MIG welding consumables are a critical but often overlooked part of the welding operation. Unfortunately, without a clear understanding of the problems that can arise with consumables – and the best way to fix them – companies stand to lose productivity, jeopardize quality and increase costs. In some cases, the biggest issue is choosing the wrong consumable for the job. Consider this real-life example: One shop with 90 arcs is using five contact tips per day, per welder – that adds up to 450 contact tips a day. By simply changing to a more robust consumable system, the company could potentially use one contact tip per welder every three to four days. The savings in reduced downtime and purchasing costs in this situation is significant. So how can companies avoid common pitfalls? A willingness to look at the impact of welding consumables on the overall operation, not just the product purchase price, is key. Training is also a vital part of success. Welding operators and maintenance personnel should know how to properly select, install and maintain consumables and troubleshoot problems when they arise. Or better yet, understand how to prevent them in the first place.
MAKING SENSE OF WELDING NOZZLES
Welding nozzles play an important role in the welding operation, directing shielding gas to the weld pool to protect it from contaminants. Incorrect contact tip recess within the welding nozzle is among the biggest problems. The more the contact tip is recessed, the longer the wire stickout, which can lead to an erratic arc and increased spatter in the nozzle. It can also negatively impact shielding gas coverage. In approximately 90 percent of applications, a 1/8 in contact tip recess provides the best shielding gas coverage with a welding wire stickout that helps support consistent arc stability. Using the wrong welding nozzle for the application can cause downtime for changeover due to premature failure. For a standard welding application (100 amps to 300 amps), a copper nozzle provides good heat resistance. Copper nozzles also resist spatter buildup. For higher-amperage applications (above 300 amps), a brass welding nozzle is the better choice. Brass does not anneal as fast as copper, so the welding nozzle will maintain its hardness longer under higher temperatures.
Choosing the wrong shape and size of nozzle can be problematic. Too large of a nozzle can make it difficult to obtain the joint access needed to complete a sound weld. Long or short tapered nozzles work well for restricted joints. However, there is an increased risk of spatter buildup due to the narrower bore, which can shorten the consumable’s life. To gain good gas coverage, use a longer nozzle when possible.
AVOIDING CONTACT TIP DOWNFALLS
MIG welding contact tips provide the current transfer to the welding wire to create an arc. Using a contact tip with an inside diameter (ID) that’s too small can lead to poor wire feeding and, potentially, a burnback. Using a tip with too large of an ID can cause the welding wire and arc to wander. Every consumables manufacturer has proprietary formulas for gauging contact tip ID and implementing it into their design. Select a high-quality contact tip for consistent tolerances, and match the contact tip ID to the diameter of the welding wire to gain the best electrical conductivity. This happens because the contact tip ID is actually slightly larger than the specified measurement. For example, pairing a contact tip with an ID of 0.035 in and a wire with the same diameter allows the wire to feed smoothly through the bore, connecting enough to generate a stable welding arc. The wrong contact tip outside diameter (OD) can also cause problems. For higher amperage applications, use a contact tip with a larger OD to better withstand heat.
Pay close attention to the contact tip material to avoid premature failure. Consider these options:
- Copper contact tips provide good thermal and electrical conductivity for light- to medium-duty applications.
- Chrome zirconium contact tips are harder than copper ones and are good for higher-amperage applications. They are also a good option if a company experiences ongoing instances of keyholing – oblong wear on the bore that can lead to an unstable arc and premature contact tip failure.
- Contact tips are available in the marketplace that feature proprietary materials and design. These tips cost more than copper or chrome zirconium contact tips but have been shown to last more than 10X as long. They are designed for pulsed, spray transfer or CV MIG welding.
Cross-threading the contact tip is another issue that can lead to downtime. When a contact tip isn’t threaded properly during installation, or if the welding operator introduces dirt or debris to the threads, the gas diffuser can be damaged during installation. This will require replacement and increase costs. To avoid cross-threading, look for contact tips with coarse threads that install with fewer turns.
GETTING IT STRAIGHT ABOUT LINERS
The welding liner has a single and relatively simple purpose: to guide the welding wire from the wire feeder through the power cable to the contact tip. However, it is capable of causing significant problems if it isn’t installed properly. Trimming a liner incorrectly is the most common installation error. A liner that is too short lessens the support of the welding wire as it passes through the length of the gun. This can lead to micro-arcing or the formation of small arcs within the contact tip. Micro-arcing causes welding wire deposits to build up in the tip, resulting in an erratic arc and burnbacks. In more extreme cases, micro-arcing can cause MIG gun failure due to increased electrical resistance throughout the front-end consumables and gun neck. It may also prompt the welding operator to increase voltage in an effort to rectify poor welding performance, which can cause the gun to overheat. On the other hand, a too-long welding liner can lead to kinking and poor wire feeding.
When trimming a conventional welding liner, avoid twisting it and use a liner gauge to ensure the proper measurement. There are also consumable systems available that provide error-proof liner installation and require no liner measuring. The gas diffuser locks the liner in place while concentrically aligning it with the power pin and contact tip to eliminate any gaps. The welding operator or maintenance personnel feeds the liner through the neck of the gun, locks it in place and cuts the liner flush with the back of the power pin. As with contact tips, remember that quality matters when it comes to welding liners. Always select a stiffer liner, so it is capable of supporting the wire as it feeds from the spool through the power pin and the length of the gun.
Paying close attention to MIG gun consumables is important to gaining good welding performance. That means looking at the overall quality of the products being purchased; the manner in which they are inventoried, stored and handled; and how they are being installed. Always follows the consumable manufacturer’s recommendations, and when in doubt, contact their customer service or a trusted welding distributor for help.
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