Laser Engraving
Key Takeaways
- Engraving removes material, going deeper than etching and far deeper than surface marking.
- CO2 at 10.6 µm is the workhorse for polymers, which absorb infrared strongly.
- Short pulses reduce heat diffusion, producing cleaner edges and finer detail.
- Wavelength selection is material-specific, and getting it wrong causes damage rather than depth.
Laser Engraving
Laser engraving removes material to create a recess of measurable depth, as distinct from marking, which changes surface colour without removing material. On plastics the beam raises the polymer past its vaporisation threshold and the material leaves as vapour and ejected particulate, cutting a cavity typically in the 0.05–0.5 mm range depending on passes and settings.
Depth is what defines the process, and depth is also what makes it slower, more thermally aggressive and more demanding of extraction than surface marking.
Engraving, Etching and Marking Compared
| Process | Depth | Mechanism | Typical use on plastics |
|---|---|---|---|
| Marking | None — surface effect only | Colour change: carbonization, foaming, bleaching | Codes, logos, traceability data |
| Etching | Very shallow, typically under 0.025 mm | Surface melting and slight removal | Texture change, matte or frosted appearance |
| Engraving | 0.05–0.5 mm and beyond | Vaporisation and material removal | Tactile marks, mould tooling, wear-resistant ID |
Achieving Depth Without Damage
Depth on polymers comes from repeated passes rather than raw power. Driving a single pass harder deposits heat faster than it can dissipate, and the result is melting, discolouration, internal stress and a rolled lip of resolidified material at the cavity edge. Multiple lighter passes with adequate cooling between them give a cleaner wall and better dimensional control.
Points that determine success:
- Melt re-deposition. Unlike metals, thermoplastics melt before they vaporise. Displaced material can resolidify at the rim as a raised burr, which may need to be designed around or removed.
- Heat-affected zone. Cumulative heat causes haze, crazing and residual stress around the cavity — a durability concern in load-bearing or environmentally stressed parts.
- Hatch strategy. Cross-hatching between passes and rotating the hatch angle produces a flatter floor than repeatedly scanning the same vector direction.
- Fill and filler behaviour. In glass-filled resins the polymer vaporises but the glass does not, leaving exposed fibres at the surface — addressed in solving glass fibre emergence.
Safety and Emissions
Engraving generates far more decomposition product than surface marking, and polymer chemistry determines how hazardous that is. PVC must not be laser processed — it evolves hydrogen chloride, which is corrosive to the operator, the optics and the machine frame. Fluoropolymers such as PTFE release hazardous decomposition products on thermal breakdown. Even benign polymers produce particulate and organic vapour in quantity.
Adequate local exhaust ventilation with appropriate filtration is a requirement rather than an option, alongside the beam-hazard controls expected of a Class 4 installation under ANSI Z136.1 and the oversight of a designated Laser Safety Officer.
When Engraving Is the Right Choice
Specify engraving where the mark must survive abrasion, chemical exposure or long service life; where a tactile or Braille feature is required; where mould and tooling cavities are being produced so that the feature appears on every moulded part; or where depth itself is functional. Where the requirement is simply a permanent, readable, high-contrast code, surface marking is faster, gentler on the material and usually the better engineering answer.
Parameter Strategy for Depth
Depth on polymers is built up, not driven in. The parameters interact, and the order in
which they are adjusted matters more than the values themselves:
| Parameter | Effect on depth | Effect on quality | Adjust |
|---|---|---|---|
| Number of passes | Roughly linear increase | Improves wall quality if the part is allowed to cool between passes | First — the safest route to depth |
| Marking speed | Slower cuts deeper per pass | Too slow concentrates heat and melts the cavity edge | Second |
| Average power | Strong increase | Degrades quickly — melt rim, haze, internal stress | Last |
| Hatch angle between passes | Neutral | Rotating the angle each pass gives a markedly flatter floor | Set once, as strategy |
| Hatch spacing | Minor | Too tight double-heats; too wide leaves ridges in the floor | Set with spot size |
| Focus offset per pass | Maintains removal rate as the cavity deepens | Without it, later passes defocus and stop cutting cleanly | Needed beyond roughly 0.2 mm |
| Cooling delay between passes | None directly | The single most effective quality lever on thermally sensitive resin | Add before adding power |
Troubleshooting Engraved Features
| Symptom | Likely cause | Correction |
|---|---|---|
| Raised lip around the cavity | Melt displaced rather than vaporised, resolidifying at the rim | Lighter passes with cooling between them. Design the lip out with a chamfer, or plan a deburring step. |
| Cavity floor uneven or ridged | Hatch strategy repeating the same vector direction | Rotate the hatch angle between passes, typically by 45° or 90°. |
| Depth stops increasing with more passes | Focus no longer at the cutting surface as the cavity deepens | Apply a focus offset per pass beyond roughly 0.2 mm of depth. |
| Haze or crazing around the feature | Cumulative heat-affected zone | Increase the cooling delay between passes. On polycarbonate and acrylic, check again after 24 hours — crazing can appear late. |
| Exposed glass fibres in the floor | Polymer vaporises below the glass transition of the filler | Expected in filled grades. Reduce energy per pass, or reconsider whether engraving is the right process for this material. |
| Sooty black residue in and around the cavity | Inadequate extraction; decomposition products redepositing | Improve local exhaust at the work point. Residue also fouls the optics and will degrade every subsequent part. |
| Part distorted or warped after engraving | Heat input relieving moulded-in stress asymmetrically | Anneal before engraving, reduce energy per pass, or move the feature away from thin sections. |
Specifying an Engraved Feature
Engraving removes structural material, which makes it a design decision rather than
purely a marking one. A drawing that calls for an engraved feature should carry:
- Depth with a tolerance, not a nominal figure. Depth varies with resin
lot, colour and moulding conditions, so an untoleranced call-out cannot be inspected. - Remaining wall thickness at the engraved location, stated as a
minimum. This is the number that matters for structural integrity, and it is the one most
often omitted. - Position relative to stress features. Keep engraving away from gates,
weld lines, ribs and radii where residual stress concentrates — a cavity there
becomes a crack initiation site in service. - An edge-condition requirement, since some melt lip is normal on
thermoplastics. Either permit it with a stated maximum or specify a secondary operation. - The measurement method. Stylus profilometry, confocal microscopy or a
sectioned sample all give different answers on a cavity with a rounded floor; naming the
method is what makes the tolerance meaningful.
Where the requirement is only a permanent readable code, revisit whether depth is needed
at all. Surface marking is faster, removes no material and introduces none of these
constraints.
Related Terms and Reading
- Plastics laser marking solutions
- Laser etching
- Troubleshooting laser engraving problems on plastics
- How to mark plastic with a laser
Applying this in production
The Sabreen Group provides independent engineering support for laser engraving process development, depth control and emissions handling. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.
Frequently Asked Questions
What is laser engraving?
A high-resolution material removal process using a focused beam to ablate the surface, creating permanent deep markings or patterns. Unlike etching and marking, engraving physically removes material to form a recessed feature.
How deep does laser engraving go?
Deeper than etching, which affects only the upper few microns, and far deeper than marking, which may involve no material removal at all. Actual depth is controlled by power, pulse duration and frequency, scanning speed and the number of passes.
Which laser wavelength suits polymer engraving?
CO2 lasers at 10.6 µm are the most widely used for polymers and organic materials because of strong infrared absorption, enabling direct engraving with minimal thermal damage to surrounding areas.
What parameters control engraving quality?
Laser power sets the material removal rate but risks thermal damage if uncontrolled. Pulse duration and frequency affect heat diffusion, with shorter pulses giving cleaner edges and finer detail. Scanning speed and focus complete the set.
What problems should be watched for?
Material-specific absorption means the wrong wavelength engraves poorly or damages the part. Excessive heat causes melting, discolouration or micro-cracking. And fume extraction is necessary, since ablation generates byproducts that also foul the optics.
How should depth be increased without damaging the part?
By adding passes, not power. Multiple lighter passes with a cooling delay between them give a cleaner wall, better dimensional control and far less residual stress than one aggressive pass. Beyond roughly 0.2 mm, apply a focus offset per pass or the beam defocuses as the cavity deepens and depth stops increasing.
What should an engraving call-out on a drawing include?
Depth with a tolerance, the minimum remaining wall thickness at that location, the position relative to gates and weld lines, an allowable edge condition since some melt lip is normal on thermoplastics, and the measurement method. Remaining wall thickness is the number most often omitted and the one that governs whether the feature is structurally acceptable.
Why does the cavity floor come out ridged?
Because successive passes are scanning the same vector direction. Rotating the hatch angle between passes, typically by 45 or 90 degrees, produces a markedly flatter floor. Hatch spacing matters too — too wide leaves ridges, too tight double-heats the surface and brings haze with it.
