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Home / ROOTING OUT RESISTANCE: ELIMINATING THE HIDDEN VARIABLE

ROOTING OUT RESISTANCE: ELIMINATING THE HIDDEN VARIABLE

Resistance is frequently characterized by random and intermittent welding issues that are difficult to repeat. But even though resistance-related problems can have many symptoms, their root cause is always the same – not enough current is flowing in the electrical circuit. Nick Petersen of Miller Electric shares some tips on how to pinpoint and root out this frustrating problem.

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Resistance is frequently characterized by random and intermittent welding issues that are difficult to repeat. But even though resistance-related problems can have many symptoms, their root cause is always the same – not enough current is flowing in the electrical circuit. Here are some tips on how to pinpoint and root out this frustrating problem.

 

Regardless of your experience level, diagnosing and troubleshooting welding problems caused by resistance can be difficult and frustrating. Too often, problems caused by excessive resistance in the welding circuit are misdiagnosed as problems with the welding power source or the wire feeder.

Bryan Erpelding of Erp’s Mobile Maintenance LLC (Glendale, AZ), a welding repair technician and facilities maintenance expert, says that resistance is often the last factor welders usually consider when diagnosing their welding symptoms. “There are so many variables that go into the welding operation, and yet most people immediately look to their power source when something goes wrong,” says Erpelding. “In fact, the machines are almost always doing what they should and it’s something outside of the machine, such as a poor work lead or dirty work piece, that is causing the problem. Sometimes the machine just isn’t wired to the primary power correctly.”

Resistance-related problems can have many symptoms, but their root cause is always the same – not enough current is flowing in the electrical circuit. Frequently, resistance is characterized by random and intermittent welding issues that are difficult to repeat. One minute your welds are smooth and flawless, and the next minute they’re lumpy and porous and you can barely sustain the arc. Fortunately, excessive electrical resistance is fairly easy to diagnose and troubleshoot if the welder is aware of its common symptoms.

RESISTANCE BASICS
To understand how and why excessive resistance can lead to welding problems, it first helps to understand what it is and the role it plays in the welding circuit.

Resistance, in the context of the welding circuit, is in opposition to the flow of electrical current in a conductor. This opposition to current flow changes electrical energy into heat energy and is measured in ohms (Ohm’s Law: V=IR [Voltage (V) = Amperage (I) X Resistance (R)]. “In every welding circuit there is voltage and amperage, but there is also resistance, and many people don’t realize that resistance is not a constant,” explains Erpelding. “Resistance can change from one minute to the next, critically impacting your weld quality and consistency.”

Eliminating excessive resistance is particularly important for applications that use advanced welding technologies that constantly change the arc conditions. These advanced MIG processes rely on accurate information from the arc in order to adjust the welding current to the optimum levels. They also adjust the welding current levels from high to low values within a fraction of a second. If there is resistance in the work clamp or work lead, the correct current levels cannot be reached as precisely and as fast as they need to and weld quality may suffer.

Poor arc starts, increased weld porosity and inconsistent weld quality are common symptoms associated with excessive resistance in the welding circuit. These problems can also have other sources, but checking the common signs of resistance – unusually hot cables, loose couplings and poor work clamp connections – are easy to conduct and should be one of the first steps in the troubleshooting process.

Another factor that plays into the impact that resistance has on the welding circuit is heat. Heat is both a cause and a result of resistance, creating a cycle whereby resistance causes heat in the circuit and that heat causes even more resistance. Leaving a resistance problem unresolved can exponentially hasten the failure of the welding components!

“Many welders will respond to reduced welding output by simply increasing their current and voltage at the power source,” says Erpelding. “Doing this might work temporarily, but it ends up exponentially increasing the problem until a total failure occurs. It also makes your machine work harder than it needs to, causing other problems like using more power than you need to, or a failure in the machine.”

Troubleshooting these problems requires attention to many different possible sources of resistance in the circuit, including the work lead and work clamp, as well as the contact tip, liner, gas tube, connectors and lugs.

TROUBLESHOOTING: WORK CLAMP
Whether it’s insufficient spring tension, using the wrong materials or a dirty work surface, the work clamp is one of the most common sources of resistance in the welding circuit. “On one of the calls I went on, a guy actually took the time to make a steel work clamp with a spring rather than just purchasing one,” recalls Erpelding. “Steel is not a very good conductor, and resistance built up from the current trying to flow from the copper cable. His weld quality was very poor, and he didn’t understand why.”

“Work clamps made of aluminum, copper or bronze,” notes Erpelding, “are superior due to their higher conductivity. Some work clamps have rounded ends on both jaws to accommodate different material sizes.” Not having at least one flat end to create good clamp-material contact minimizes the clamp ends’ surface area and thereby affects conductivity. Excessive weld spatter on the clamp, or paint or mill scale on the work piece also will interfere with good contact with the work clamp and will increase resistance.

2 Comments

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  • Bill Nielsen wrote:

    I have a small 220v wirefeed. I have been going crazy trying to figure out why my wire feed machine will lay a perfect weld, and the next time, within a minute or less, or even in the middle of the weld, will appear to be welding with no shielding gas at all. It is extreme porosity!
    I am anxious to go back out to the shop and start checking the causes you stated. If you did nothing more than stop me from going crazy for a few more hours, please know I really appreciate it! Unfortunately, I can see that it may be any of about a half-dozen reasons, but at least now I have a place to dig-in to it. Thanks for your article for us dummies!

    • Nick Peterson wrote:

      Hi Bill,
      Porosity can drive a welder crazy! Porosity is not so much a result of poor electrical connections in the welding circuit but a loss of shielding gas. A number of things could be happening:

      (1)  The gas hose inside the GMAW gun could have problem where the cable bent in one direction keeps a seal and bent in the other direction it opens up (hard to find and rare).

      (2)  The o-rings on the part of the gun that plugs into the machine could be worn or the gun may not be pushed in all of the way and tightened down (just a small distance can cause this and this is very common).

      (3)  The gas solenoid that controls the on / off of the shielding gas in the machine may be worn out and not opening correctly (Contact an authorized repair technician).

      (4)  If 100 percent Carbon Dioxide is being used as the shielding gas a couple of problems could be happening:
          a. CO2 freezes, makes ice chunks, and could be clogging the hose etc.
          b. If using CO2 with a flowmeter/regulator that is not designed to use CO2 could be causing the flowmeter to fail.

      (5)  The nozzle or gas diffusor could be clogged with weld spatter.

      (6)  From a welding perspective any contaminants could cause porosity especially oil or water (aka hydrogen).

      I may be missing something here but either way there seems to be an issue with the delivery of gas. The best course of action would be to call a Miller Service Technician, and be sure you have the model name and serial number. If you do not have the serial number the service technicians will not be able to accurately troubleshoot what may be happening. The Miller Service technicians do an excellent job of troubleshooting issues like this over the phone to determine if it may need to go into a repair shop or if it is something simple to resolve. Miller Service Technicians can be reached at 920-735-4505 and follow the prompts (be sure to get to a service/warranty/repair technician).

      I hope you can find the cause it should not be too crazy but when things are intermittent they are much harder to find.

      Thank You,
      Nick

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