Laser cutting is an incredibly quick and precise method for producing parts out of a variety of materials – it can equally cut steel, aluminum, tungsten, brass, nickel or copper – making it a popular choice in metal fabrication shops. The extreme versatility of laser cutting is in part due to the power levels that have been achieved in years past.
Laser power edges ever higher as laser OEMs try to provide faster cutting speeds and increased material thickness capacity while still providing good edge quality. As power increases, however, the laser optics and cutting heads must be able to respond to allow users to take full advantage of the laser’s capabilities.
For one, controlling for focus drift in the cutting head can be a challenge with higher power lasers.
“With higher power levels of 8 kW and up, there is a chance that the focus might start to be a little inconsistent,” says Brett Thompson, TruLaser technology and sales consultancy manager, Trumpf Inc. “To account for focal drift, the Smart Beam Control monitoring system, available on the TruLaser 5030 Fiber, checks the kerf diameters at different focal positions. Through a sensor integrated into the cutting head, the system views an image that is actively being recorded and compares the current spot size with the needed spot size and then adjusts the focal position dynamically.
“This is critically important, particularly with long straight cuts,” he continues. “Without the ability to adjust the focus, you would have to spread the energy over a larger area on the focusing lens. This would give you a little bit less capability as far as beam diameter ranges are concerned. Smart Beam Control is looking at the focus of the laser and noting if the focusing lens is shifting. To compensate, it automatically adjusts the position of the focus.”
Active Speed Control is another intelligent sensor system, also available on the TruLaser 5030 Fiber, that allows users to take full advantage of the laser’s capabilities. Through a sensor in the cutting head, this technology responds to feedback from the workpiece related to cut quality.
“A camera above the nozzle records the actual shape of the kerf,” Thompson says. “It can account for material thickness variations, alloy variations, surface condition variations, etc. It detects where the edge quality is the best and regulates the laser to make sure the expected cut quality is what is achieved. Users see about a 7 percent increase in feed rates. When the machine goes out the door, it will cut 100 ipm for example, but because the laser can speed itself up to 20 percent over what the base feed rate is, it will be cutting at 107 ipm.”
Technology that allows for increased material thickness capacity, among other things, is BrightLine fiber technology, available on a variety of Trumpf fiber lasers. The function of BrightLine fiber is ultimately to control the beam sizes and the beam mode adjustment. A small high-density beam is ideal for cutting thin materials at high speeds. But, in thicker materials, having a small beam diameter and the smaller kerf starts to affect quality because the molten material can’t be actively ejected from the kerf. So, the amount of adjustability in the beam diameter is going to be limited by the size of the delivery fiber cable.
“With BrightLine Fiber, we coaxially deliver the cable,” Thompson says. “We can switch between a 1-micron and 400-micron cable programmably in about 45 milliseconds. That provides a beam diameter range that is very large so when cutting thicker materials, we can use a large beam and efficiently eject the molten material from the kerf and get a really consistent flow of gas through the kerf. The part quality is really good and that is because the process stability is fantastic.”
Look at nozzles
Other features that can help users take advantage of the laser’s power and speed capabilities involve the nozzles. For materials 3 mm thick and up, Trumpf’s high-speed nozzles
are low-pressure-load, fusion cutting consumption nozzles that stabilize the gas flow. With higher rates of speed, the speed of the gases coming out of the nozzle must increase, as well. Otherwise, the laser moves so quickly the gas just bounces off the material surface. High-speed nozzles stabilize the gas and force all of it through the kerf.
“This is why we are able to double the cutting speed compared to our regular nozzles,” Thompson adds. “It’s all about ejecting that molten material from the kerf.”
When cutting thin sheet, there is always a chance of collisions due to tip-ups. Collisions are obviously to be avoided, especially when using expensive high-power lasers. Most cutting heads, whether spring loaded or magnetically connected, are made to swing so that if there is a big enough collision to knock it sideways, the swinging action allows the cutting head to avoid damage.
As far as avoiding collisions, good programming is important. Trumpf also offers Smart Collision Prevention that chooses travel paths that go around potential tip-ups. It uses a work sequencing strategy that calculates in the tilting of parts that have been cut to effectively prevent collisions. This frees up the operator from monitoring the cutting.
Easy to use
Other ways fiber lasers free up operator time is low maintenance requirements. Today’s fiber lasers are available with fully enclosed cutting heads to protect the lenses from contamination. Ideally, the cutting head never requires service. Trumpf considers it a lifetime component.
“The most important thing is that there is no contamination inside of the cutting unit,” Thompson says. “There is a lot of energy running through that focusing lens and it is going to get hot. Contaminants could heat up the lens and cause damage. If the focusing lens were to absorb laser power, it would have an effect on cut quality. The cutting heads are designed to ensure the contamination isn’t an issue.”
The condition of the protective glass lens is monitored. If there is contamination on the protective glass and it needs cleaning or changing, it alerts the operator. There is no need for manual checking of the lens, and the machine is only idle for a short amount of time for the cleaning or changing.
Most laser cutting machines feature a nozzle changer that enables the nozzle to be changed automatically at the cutting head. Taking it further, Trumpf’s Smart Nozzle Automation feature additionally inspects the nozzle for wear and changes it as necessary.
“It’s looking for anything that can disturb the flow of gases or that could potentially cause offset issues, such as spatter buildup,” Thompson says.
“Overall, there is little interfacing with the operator,” he concludes. “We put a lot of effort into developing really good processing parameters. We also build for the market. We develop parameters for the laser source here in the United States rather than use what we developed in Germany. So, we’re building for U.S. materials, alloys, thicknesses, etc.”
The industry focus on higher power for lasers means there is an ongoing need for technologies that can allow the machine to keep pace. Laser equipment manufacturers like Trumpf will continue to respond with new, innovative solutions.