Depth control in laser engraving behaves nothing like a milling depth of cut
There is no tool to set. Depth accumulates from pass count and removal rate, and removal rate changes as the cavity deepens.
An engineer specifying a laser-engraved feature to a depth tolerance often expects the process to work like milling: set the depth, the tool removes to that depth, done. Laser engraving accumulates depth through repeated ablation passes, and the relationship between passes and depth is not linear.
Why removal rate falls with depth
As a cavity deepens, several effects reduce material removal per pass.
Ablated material must escape the cavity. In a deep, narrow feature, ejecta redeposit on the walls and floor, and some of the incoming energy is absorbed by the plume rather than by the workpiece.
Focus position shifts relative to the surface being ablated. Unless focus tracks depth, later passes work progressively further from best focus, spreading energy over a larger area.
Wall taper develops because the beam has a finite convergence angle and because the walls receive glancing energy.
What that means for control
Depth cannot be commanded. It is achieved by characterising removal per pass for the specific material and parameter set, then running the required pass count — and verifying.
Because removal per pass declines, the characterisation must cover the depth range of interest rather than being extrapolated from a shallow test.
Practical control methods
Focus tracking. Adjusting focus downward as passes accumulate maintains removal rate and reduces taper.
Pass strategy. Alternating hatch angle between passes produces a flatter floor than repeating the same direction.
Roughing and finishing. High removal parameters for depth, then low-energy passes for surface quality, mirrors machining practice even though the mechanism differs.
Measurement. Depth verification by optical profilometry during process development, and periodic checks in production.
Where tolerance is achievable
Shallow features hold tolerance well. Deep cavities accumulate variation, and specifying a tight depth tolerance on a deep engraved feature is asking for measurement and rework.
Designers who understand this generally specify depth loosely where function permits and tightly only where it matters, which is the same discipline that applies to any accumulating process.
This article was produced by the LasersNews AI desk and reviewed by our editors.
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