Is it the right time to automate your welding operation? Worried about how long you can keep your experienced welders? Need to increase your throughput but don’t see how with the available workforce? Challenged by tougher materials? A variety of technical advances make it relatively easy to solve these problems by automating your welding operation, with a surprisingly fast payback.
Three Times Faster
There are two broad categories of automated welding, so-called “fixed” automation and “flexible” (or robotic) welding. Fixed automation is often specific to the application and it’s best when the part geometry and the weld are very simple. For example, it’s generally the best solution for welding pipes. But for most industrial applications and anything complex, robotic welding is ideal and is the focus of this article.
As Jason Lange, manager inside sales, Lincoln Electric Co. (Cleveland) explained, “The main purpose of a robot is to help with the repeatability of a weld. Number two is to reduce the abuse on the welder. Moving parts all day long and crawling under different fixtures is taxing on a human. Robots help the ergonomics.”
It’s doubly important to make it easier on welders because they’re becoming harder to find. “There are lots of tech schools throughout the country investing in welding programs to try to help bridge that gap,” Lange continued. “But on any given day, the numbers of people retiring exceeds the incoming replacements, creating a void. Robotic welding helps fill that void.”
At the same time, “the payback on a robotic system is typically much better than you might think,” explained Erik Miller, business development manager—laser group at Miller Electric Mfg. Co.(Appleton, WI). “One robot system will make as many parts as three welders. You’re saving two salaries per shift and the average pre-engineered cell cost is $100,000 to $120,000. It pays for itself in about a year. Typically, if you can automate a process and get payback in less than year, that’s something you do right away. If it’s two years, it’s something you should seriously consider.”
So robotic automation is a huge help in increasing throughput. But sources interviewed for this article stressed that it’s not a substitute for skilled labor. “You still need a quality welding person to run that robot,” as Lange put it.
Changing Materials Another Reason to Automate
Changes in work materials over the past ten years have driven improvements in welding, many of which are impossible to apply manually, such as laser welding, according to Erwin DiMalanta, director, welding & cutting business line, ABB Robotics(Auburn Hills, MI). “The manufacturers of everything from mining vehicles to automobiles are using different materials to reduce cost and weight and to accommodate different powertrain solutions,” he said. “Automotive manufacturers have switched to more high-strength and ultra-high-strength steels, which have metallurgical properties making them stronger, lighter, and more corrosion resistant, yet with high formability and weldability. That’s drastically changing how metal structures are designed, formed and assembled.” Whereas manufacturers may have used traditional stamping dies to cut features in the part, they are now using hot stamped processes and automated laser technologies to form and cut the parts.
“Another example is the switch to aluminum for more applications,” said DiMalanta. “Depending on the car, as much as 90% of the body might be aluminum now. Owing to its higher conductivity, you need more electrical current to spot weld aluminum and current is synonymous with heat. Yet we’re going to thinner gage materials. In some vehicles, the materials are about 1-mm thick. So how do you deal with these trends that are going in opposite directions?”
The answer is improved technology for both electronic and mechanical control of arc welding, and increased use of laser welding. For arc welding, DiMalanta said that “power sources are now extremely advanced and electronically controlled. The deposition of material into a weld pool is carefully controlled, with customized waveforms.” Miller added that such special waveforms “control the heat input on parts, which can reduce distortion, and also improve the cosmetic appearance of welds.”
He also pointed to a mechanical method called Active Wire from Panasonic. “It’s a bi-directional wire feed in which the wire feeds forward to create the short and then reverses out of the puddle, repeating this sewing machine-type action at 120 Hertz. This reduces heat input and also greatly reduces spatter. It also improves the consistency of the arc strike on every weld. It’s very popular for aluminum welding and for thin sheet metal welding.”
The lighter the component, the more advanced the materials have to become to allow for complex structures while maintaining strength, said DiMalanta. “Robots and their advanced software systems help to connect the processes to handle these materials with the path of the robot.”
Laser Welding a Compelling Option
With its lightning-fast ability to weld a wide variety of materials (including dissimilar materials), laser is probably the biggest thing to happen to welding in decades. And as Masoud Harooni, senior advanced technology engineer—laser welding at Trumpf Inc. (Hoffman Estates, IL) puts it, “the biggest news in laser welding in recent years is the drop in laser prices.
“Laser welding systems are easier to control,” Harooni continued. “You select one power and one speed. Once it’s adjusted, you process the whole part with little spatter. In arc welding you have to maintain the arc and the welding parameters are sensitive to any changes in the distance between the torch and the workpiece. Different parts of the [workpiece] require more current, or less current, and this causes less process stability. Even though the feedback loops on modern arc welding systems are very good, these systems are never actually perfectly adjusted. Laser-welded components require much less post-processing than arc-welded components, which often have to be ground. You also have the problem of dealing with the spatter and needing to clean the nozzle in arc welding systems.”
Perhaps more important, laser welding can achieve a deeper weld without heat damage, even in materials like aluminum and magnesium that would be susceptible to cracking or porosity with arc welding. Harooni explained this is because laser can reach a power density of 108 watts per square centimeter. This generates a keyhole, a deep hollow area created by vaporizing the metal of the workpiece. As the laser beam moves along the part it maintains this tiny keyhole surrounded by a molten pool, while the material behind solidifies.
“You get a strong, deep weld without extreme heat input into the part,” he said. “Arc welding does not have the power density, so the only way to achieve a deeper weld is to increase the heat input. The mechanical properties of welded parts that have less heat input and less distortion are much better than parts with higher heat inputs.”
Miller stated that “laser welding’s initial impact has been in automotive welding, due to the high volume and [technical advantages]. Sheet metal manufacturers should also look at laser welding. The real benefits are in replacing resistance spot welding, which can be challenging for medium to lower volume manufacturing. Fixturing can be difficult, as access is required to both the top and bottom side of the part, whereas laser welding requires only top side access, so it’s easier to automate. You can also use a lower payload robot for laser welding, along with a simple fixed optic.”
Compared to a large payload robot with a strong arm carrying a large tool with two electrodes, manufacturers can now use a safer eight kg robot, mount a process head to it, and automate resistance spot welding relatively easily.
“The other area in sheetmetal where laser welding is beneficial is in box manufacturing,” he said. “Outside corner welds that require a cosmetic appearance, and that require little to no metal finishing afterwards, is an area where we’ve seen a lot of interest.”
According to Miller, laser provides a good solution on parts where access is limited. A laser only requires line of sight to make the weld, whereas in an arc welding application the robot has to move a bulky torch in and around parts, which can be very difficult. “In laser welding, we’re often 500 mm away from the workpiece. It’s like shooting a ray gun. Laser has also much higher processing speeds and lower overall heat input into the part, which reduces distortion. It’s a perfect tool for autogenous welding.”
The disadvantage to laser welding, explained Harooni, is you “either have to make sure you have virtually no gap between components, or use a fusion line, which combines laser welding with wire assistance, in which you melt the wire into the pool so you can cover the gap. But laser welding is so much faster that it’s well worth the extra investment in fixturing. For example, if you’re making 50 parts a day with robotic arc welding, robotic laser welding could produce 300, 500 or even thousands of the same part in a day.”
Getting into Welding Automation
Taking the plunge into welding automation is easier than ever. First, the main players offer off-line setup software that programs the next job on a PC with a high degree of realism, transfers that program to the robot, and starts the weld. ABB even uses virtual reality techniques to enable users to “collaborate” with robotic welding equipment.
“You can literally take the robot by the neck, so to speak, and direct it just as you would a dog on a leash,” explained DiMalanta. “This can be a lot more intuitive than using a teach pendant.”
Second, these systems can have mechanisms that automatically adapt to positional changes from one part to the next and monitor weld quality.
As David Schaefer, product specialist at Miller Electric explained, “There are several sensor types that deal with changes in joint location. One is simply touch sensing and other is through-the-arc seam tracking. When using touch sensing, the robot can come down and use its arc welding wire to probe the part. It checks the delta between the programmed location and the actual location to basically reprogram itself.
“In through-the-arc seam tracking, when you weave across a joint, as with a fillet weld or a lap weld if it’s thick enough material, it detects the change in amperage and determines when it’s in the joint and when it’s out of the joint, and then follows that weld while it’s welding,” Schaefer continued. “You also have the option to use laser optics instead of wire type sensing, but it’s the same basic idea.”
Lange of Lincoln Electric said that “another way to do it is through a camera that takes either a 2D or 3D picture of the part. We can offset programs and offset joints based on the physical location of the parts. Newer cameras are not as affected by glare off a part as cameras might have been even a few years ago. They’re able to see more color and read the definitions of a part, distinguishing shadow and reflections from the part.” Harooni added that “today’s optics also give us the ability to check the quality of the weld in real time without the need for destructive testing.”
Third, the robots all offer some form of collision detection. Miller of Miller Electric said that represents the most significant improvement in the robot arm itself. “Previously, a customer would create his program based on the known X-Y-Z position of the torch. Let’s say the robot has been welding half the shift and the operator leaves a clamp open. The robot would likely bang into the clamp, bending the torch. That would cause every weld in that program to be out of alignment because the end of the torch has been bent and that position has changed. Today, if the robot hits an object, even at high speed, it reads the resulting current spike as an obstruction. This causes the robot to immediately go into flex servo mode, which delays the application of the brake for a certain distance that’s specified for each axis. The robot goes ‘limp,’ in effect. This allows the robot to dissipate the momentum, minimizing damage to the tool. This means you can have a high-speed collision without bending the torch.”
Four, all the major players offer pre-engineered robotic cells with everything you need on a pallet (or several). “A work cell would be a fully designed unit with all the safeguards in place,” said Lange. “You’d typically see fencing or steel walls, usually safety scanners, lights, push buttons to enable the robot to go, key interlocks, and some sort of positioning device in front of the robot, such as a turntable or a ferris wheel. These devices bring the part into the work zone while the operator loads additional parts on the opposite side. Or you could have just a fixed table where the robot is going to process. There would also be a welding power source, the torch, and some reamers to clean the bits if needed. You just need to connect it to electricity and a gas source.” And if one of the off-the-shelf solutions doesn’t work, customized turnkey solutions are available.
So What’s to Worry About?
“When we consult with a potential customer about welding automation, we look at their upstream fabrication,“ explained Schaefer of Miller Electric. “If they’re using lasers and CNC equipment to bend, brake, and cut the material, they’ll have much better success at robotically welding it than if they were hand cutting it or using a chop saw. Those shops can get away with it now because when they hand weld the parts the welders can adjust accordingly, but the robot won’t.” Miller added that welding is usually the last thing that gets automated at a facility because upstream processes must be accurate first. “Parts have to be cut accurately, then bent accurately. Then you can weld them,” he said.
Besides assuring that parts are repeatable, fixturing that limits or eliminates the gaps is required, as Schaefer explained: “You can’t weld air. A human operator can see a gap and react accordingly, generally by increasing the wire stickout in order to reduce the amperage, which reduces the heat and the penetration, and then start to weave to fill the gap. A robot won’t do this. It will burn through.”
Conversely, Lange said some customers have been spending thousands or hundreds of thousands of dollars in some cases on tooling to hold parts when they could cut that price in half by improving upstream processes. That provides the required repeatability downstream, which ultimately lowers the cost of the tooling and decreases the amount of rework and scrap.
After part quality and repeatability, the next most important concern is “knowing and understanding the welding process as it relates to welds itself and welds through the automated device,” said Lange.
So who should you train to run the automated welding? Either an experienced welder or someone who’s eager to learn welding (which takes weeks) plus welding automation.
Schaefer cautioned that “You need the right culture in the facility. People with jobs can feel threatened by automation coming into the facility. I’d be very up front with my people about the benefits, how it will make the company more efficient, help it grow and be more competitive and ultimately hire more people.”
Finally, batch sizes must be big enough for automation. As Lange put it, “The time it takes to do off-line programming, put in on the robot and do a quick setup definitely produces a good return if your batch sizes run for roughly a day or a day and a half. If you’re changing a part very hour, you might not be quite as effective in ROI.”