Four tips for creating readable laser marks

As experienced users know, it pays to take care of the basics when setting up a scanning system. These four detailed tips will help correctly set-up, adjust and test laser marking settings.

1. Align the input beam perfectly into the scan head

The best results are achieved when the input beam is perfectly aligned into the scan head without it contacting non-transmissive surfaces. The input beam should be expanded and collimated so that the energy fills the mirrors without overspill.

For example, if using a 10 mm scan head, the input beam diameter should be just under 10 mm. Using a larger input beam diameter results in the beam contacting the housing, causing interference and compounding the focus at the target.

Additionally, the angle of beam entry is also key for best results. Typically, the beam should be perpendicular to the scan input plate. Beam angle misalignment can lead to field skew and mark distortions.

2. Pay strict attention to parallelism between the scan head and the target

Be aware that the wider the angle scanned to the field extremities, the more the spot will change from a perfect circle into an ellipse. If you use focusing lenses after the mirrors, more diffraction will be introduced.

The parallelism and flatness of the marking surface in relation to the scan head output plate is also critical. Tip/tilt of the mark surface will lead to unfocused marks throughout the field.

3. Find the best laser and marking parameters before marking

First, ensure any pointer laser is aligned to the main processing beam. Mark 5 points (center and corners), and position the pointer to the same points, adjusting until it falls perfectly on the marks.

Mark a series of 10 close parallel lines across roughly half the field size. At this point, do not worry about the starts and ends of the lines. The first goal is to find the best laser and marking speed settings for the adsorption of the energy by the target material.

Set Line 1 at the minimum and Line 10 at the maximum Mark speed best suited for the marking material. Set Lines 2 through 9 in incremental Mark speed steps between the minimum and the maximum. This gives an indication of the best results, but it may be slower or faster than expected; adjust the speed range and mark again. When you have a good result, reduce the range to finetune the Mark speed.

Set the best Mark speed to all lines. Set a range of incremental laser frequencies between the minimum and the maximum that is best suited for the marking material and mark again. Because various types of materials may absorb differently at differing frequencies, you may see further improvements. 

Once the best parameters have been determined, set all lines the same and repeat the incremental Mark speed variations on either side of the setting for the frequency optimization. Repeat these two steps until best results are achieved.

4. Use a step-by-step approach to optimize delays

Rather than changing several parameters at the same time, optimize each one by using a step-by-step approach. Depending on your laser software program, you may be able to download a delays.plt file; if so, place it in your marker/graphics/vector folder. Open a new job and import the delays graphic. Four simple lines will be marked, joined by double-jump.

Most delays.plt files are in their simplest forms and will mark over 80% of the field, starting with the index lines A-B-C. The scanners will then double-jump without marking via C-D-E, before marking the calibration lines E-F-G.

  1. Set the Jump speed the same as the Mark speed, the Laser On
  2. Set Jump and Mark delays relatively long (1600 µs)
  3. Set Poly and Laser Off delays relatively short (80 µs)
  4. Mark and check Point E (See diagram)

A tail in the direction D-E leading into the marked line E-F should mark.

If the tail is around 2 mm, reducing the Laser On delay to 400 µs will roughly halve it to 1 mm (speed and laser dependent). Continue reducing the Laser On delay until Point E starts the mark perfectly in the middle of the A-B index line.

Now increase the Jump speed until Point E starts to lose position. Reduce the Jump speed slightly until Point E is clear again.

Now reduce the Jump delay to 800 µs. If there is no difference, halve it again. Keep reducing the Jump delay until Point E starts to lose position, then slightly increase the Jump delay until Point E starts the mark perfectly in the middle of the A-B index line.

Minimize the process timings because a Jump is a reposition of the mirrors. The faster the Jump speed, the longer the Jump delay to allow the mirrors to settle. To gain faster overall process times, reduce the Jump speed to reduce the Jump delay.

Concentrate on Point F where the 2 vectors E-F and F-G meet. If Point F over-burns, reduce the Poly delay. If Point F is rounded, increase the Poly delay until a crisp result is achieved.

Finally, check Point G where the vectors end. Increase the Laser Off delay until Point G ends the mark perfectly in the middle of the B-C index line. Reduce the Mark delay until the mark moves away or over-burns, then reduce slightly until it marks perfectly in the middle of the B-C index line again.

Set the optimum parameters for the marking material. Be sure to save these parameters by adding them to a profile and naming it.

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