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When you invest in automation, the goal is to gain productivity and quality improvements that set your welding operation apart from the competition and help increase your bottom line. To achieve success with an automated welding system, however, you need to ensure that the parts you are welding are consistent and repeatable, to confirm that your welding operation has good workflow and to have properly trained welding operators to oversee the system. You also need the right equipment for the job.
In addition to working with a reliable robotic integrator to select and implement the robot, you should also take care to select the right robotic MIG gun and consumables — contact tips, nozzles, liners and retaining heads — for the application. The consumables, in particular, are an easily overlooked part of an automated welding system, but they can have a measurable impact on downtime and day-to-day costs. Consider these suggestions for getting the best performance from these components.
The contact-tip-to-nozzle relationship for an automated welding system varies according to the application, but it still has an impact on the welding performance and quality you achieve. Applications that have complex joints or tooling often require an extended contact-tip-to-nozzle relationship. This relationship provides greater access into more complex joints and can help you better accommodate for complex tooling.
You should be mindful that this relationship also makes your contact tip more prone to spatter accumulation and may reduce the tip life due to it being more exposed to the heat of the arc. The application of an anti-spatter compound can offer some protection against such situations, but you will also need to monitor your contact tips regularly for signs of wear. Remember, preventive maintenance is better than downtime for resolving problems. Change over your contact tips before issues occur.
Using heavy-duty or extended-duty contact tips composed of chrome zirconium is also a good option for gaining longer performance. Chrome zirconium contact tips are harder and more durable than copper ones, and while they offer slightly less conductivity, the difference is negligible. Typically, you can identify these types of contact tips by the machined groove at the base of the thread.
Checking your contact tips, retaining heads (or diffusers) and nozzles for good connections can also have a measurable impact on your welding performance. Solid connections help ensure reliable electrical conductivity and minimize heat, which in turn provides more consistent weld quality and helps your consumables last longer. Look for consumables that are designed to thread together and mate securely, too, as these can further increase their longevity.
The welding wires you use can impact the performance of your contact tips and can also affect what size you should select. Larger drums of wires — 500 to 1,000 pounds — are commonly employed for automated welding systems to minimize changeover. However, the wire in these drums tends to have less of a cast and/or helix than wire that feeds off a smaller spool. As a result, the wire often feeds through the contact tip relatively straight, making little or no contact with it.
The effect is twofold. First, it minimizes the electrical conductivity necessary to create a good arc and a sound weld. Second, it can cause the welding wire to contact the part being welded and arc back into the contact tip, thereby creating a burnback. This condition automatically creates downtime to change over the contact tip. As a solution, consider undersizing your contact tips, particularly if you are using a solid wire. For example, a .040-inch (1 mm) diameter contact tip could work for a .045-inch wire. Check with a trusted robotic integrator or welding distributor if you are using metal-cored wires, as undersizing them is not always feasible due to their tubular construction.
You should also consider the impact that the wire you are using has on the longevity of your contact tip. For example, non-copper-coated solid wires tend to wear contact tips (and liners) more quickly than copper-coated ones. The copper on a copper-coated wire acts like a lubricant to improve feedability and can often extend consumable life. It may be worthwhile to factor in the higher upfront cost of these wires compared to the increased cost of purchasing more contact tips for use with a non-copper-coated wire, as well as the downtime for changeover.
Automated welding systems require consumables that are capable of withstanding longer periods of welding — and most often higher amperages — than a semi-automatic application. The specific mode of transfer for gas metal arc welding (GMAW) or metal inert gas (MIG) welding you use can also impact the type of consumables you require. For example, pulsed welding programs in which the power source “pulses” between low background currents and high peaks are especially harsh on consumables due to the higher levels of heat that the process generates. They tend to cause the contact tip to erode more quickly and therefore require more frequent changeover.
You should carefully monitor your contact tip usage if using such a welding program so that you can determine how often the contact tips need to be replaced. Changing over these consumables before they experience problems can help prevent issues like loss of electrical conductivity, burnbacks or excessive spatter accumulation, the latter of which tends to occur when the contact tip becomes too hot and the consumable material softens. Use the time during routine pauses in production for contact tip changeover to avoid interrupting arc-on time. You should also consider using heavy-duty contact tips for higher heat applications. Again, contact tips made of chrome zirconium are a good choice.
Typically, the tooling on your automated welding system dictates the type of nozzle that you will need to use. Bottleneck, straight or tapered nozzles are common choices since they are narrower than standard nozzles and can provide better access around tooling or into complex joints. Still, always consider the duty cycle and amperage of your application when deciding which nozzle to use. The more tapered a nozzle, typically the thinner it is and the less able it is to withstand higher amperage or higher-duty cycle applications. If your automated welding system welds at higher amperages (300 amps or greater) and has high levels of arc-on time, it may be a good idea to select a heavy-duty style since these have thicker walls and insulators and are more able to resist heat.
Nozzles composed of copper are also a good option, as are those featuring high-temperature fiberglass insulators. Work with your robotic integrator or welding distributor to make the right nozzle selection. Remember that you need to be sure to select one that provides access to the joint but that is not so narrow (especially in relation to the contact tip) that you compromise shielding gas coverage or unnecessarily shorten the consumables’ life.
For all styles and types of nozzles, it is recommended that you employ a nozzle-cleaning station or reamer to help maintain them. A nozzle-cleaning station cleans the robotic gun and nozzle of spatter and clears away debris in the retaining head that accumulates during the welding process. These stations can also be outfitted with a sprayer that applies a water- or oil-based anti-spatter compound to protect the nozzle, retaining head and workpiece from spatter after it has been cleaned. The nozzle-cleaning station should be placed close to your robot so it is easily accessible. Also, you should program your robot to use it in between cycles — during part loading or tool transfer — so as not to interrupt your welding operation. It should only take a few seconds for the nozzle-cleaning station to complete its job.
As a general rule, it is best to select consumables that are well-machined and have smooth, round surfaces, as these are less prone to collecting spatter and tend to last longer. It is also important that you use the heaviest-duty consumables for your application that will still allow access to tooling. Doing so can help extend their life.
Keep in mind that you also need to pay attention to your retaining head selection and the liners that you use in your robotic MIG gun. The retaining head should match your nozzle and contact tip appropriately and offer a secure connection so that you obtain the best conductivity. Also, always trim and install liners according to the manufacturer’s recommendation, using a liner gauge to determine the appropriate length. A liner that is too short or too long can cause wire-feeding problems that require downtime to rectify.
As with any part of an automated welding system, the goal is to keep your consumables in working order so that you spend more time reaping the benefits of the process and less time troubleshooting problems.
For more information, visit www.tregaskiss.com.