How to mark blank metals
Without marking solutions, the CO2 laser source with a wavelength of 10.6 µm is basically not suitable for marking metals. Blank metals can be marked with a CO2 laser engraver only if you use a laser marking solution. The metal marking solution must be applied to the workpiece prior to processing with a laser machine. The parameters “power” and “speed” play an important role when working with the CO2 laser source. The z-offset, selected resolution and lens also have a significant influence on the results.
The perfect tool for metal marking in terms of productivity and quality is the fiber laser. Fiber lasers are available in the form of laser plotters in the Speedy series as well as in the form of galvo lasers in the SpeedMarker series. Deciding whether a laser plotter or a galvo laser is more suitable depends on what the laser machine is being used for.
In the following training, we will concentrate on the laser plotter Speedy series and give you a step-by-step guide, how to find your desired parameters. When using fiber laser, additional focus must also be placed on the selected frequency, besides the power, speed and Z offset. The higher resolution, between 500 and 1000 dpi, also plays an important role in achieving good results with fiber laser source because of the small beam diameter of approximately 25 µ.
We used a graphic comprised of 16 quadrants and corresponding to the 16 process colors for the parameters determination. To find out the correct frequency, set the speed v and power P for all 16 colors to the same value. Set the resolution between 500 and 1000 dpi in the printer driver settings of JobControl®. Use "Color" as the grid, since only with this process can the individual colors be assigned to the parameters.
Machine example: 20 watts FLP; 2.85" lens; P: 100 % ; v: 5.5 %
Now, select a frequency value for each color. Start with the lowest frequency possible of 20,000 Hz for black and then increase the value by 5,000 Hz for each successive color. Adjust the Z offset to the desired result as well. An offset of 0.5 mm to 2 mm can result in a more homogeneous color change.
Tip:
The start frequency always depends on the laser power, since the lowest possible pulsation must match the power: In other words, in order to achieve the nominal power, for example 20 watts, of the laser source, the frequency must be above 20 kHz.
Below this nominal frequency, the number of pulses is not sufficient to reach the maximum average power. Any value below this Hz level throttles the power.
Before processing blank metals with a CO2 laser, a marking solution has to be applied.
Determining the parameter for the CO2 laser source can be done simply using the grayscale matrix. If no parameters are available, you can easily download tested parameters for the metal marking solution 'MarkSolid' them.
The matrix is sent to the laser with the laser process “Relief” and a resolution of 600 dpi. After cleaning, a parameter can be read directly from the material. For more information about the application of the grayscale matrix, please follow these instructions.
| CO2 with prior application of marking solution (eg MarkSolid) | Marking with fiber laser by annealing |
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Other production processes are possible using the fiber laser. Depending on the parameter and frequency, a metal can be marked white or deep engraved with another parameter.
White marking is an abrasive procedure that only changes the uppermost layer of the material and thus gives the surface a white shine. This process can also be used to clean up another processing options, such as a deep engraving. This procedure is engraved at high speed and low power. We recommend a frequency between 25,000 and 50,000 Hz.
To engrave metal, a high power and low speed is selected. We selected a low frequency for the engraving to exploit the high pulsing peaks.