Conventional machining – whether a chop saw, bandsaw or other machine – is an effective method for cutting tubing to length. But, there are numerous ways in which laser tube cutters are far more effective at producing results.
When sawing, the accuracy of the saw and how the operator sets up the job have an impact on the overall quality and length of the cut, which affects the tube’s readiness for downstream processes, such as assembly, welding and finishing. Also, the lack of precision and versatility of the saw means it takes more time to complete the job.
“The cut quality is based on how good the saw blade is at that point in time,” says Rick Jackson, tube laser product sales manager for LVD Strippit. “As it degrades, the blade becomes duller and draws more and more burrs. Those sharp edges have to be removed and that becomes an issue for the welder, who has to spend extra time deburring before welding.”
Laser tube cutters provide high-quality cuts and hold tight tolerances on length, meaning that oftentimes secondary operations can be eliminated. And laser cutting, with its freedom of movement, enables holes and shapes to be cut out on the tube with a single machine using a single tool, eliminating the saw and drill method.
The laser tube cutter can also create notches and tabs to connect mating parts – yet another machine capability that makes a welder’s job easier – and faster. Being able to minimize or eliminate the need for jigs and fixtures to weld the part saves incredible amounts of time and, therefore, money.
Twists and turns
Other features important in a laser tube cutter include twist detection and bow compensation. If the tube is twisted or bowed, it affects any shapes that are cut in the tube. It also impacts feature centering like holes and slots, V notch fit-up, hook and tab fit-up from part to part, and hole centering from side to side.
“Square and rectangular tubing is inherently not straight; there is some twist,” Jackson says. “Because there is a flat surface, there is always a tolerance to an edge. With round tubing, if there is twist, it doesn’t show up because there is no edge; in most cases, it doesn’t make any difference. Twist detection allows the machine to make sure the area being cut is flat and the twist is on the opposite side so the cutting area will remain flat.”
The twist deflection and bow compensation features ensure perfect centering of the workpiece. The bow detector uses a laser measuring device to determine where the outer wall of the tube is compared to where it is programmed to be. If the outer wall is not in the correct location, the bow detector automatically adjusts the Y-axis on the cutting head to compensate.
With tubing, bow refers to the variation from a straight line in the vertical plane of the tube.
“The way LVD Strippit handles bow is unique,” Jackson continues. “There are other methods such as mechanical chucking or using a touch probe. We use a non-touch probe. This is a benefit because of how little time it takes to probe or scan. The system works at the speed of light.”
Can a laser tube cutter do its job without twist detection and bow compensation features? “It would affect the tolerances,” Jackson says. “The cutter could do the work, but the tolerances you could achieve from the equipment would be much looser.”
Seams and shapes
As far as tubing that has been welded, the weld seam itself can be fairly thick. “I’ve seen the weld seam buildup almost as thick as the base material itself,” Jackson says. In extreme cases, the operator might have to increase the power of the laser over the weld seam to ensure the part will cut well.
Another problem is the weld seam material can be softer than the base material because of the filler material. And, in some cases, the seam does not cut as well as the base material.
Typically, however, the biggest problem with the weld seam is it can interfere with the final assembly. The location of the seam on a tube can be critical for bending and other secondary operations to minimize the seam’s impact on the part.
Therefore, LVD Strippit’s TL-series of laser tube cutters uses weld seam detection to identify the seam so when it is cutting features into the tube they are correctly oriented to the seam.
“The biggest reason we detect the weld seam for orientation, however, is if it is going into a bending operation,” Jackson says. “With the seam being a bit different in material composition, it will cause the part to bend differently in that area. You want to try to keep the seam consistent so your springback after bending becomes consistent. You can compensate for the seam and make the part correctly.”
Shape detection is another nice feature on LVD Strippit’s cutters. A measuring device on the machine checks the size and shape of the tube after it’s loaded to make sure the operator has loaded the correct workpiece. Although this may seem like an unnecessary step, the lack of skilled workers and entry of newer workers in the industry means an extra check to make sure the correct workpiece is in the machine can’t hurt.
Also, it’s helpful to be aware that when working with welded tubing that it starts out as steel that is rolled, coiled, uncoiled, formed and welded. This leaves varying amounts of residual stress in the base material, which can be a challenge.
“When you are cutting with a laser, you are relieving stress in the material,” Jackson says. “The material wants to go back to its relaxed state. From a laser standpoint, stress in material doesn’t make it any more difficult to cut. What it does do is cause the material to relax and that can, in and of itself, cause some issues such as being able to maintain tolerance and hold diameters if the material has a tremendous amount of stress in it.”
Another factor in laser tube cutting machine selection is feeder capability. LVD Strippit’s TL 2450-FL and TL 2665-FL cutters come standard with a 7-position magazine loader. The TL 2665-FL can be equipped with an automatic bundle feeder, as well. Together, the two systems provide flexibility for high-volume production and low-volume runs. The bundle feeder is for large batches and long runs and the magazine loader moves from one job to the next for short runs or small batches.
As for the bundle loader, “one of the things we’ve seen in the industry is that a shop may order 5,000 or 10,000 pieces, but they are going to receive 200 to 300 pieces at a time,” Jackson says. “So sometimes, this isn’t the best application for bundle loading. If the job turns out to need five or six sticks out of a bundle, you put those sticks in the magazine loader on the front of the machine and it runs automatically from there. But, if you want to run fully automatic, we can indeed put a bundle loader on the back of the machine.”
The TL 2450-FL has all-around capacity, processing round tubing from 0.375 in. to 5 in. in diameter and rectangular tubing up to 4 in. by 2 in. Maximum infeed is 24 ft. The TL 2665-FL processes rounds from 0.75 in. to 6.5 in. tube lengths up to 26 ft.
Both are fiber lasers. The TL 2450-FL is 1 kW with a 2 kW upgrade. The TL 2665-FL is standard with 2 kW.
Jackson also likes the nondestructive crash protection on the TL 2665-FL’s cutting head. In the case of a collision between the workpiece and the head, the head has a flexible unit that aligns back into position when the crash is cleared.
“With nondestructive crash protection, if you do crash, you can just jog it up off the crash and start the program again,” he says. “Simply pick up where you left off. Other machines have breakaway rings or bolts. When you hit a tip-up hard enough to break the bolt, you have to go find the maintence guy to fix the machine or fix it yourself. Either way takes valuable time.”
While the laser tube cutter offers all these benefits, the cost of the machine is relatively high. But again, the cost consideration when comparing various machining methods is how downstream processes will be affected. The quality of laser cutting often reduces the amount of setups and secondary operations required in the final part assembly. The final cost justification is in the cost of quality.