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Best practices for laser cutting tube, pipe, profiles

Industry professionals provide sound strategies for successful cutting

The latest feat of engineering to come screaming out of Sant'Agata Bolognese, Italy, is Lamborghini’s bold-looking Centenario LP 770-4. Sleek and aggressive, it’s powered by a 6.5-liter engine that develops 770 horsepower at 8,500 revolutions per minute and accelerates from 0 to 62 miles per hour (MPH) in a mere 2.8 seconds. At 217 MPH, the top speed is nearly triple the speed limit in many U.S. states.

Of course it wouldn’t perform at this level if it were outfitted with the cheapest tires available, if it had been driven for years with no maintenance, and if the tank were full of stale, low-octane fuel. It would run, and it might even run fast, but it wouldn’t run very fast for very long. A high-performance system needs premium inputs for a premium output.

By the same token, when using a precision machine tool, the inputs have a big influence on the output. As the machine becomes more technologically advanced, the user needs to pay greater attention to get the best possible results.

According to interviews with several equipment manufacturers, when using a laser to cut tube, pipe, or profiles, every detail warrants consideration. It starts with the material—how it’s specified, transported, and stored. Material handling, specifically loading the raw stock and unloading finished parts, likewise is critical. It doesn’t end there. Equipment maintenance, operator training, and software updates help to get the most out of the machine.

Material Matters

Alloys are specified by a handful of standards bodies. The main ones—American Society of Testing and Materials, American Iron and Steel Institute, Society of Automotive Engineers, and the Aluminum Association—are called out in the full names of common metal alloys, such as ASTM A-500, AISI 316, SAE J525, and AA6063. Fabricators should be aware that a tube or pipe that complies with one of these commercial standards isn’t necessarily the best product for laser cutting.

Dimensional Accuracy. While perfectly straight and true material would be ideal, this is a steep challenge for tubular products. Welded tube and pipe start out as steel that is rolled flat, coiled, shipped, uncoiled, formed, welded, and quenched, which leaves no small amount of residual stress in the material. Common commercial specifications allow some amount of bow and twist. While many tube and pipe suppliers today can provide laser-quality products—lengths that have tight dimensional tolerances—many don’t.

To compensate for material with loose dimensional tolerances, modern laser cutting heads usually incorporate height sensors or touch probes. Before the cutting begins, the cutting head approaches the tube’s surface at several points and takes a series of measurements. If the tube has a constant amount of twist, the machine needs just a few moments to measure the amount of twist near the tube’s end, said Rick Jackson, tube laser product sales manager for LVD Strippit.

However, a single measuring cycle might not be good enough. For example, if the amount of twist varies along the tube’s length, the machine takes more time to verify the dimensions because the laser head has to take measurements from one end to the other to determine the entire tube’s geometry.

Some machines are programmed to do additional checks to improve cutting accuracy and to provide an extra measure of crash prevention.

“TRUMPF’s software uses several measuring cycles, which can do a Y-axis offset and compensate for A-axis deficiencies,” said David Gilmore, TRUMPF’s senior applications engineer for laser tube products.

Figure 1
Holes drilled in the centers of opposing walls of a properly formed square tube align well and can accommodate a pin or other hardware inserted in a subsequent step (left). If the square is poorly formed (exaggerated in this illustration), the holes don’t align, making it impossible to insert a pin (center). A laser cutting machine’s measuring capability and software can detect this situation and compensate by adjusting the hole locations (right).

An option on Mazak machines is the company’s Profiler, which uses a noncontact device that scans the machine’s control software to prevent a crash.

Another problem that can crop up when cutting nonrounds is inconsistency in the shape. A primary problem concerns corner radii. Two or three corners might be right on, but sometimes the last one formed is a lazy corner. For most fabricating machines, this doesn’t matter, but the laser’s standoff distance is so small and laser cuts so precise that a lazy corner can cause a problem if it isn’t detected before cutting begins.

Another issue with nonrounds is the shape itself. In some cases, the corners that form square tube aren’t perfect 90-degree angles and the shape isn’t a true square. Often two angles are more than 90 degrees and two are less than 90 degrees, forming a parallelogram. In such a case, an accurate measuring process is critical. Two opposing holes placed in the center of the tube would line up if the tube were square, but they would be offset if the tube were a parallelogram. When the measuring cycle determines that the tube’s shape isn’t perfect, this information is fed to the control software so it can adjust the hole locations accordingly (see Figure 1).

Even if the tube or pipe is straight when it leaves the mill, proper loading and transport are critical to maintain its original straightness. Tube needs proper slinging before lifting and sufficient dunnage when it’s loaded into a truck bed. If it’s not supported along its length, it’s likely to sag. Having conversations with the supplier and the carrier can be a good start in resolving this sort of dimensional problem.

Wall thickness also is a factor. A tube or pipe that is straight when stored on a floor can sag in a laser machine if it’s secured by end chucks only. As the length and wall thickness increase, so does the weight, and therefore so does the amount of sag.

A machine with several chucks can help to straighten sagging or bowed workpieces, but this isn’t a cure-all. The thicker the wall, the more difficult it is to straighten.

Surface Condition. Removing rust, paint, or lacquer isn’t a requirement for making laser cuts, but it is a requirement for making fast, high-quality laser cuts. Three common surface difficulties are corrosion, lacquer, and paint. Of the three, lacquer tends to provide the worst cut quality, said Mark Mercurio, applications manager at Mazak Optonics Corp.

Corrosion usually isn’t a problem on thin-walled tube because the tube normally is stored indoors, according to Mercurio. Cutting large items is a different story. First, wide-flange sections such as I-beams, C-channels, and H-beams tend to have more mill scale than most other steel products. Second, large-diameter tube and pipe take up a lot of room, so these products often are stored outdoors, leading to corroded surfaces.

Most of the materials that can rust—that is, ferrous materials—need oxygen to assist cutting, and this is where the cutting problems start, Mercurio explained. The rust contaminates the oxygen, and the cutting is uneven, resulting in striations. Another problem is that some of the debris sticks to the wall of the tube, he explained. This isn’t necessarily a problem on every type of cut feature, but the debris can cause an interference downstream, such as when installing a pin or a bolt into a small-diameter hole that has little clearance.

“It can result in omissions and welds,” Gilmore concurred.

Cutting slower and tolerating a slightly jagged, striated cut is one option. Another is mechanical descaling and corrosion removal. A third option involves using the laser machine to do the cleanup work along the cut paths. Gilmore explained that TRUMPF’s software provides a subroutine that retracts the laser’s head, changes the focus to provide a wide beam path, and drops the power to about 500 watts. The machine then blasts the surface with a short pulse of laser light that vaporizes the corrosion, and the parameters return to normal for cutting. The laser’s head uses this clean-then-cut process as it proceeds from one cutting location to the next.

Jackson reported that one of LVD Strippit’s customers discovered that a tube supplier had been using a nitrogen environment for its cooling process, which resulted in a better surface than cooling in air. The material cooled in nitrogen had a silver-colored finish rather than the conventional black or brown scale finish, and the laser was able to cut it much more quickly. Tube that had the conventional scale would require a decrease in cutting speed of 30 to 40 percent, Jackson said.

A corrosion inhibitor likewise requires a slower cutting speed or use of the laser to burn it off. Jackson said he has seen instances in which a chemical such as acetone couldn’t remove the corrosion inhibitor and a laser couldn’t cut the material.

The outside surface condition isn’t the only one that can cause concern. Lubricants from upstream processes, such as sawing, can remain inside a tube or pipe when it arrives at the laser.

“This doesn’t seem to cause any cutting problems and might actually be a benefit because a lubricant can help disperse some of the heat,” Gilmore said. “The downside is that the heat vaporizes some of the lubricant, which can result in buildup on the optics, sensors, and other hardware, so additional cleaning is necessary.”

Managing Material Movement

A high-powered resonator and fast carriage are necessary for fast cutting speeds, but the cutting cycle includes two other processes that also can have big influences on cycle times: loading and unloading. Sheet metal lasers can run more or less unattended for long periods of time—the material on the infeed side is flat, the parts on the outfeed side are flat, and fabricators have options such as shuttle tables, loader/unloaders, and tower storage systems—but the infeeding and outfeeding of tube, pipe, and profiles takes a little more planning.

“We offer two types of infeed: bundle and versatile,” Mercurio said. “The bundle feeder is good for a single size of material, but the versatile feeder is equipped with a series of holders that can hold a variety of different tubes.” The first option is good for big batches of components made from a single tube size and shape. The second option is for fabricators that need to make kits of parts from a variety of shapes and sizes of tubing, supporting one-piece flow and reducing work-in-process.

“The chucks are universal, so the machine can clamp the tube that comes next, without operator intervention,” Mercurio said. “It could run two rounds, then a rectangle, then an I-beam, then back to round.

“The outfeed side is also important because, when it comes to tubing, you tend to have a longer, heavier part than you have when processing sheet metal,” Mercurio said. Many laser-cut sheet components are small and don’t weigh much, so dropping them into a collection bin isn’t a problem. However, a tubular component for a harvester or a combine can be 20 ft. long and weigh 300 pounds. Nobody makes a collection bin or basket that size, and using gravity assist—that is, dropping the part into the collection bin—would damage the machine.

Even if the parts are small, a bin isn’t always the best option. Because the parts aren’t flat like sheet parts, each one takes up a lot of space. They fill the parts bin in a hurry, and a full parts bin is a problem.

“When the bin gets full, the machine stops,” Gilmore said. Using a conveyor to transport parts to a larger bin would help, as would using two conveyors in combination, going from one to another. The key is to keep the parts moving.

Running a tube laser unattended around the clock is an attractive idea, but it’s much easier said than done. First, because tubular material doesn’t stack up, it’s usually bundled, and a bundle can weigh 8,000 lbs. It’s difficult to automate loading the loader, said Todd O’Brien, BLM Group’s North American product manager for lasers. A storage-and-retrieval system is another option; a few are known to have been installed to feed tube lasers, but these are large, sophisticated systems that are beyond the needs of most fabrication shops. For all that, having the outfeed side run unattended is far more difficult for the aforementioned reasons. A robotic unload system might be a workable option in the future, Gilmore said, but until then, tube and pipe lasers will continue to need at least some level of operator intervention to empty parts bins to keep the material flowing out of the machine.

Maintenance

Like any other car, the Centenario needs its oil and filter changed regularly, and every car owner knows that strict adherence to the preventive maintenance schedule is the key to maximizing its performance.

Lamborghini’s latest costs about $2 million and the price leaves little doubt that Centenario owners are conscientious in their efforts to adhere to the maintenance schedule. Nobody would spend that much money on a car and risk turning the engine into a red-hot pile of scrap metal because it was running low on oil. At the same time, most Lamborghini customers have another car or five, so using a substitute car—maybe a Ferrari or a Rolls Royce—while the Centenario is in the shop for maintenance doesn’t pose a problem.

When it comes to industrial machinery, finding time for maintenance is a little more complicated. An idle machine makes no money and therefore doesn’t contribute to the shop’s return on investment or profitability.

Depending on the machine, downtime is easy to justify. A shop that has five band saws can justify some time for inspections, cleaning, adjustments, and other periodic maintenance, taking one saw out of service and relying on the other four to carry the burden of five. However, as the machine’s price increases, its uptime becomes increasingly critical, and the machine is less likely to be accompanied by redundant equipment. Shutting the machine off becomes increasingly difficult to justify.

Still, many fabricators understand the gravity of the word preventive in the phrase preventive maintenance.

“Most companies schedule downtime because they know that putting off the maintenance can cause large issues down the road,” O’Brien said. Delayed maintenance can cause near- and long-term problems. “It can degrade the cut quality and result in potential damage to the machine,” he said. BLM’s software includes a preventive maintenance schedule and instructions to assist fabricators in managing equipment upkeep.

Still, laser users vary in how much maintenance they schedule.

“We have some customers who feel that the machine should just take care of itself, and we have some who are meticulous, scheduling some machine downtime weekly,” Gilmore said. “At the very least, it’s important to keep the machine clean,” he said.

He also looks at it from the point of view of a service technician.

“If you were a service technician and you had to work on a filthy machine, you’d probably do the minimum, but you’d take a little more time and do a few more things if the machine were clean.”

Gilmore suggests one maintenance step that should be carried out once per shift is cleaning the chuck rollers. These rollers can accumulate dirt quickly, depending on the quality of the tube, and cleaning them helps to maintain the positional accuracy of the part’s features

“The rollers get dirty quickly and should be wiped down after every shift,” he said. Accumulated oil can cause the tube to slip, which degrades the accuracy slightly as the tube or pipe rotates.

Software Training Sessions: Where Operators and Programmers Meet

Machine control software is becoming more capable with each passing year, and in many cases a single mouse click is enough to import a part drawing from most of the commonly used drafting programs. While the software automates some of the steps, operator training is far from unnecessary. Tubes, pipes, profiles, and wide-flange sections are 3-D items that require 3-D thinking, but this skill doesn’t come easily to everybody.

“Angle cuts, bevels, and chamfers can be tough to do, so Mazak takes training seriously,” Mercurio said. The company’s tube laser training course runs two weeks, which is twice as long as its sheet metal laser course.

Mazak’s program is comprehensive in that it teaches the programmers about the software and the operators’ role, and it teaches the operators about the programmers’ role.

“It isn’t uncommon for an operator to mention that a certain programmer always makes the same mistake every time, and the operator has to compensate for it, so we decided to include the programmers in our training,” Mercurio said. “We have had instances in which our trainers introduced the customer’s operators to its programmers.”

Gilmore said that while working in a 3-D computer-aided design environment can be a more complex concept to grasp, the current generation of programmers has an advantage over their predecessors. The latest generation started using 3-D software at the outset, rather than learning to work in a 2-D environment and then transitioning to 3-D. Still, quite a bit of training is needed, and TRUMPF breaks the training into two sessions: basic and advanced.

“TRUMPF has an entire department to support the training regimen, which is one week of training each for operators and programmers, while the machine is set up and commissioned, followed by two to three days of advanced training at a later date,” Gilmore said. The advanced training is specialized to each customer. It doesn’t have a prepared format but instead addresses specific application questions that have come up during the month or so of machine use since the first training session.

Customers have options in training that goes beyond the standard sessions. For example, TRUMPF can visit the customer’s site, provide web-based sessions, or the company’s technicians can connect to the customer’s software to show specialized techniques and explain the processes behind them, Gilmore said.

LVD Strippit offers eight days of onsite training; even so, it has found that laser capabilities often are underutilized for many parts. The automatically generated cutting paths typically are good, but a little tweaking could help reduce cycle times noticeably. Most of the company’s customers take a realistic approach in that they concentrate their efforts on optimizing the parts they cut in highest volumes and most frequently, but don’t put time into reviewing short-run or infrequent parts.

Training can take place at the vendor’s site, but training at the customer’s site is less costly in terms of travel. The drawback is the same one that gets in the way of scheduled maintenance—fabricators are reluctant to spend a lot of time on anything other than production. The upside is that training on-site means that all of the operators get the same training.

Fabricators are advised to provide supplier-based training for all of their operators. It’s tempting to have some

operators take the training and then pass along what they have learned to others, but this isn’t usually fully effective or complete.

“The biggest mistake is having Operator A train Operator B,” O’Brien said. “It’s much better if they come to our facility so we know that they are completely trained in the correct ways to operate the machine,” he said.

Upgrading operators and programmers with extra training is one thing; upgrading the machine with the latest software is something else altogether. Like maintenance, some customers pay close attention to it and some don’t. Machines can run just fine for years on the original software, but fabricators who never update the software risk falling behind others who take advantage of all of the periodic software upgrades.

Getting the Most Bang for the Buck

A laser cutting machine is a complex piece of equipment that requires a complex analysis to maximize its output. Today’s lasers have more power and faster traverse speeds than their predecessors of decades ago, but the cutting speed is just one of six processes in the laser cutting cycle: load, measure, find the weld seam, compensate for irregular material, cut, and unload. Maximizing the machine’s throughput is a matter of evaluating each step in the cycle, not to mention evaluating the raw material that feeds the laser and the capabilities of the software, the programmers, and the operators.

A shop with the biggest resonator and the fastest carriage might be a contender, but it will have a tough time competing with a shop that has evaluated all of the steps in the cutting cycle, researched all the equipment and software options, and considered how the laser will complement other processes and workflow.

Especially if the second shop cleans the rollers after every shift.

About the Author
FMA Communications Inc.

Eric Lundin

2135 Point Blvd

Elgin, IL 60123

815-227-8262

Eric Lundin worked on The Tube & Pipe Journal from 2000 to 2022.