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Materials making sense

Whitney tests exotic materials for customers to see if they are viable candidates to be fiber laser cut

Whitney recently tested fiber laser cutting pure zinc plate used to make wire forms to hold tiles in place for patterned flooring. The pieces that are cut are 1/4 in.-thick and 1/8-in. wide and have complex shapes.

Whitney is often asked to test and evaluate cutting of new or exotic materials with fiber lasers. The company has experimented on laminated aluminum and stainless steel used in the aerospace industry, a magnetic material for rotors and a zinc plate material for the flooring industry, just to name a few. The successes and challenges of cutting these materials with a fiber laser as opposed to nonthermal machining processes are laid out. The success of cutting reflective materials with fiber vs. CO2 lasers is explained, as well.

Whitney is approached by customers with special materials that they need tested from a variety of industries, including aerospace, store fixture manufacturing, architectural, construction and transportation and from a range of custom fabricators. While these materials have not been historically cut with a fiber laser, the customer is looking to see if a fiber laser can outperform their current process.

Whitney’s fiber laser machines can process a range of material types, including laminates, composites and highly reflective sheets. They offer increased cutting speeds, reduced operational costs and minimized maintenance requirements.

Shim success

One example of a material Whitney recently tested is a laminated material used in the aerospace industry for making shims. The base is 0.030 in. of solid material. Layers 0.003-in. thick are laminated on top of the base for a total thickness of 0.060 in. Both stainless steel and aluminum laminates were tested.

“To get the shim to be the precise thickness needed, the customer might need to peel off a layer or two to get it to precisely fit into whatever space it is going in,” says Dale Bartholomew, global sales and product specialist at Whitney.

Historically, the shims are machined. “The problem with that process is that it’s slow,” Bartholomew says. “Also, the mechanical process of machining tends to cannibalize some of the layers. The top layer peels back, for example.”

Therefore, the cost and issues of producing the shims mechanically made the customer seek out a better way of doing it, which meant experimenting with fiber laser cutting.

Whitney first tested the material by cutting small coupons and establishing a range of cutting parameters, then subsequently testing the cutting of actual parts. Whitney tested the material in a variety of ways, including if it cuts better if the laminated side is up or down.

“Another aspect was to have the precise configuration setup needed to cut so we didn’t weld the part edges together, which is a big concern with cutting thin pieces,” Bartholomew says. “If the edges weld together, you can’t peel off a layer.”

Whitney cut dozens of samples in various configurations – laminate up, laminate down, various cutting speeds – and established the fiber laser could cut the material successfully with no welding at the edges and no cannibalizing of the layers. “At this point, we’ve cut the material anywhere from 900 ipm for the aluminum down to about 120 ipm for the stainless steel,” he says.

While Whitney has proven they can cut the material with fiber lasers, the aerospace customer must do some testing of its own. “They are concerned about fatigue,” Bartholomew says. “Because the material is not typically thermally cut, it must be tested to see if the heat used in the cutting process increases the possibility of failure. Obviously, the mechanical process typically used does not induce that heat.”

So what does the fiber laser machine need to cut the laminated material? “What you really need to bring together is the fiber laser delivery system,” Bartholomew says. “Different fiber diameters, collimator lengths and lenses and focal lengths in combination affect how the beam interacts with the material. This is the challenge.”

All of those things play together, he adds. “What might work on one material might need to be tweaked to work on a different type of material. For the laminated material, the power level and focusing head components were the biggest issues.”

The advantages of a fiber laser resonator vs. a CO2 resonator.

Magnetic magic

Another example for Whitney of a material they just completed testing on is a magnetic type of stainless steel used in laminated metals in the construction of the rotors for motors and generators. The parts have complex shapes with tight tolerances made from material about 0.0025-in. thick. Each piece is cut precisely identical and the pieces are stacked afterward with other material, determined by the manufacturer, in between them.

The parts are made by stamping where precise die cuts are needed. “The customer is looking for a way to cut the parts in lower volumes,” Bartholomew says. “The die sets for stamping can be very expensive so they are looking for a lower cost operation, not a faster operation.”

Whitney was able to use standard fiber lasers with some adjustments to cut the magnetic material successfully at approximately 400 ipm. Adjustments were made to the power, speed and focus position. Assist gas pressure and nozzle type were optimized to produce the fastest and cleanest cut possible.

The challenges in fiber laser cutting this material are not in the cutting but in the final application. “The magnetic properties of the material can’t be compromised,” Bartholomew says, “because that will change the way the laminate works with the motor and the magnetic fields. Again, we’re putting heat into the material and that can affect the structure of the material and, therefore, the magnetic properties.” The customer is performing tests to determine if fiber laser is going to be viable.

Forming flooring

A third example of a material Whitney recently tested with its fiber laser is a pure zinc plate. The customer that requested the testing uses the plate to make wire forms to hold tiles in place for patterned flooring. The pieces that are cut are 1/4-in. thick and 1/8-in. wide and have complex shapes.

Typically, waterjet machines are used to cut the forms, but it is a slow process – only approximately 14 ipm. Whitney developed a fiber laser process that can cut the zinc plate at 400 ipm.

One possibility

One material Whitney has been asked to experiment on but hasn’t performed yet is a composite material with metal and plastic layers. “We’re not sure if we can successfully cut it,” Bartholomew says. “We know we can do the metallic areas, but we’re not sure about the plastic sandwiched in between. The fiber laser might go right through it as opposed to being absorbed so it can make the cut.”

Fiber laser is not generally used for plastic, he adds. “For the same reason the fiber wavelength is good for metals, it is not quite so good for plastics and acrylics. The CO2 laser can cut it pretty well because of the wavelength, which the plastic does absorb. This is a differentiator between fiber and CO2 laser. But fiber might be a possibility, and we’ll give it a try.”

And the reason the fiber wavelength is better for metals is because it is only 1.06 microns, whereas the CO2 wavelength is 10.6 microns. The fiber is 1/10 the wavelength of CO2 so the way the material absorbs that power is significantly different.

Cutting unique materials with a fiber laser requires substantial knowledge about the power and quality of the beam, assist gas type and pressure, nozzle design, focus position and cutting speeds. Optimizing and balancing these parameters can sometimes lead to necessary machine modifications. For example, typical laser head height sensing only works on metals. So if the application has nonmetallic components that compromise the performance of the height sensing, different height sensing technology might be needed.

A fiber laser cutting head is completely sealed to prevent contamination. Maintaining the head requires strict attention to procedures, cleaning materials and methods, and environment.

Reflective materials

Reflective materials, while a proven technology, are another differentiator between fiber and CO2 lasers. “If you are cutting a reflective material with CO2 laser, and you lose the cut for whatever reason, the power or the light you are putting into that material is reflected back up,” Bartholomew says. “Because the CO2 laser beam path is made of mirrors, it is going to be reflected back into the resonator. There is a huge influx of power that can destroy or damage the resonator. So you need to have some accommodations, either through sensors or special reflective optics that don’t allow it to go through. This becomes complex and difficult.”

A fiber laser is much more suitable for cutting any kind of reflective material. “With a fiber delivery cable that is properly designed,” he says, “if you get that back reflection into the cable, the cable actually absorbs it so it never gets back to the power source. There is no opportunity for the reflection to get propagated back to the source.”

But the fiber optic cable has to be designed in this way, Bartholomew notes. “It has to be a properly designed cable. There are fiber laser manufacturers that say they have a fiber delivery cable to generate that laser beam at a similar wavelength, but they deliver it in a different way. Their components and resonator are not necessarily solid state. With that type of system, that beam can still affect the performance. If you are going to cut reflective materials, use fiber lasers that are completely solid state and are known to be designed to eliminate the problems with reflectivity, like the ones we use from IPG.”

Fiber vs. CO2

The big difference from a user standpoint between CO2 and fiber laser is the cost of operation. “A CO2 laser costs on average about $12.50 per hour to operate, which doesn’t include the cost of the cutting gas,” Bartholomew says. “That is just maintenance and operating costs. It costs about $3.50 per hour on a fiber laser.”

Also, CO2 is not as fast as fiber laser for cutting thin materials when using nitrogen as the assist gas, according to Bartholomew. “The fiber laser cuts faster in thinner materials because there is better coupling of that laser beam through the material so it cuts more efficiently. Depending on the power level, for materials above 1/4 in., you start cutting with oxygen. Then the CO2 and fiber cutting speeds become comparable.”

And that is when the fiber laser is less expensive because of the maintenance. One of the biggest maintenance costs is that the CO2 resonator has to have components rebuilt or replaced on a schedule. “Every 12,000 hours or so, you have to have a technician come out and you have to spend $20,000 to $40,000 to rebuild the resonator,” he says. “Fiber lasers don’t require any kind of a rebuild.”

The cost of operation is a significant drawback, as well. The way the laser beam is produced in the resonator requires a lot of support equipment to generate that beam, including blowers, mirrors, cutting gas and high voltage, according to Bartholomew. And to deliver that beam to the cutting head and get it to work requires cooling and beam path purging.

All of those cost aspects disappear with fiber. “A true fiber laser like we use that is supplied by IPG is solid state, and the generation of the laser beam is delivered through a fiber optic cable to the cutting head,” Bartholomew says.

“Also the conventional wisdom is that you can’t cut thick material with fiber lasers, that you are limited to under 1/4 in.,” Bartholomew says. “Whitney is showing that to be not true. We’ve shown you can cut 3/4-in. plate with fiber. We even have a 12-kW fiber laser cutting 1/4-in. steel at 500 ipm. That is even faster than plasma cutting.”

It should be noted that a fiber laser cutting head is more complex than a CO2 cutting head. The fiber head is completely sealed to prevent contamination. Maintaining the head requires strict attention to procedures, cleaning materials and methods, and environment. While the changing of cover slides and nozzles can be done at the machine, cutting head disassembly and maintenance should be completed in a clean ventilation system.

Because of the advantages of fiber laser, Bartholomew sees the laser industry beginning to change. “The industry is sort of in an in-between state. A lot of laser machine manufacturers have a huge investment in CO2 laser so they need to promote that over the fiber. And CO2 has been around for many years so many companies have those capabilities dialed in for a lot of their processes already.”

So it comes down to the technology becoming more well-known. “Companies have to look at it a little bit differently than from a conventional perspective so they can change the way they are doing things,” Bartholomew says. “There is an attitude that what you did with CO2 should just be plowed into what you are doing with fiber, but you have to come in with a new perspective in order to be able to optimize that fiber laser process.”

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