September 5, 2013
Contact tips are highly misunderstood components in a welding gun setup. Choosing the correct contact tip for your welding application and understanding how to keep it performing at its best are just as critical as anything else needed to produce a quality weld.
Contact tips are one of the most frequently misunderstood and most often replaced components of a welding gun setup. The contact tip is responsible for guiding the wire and transferring the current from the conductor tube—sometimes referred to as a swanneck or gooseneck—through the filler wire and ultimately to the workpiece. Its critical functions include current transfer and wire targeting.
Contact tip size determines what wire size you can use and the amount of filler material that will be distributed during welding. When a contact tip begins to wear, the through-hole elongates and loses electrical conductivity, which greatly affects the gun’s ability to transfer current to the welding wire. Additionally, the tool center point (TCP) begins to fluctuate as the wire dances around inside the now oversized tip. These conditions lead to poor arc starts, lower penetration, and decreased weld quality.
Choosing the correct contact tip for your welding application and understanding how to keep it performing at its best are just as critical as choosing all the other components and parameters needed to produce a quality weld.
Three types of contact types are most commonly used in welding applications, and each has its pros and cons.
Standard Copper Contact Tip (E-Cu). A standard copper contact tip has a relatively high current transfer rate at greater than 55 S/m* electrical conductivity, and it is used mostly in hand-held welding applications.
Although standard copper offers the highest conductivity of all of the standard alloys, it is more susceptible to mechanical wear than other materials. As a raw mineral, copper naturally is relatively soft, which means it makes current transfer easier, but it also means the material has a lower melting point. As the temperature rises in an E-Cu tip, it becomes softer than the wire that is being fed through it. As the copper softens, the wire wears and deforms the internal diameter of the tip. This prevents the wire from contacting the tip correctly, which decreases conductivity and leads to arc-start issues, burnback, and poor welds.
The E-Cu tip is usually the most affordable, so it’s generally an acceptable trade-off to frequently replace it when precise wire targeting is not critical.
Copper-Chrome-Zirconium Contact Tip (CuCrZr). A copper-chrome-zirconium tip generally is used in automated and robotic welding applications where precise TCP is needed and high duty cycles occur. Although there is some decline in electrical conductivity compared with the standard copper tip (50 S/m), it is sufficient for most steel applications.
However, since CuCrZr alloy softens at a much higher temperature, it tends to have a longer life span than standard copper tips. Generally speaking, the tip maintains its shape up to approximately 932 degrees F versus 500 degrees for E-Cu. Therefore, the higher-density material leads to a lower wear rate and increases the tip’s performance and productivity.
Silver-Plated CuCrZr Contact Tip. Over the years technological advancements in contact tips have revealed that silver plating the interior and exterior of a CuCrZr tip further enhances its overall performance.
Silver is more conductive than copper (62.1 S/m), which reduces microarcing, extends contact tip life, improves arc starts, and provides consistent weld quality. Silver is approximately 17 percent denser than copper and it has a higher melting point. Silver’s shiny surface helps to reflect heat. As a result, spatter doesn’t adhere to the tip as easily and it doesn’t wear down quite as quickly. In fact, the life span of a silver-plated CuCrZr contact tip can be nine times longer than that of a standard precision-drawn copper tip.
With significant improvements in material, a silver-plated contact tip can cost up to 50 percent more than the standard nonplated CuCrZr tip. Welders who choose to use a silver-plated contact tip usually do so for one reason—less welding downtime. The more a robot welds, the greater the throughput. Based on the overall longevity, current transfer, and quality of material, the silver-plated tips are an excellent choice for automatic and robotic welding applications.
Advice to Avoid Common Contact Tip Problems
Once you’ve matched your contact tip to your welding application, there are a few things you can do to make sure you are getting the most out of it and not inadvertently creating problems that could decrease its life span or effectiveness.
* S/m, siemens per meter, also written as m/Ω mm2, meter per ohm millimeter squared, is a unit of measurement for electric conductivity.
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