While fiber is all the rage in laser cutting, CO2 is still the workhorse of the fabrication industry. If the CO2 laser cutting machine isn’t maintained properly, however, the end result could be costly. The warning signs that indicate there’s a problem with a machine include bad parts, inconsistent part quality, irregular cuts, slower cutting speeds and burr creation. On thicker materials, the cut may not go all the way through, resulting in inconsistent parts not dropping out of the nest.
As with any industrial tool, adhering to a maintenance schedule can eliminate any production surprises in the form of unscheduled downtime. Good maintenance practices help reduce the overall cost of fabricated parts and reduce the need for expensive replacement parts and service time.
The laser cutting machine builder provides a recommended maintenance schedule, and every shop should follow these recommendations to ensure maximum performance. A maintenance schedule involves monitoring the internal laser optics, external optics and beam path; assist gas circuit; chiller operation; vacuum pump and laser gas circulator; drive axis lubrication; mechanical lubrication; dust collection maintenance and overall machine cleanliness.
Nested parts on 16-gauge mild steel. Unlike this sheet, indications there’s a problem with a machine include bad parts, irregular cuts and burr creation.
Typically, maintenance is a manually monitored task and is guided by the recommended maintenance schedule from the machine manufacturer. “The machines have timers and alarms built into the controls to serve as alerts or reminders, but it’s usually up to the end user to schedule maintenance accordingly,” says Tom Hejlik, laser technical support manager, Cincinnati Inc. “A history of faults and basic runtime information is also archived in the control. But as of yet, tracking and predicting problems have not been engineered.”
Most laser cutting machine manufacturers offer preventive maintenance contracts. With prescheduled maintenance appointments, the machine manufacturer’s service team can perform a comprehensive inspection to keep the laser optimally performing.
Optical components need to be checked regularly to determine if the laser cutter is operating as it should.
Optical issues
In CO2 laser cutting machine operation, the laser beam is created by the resonator, travels from the resonator through the beam delivery system (conducted by mirrors) to the machine cutting head where a lens focuses the beam and a nozzle directs the beam and the assist gas on to the material to be cut. A COâ‚‚ laser uses an assist gas to help cut the material. Oxygen, nitrogen and shop air are the most common assist gases. Which one is used depends on the application.
“The most important part of CO2 laser maintenance is maintaining the condition of the optical circuit and the alignment of the laser beam so it is exactly the same at all four corners of the table,” says Frank Arteaga, head of product marketing, Market Region NAFTA, Bystronic Inc. “Material parameters are stored digitally and should repeat each time. The variable is mostly in the condition of the optics followed by the consistency of the material itself. The lens is by far the optic that is the most critical in the day-to-day operation of the laser.”
Bystronic’s BySprint Pro CO2 laser cutting machine.
As one would assume, some maintenance tasks must happen with greater frequency than others. Daily maintenance is typically associated with the cutting head. “Visually checking the condition of the cutting lens, and cleaning it, if necessary, should be done daily,” Arteaga adds. “The lens should be replaced after 500 to 1,000 hours, depending on power level usage.”
Checking the nozzle and its alignment to the laser beam should also be done daily. Running the equipment with the nozzle misaligned results in a poor-quality cut, and nozzle damage is possible.
Weekly maintenance typically involves checking laser beam alignment and overall mechanical functions of the shuttle tables and guides. Also the beam delivery bellows, which provide a clean dry atmosphere for the beam to be delivered, should be checked for tears or rips. A good dust collector should be used with a CO2 laser cutter, and dust collector filters and bins should be checked weekly and emptied when necessary.
Other optical components need to be checked as well to determine if the laser cutter is operating as it should, although not necessarily on a weekly or monthly basis.
An overall optics check should be conducted every 2,000 hours. Power level checks can determine the condition of the internal optics.
“The output coupler mirror is most susceptible to fatigue and should be replaced every 1,500 to 2,000 hours, depending on power levels being used while cutting,” Arteaga says. “External optic mirrors need to be kept clean and in alignment so that the laser beam is centered at all four corners of the cutting table.”
The beam profile (mode) needs to be checked to make sure that the beam is round and the energy is evenly distributed within the raw beam diameter, he adds. Not having a round beam or one where the energy is not evenly distributed can affect the cutting quality on different sides of a cut part as the energy intensity is not the same on all sides of the beam.
Bystronic’s ByLaser 4400 W CO2 laser source.
Gas flow
Assist gas delivery equipment must meet purity, pressure and flow requirements to ensure the best results. Therefore, the laser gases must be high purity, contamination-free and there must be no leaks in the system.
If compressed shop air is used for the assist gas, it’s critical that it is filtered and dry and has a high enough PSI to sustain good assist gas flow. “This sometimes involves purchasing a unit for this specific purpose versus ‘tapping into’ the shop air, which may run at too low of a pressure,” says Hejlik.
Ensuring the gas delivery system is free of contaminates and leaks is accomplished at installation or any time during routine maintenance where a problem may be detected.
“Two systems have to be checked, the positive pressure (supply lines) and negative pressure (vacuum chamber),” Hejlik notes. “This is done by pulling the vacuum to a very low value and checking how much it leaks back up in a certain time frame. While this is done, the positive pressure is shut off and the tank pressure is monitored. To ensure proper pressure, a calibrated vacuum gauge that is at least 10 times more accurate than the pressure transducer that system being tested is using, is set at a T into the system and compared to the indicated pressure.”
Other factors
As for chiller performance in CO2 laser cutting machines, “they are designed with a specific heat load, pressure and flow rates and perform quite well and with very few problems,” Hejlik says. “This is true as long as the filters are regularly cleaned, the inline filters are replaced at the correct maintenance interval and the correct fluid concentration is controlled. If the correct mixture is maintained, yearly flushing of the system typically can be skipped and only flushed when problems arise.”
Other more complex chiller systems require more frequent change of the water and filters. The task also includes adding chemicals to the chiller circuit each time.
One of the most obvious yet overlooked areas of laser machine maintenance is keeping the equipment clean. Processing areas, support slats, scrap drawers and pallet ways are all areas where buildup of debris, dust and grease can affect the machine’s performance. “Cleaning is typically performed only when maintenance is performed,” Hejlik says. “We strongly suggest cleaning the machine any time it is idle.”
Overall, the maintenance team needs to ensure the production environment is suitable for laser cutting. If the laser machine is located in an area with high concentrations of moisture, oil or dirt, maintenance may have to be performed more frequently to keep the laser performing efficiently.
Each individual fabrication shop must find the best solution to properly manage maintenance on their machine. But they will quickly learn that performing regular maintenance results in a more consistent, reliable and cost-effective operation. In the long run, proper maintenance also extends the life of the laser cutting machine – perhaps the greatest benefit of machine upkeep.
