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
A high production automotive part may benefit from more than one connection.
|A high production automotive part may benefit from more than one connection.|
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.
|Be careful not to allow the welding current to flow through sensitive electronic components.|
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. Be careful not to allow the weldingcurrent to flow through sensitive electronic components.
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
A rotating piece needs a special "moving" connection. 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.
|A rotating piece needs a special "moving" connection.|
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.
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.
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.