding brushes, preloaded, tapered roller bearings are excellent for
rotating grounds. To assure trouble-free performance, the contact area
of the bearing should be sufficient to carry the current capacity of the
welding cable used in the installation. Since most mechanized welding
installations use two 4/0 cables in parallel, the tapered bearings are
usually fairly large.
Regardless of how
the work lead connection is made, it should be a secure positive connection,
properly placed to minimize any welding interference or arc blow. The
experienced welder knows that good work lead connections are essential
for good welds and should not be overlooked.
Using Steel Bars
or Reinforcing Rods
In some welding applications,
a steel bar or a steel reinforcing rod may be used as a work lead connection
or between two or more weldments. When using steel bars, care must be
taken to assure that the bar has adequate cross-sectional area to match
the copper welding cable in total electrical conductivity. Since the conductivity
of copper is almost seven times that of mild steel, the cross-sectional
area of the steel bar should be at least seven times the cross section
of the welding cable conductor. A bar that is inadequate in cross section
may result in an overheated connection and result in poor welding performance.
The arc itself is
a very complex phenomenon. In-depth understanding of the physics of the
arc is of little value to the welder, but some knowledge of its general
characteristics can be useful.
Cleaning the Work
Lead Connection Area
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A rotating piece
needs a special
"moving" connection.
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A point to bear in
mind is that the work lead clamping area should be at least equal to the
cross-sectional area of the conductor. This means that the area of contact
must be free from any scale, rust, oil, grease, oxides, or dirt that may
act as points of insulation. Cleaning the area of contact with sandpaper
or a wire brush before making the connection is good practice.
Testing the Circuit
A simple way
to test the soundness of the circuit is to run a hand over the length
of the cable from the power source to the electrode. This should be performed
immediately after an hour or more of welding after the power source is
disconnected. For safety, always make sure the power is off before performing
this test. If a "hot" section of the cable is felt, this is
a potential problem as it's an area of increased electrical resistance.
If the hot section is near a terminal, the connection at the terminal
is suspect; if any place along the cable; the cause is probably damaged
strands within the cable. If the entire cable is hot to touch, it is probably
undersized for the welding current being used.
Also, this is good
time to inspect the electrical cables connected to the welding power source
and determine if the cables can be safely used or needs to repaired or
replaced. For everyone's safety, always keep your cables in good condition.
Troubleshooting
Poor work lead connections
may arc and weld the connection to the workpiece. In addition, poor connections
reduce the voltage at the welding arc. This may cause poor arc starting,
excessive spatter, poor bead shape, and reduced weld quality. If any of
these conditions occur, inspect your work lead connections immediately.
Safety
The hazard of electrical shock is one of the most serious and immediate
risks facing personnel working in the welding area. Contact with metal
parts that are "electrically hot" can cause injury or death.
With this in mind, always unplug the input power cord or disconnect the
main power before attempting to inspect or service electrical problems.
When in doubt, refer to the equipment's operation manual or call a qualified
electrician.
Suggested Reading
ANSI/ASC Standard Z49.1, Safety in Welding and Cutting.
Arc Welding Safety, E205, Published by the Lincoln Electric Company, Cleveland,
Ohio 44117
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