The entire surface of the drum is alternately engraved by a continuous spiral mesh cavity track. When the drum speed reaches 20 rpm, the processing head moves at a traverse feed of 15-150 microns / revolution, parallel to the axis of the drum (depending on the screen resolution). The thickness of the mesh wall between the cells is only 4-6 microns at the maximum tone value. This requires the laser Engraver beam to reach the aiming accuracy of about 1 micron.
Another method is to use a pulse-modulated high-power fiber laser (average power of 500 watts), whose pulse repetition frequency can be modulated in the range of 30-100 kHz. When the frequency is 35 kHz, there is more energy on each pulse, so that a single shot can drill a large hole (such as a diameter of 140 microns when the screen is 70 lines / cm). When the frequency is 100 kHz, the energy on each pulse becomes less, so a small mesh is carved (for example, a screen with a diameter of 25 microns is 400 lines / cm).
Laser Engraver's beam operation is non-contact, which is a key advantage compared to electromechanical engraving using diamond pens. As long as the printing process is predictable and repeatable, the engraving uniformity can be guaranteed over the entire width of the cylinder. Because of the high repeatability, the single-shot single-hole laser process is about 10 times faster than electromechanical engraving.
There are many different substrate materials on the printing market (such as paper or flexible foil), each with different surface characteristics. The optimization method of ink transfer depends on: substrate surface (such as roughness, ink absorption capacity), ink parameters (such as pigment viscosity or model), and printing plate. For each different situation, different shapes of sculpted mesh cavities can be used to achieve the best.
In addition to heat conduction and convection, the cells accurately represent the focal intensity waveform of the laser beam. In order to make each cell reach a specific shape, the three-dimensional intensity waveform of the beam is actively formed in real time, and the frequency controlled by the image data is up to 100 kHz. The overall scheme of this stereo modulation technology.