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.
When the mark is a regulatory identifier rather than a brand mark, the placement, sizing and grading rules change, and we set those out in our UDI direct part marking guide.
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.
Laser marking solutions for metal parts
Almost every laser marking for metal parts job falls into one of three categories, and each one points at a different parameter set. Identity — part number, brand mark, logo — wants contrast and cosmetics. Traceability — serial, heat lot, Data Matrix — wants verified machine readability after every downstream process. Instruction — assembly orientation, torque values, calibration scales — wants durability. Specifying all three the same way is the most common reason a mark looks perfect on the bench and fails in the field.
CNC marking steel: plate, mild steel and stainless
CNC marking steel splits cleanly by alloy. On mild steel, fiber laser annealing produces a dark oxide mark with no material removal, which is what you want when the part needs corrosion resistance afterwards — but bare mild steel will rust through an annealed mark in a humid container, which is why we recommend marking after coating rather than before on carbon steel plate. Marking steel plates thicker than about 6 mm usually means the part is structural, and the binding constraint stops being mark quality and becomes fixturing repeatability and datum access.
Stainless is the forgiving case: annealing forms a chromium-rich oxide that is both dark and corrosion-resistant, so a single anneal step usually satisfies UDI and traceability requirements with no post-treatment. Markings on mild steel and on plated steel are the ones that need the inspection state — before or after coating — written onto the drawing, exactly as it is written for dimensional tolerances. The alloy selection logic behind this is the same reasoning covered in our stainless steel CNC machining guide.
Laser traceability service for machined parts
A mark only becomes traceability once it is tied to a record. Our laser traceability service for machined parts generates the serial or Data Matrix sequence during the marking operation, verifies it to an ISO/IEC 15415 grade on the line, and returns the serial list with the shipment — so a recall or a field-failure investigation can be run against heat lots, process windows and inspection results rather than against guesswork. When the part goes into an IATF 16949 or ISO 13485 programme, ask for that list at RFQ stage; retrofitting serialisation data after a programme launches is considerably more painful than specifying it at the start.
Coding and Marking on Coated Metal
Coding and marking on coated metal is the one marking job where the constraint is not legibility but corrosion. A mark on bare metal is a surface change; a mark through a coating is a breach in the corrosion barrier, and on a part that will see salt, humidity or a sterilisation cycle, that breach is where failure starts. The decision therefore reduces to choosing where in the finishing sequence the mark goes, and that has to be written on the drawing.
There are three workable routes. Mark before coating keeps the coating intact over the mark: the code sits underneath the film, corrosion protection is unaffected, and the mark is permanent in the sense that it cannot be removed without removing the coating. The limit is film thickness — a powder coat of 60–100 µm will soften or close up a shallow mark, so this route needs the mark deep enough to survive the film and the coating spec thin enough to keep it readable. Mark after coating gives the highest contrast, because the laser ablates the coating and exposes bare metal underneath, but it deliberately removes protection in the marked area and usually needs a sealer or a sacrificial-zone callout on the drawing. Mask and coat around the mark is the third option where the code area is taped or plugged before coating, leaving a bare window that is then marked.
Anodized aluminium behaves differently again, because the coating is an oxide grown from the substrate rather than a film laid on top: marking after anodizing ablates the dye and gives a light mark on a dark background, while marking before anodizing leaves a dark mark sealed under the oxide. That is why our anodizing guide treats mark timing as a process parameter rather than a finishing detail. For painted or powder-coated carbon steel, the practical rule is to specify the coating thickness, the method and whether the marked area is allowed to be bare — and if it is not, to specify the verification, typically a salt-spray hours figure on a marked sample. Ruijin runs fiber laser marking in-house alongside machining and coating, so all three routes can be quoted side by side on the same part; see the surface treatment page for the full finishing envelope.
Metal Part Marking After Machining: What Changes With Material
The fiber laser settings that produce a crisp dark code on one alloy will barely register on the next, and this is where most laser marking of metal parts actually goes wrong. The variable is not the machine — it is how each alloy's surface chemistry responds to heat. Choosing a laser marking service on parts therefore means choosing the interaction mode for each metal, not simply setting a power number.
Steel is the easiest family to reason about because one mechanism covers most of it. For CNC marking steel in the mild, carbon and low-alloy ranges, both ablation and annealing give a readable mark, and annealing is usually preferred: the black magnetite film develops within the top few micrometres with no measurable material removal, which matters when the marked area doubles as a sealing face or a bearing journal. The trap in marking steel parts is heat input. The beam heats a localized spot, and on a component hardened to 45 HRC or above that heat can draw back the temper locally. For hardened work we either run the anneal at conservatively low fluence or move to a cold process entirely.
Stainless needs its own parameter set. The anneal route grows a chromium oxide film whose apparent colour depends on film thickness, which is why a single stainless coupon can be walked from straw through blue to black purely by changing scan speed and fluence — and why a black stainless mark drifts if the incoming surface finish moves between batches. Laser DMC marking on stainless steel destined for UDI codes or internal routing is normally run as an anneal for exactly this reason: ablation would cut through the passive layer and undo the corrosion resistance the grade was specified for.
Marking steel plates and markings on mild steel share one practical requirement. Plate generally arrives with mill scale, and mill scale is optically and thermally inconsistent — it absorbs unpredictably and spalls under ablation. Shot-blast or machine the pad before you mark it. A flat pad the size of a coin costs minutes to prepare and is the cheapest insurance available against a failed first-article inspection.
Cast surfaces are the least forgiving category, and both cast steel part marking and industrial cast iron part marking fail for the same reasons. Foundry skin, fluctuating silicon and graphite content, and subsurface porosity scatter the beam and break up the thermal coupling, so contrast drops and edge definition suffers where the identical artwork reads cleanly on wrought material. Our standard answer is to machine or blast a flat pad first, then anneal-mark it; where that is not possible we quote dot peen instead, which tolerates the surface variation because it displaces metal rather than heating it.
Marking on stamped sheet metal brings a different constraint: the part is thin, so ablation depth is limited by what the section can lose, and the tooling usually leaves the mark area curved or drawn. Annealing at low fluence keeps the part full-thickness.
Castings follow their own rules: our cast part identification marking guide covers where the code goes and how deep it has to be on iron and steel.
Sequencing relative to heat treatment matters as much as material choice. Metal marking after heat treatment is almost always the better route: black oxide, nitriding, plating and anodizing are all applied once the metallurgy is final, and a mark laid down underneath a finish inherits every defect in that finish. If the mark genuinely has to precede finishing, specify it explicitly and require the finisher to mask the marked area — and remember that some conversion coatings change the mark's contrast enough to fail grade verification.
Turned work has its own geometry problem. Laser marking of screw-machined parts usually means the logo or code lands on a cylindrical surface, and on a curved surface only the strip near the top of the tangent stays in focus. Keep marked text below roughly 25% of the part circumference, or step the rotary axis so the focal distance tracks the surface.
Where the part is permanent and the regulation is strict, aerospace steel marking adds two constraints that override everything else: no process may create a stress riser that could initiate cracking, so aggressive stylus stamping and deep engraving on thin walls are usually prohibited; and the mark has to remain legible for the service life of the part. Aerospace programs commonly reference MIL-STD-130 for item identification content and SAE AS478 for the marking method itself, and both are worth citing directly on the drawing so there is no ambiguity later.
Two situations come up often enough to plan for. Marking non-removable parts — welded assemblies, press-fitted shafts, riveted structures — usually cannot be brought to a bench laser, so the choice sits between a portable unit and a pre-applied solution, and deciding this before assembly rather than after saves considerable rework. The same logic applies to laser serial number marking on metal and to on-site part marking: if the serial population is generated at goods-in rather than at final assembly, say so on the drawing, because it changes how the variable data will be created and verified. Taken together these are the practical laser marking solutions for metal component marking that a buyer can put on a drawing without sending it back to their own engineers for a second round.
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.
How to Mark a Metal Part: Step by Step
Marking a metal part is a five-step decision, and taking the steps in this order prevents most of the rework that lands on marking jobs: choose the method, choose the contrast mechanism, fix the location against a datum, specify the code content and its verification grade, then decide whether the mark goes on before or after finishing.
Method first. Stainless steel, titanium and plated steels are normally marked by fiber laser annealing or ablation because both survive corrosion and cleaning. Aluminium that is going to be anodized is either marked before anodizing, so the mark ends up sealed beneath the oxide layer, or ablated after anodizing to expose bare metal through the coating. Bare mild steel marks easily but has no corrosion reserve of its own, so the method choice is really a question of what finish follows it.
Datum third. A mark with no stated position is unmeasurable, which is exactly what turns a marking dispute into a scrap dispute. Give a dimension from a functional datum to the mark boundary, state the orientation, and state the keep-out area around any hole, seal face or bend line. A mark placed 2 mm from a bend will distort; a mark placed across a sealing face will leak.
Code content and grade fourth. State the symbology, the module size or x-dimension, and the verification grade you want — ISO/IEC 15415 for 2D codes such as Data Matrix and QR, ISO/IEC 15416 for linear barcodes. Machine readability is a graded property, not a yes/no one, so “scannable” on a drawing is not a specification.
Sequence last. Write on the drawing whether the mark happens before or after coating, plating, anodizing or passivation. This single line removes the most common cause of a marking job being redone, because a mark applied before a coating can be buried by it and a mark applied after one may breach a corrosion barrier that the coating was specified to provide.
Marking Steel Parts and Mild Steel
Mild steel and other low-carbon steels absorb 1064 nm fiber laser energy readily, so they darken quickly with modest power and short cycle times. That makes laser marking on steel parts one of the cheapest permanent marks available — but the mark itself does nothing for corrosion. If an unplated, unpainted mild steel part is going into a humid or outdoor environment, specify passivation, oiling or a coating after marking, or the darkened zone becomes the first place rust starts.
Stainless steel behaves differently. Laser annealing grows a thin oxide on the surface without removing material, so the passive layer stays intact and the mark is corrosion-resistant — which is why annealing is the default for medical, food-contact and marine stainless parts. Where a deeper, tactile mark is needed, ablation removes a controlled depth of material; check that depth against the minimum wall thickness and, on case-hardened or nitrided steel, against the case depth, because cutting through the case defeats its purpose.
FAQ
How to mark a metal part?
Pick the method for the material and the environment, then fix the location against a functional datum, specify the code symbology and verification grade, and state whether the mark goes on before or after finishing. For stainless and titanium that usually means fiber laser annealing; for anodized aluminium it means marking before the anodic layer or ablating through it afterwards; for bare mild steel it means marking and then protecting the surface, because the mark adds no corrosion resistance of its own.
What are the permanent part marking methods?
Four are in regular industrial use: laser marking (annealing, ablation or engraving), dot peen marking, electrochemical or chemical etching, and ink-based printing such as inkjet or pad printing. Laser and dot peen are the two that survive abrasion, solvents and heat without consumables; etching is permanent but needs masking and chemical handling; printing is fast and cheap but is not permanent unless it is subsequently covered by a coating.
Is laser marking suitable for metal parts?
Yes — laser marking is the most widely used permanent method for metal parts because it needs no consumables, no tooling contact and no post-marking cleaning, and it holds up under abrasion, solvents and elevated temperature. Fiber lasers around 1064 nm cover steel, stainless, titanium and most copper alloys; UV is used where heat input must be minimal, such as thin foils and some plastics. The main exclusion is highly reflective pure copper, which needs specific wavelengths or higher peak power.
Choosing between part marking methods comes down to depth, substrate and coating. Our part marking methods comparison sets out all six with production numbers.
How do you mark steel parts and mild steel?
Fiber laser marking is the standard answer: mild steel darkens quickly at low power, giving good contrast in seconds per part. The caveat is corrosion, not legibility — a laser mark on bare mild steel is an oxide layer, not a barrier, so the part still needs paint, plating, oiling or passivation if it will see moisture. Markings on mild steel that will be welded or formed afterwards should be placed away from the heat-affected zone and the bend line.
Can screw-machined parts be laser marked?
Yes, and it is one of the most common applications, because screw-machined parts are small, high-volume and usually serialized. A turned part can be marked on a flat, on the OD or on the face; the flat gives the most reliable read because curvature reduces the usable code area. On very small diameters the limiting factor is the code size, not the laser — check that the Data Matrix module size still meets your verification grade once it is wrapped around the available surface.
What marking method suits non-removable parts?
Non-removable parts — installed panels, structural members, parts that are welded or riveted in place — need a mark that cannot be removed without visible damage, which points to laser annealing or dot peen rather than a label or printed ink. Annealing is preferred where the part is stainless and corrosion matters, because it does not cut into the surface; dot peen is preferred where a tactile, verifiable-by-touch depth is required. Avoid deep engraving on load-bearing sections, since material removal creates a stress riser.
What laser marking solutions for metal do you offer?
Ruijin runs fiber laser marking in-house, alongside CNC machining, sheet metal fabrication and anodizing, so parts are machined, marked, finished and inspected without leaving the facility. We mark serial numbers, Data Matrix and QR codes, part numbers and logos on stainless, carbon steel, aluminium, brass and titanium, and we can verify 2D codes to ISO/IEC 15415 where traceability requires a stated grade. Send the drawing and the required code content for a quote — most go out within 24 hours.
Is laser marking metal parts permanent?
Yes, when it is the right kind of laser mark for the material. Annealing alters the oxide layer beneath the surface and does not remove material, so the mark survives finishing and does not create a corrosion site or a stress raiser; ablation removes the coating or anodic layer down to bare metal; engraving cuts a groove and is the most wear-resistant but does remove material, which matters on thin walls and load-bearing sections. What is not permanent is ink or a label, both of which fail Heat, solvent and abrasion. For laser marking metal parts that will be welded or formed afterwards, place the mark outside the heat-affected zone and clear of bend lines, as covered above.
For cast substrates the complementary method is dot peen, and the depth and hardness limits are worked out in our deep marking guide for castings.
When should marking on metal parts be applied — before or after finishing?
Sequence decides whether the mark survives the part. Marking on metal parts should follow machining and any heat treatment, because scale and distortion ruin a code; it should precede plating or coating only where the coating is thin enough not to fill the mark, otherwise the part is marked after finishing and then protected. On anodized aluminium the practical choice is either to mark before anodizing so the mark is sealed into the layer, or to ablate through the layer afterwards. On bare carbon steel the mark itself adds no corrosion resistance, so it needs paint, plating, oil or passivation over it whatever order you choose.
What does a laser marking service on parts include?
Four things: a drawing review that fixes the code content, symbology and the zone it must sit in; a marked sample on your actual material and finish; the fixture that makes part two identical to part two thousand; and the acceptance criterion, usually a stated ISO/IEC 15415 grade verified on the reader your line uses rather than a visual check. Send the drawing and the required code content, and most quotes go out within 24 hours.