Laser Physics & CAM Prepress

Fiber Laser Vector Hatching, 2.5D Relief & Marking Guide

Master technical guide for preparing vector artwork for fiber laser engraving, galvo mirror scan optimization, MOPA pulse overlap, and multi-angle 2.5D coin die relief.

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1. How Galvo Fiber Lasers Process Vector Geometry

Unlike gantry CO2 lasers that physically move a heavy cutting head across rails, galvo fiber lasers (1064nm) use ultra-fast galvanometer mirrors rotating at speeds up to $10,000 ext{ mm/s}$.

To engrave a solid area (fill), the CAM software (EZCAD2, EZCAD3, LightBurn) takes the vector perimeter and mathematically computes a raster fill pattern known as Hatching.

The 3 Mathematical Conditions for Clean Hatch Fills

  1. 100% Closed Vector Boundaries: Any gap in a vector contour (even $0.01 ext{ mm}$) causes the hatch algorithm to fail or bleed hatch lines uncontrollably across the entire work envelope.
  2. Zero Self-Intersecting Polylines: Figure-8 crossing lines cause the even-odd winding rule to invert, turning filled solid areas into un-engraved cavities.
  3. Coincident Path Elimination: Double vector strokes cause the laser to dwell twice at identical coordinates, creating deep gouge marks along boundaries.

2. Physics of Pulse Overlap and Line Spacing

Pulsed fiber lasers (Q-switched or MOPA) emit discrete nanosecond pulses of laser energy. As the galvo mirror sweeps the beam across the workpiece at speed $v$, each laser pulse strikes the surface at a distance $p$ (pulse pitch):

Pulse Pitch p = Mark_Speed (mm/s) / (Frequency (kHz) * 1000) Pulse Overlap (%) = (1 - (p / Beam_Spot_Diameter)) * 100 Hatch Interval Overlap (%) = (1 - (Hatch_Line_Spacing / Beam_Spot_Diameter)) * 100

For deep 2.5D metal engraving (such as brass coin dies, firearm slides, or tool steel stamps), aim for a pulse overlap of 35% to 55% and a hatch line spacing matching the beam spot diameter ($approx 25 ext{ to }35 mu ext{m}$).

3. 2.5D Deep Engraving Multi-Pass Angle Rotation Schedule

When removing significant depth in metal ($>0.5 ext{ mm}$), engraving continuously at a single angle (e.g. 0°) creates micro-trenches (corduroy texture) and traps laser slag.

To achieve a mirror-flat cavity floor, rotate the hatch angle by $+45^circ$ or $+90^circ$ on every consecutive layer:

Pass Number Hatch Angle Hatch Type Function
Pass 1 Unidirectional or Bidirectional Primary bulk ablation
Pass 2 45° Cross-hatch angle Eliminate ridge formation
Pass 3 90° Perpendicular cross-hatch Even bottom leveling
Pass 4 135° Opposing diagonal Final layer flattening
Pass 5 (Clean) 0° (High speed / High kHz) Contour outline only Vaporize slag & edge burrs

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