July 8, 2014
Q: I weld in a large pressure vessel shop and use many welding processes, including SMAW, GMAW, FCAW, and SAW. Regardless of the process, our work clamps always get very hot. We’ve even had some arcing from the ground clamp. We have welded several grounds to the workpiece to remedy this problem, but they still get very hot. How can we fix this?
A: The heat you are experiencing is generated by an excessive resistance in the welding circuit, generally caused by poorly or inadequately grounding the work clamp. This increased resistance has a negative effect on the welding current supplied by the power supply. When you’re using the GMAW or FCAW process, for example, a poor work clamp connection will require the machine to increase output to achieve the same voltage level for proper weldability.
Excessive resistance may be caused by a welding cable that is too small, flattened, frayed, or old. Coiling the cable also can cause added resistance. Fastening the work clamp to the work insecurely will cause it to overheat.
Both the size and length of the cable affect voltage drop. For instance, if you’re welding at 300 amps with 100 feet of 2-gauge welding cable to acquire 25 V at the welding arc, you will have to dial in almost 31 V to make up for the resistance caused by the improper cable size and length.
To address this, change the welding cables to the suggested size based on the welding current you use. You may need a larger cable size, or in some SAW applications, you may need to use more than one ground cable to transfer the current efficiently. When grounding your part, it is good welding practice to place your ground as close as possible to the actual welding.
In GMAW-P applications, improper grounding, often overlooked, will cause inconsistencies in the arc. Most power supplies that pulse have a feedback system that changes the output of the machine to maintain a consistent arc length. An increased resistance in the circuit will cause the feedback voltage to vary, resulting in arc inconsistencies. Attaching the work clamp securely will result in a more consistent welding output. When grounding multiple weld stations, try to avoid using a common ground by welding steel bars to ground each station. Instead, ground each table independently to reduce resistance that may cause an issue with unstable welding arcs.
If the work lead clamp continues to overheat after trying these remedies, contact your welding distributor for further assistance.
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