Considerations for Consumables in Robotic Welding Applications

Investing in a robotic welding system goes beyond the initial purchase. It is equally important to find ways to maximize the abilities of this equipment. When implemented properly, speed, accuracy and cost savings are fundamental benefits of welding automation. These factors rely on everything from the robot itself to the personnel overseeing the weld cell to the smallest factors, like the front-end consumables on the robotic MIG gun. Although consumables may seem insignificant, the nozzles, contact tips and gas diffusers can have a huge impact on performance. The right combination reduces downtime and waste and improves productivity and quality. In fact, a contact tip often serves as a barometer of the overall effectiveness of the welding process by indicating how optimized it is – or isn’t.

Always consider consumables as a part of the planning process when working with an integrator to design a robotic welding system. Doing so prevents issues with joint access. If the consumables are an afterthought, it’s possible that the front-end of the robotic MIG gun won’t be able to maneuver properly around the part or the fixturing to reach the joint. Reconfiguring the system can be time consuming and costly.

SPACE AND DUTY CYCLE FACTORS
Bottleneck, straight or tapered nozzles can help accommodate for joint restrictions since they are narrower than standard nozzles and provide better access. Take caution when using tapered nozzles, however, as they are thinner and may not be able to withstand the higher amperage or higher duty cycles of robotic welding, leading to more frequent changeover. They may also collect more spatter buildup due to their narrower bore.

For jobs requiring 300 amps or greater and/or those with a high level of arc-on time, a heavy duty style nozzle with thicker walls and insulators will be more heat resistant. It’s usually best to select the heaviest duty consumable for the application that still allows access to the tooling. Consult a robotic integrator or welding distributor whenever in doubt.

CONSUMABLE MATERIALS AND SIZES
Consumables come in a variety of materials and sizes. For example, heavy duty contact tips are available in copper or chrome zirconium and feature an outside diameter (OD) of around 0.3125 in. In addition to pulsed welding (discussed further below), higher amperage applications can benefit from chrome zirconium contact tips, as they generally offer a longer performance life than copper contact tips. Nozzles are typically available in brass or copper. The brass variety tends to be more spatter resistant. However, these nozzles have a lower melting point and can fracture or deteriorate more quickly than copper if they come into direct contact with the molten weld pool. This factor makes them ill-suited for tight access applications.

Extra-heavy duty consumables are also available in the marketplace and are good for high amperage applications requiring larger diameter welding wires – 0.052 in and greater. Contact tips in this category generally have an outer diameter of about 0.375 in. Regardless of the material, look for consumables that are well-machined with a smooth, consistent surface. These are less prone to spatter buildup and may therefore last longer. In some cases, these consumables may be more expensive, but it’s important to weigh the upfront costs with the longer-term savings of minimizing changeovers and downtime. Likewise, poorly functioning consumables, or ones that are simply not appropriate for the application, can generate weld quality issues that compound productivity delays and could lead to expensive rework.

HEAVY DUTY VS. STANDARD DUTY
Robotic welding systems typically operate for longer periods of time at higher amperages than semi-automatic applications. As mentioned, heavy duty consumables that are more heat resistant than standard duty consumables are often used. But they aren’t always necessary. In some cases, standard duty consumables can replace them. For example, in applications with low duty cycles, there is less heat because less time is spent welding and standard duty consumables will suffice. It is important, however, to test for durability on a given application before introducing them into the welding operation. Also, when frequent consumable changeover is part of a shop’s protocol, standard duty consumables could work on high amperage applications because the welding operator changes them over before a failure occurs from high heat levels.

WELDING MODE AND WEAR
Mechanical wear on the contact tip is inevitable in any welding application because the constant friction of the welding wire feeding through the tip naturally wears on it. But electrical wear also can be an issue in high amperage welding that uses a pulsed welding mode. Pulsed welding programs have a unique waveform that causes the power source to move between low background currents and high peaks, which is particularly harsh on consumables. Often these waveforms reduce weld spatter but are harder, electrically speaking, on the contact tip. It is important to select contact tips that are durable enough for the application, and often chrome zirconium contact tips are the best choice for this welding mode.

It is also a good idea to monitor contact tip usage regularly in pulsed welding applications. Changing over contact tips before they are too damaged can help to prevent issues such as loss of electrical conductivity, burnbacks and excessive spatter that result in poor weld quality, rework and downtime. Welding operators can use the time during their routine breaks in production to changeover contact tips and maximize efficiencies.

CONSIDER THE IMPACT OF WELDING WIRE
Robotic welding often uses large 500 lb to 1,000 lb drums of wires to minimize changeover. The wire in these drums tends to have less cast or helix than wire that feeds off of a smaller spool and, as a result, feeds through the contact tip in a relatively straight fashion, making little or no contact with the tip. This action minimizes the electrical conductivity that is necessary to create a good arc and a sound weld. It also can cause the welding wire to contact the part being welded and arc back into the contact tip, creating a burnback. This condition automatically creates downtime because the contact tip needs to be changed.

Undersizing contact tips, particularly when using solid wire in a high amperage application, is a good fix. For example, a 0.040 in diameter contact tip could work for a 0.045 in wire. The welding operator should check with a trusted welding distributor for applications requiring metal-cored wires because undersizing is not always an option. It’s worth considering the impact that the wire type has on the longevity of the contact tips as well. Non-copper-coated solid wires, for example, tend to wear contact tips more quickly than copper-coated ones because the coating acts like a lubricant to improve feedability. Improved feedability can, in turn, lead to longer contact tip life.

MAINTAINING CONSUMABLES
A nozzle cleaning station or reamer cleans spatter from the robotic gun nozzle and clears away debris in the gas diffuser that accumulates during the welding process. Reamers can be outfitted with a sprayer that applies a water-based anti-spatter compound to protect the nozzle, retaining head and workpiece from spatter. Reamers and anti-spatter combined are a good defense against premature consumable failure and poor shielding gas coverage (caused by spatter-blocked gas ports), and can help extend the life of front-end consumables.

For the best results, place the nozzle cleaning station close to the robot so that it’s easily accessible and program the robot to use it in-between cycles – during part loading or tool transfer, for example. It should only take six seconds for the nozzle cleaning station to complete its job and the results are measurable: less spatter and longer consumable life.