FIBER LASER VS. THIN DISK AND CO2

Since the acceptance of fiber lasers in 2008 there has been a substantial increase in the ability of fiber lasers to cut materials along with reliability of the laser. The evolutionary development that took 15 years for CO2 lasers took less than 3 years for fiber lasers, namely, the the ability to go from a 1 kW laser to a 4kW with reliability. In the larger kW lasers, power losses are expelled from the system via large amounts of heat creating the necessity for a chiller unit. Along with the increased reliability has come the decrease in operational cost due to different efficiencies in the various lasers.

At present there are primarily three different lasers being used to process metals in the fabrication industries. All three have different characteristics and efficiencies that translate into different operating costs.

The CO2 laser has a typical wavelength of 10.6 µm with approximately 8% efficiency. It consists of the chiller unit, power supply, and the resonator (oscillator). There are several variations on this high power laser with the fast axial and the transverse flow resonators. Both will require internal optic alignments/replacements/cleanings, rebuilds/cleanings, and oil/grease replacements. External optics alignment/cleaning/replacement is also needed.

There is also a Thin Disk (Yb:YAG) which has a typical wavelength of 940nm with approximately 28% efficiency. It also requires internal optics alignment/cleaning/replacement, as well as external optics alignment/cleaning/replacement.

There is the Fiber Laser (Yb-doped fiber) which has a typical wavelength of 1069nm with approximately 38% efficiency. The Fiber Laser only requires external optics alignment/cleaning/replacement; there are no internal optics to maintain.

The chart below illustrates the differences in just the electrical cost of the three lasers.

[Please note that all costs listed in this article reflect 2015 prices and should be adjusted for inflation. They are listed here for comparative purposes only.]

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As one can see there is a substantial savings on the operational cost of the fiber laser. One must also take into consideration the following items:

• Laser rebuild costs
• Laser reliability
• Laser beam stability
• Lasing gases
• Cutting gases
• Optics internal to the laser
• Internal optics alignment
• Optics external to the laser
• External optics alignment
• Focus lens length
• Spot size
• Beam quality
• Metallic materials processed
• Feed rates

LASER RESONATOR OPERATING COST COMPARISON

We can now focus on the cost involved in the generation of the cutting beam.

Fiber lasers as well as disc lasers do not require any lasing gases to generate the beam. CO2 lasers require Helium, Nitrogen, and Carbon dioxide as a minimum (some lasers require Carbon monoxide as well as other noble gases). CO2 lasers also require internal, external wear items, as well as a purge gas (usually Nitrogen) for the external beam guide. The following chart illustrates these added costs.

As can be seen, there are other costs associated with the CO2 laser that the solid state lasers do not have. Solid state lasers require a fiber cable to transmit the beam to the cutting head. This cable replaces the external mirror requirements and the need to purge the CO2 laser beam path with nitrogen to keep air-born particles out of the CO2 laser beam path. These air-born particles can have a drastic effect on the CO2 laser beam size and quality.

Internal wear items for the CO2 include bending mirrors, rear mirror, output coupler, and transmitter tubes. Missing are the costs associated with resonator cleanings, rebuilds, and complete resonator replacement. This can drive the cost of the CO2 laser to even higher values.

As demonstrated, it is necessary to evaluate the total and true costs of the various lasers when determining which laser has the best value for your dollar.

LASER COMPARISON – CUTTING SPEED AND RATE OF FEED

We can recap the above by looking at chart #1 below. It shows the operating cost over 8 years for a 4kW laser.

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We can also see by chart #2 the actual differences of energy consumption for solid state lasers.

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The differences in the operating cost are based on the maintenance and the efficiency of the style of laser being used. Chart #3 illustrates the different efficiencies for the various cutting lasers.

The final piece of the puzzle for laser processing is the cutting speed. Approximately 80% of the time while the program is running the laser is cutting, this is the majority of the processing time. The cutting capabilities of the laser is directly proportional to the beam quality and beam waste of the laser. Chart #4 illustrates the characteristics for the four cutting lasers.

Things to be aware of are the mode quality, beam waste, spot size, and depth of field. The depth of field generated by the laser will affect the cut quality and the thickness of the materials processed. The depth of field is the usable portion of the unfocused beam. This occurs on both sides if the beam waste (smallest spot size). As the focal position is shifted up and down to enhance cutting the operator must always keep the material within the depth of field or the material will stop cutting.

Finally we would like to share some comparative cutting charts to show the difference in feedrates for the CO2, Disk, and Fiber lasers.

STEEL (USING O2)

STEEL (USING N2)

STEEL (USING AIR)

STAINLESS STEEL (N2)

ALUMINUM (N2)

ALUMINUM (AIR)

COPPER (O2)

BRASS (N2)

As can be seen from the published feed rates, due to beam characteristics, the fiber laser has the best coupling of the three lasers illustrated by the actual feed rates. When looking at the highly reflective materials like copper and brass the CO2 laser cannot perform at all.

When taking all the ingredients necessary to process metal with a laser the fiber is the least expensive and most productive of the three lasers.