Keeping sheets and parts moving with automation
Material loading/unloading automation tries to keep up with modern laser cutting technology
Modern laser cutting technology can achieve speeds of more than 400 inches per minute, and that puts pressure on the automation used to load sheets and unload cut parts and skeletons. If the automated material handling system can’t keep up, the fabricator won’t be able to maximize uptime on the laser cutting machine.
Owning a fiber laser cutting machine and not being able to run it at full speed is like trying to enjoy the thrill of driving a Porsche 911 Turbo S in the mall parking lot during Christmas. The continuous stop-and-go drives you crazy.
If a fabricator has made the large investment in a solid-state laser cutting machine, he wants that piece of equipment to fly. With speeds that can reach upwards of 4,000 inches per minute, fiber laser technology puts incredible pressure on material delivery and parts and skeleton removal.
(As a quick refresher, fiber lasers are laser cutting devices that use fiber-optic cable to deliver the laser light from the solid-state generation source to the cutting head. In CO2 laser cutting machines, a gas mixture, which includes CO2, is the medium in which the laser is created; mirrors then direct the laser light to a cutting head.)
“The evaluation of what automation can do now is in the forefront versus when it was first developed,” said Jason Hillenbrand, laser product manager, Amada America Inc. “In the past automation was developed purely to get the material on and off of the cutting equipment without the human being there. But today we’re saying it has to do that, but it also has to do it in a specific cycle time.
“I would say that you are going to start to see that evolution, but in fact it is already happening,” he said.
Getting the Sheet There
Automated sheet metal delivery to a fiber laser cutting machine shouldn’t be much of a concern for metal fabricators, but they must realize that nothing is perfect. Stuck sheets happen.
It’s a simple fact that sheet metal, especially the thinner gauges, sometimes sticks together (see Figure 1). If a metal fabricator often receives oil-laden material from its supplier, that’s another concern.
“In general, it is less of a concern today,” said Lutz Ehrlich, punching and automation product manager, Prima Power North America Inc. “But does it pop up here and there? Yes, it does.”
Safeguards have been designed into these automated material storage and delivery systems, however, and for most laser cutting equipment-makers, these offerings are standard features, not options. It all begins with a sheet separation cycle and double-sheet detecting sensor, which can verify whether the load being picked up is the thickness it should be. If two sheets of 20-gauge sheet stick together and are picked up, the sensor determines that this is thicker than one sheet and initiates separation steps. Most material handling systems include some combination of the following technologies to separate those sheets:
- Peeling devices. A cup, cylinder, or some other interface physically engages the corner of the joined sheets to encourage separation.
- Air blowers. These devices shoot a jet of compressed air between the sheets in an attempt to create space and force the bottom sheet to disjoin from the top sheet. This sometimes occurs just after physical engagement of the peeling device.
- Vibrators. Not too unlike vibration units available in most supply catalogs, these devices shake the sheets intensely for a short amount of time.
- Magnetic separators. A magnet is placed near the mild steel sheets, and the magnetic draw helps to fan out the corners of the sheet, forcing some separation to occur. Fabricators obviously won’t find this useful for nonferrous materials.
Again, there is no guarantee of sheet separation when these technologies are applied. That’s why automated material handling systems might have to engage these separation steps two or three times before finally timing out.
“That’s where things have gotten much better,” said Jim Rogowski, director of machines and power tools, TRUMPF Inc. “If we do have a situation where the automation has reached a point that it can no longer move forward without the intervention of a human, we have great communications available to us.”
An example of such communication is a system that sends messages or e-mails to computers or mobile phones, which is particularly handy if no one is in the facility at the time of the stuck-sheet incident. Depending on the system design, a camera might be able to offer a glimpse of the material handling glitch, which an operator can view via the Internet. In the event people are around, the system can set off an alarm to capture their attention.
Fortunately, most of those experienced with automated sheet metal material delivery know that today’s systems prevent the double-sheet scenario a majority of the time. While it can happen, it’s not a major threat to a fabricator getting the most out of its fiber laser.
Looking beyond stuck sheets, fabricators should keep in mind a couple of other scenarios that might delay sheet delivery to a fiber laser cutting machine:
Getting the Parts Out
Simply put, the process of separating parts after they have been cut by a fiber laser is no simple task. It’s completely different from separating parts cut on a CO2 laser.
“If you have never rolled up your sleeves and pulled a part out of the nest, do a test with a CO2 machine and feel what’s it like to pull a 3⁄16- or 1⁄8-inch mild steel part out of the nest. Then compare that to the same part cut on a fiber laser cutting machine of the same power,” Rogowski said. “It’s a much tighter cut kerf on a fiber machine, which presents a lot of challenges.”
The fiber laser produces a much smaller focused beam, which doesn’t allow for much kerf during cutting. That results in parts that fit snugly into the nest after cutting and can prove to be difficult to remove. (CO2 lasers have larger-diameter beams and produce more kerf during cutting.)
Fabricators also have to worry about small parts shifting after being cut. This is a particular problem for thin-gauge parts, because the slightest shift in the sheet can cause unplanned movement of the part. The odds of this scenario occurring are increased greatly on fiber lasers because they cut thin gauges a majority of the time; the fiber beam’s higher absorption factor and the higher power density help it to blaze through material 1⁄8 in. and less.
To “cope” with the fiber laser’s incredible cutting speeds, many fabricators are turning to manual parts separation. Humans are flexible enough to handle difficult-to-remove and awkwardly positioned parts in a nest—even if it means they might be there for a shift or longer going through a stack of skeletons and parts.
It’s not the most modern of material handling solutions, but it might be necessary for that particular fabricator. Often the suppliers of the fiber laser cutting devices and the accompanying automated material handling technology can help to diagnose if the product mix makes sense for complete automation. If the job mix includes a healthy dose of parts in the midrange thicknesses—between 3⁄16 and ¼ in.—or are large shapes, the fabricator definitely should consider robotic parts separating (see Figure 2). If a majority of the part portfolio is thin-gauge and has complex geometries, the fabricator needs to be certain that robotic arms can separate parts consistently without causing too much downtime.
Those fabricators not comfortable with the expense associated with robotic part separation can look at the use of conveyors to assist in manual parts separation (see Figure 3). Many times these conveyors transfer the parts and skeleton away from the cutting area so that more room is available for part separation, and the parts are more easily transferred to the next downstream fabricating activity.
“Sorting parts has been a problem for many years, and the fiber lasers are causing even more of a problem than ever before because of the number of nests that are being cut,” Rogowski said. “The pressure is on the automation experts to innovate ways to help with the sorting and organization of parts.”
To assist with smooth separation of parts, either by robot or human, experts offer a couple of tips:
- Keep the slats as clean as possible. Carbon steel slats will collect the molten metal removed from the material being processed, and that material essentially welds to the slats. Additionally, the slats will heat up as sheet metal parts are laser-cut on top of them and begin to melt away. The resulting dross on the slats can act as a trap for small or complex parts as the parts and skeleton are removed from the cutting bed. (This degradation process becomes more rapid as thicker material is cut.) Hillenbrand said fabricators have looked at numerous slat designs, such as deeper V shapes for the molten metal to flow better, but still have the same problem with dross buildup. He recommends copper slats for most applications. They will stand up to the heat and last much longer, but there is an obvious upfront expense associated with that type of material.
- Adapt software programming for fiber laser cutting. If a programmer sees an outside contour of a part that might not separate easily after being cut on a fiber laser cutting machine, he might want to select an option that provides for cutting more material through that contour. “That may take a half, one, or two seconds more, but it also allows for sustainable automation,” Ehrlich said.
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.