by Noelle Stapinsky
Selecting the right torch for your process is a critical decision
With all of the different material types and processes welders face, knowing what to look for when choosing the right welding gun is vital to delivering quality consistent welds on schedule. To explore such selection criteria, Shop Metalworking Technology enlisted three industry experts: Jim DiLeo, Abicor Binzel’s regional sales manager for Ontario and western Canada; Andrew Newman, Fronius’ senior welding application technologist; and Jerome Parker, product manager for Bernard and Tregaskiss.
Jim DiLeo: In manual applications, ergonomics is an important factor to consider, especially in heavy production environments. Welders have to constantly adapt their posture to effectively access their work, while simultaneously focusing on maintaining a solid welding arc at all times. For this reason, every welder wants a robust welding torch that can perform the job needed that is light and powerful and is equipped with a torch neck that has been optimized for the job. Some options include extended or dual schedule triggers, different neck lengths and angles, and the cable length.
Andrew Newman: If you’re manually going around with a heavy torch all day you want to make sure the handle grip is nice and comfortable. Make sure there’s functionality to it for trigger lock, which is often set through your power supply, so you don’t have to hold the trigger down the entire time. The torch we sell is basically formed around what your hand would hold with the trigger and it has a swivel ball joint for extra support for your wrist. Also look at the angle of the torch and make sure you have the right angle for the most comfort of the welder. We try to make it so that the balance of the weight is centred on where your hand will be holding it so that it’s not pushing too far forward.
Jerome Parker: Consider the length of your gun and what type of power you’re delivering to the weld. How do you want the handle to feel in your hand? What is your base material going to be and what kind of wire are you running? With all those things in mind, the most important part of the gun is the cable itself since this is where your power is coming through. We perform testing on all of our guns to make sure the heat build up in the cable is as little as it can be for the welder to be comfortable. We also use a jacketing system on our cables—a rubber material that’s resistant to cuts and scratches. If you disrupt that power feed by cutting through the jacket, which reduces the power reaching the weld, you’re not going to get the best forms or welds that you can with your gun.
Amperage and duty cycle time considerations
AN: Typically, your lowest duty cycle is going to be in a manual application and you can only weld what your arm span is. Some guys can walk with the torch, but generally speaking your arc on time is going to be fairly low. The key to remember is that when you’re talking about a torch or power source, they’re all rated on duty cycle, which is the time that you’re welding. If you’re at 60 per cent at 300 amps, you can weld at that rate for 10 minutes. Or you can weld at 200 amps for 100 per cent of the time. Make sure that you have the right duty cycle to match what your application is. When you start getting into automated environments, such as automotive, these guys are running all day long and sometimes there’s only 10 seconds between a part coming in and starting again. These welders would be at the 70-90 per cent of duty cycle time and you have to look at whatever your amperage rating is. You need to make sure that you have the right amount of duty cycle to back up the amperage and what it’s rated at.
JP: The biggest consideration is arc on time and how long that welding unit is going to be active. For semi-automated processes we look at an operation time of 10 minutes. And we grade all our guns based on the conditions they will be used in.
The material type also has a part to play. Thinner base materials don’t require as long of an arc on time as the thicker materials. Also the shielding gas that you choose to use plays a part in how much heat builds up when you’re welding over time. Some gases have the ability to cool better than others, as well as providing good shielding capabilities. For example, C02 creates hotter welds, which provides better penetraton, but it actually cools quite well. Conversely, higher levels of argon (in a mixed gas combination) tend to increase the heat felt by the welder.
The right gun selection for different processes and material types
JD: You need the right quality tool for the job to optimize performance, productivity and longevity of the gun and its consumable parts. And you need to consider the welding parameters for the application, such as the base material to be welded, filler metal type, voltage and amperage, the shielding gas being used and the length of cable needed. Since the column strength of aluminum wire is less than other filler metals, you may want to use a push-pull gun for feeding the wire consistently and to avoid bird nesting of the wire, which causes down time. When welding stainless steel you may want to use a fume extraction gun that captures toxic hexavalent chromium fumes at the source. All welding fumes are toxic, so you may want a fume extraction gun in applications where other methods of fume capture are not available.
AN: Fronius has a process that uses a unique push-pull torch that has a buffer in the middle of the feeding system. It creates a bit of play between the main driving motor in the back and the push-pull in the torch. It’s part of our cold metal transfer process (CMT).
When you’re working with aluminum, you’re going to want to use a push-pull torch because trying to feed that softer aluminum wire, especially when it gets to a smaller diameter, becomes more difficult. Next, look at the application. Am I welding sheet metal or am I welding things like big heavy steel where I might be welding at 100 amps in one case or 300 amps in another case. With that you can go with a smaller, lighter torch that’s air-cooled for lighter gauge materials. If you get into really heavy duty cycles, maybe you want to look at a higher amperage water-cooled torch.
JP: If you have a weld or a wire that requires a lot of energy to achieve the penetration and deposition that you need, you’re probably going to want a higher amperage gun so you can provide the right amount of power through the gun to your wire. If the welder is going to be welding for an extended period of time, they’re going to want the best setup for that actual process or procedure. They could be supporting or holding the neck of the gun when they weld. Depending on the type of joints they’re trying to access, they might want a specific neck bend or length, or they might need consumables of a specific size on the front of the neck for proper shielding gas coverage.
Upfront costs and associated costs over a gun’s lifespan
JD: Welders should get the most bang for their buck when choosing a welding gun. They not only need to look at the upfront costs, but also the total cost of ownership over the lifespan of the gun, which includes consumable costs and longevity and replacement parts. Looking at the overall quality, warranty terms, availability of parts and aftermarket support are also factors to consider. What is the welding power source limit? Purchasing a 500 amp-welding torch for a welder that has a maximum output of 300 amps is overkill and you’re spending more money than necessary.
AN: If you have a basic air-cooled torch, you’ll have your liner inside, a contact tip, a diffuser and the nozzle, all of which is going to wear down at some point. When you look at air-cooled vs. water-cooled, the water-cooled is going to be much better for your contact tip, diffuser and nozzle, because it’s all going to be cooled down and not have as much effect from the thermal cycling of welding, especially when you have higher currents.
Then you look at the type of liners and wire that you’re using. Steel coil liners are great for steel but not so much for aluminum, in which case you want to make sure you have some form of a graphite or Teflon-type liner, so you get a better feed.
Different material types and the impact of nozzle selection
JD: The main thing to consider is accessibility. Can the nozzle get into the area you need to weld? Do you need a nozzle with a smaller front end? Shapes of nozzles are generally cone, bottleneck or straight bore. In heavy spatter applications like welding galvanized base materials or C02 shielding gas applications, you should use nickel plated nozzles which have better spatter resistance. You should also use an effective anti-spatter in these applications such as ceramic spray.
AN: You can have more robust gas nozzles for heavier duty cycles. They cost more money because there’s copper involved, but you can have them coated with a reflective coating to refract the light radiation away and prevent the heat. A smaller nozzle is going to be closer to your contact tip; therefore it’s going to get hotter than a larger nozzle. There are also materials that are more sensitive to the atmosphere than others.
Sometimes with steel we can use shorter gas nozzles because we don’t need as much gas coverage over the top of the area, and that helps increase your consumable life because it’s recessed further back from the work piece.
Also consider the process you’re working with. If you’re working with a short circuit transfer range with low amperage, you can go with a smaller nozzle because the weld size is going to be smaller. If you’re working with really heavy spray transfer in the high arc ranges, your puddle is going to be much larger and you’ll need more gas to cover it.
JP: If you’re outdoors, you’re not going to have good shielding gas coverage, so you’re going to want wire that has internal flux to protect the weld when you lay it down. You can choose a gun that is best set up to receive wire that has flux; you don’t need a full size heavy duty nozzle to direct the shielding gas to cover the weld puddle.
If you do have a very heavy duty indoor process, you might want a nozzle that has a different recess so you can control your arcing a little better and make sure you’re allowing the wire to burn properly as it enters the weld well.
JD: Look for maintenance friendly guns that are easy to repair and include features such as easy to access handles, extra trigger leads, and cone and cone-nut connections—which are easier to repair in the field. Inspect consumables on a regular basis, including the wire liner, to ensure smooth arc starts and to reduce the chance of porosity. Make sure any O-rings are lubricated and not dried out or cracked, which can lead to shielding gas loss. Check all connections on a regular basis—be sure they are all tight and clean. Loose connections add electrical resistance during the welding process, which causes heat build-up that will lead to premature failure. A preventative maintenance schedule should be developed to help reduce downtime. The key is to ensure the best longevity of parts and to replace them ahead of failures.
AN: Make sure it’s easy to do. Obviously the more complex the system gets the more you’ll need. If it’s scheduled maintenance, that’s fine. But if something happens and you need to fix it quickly, you need to make sure that’s done in a timely fashion or else you’re shutting things down. SMT