Laser Cutting and Welding Technologies Advance
Laser technologies for cutting and welding parts have been steadily refined since the laser was invented some 50 years ago. Today, laser technology is easily used to quickly cut 2-D or 3-D sheetmetal parts and to make high-quality welds. The flexibility of lasers has led to adoption of robotic laser processing and five-axis laser cutting and welding in many areas, including cutting the newer high-strength steels in today’s automobiles and cutting and welding processes used in medical device manufacturing.
Advances in lasers’ power, improved cutting speeds and edge quality, and lower operating costs have opened more avenues for use of the technology. Gains in power, speed, and laser beam quality during the past decade have helped manufacturers use the systems in more areas, and better beam quality also reduces the need for secondary operations.
Newer applications include more widespread use of lasers to cut the automotive industry’s latest hot-stamped, lightweight, ultra-high-strength steels (UHSS) that are being used to make smaller, more fuel-efficient automobiles much stronger and safer than earlier models. Lasers can efficiently cut the hot-stamped steels and hydroformed parts that make up some of automotive’s strongest sheetmetal components, such as car and truck A and B-pillars, as well as dashboard structures.
Robotic laser processing on UHSS components has made inroads in recent years, as has five-axis laser cutting of these critical components, as automakers seek more efficient methods of handling newer steels that are too difficult to process with typical stamping operations. "For us right now, the big growth is in automotive components," notes Joe Campbell, vice president, Robot Products Group, ABB Robotics (Auburn Hills, MI). "That’s where all the market forces come into play—brutal competition, they’re moving to high-tensile strength steel, and they have to go deal with the manufacturing process. We have a couple customers who are starting to figure out that it [robotic lasers] could be used as an offensive tool. It’s not just, ‘I’ve got to do this because the guy sent me the spec on the material.’ They’re starting to figure out that it may be a better manufacturing process."
Using robotics for laser processing can offer manufacturers advantages over much more expensive five-axis laser systems including lower costs and greater flexibility, according to Campbell. "There’s a convergence of multiple technologies that finally gets to critical mass. The automotive manufacturing business is kind of brutal—it’s cost per part. They’re really not interested in how sexy your stuff is. But there’s been a combination of improvements, in the lasers themselves, the delivery vehicles, the heads, the robots, the software—everything’s been incrementally improving to the point where we’ve got a very nice package, which has fueled some growth. And then there’s been a pretty significant change in a lot of the material or the metallurgy going into vehicle components in order to get weight out. These lightweight, high-strength steels are great, but they’re hell on die sets."
If automotive manufacturers had a choice, they would stamp their parts, contends Doug Hixon, ABB robotic laser cutting and welding specialist. "If the Tier Ones could trim and pierce features within their current forming process without accelerated die wear, they would do it in a heartbeat, but currently laser cutting is their best option," he adds.
Automakers need to quickly process higher volumes of hot-stamped parts, leading some suppliers of five-axis laser systems to introduce systems specifically tailored for laser cutting of UHSS auto parts. Laser systems builder Trumpf Inc. (Farmington, CT) recently introduced its new TruLaser Cell 8030 five-axis laser cutting system, and in May, the company announced an order for 50 of the TruDisk fiber-guided laser machines to be delivered to Volkswagen AG for use in VW’s Wolfsburg, Germany, headquarters, and at other sites.
"What the automotive industry is faced with is that the customers are demanding smaller, lighter, and safer vehicles with better fuel mileage, and one way to accomplish that task is by the use of ultra-high-strength steels," states Frank Geyer, product manager, five-axis laser systems, Trumpf Inc. (Farmington, CT), "because with conventional steel you would have to use more material, making small cars heavier and slower.
"In the hot-forming process, a special ultra-high-strength steel is used for the blanks; those get heated up to about 900°C, formed, and then quenched while in the die," says Geyer. "What that does is it arranges the grain structure and makes the part extremely hard and stiff. The resulting sheetmetal parts are of very high strength, and that leads to a dilemma—because of their properties, they cannot just be blanked or cut conventionally. Due to their martensitic structure, the ultra-high-strength steels are so hard that a conventional blanking die wears out after about 1000 hits, making the process uneconomical."
In comes the laser, which is cutting with light, with no wear on the tool itself, Geyer notes. Over the years, lasers have significantly improved in power and beam quality, he adds. "The combination of these high-power lasers with high beam quality and high-performance five-axis systems has evolved into a solution with the TruLaser Cell 8030 that was developed for the hot-stamping business. Typical customers are Tier One suppliers that provide the stamped panels or even the completely welded bodies to the automotive manufacturers."
The automotive market requires very high productivity, output, and flexibility, says Geyer, adding that here the fully programmable five-axis laser systems have many advantages over conventional systems. "You don’t have degradation of the tool, for example, like with conventional die blanking—those tools wear out and your product changes, and with the laser it does not. The cutting process is very consistent and efficient. As small cars have a greater percentage of the ultra-high-strength steels than they used to have, they have an increased volume of parts per vehicle, and so high productivity is crucial to helping meet the ever-increasing demands of customers.
"High productivity also usually brings down the costs of the operation. That’s where the TruLaser Cell 8030 equipped with the TruDisk, a solid-state laser with a fiber-delivered beam, comes in play. It has a small footprint, is very fast, and it consumes significantly less energy than conventional systems, compared to CO2 systems."
The Trumpf TruLaser Cell 8030 system comes standard with a 3-kW laser resonator, with a 4-kW resonator available as an option. Cutting UHSS materials doesn’t necessarily require higher-power lasers, Geyer notes. "Typically, the thickness of those materials rarely exceed 2–2.5 mm, so the materials themselves do not require a higher-power laser, and the complexity of the 3-D component limits the cutting speed. You can’t just go with full speed, like with flat-sheet cutting," he states. "You have process speed limitations when cutting complex 3-D geometries. A 3-kW laser is efficient enough to cut about 90-95% of the parts. If the part has a very simple geometry, a 4-kW laser can give you a little more of a speed advantage. Going for a 5 or a 6-kW laser is not going to give you any advantage, because you’re simply not reaching a higher processing speed; the laser would be just too powerful for what you can do."
For welding, Trumpf also offers its laser metal deposition (LMD) process that welds powder on a metal surface for components used in harsh environments. "These applications are where you need to tailor the surface of a part, specifically for corrosion or abrasion resistance, and include industries such as the petrochemical and offshore industries, and the turbo engine industry or agricultural. These are the types of companies that make components and use components that see a lot of abrasion and corrosion," notes Dave Locke, LMD applications manager. "It’s a technology that’s been around a long time, but with the advances that we’ve seen in the last handful of years, specifically the fiber-delivered lasers and higher powers, it’s suddenly made it much more practical to do a lot of powder deposition in applications that have always been there, but in many cases, haven’t been economical."
Hot-stamping of boron steels began in Europe, where it was introduced in the 1980s by European automakers initially for production of side-impact beams, notes Terry L. VanderWert, president of Prima Power Laserdyne (Champlin, MN). The process has since gained momentum in other regions, including North America. Prima recently announced it has expanded its Minnesota facility to handle final assembly, test, and customer installations of its Rapido Evoluzione five-axis system that can quickly trim and cut features in hot-stamped automotive components. With its fiber laser, the system offers users rapid traverse rates of 175 m/min, and is said to be capable of cutting and trimming an automotive B-pillar in under 50 sec.
"The steel blanks are heated to 900°C or higher, formed at near this temperature, and then cooled in the die. The high hardness of the formed parts makes traditional metal trimming or punching impractical," VanderWert says. "The five-axis laser is the tool of choice for that application, because of its speed and flexibility, because there are relatively high volumes because of the automotive levels of production.
"North American manufacturers were slow to adopt hot-stamping, because we had larger cars and fuel wasn’t that expensive relatively," he adds, "and as soon as the focus turned to more energy-efficient yet safe automobiles, they found the need to adopt the hot-forming process. Within the last couple years, the rate at which hot-forming is being used has clearly accelerated. Today, you will find hot-stamped parts in virtually every car and truck manufactured worldwide."
More use of fiber lasers is an ongoing trend in the laser industry, VanderWert notes, and the current Rapido system was designed around this application, both with its size and the performance of the cutting speed. The machine has longer strokes (4080 × 1520 × 765 mm) and can handle a wider size range of components. "We use both CO2 and fiber lasers," says VanderWert, "but I would say the trend is toward fiber lasers. They’re faster. It’s all about cycle time, and ultimately about part cost. The goal in many of these large components is for less than one-minute cycle time."
Fiber lasers continue to gain converts over CO2 lasers due to fiber lasers’ inherent advantages, notes Rick Neff of laser systems developer Cincinnati Inc. (Harrison, OH). Neff, a member of SME’s Industrial Laser Community (ILC), recently moderated an SME webinar, "Industrial Laser Cutting 101," covering the technical advantages of different laser-cutting technologies. Fiber lasers have a beam wavelength of about 1.0 micron so they can be delivered to the cutting head with a thin glass fiber, Neff notes, while CO2 lasers bounce the beam off mirrors and use bellows that expand and contract to contain and deliver their beam.
Beam delivery on lasers has improved, Neff adds. "The focusing lenses are different with CO2 and fiber lasers," he says. "There are newer compact heads that need to be small as they’re often put on the end of a robot."
For thicker materials, the choice often can be CO2 lasers that can easily cut through thicker, harder metals. "CO2 lasers cut all types of materials," Neff says. "Fiber has a little trouble with translucent materials. Fiber can cut thin copper but for something like a 0.5" [12.7-mm] bus bar, waterjet would be better be a better choice. A 4-kW CO2 can cut 1" [25.4-mm] mild steel with ease."
A key advantage of fiber lasers is the technology’s wall-plug efficiency—it’s simply more cost-effective to run than many other laser types. "Fiber laser can be delivered in a smaller fiber, so it provides a better beam for cutting than other types of fiber-delivered lasers," Neff adds. "Fiber and direct diode are much more efficient than CO2 in operating costs. While the fiber resonator requires no maintenance, the recommended maintenance is about every 2000 hours on a fiber cutting system. The time to do maintenance is maybe half that of C02 lasers."
Costs per 100" (0.25 m) of cutting with a C02 can run about six cents per cut whereas costs to run fiber lasers are about two cents per 100" cut, he adds.
Improvements in both lasers and robotics has enabled great progress in laser cutting and welding over the last few decades, observes Michael Sharpe, materials joining engineering, Fanuc Robotics America Corp. (Rochester Hills, MI). Fanuc Robotics developed the first integrated CO2 laser robot, the L-100, back in the early 1980s, Sharpe notes. "It was unique in its day," Sharpe says. "That was back when we were GMF Robotics. The first L-100 series was CO2-based, so beam-delivery systems were integrated into the robot. It was designed basically for tailoring of materials, either tailoring and/or welding, and it was primarily for automotive OEMs and their suppliers.
"The industry kind of softened for a number of years, and then hydroforming came along, in about the late '90s," Sharpe recalls, "and part of the problem with hydroforming is because you blow the tube up like a balloon you only have so many surfaces that can be punched, so it required a machining process. Laser machining or cutting in this case was the most viable due to the throughput."
Automakers started using improved steels for crash and rollover protection in about 2002, as the quickest way to change the vehicle’s design was to change the material, Sharpe says. "A lot of martensitic or hot-stamped type materials came onto the market with dual-phase, there are many different trade names," he recalls. "But the long and short of it is they’re very difficult to trim in a stamping die, or a trim die. They’re very harsh on tooling because they’re so hard, and that necessitated the need for robotics to do that trimming.
"Throughout the industry, it’s been driven primarily by automotive, by those demands for that requirement," he adds. "Now all along, you’ve had improvements in laser technology. If you look at the latest improvements in solid-state designs and fiber deliveries, they basically brought the cost factor down. And by bringing the cost-quality factor down, now I can do more applications, things such as robotic remote welding."
For laser cutting and for welding applications, laser developer Mitsubishi Laser/MC Machinery Systems Inc. (Wood Dale, IL) offers a wide range of systems, including the company’s most popular 2-D flatsheet cutter, the LVPlusII, notes Jeff Hahn, Mitsubishi national product manager. That system offers a 4.5-kW laser resonator as standard, and the Mitsubishi NX system is available with a 6-kW resonator for higher-power applications.
"In welding, we only go up to a 4 kW, and we have two new five-axis machines coming out," Hahn notes. "For 2-D cutting, the big interest right now is nitrogen cutting mild steel, that way a lot of people are doing a lot of work for the Kubotas and Caterpillars, and they don’t want oxidation on the cut edge, because when they paint it, it’ll chip off, and it can be awkward to remove it. So right off the machine, you can get a finished part by cutting the mild steel with nitrogen, with no oxidation layer or coating onto the cut edge. If you use oxygen, you’re going to get an oxidized edge. If you use nitrogen, you don’t get that. You get a clean, weldable, paintable edge right from the machine."
With the new five-axis machines, Mitsubishi is implementing a full-rotary axis for six-axis, simultaneous movement, Hahn adds, and the NX laser systems are also offering the new LC30 Mitsubishi control. "We use it on our EDMs and waterjet, it’s going across our product line and we’re migrating most of the machine tools towards it now," Hahn says of the control. "Everything’s faster on it, and it’s an NC with PC, so we use the Windows GUI interface on it, and you can connect to hard drives and hook the machine up as a node on a LAN very easily."
In welding, the LC30 also will help users by offering more of an intelligent control, as far as adapting what’s called DRC technology to the parts, notes Hank White, Mitsubishi welding specialist. "DROSS Reduction Control [DRC] helps with most of those parts on the five axis that are thinner," Hahn adds. "DROSS, which is what the Japanese call it, is kind of like a hybrid word meaning burr on the bottom; when you slow down, you can get a burr on the bottom, and this eliminates that."
The new controller also helps with slope control, Hahn adds, for welding applications. "What you have to do with welding is ramp power up gradually to full power, then weld, and then ramp it down when you come to the end of the weld," he says. "This offers a lot better control for that because the machine will do that on its own, once you set the parameters, so it’s like a TIG welder."
Precision cutting and welding with lasers is a focus for Miyachi Unitek Corp. (Monrovia, CA), as medical-device manufacturers demand smaller, more reliable, faster, and more cost-effective solutions. The company has recently introduced new cutting solutions and is broadening its access to different industries, notes Mark Rodighiero, the company’s vice president, systems, technology, and product development.
"We’re broadening our access to different industries," notes Rodighiero. "Another area is corrosion-resistance marking for medical devices and also for aerospace devices. There are a lot of requirements for medical to identify parts with unique identifiers or serial numbers, especially as the FDA directive on medical-device UDI marking is about to be released. So we’re branching out from welding into other areas, developing applications and machine capabilities and going after commercially valuable applications. ME
This article first appeared in the August 2011 issue of Manufacturing Engineering. For a PDF of the article, click here.