A laser marking service is the cheapest way to give a machined part an identity that outlives the product. Unlike a label, an ink stamp or an etched tag, a laser mark is part of the material itself — it survives solvents, autoclaving, abrasion and heat, and it can carry variable data so that every single part leaves the cell with its own serial number.
Yet most drawings treat marking as an afterthought: a note in the title block that says "mark part number here" with no method, no depth, no contrast requirement and no verification standard. That is how marking becomes a rejection reason rather than a traceability asset. This guide covers the four marking methods, which laser source suits which material, the numbers you should put on the drawing, and the compliance frameworks that drive most marking requirements in the first place.
The four marking methods
| Method | What the laser does | Typical depth | Best for | Changes part dimensions? |
|---|---|---|---|---|
| Annealing | Heats the surface to grow an oxide layer | 0.001–0.01 mm | Stainless, titanium — dark contrast, no material removal | No |
| Ablation | Removes a coating or anodized layer to expose base metal | Coating thickness only | Anodized aluminium, painted or plated parts | No (removes coating only) |
| Engraving | Vaporises material to create a recess | 0.01–0.5 mm | Deep, wear-resistant marks on aluminium, steel, hard metals | Yes — creates a recess |
| Temper / colour marking | Controlled heating produces interference colours | Negligible | Stainless decorative marks, titanium | No |
Choosing between them is a functional decision, not a cosmetic one. An annealing mark on stainless adds no material and removes none, which is why it is the standard for surgical instruments and food-contact surfaces — there is no crevice to harbour contamination. An engraved mark is the only one that survives aggressive abrasion, but it creates a recess that can act as a stress riser or a corrosion initiation site if placed carelessly.
Laser source: fiber, CO2 or UV
| Source | Wavelength | Works on | Notes for metal marking |
|---|---|---|---|
| Fiber | ~1,064 nm | Stainless, aluminium, titanium, brass, copper, plated metals | The default for metals; high absorption, fast, fine detail |
| CO2 | ~10,600 nm | Organics, anodized coatings,some plastics | Used on metals mainly to ablate coatings or through a marking compound |
| UV | ~355 nm | Plastics, glass, sensitive films | "Cold" marking; minimal heat-affected zone |
For metal parts, fiber is almost always the answer. Copper and brass are the hard cases — their high thermal conductivity and low absorption at 1,064 nm mean they need more power or a shorter wavelength, and sometimes a marking compound applied before marking and washed off afterwards.
Material-by-material behaviour
| Material | Recommended method | Result | Watch out for |
|---|---|---|---|
| Stainless 304 / 316 | Annealing | Dark grey to black, high contrast, corrosion resistance preserved | Too much power turns it brown or cuts the passivation layer |
| Aluminium, anodized | Ablation | White or base-metal mark against dyed anodize | Must be marked after anodizing; ablating through a Type III layer is slow |
| Aluminium, bare | Engraving | Light grey recess | Bare marks oxidise and lose contrast over time |
| Titanium | Annealing or temper | Black, or a controlled colour range | Temper colours are heat-dependent and hard to batch-match |
| Brass / copper | Engraving or marking compound | Light recess or dark fill | Highest thermal conductivity of common metals; needs parameter development |
| Steel, plated | Ablation | Exposes underlying layer | Ablating through zinc or nickel can expose a corrosion path |
| PEEK / ABS / polycarbonate | UV or fiber foaming | Light-on-dark or dark-on-light | Outgassing and melting; UV is safer for medical plastics |
The numbers to put on the drawing
Most marking disputes come from a drawing that specifies the text but not the mark. At minimum, state:
| Item | Typical spec | Why it matters |
|---|---|---|
| Marking method | Annealing / ablation / engraving | Determines whether material is removed |
| Minimum character height | 0.5–0.8 mm | Below ~0.5 mm legibility drops sharply after finishing |
| Mark depth (engraving) | 0.02–0.20 mm typical | Deep marks weaken thin walls |
| Code type and size | Data Matrix, 0.25–0.5 mm module | Sets the scanner resolution you will need on the line |
| Contrast requirement | Verified grade or visual standard | Visual "looks dark enough" is not measurable |
| Location and orientation | Datum-referenced | Marks placed by eye drift across batches |
| Inspection state | Before or after anodizing / coating / passivation | Coating can fill or obscure a shallow mark |
| Serialisation source | Supplier-generated sequence or your CSV | Avoids duplicate or skipped numbers |
For 2D codes, reference ISO/IEC 15415 for Data Matrix print quality, and ask for a grade (A/B/C/D/F) rather than a pass/fail. A grade B or better is normally achievable on a flat machined surface; anything below C should be treated as a process problem, not an acceptable variation.
Compliance frameworks that drive marking
Three programmes generate most of the marking requirements we see:
- Medical (UDI). Unique Device Identification marking on reusable instruments and implantable components must survive the full reprocessing cycle — autoclaving, chemical disinfection and abrasion — and remain machine-readable. That almost always means annealing on stainless or engraving on titanium, and it should be validated rather than assumed. Our ISO 13485 CNC machining guide explains the documentation side; medical device CNC machining covers the parts themselves.
- Automotive (IATF 16949). Traceability marks tie a part to a production batch, a heat lot and a process window. Marks are usually combined with a lot code and must remain readable through assembly and service life. See IATF 16949 for machining suppliers for how the documentation fits together.
- Aerospace and defence. Permanent part numbers, serialisation and UID/Data Matrix codes with a documented verification grade, often against AS9100-derived quality requirements.
Design rules that prevent rework
- Put the mark on a flat, unobstructed area. Laser systems have a limited depth of field — typically around 30 mm of focal variation — so heavily contoured surfaces need a fixture, and deep pockets may be unreachable.
- Keep the mark away from sealing faces, bearing bores and thread flanks. A recess on a gasket land is a leak path; a mark across a thread crest damages the fit.
- Keep marks at least 2 mm from a bend line or a weld. Marking into a heat-affected zone gives inconsistent contrast, and distortion can crack an engraved mark.
- Do not mark before surface treatment unless you intend to. Engraving before anodizing lets dye fill the mark and improve contrast on aluminium; marking after anodizing requires low-power ablation to avoid cutting through the layer. Decide which you want and say so.
- Supply artwork as vector, not raster. DXF, AI or PDF keeps small text and fine code modules sharp. A bitmap forces the operator to trace it.
- Define the serialisation format. Sequential, date-coded, or from a supplied CSV — and confirm whether the number must be unique across the whole programme or only within a batch.
- Mark after final inspection, not before. A part rejected after marking has already consumed its serial number.
The interaction with anodizing is the one most often missed. For audio and instrument panels, where the mark is part of the brand, the visual result depends on whether the mark is engraved before anodizing or ablated after — the same trade-off discussed in our brushed aluminum audio panel and anodizing aluminum guides.
Cost and lead time
Marking is a low-cost operation per part — dominated by setup, artwork preparation and fixture design rather than by the marking time itself, which is typically seconds per part. Variable data adds programming time but not per-piece cost. The things that raise the price are curved or hard-to-reach surfaces needing a fixture, codes requiring verified grading, and masking when marking must be combined with coating.
For programmes with serialisation, ask whether the supplier can supply the serial list back with the shipment. That record is what makes the mark useful in a recall or a field failure investigation.
Specifying marking on your next part
Laser marking is one of the few operations where a few extra words on the drawing remove an entire category of disputes. State the method, the size, the code type, the location relative to a datum, and whether marking happens before or after coating. Add a verification grade if the code must be machine-read.
Ruijin runs fiber laser marking in-house alongside CNC machining, sheet metal fabrication and anodizing, so a custom sheet metal fabrication panel or a machined precision fastener can be marked, finished and inspected without leaving the facility. Send your drawing to request a quote — most quotes go out within 24 hours — or see the surface treatment page for the full finishing envelope.