Laser marking
Surface-change and removal mechanisms, material and laser selection, direct-part-code verification and durability qualification.
Tags: processes, shaping, marking, traceability
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A hypothetical 20 × 20-module GS1 DataMatrix with 0.20 mm modules needs 4.40 mm overall, including a quiet zone one module wide on each side. Centered on 5.00 mm square usable area, it leaves 0.30 mm extra per side. A 24 × 24 symbol instead needs 5.20 mm. Confirm payload fit, marked-cell geometry and verifier performance. GS1 DataMatrix Guideline, release 2.5.1
Specify the required surface result and marking mechanism. TRUMPF distinguishes plastic color changes, surface alteration and layer ablation. TRUMPF: laser marking plastics
Distinguish the physical result
| Mechanism | What changes and what to define |
|---|---|
| Engraving/removal | Material is removed to form a feature; define depth, profile and allowed surface disruption. |
| Coating/layer ablation | A selected layer is removed to expose a contrasting underlying material; define which layer may be removed. |
| Annealing/color oxidation on suitable metal | Local heating generates an oxide-related color; define acceptable contrast and surface condition. |
| Polymer color change or foaming | Chemistry/pigment response or a raised, light-scattering structure creates contrast; identify the exact compound. |
| Ultrashort-pulse black marking | Surface microstructures create a dark optical response; qualify the particular material and parameter window. |
TRUMPF’s TruMark brochure, marked 202606 on its back cover, describes deep engraving as material removal and adjustable pulse duration/frequency as application controls. Its examples establish possible processes, not a universal engraving depth or an allowable cut into a fatigue-critical surface. TRUMPF, TruMark: The individual solution for your industry, printed pp. 17 and 29
TRUMPF describes annealing marks as oxide-film colors produced on suitable metals, including steels and titanium. Its discussion emphasizes a preserved, smooth surface and parameter-dependent legibility after cleaning. Do not confuse this localized marking terminology with a bulk annealing heat treatment, or assume the same color process works on bare aluminum. TRUMPF: annealing
For plastics, TRUMPF describes foaming as local melting and trapped gas bubbles producing a raised, diffusely reflecting mark. Color change and removal of a top coating are different routes. A dark plastic, a light pigment formulation and a coated button may therefore require different interactions even when their base resin family is the same. TRUMPF: plastic marking mechanisms
Material, wavelength, pulses and surface state
Record substrate grade, heat treatment where relevant, resin/additives, coating stack and thickness, surface texture, cleanliness and the stage at which marking occurs. TRUMPF notes that polymer absorption depends on both the molecular structure and additives, and that wavelength selection changes the available marking response. A successful trial on one color or compound should not automatically qualify another. TRUMPF: material absorption
KEYENCE identifies 355 nm as a typical UV marking wavelength and discusses its use on sensitive materials. That is a laser-class example, not evidence that UV is always free of surface damage or that every UV system reproduces the same mark. Select the actual source, optics and process window against the material and acceptance requirements. KEYENCE: UV laser marking
Keep wavelength separate from pulse duration, repetition frequency, delivered energy, scan speed, overlap, focus and number of passes. Agree the complete approved program and optical setup. For curved or stepped surfaces, identify the accessible marking field and focus strategy; a nominal flat-field spot size does not establish a readable code over every part orientation.
Named black-marking example and durability
TRUMPF’s black-marking description associates ultrashort pulses with nanometer-scale surface structures and a dark response with reduced viewing-angle sensitivity. Its corrosion-resistance claim is explicitly limited to certain parameter ranges. The TruMicro Mark family is a named implementation, not a generic guarantee for every black mark or stainless surface. TRUMPF: black marking
Define durability through the intended service: cleaning chemicals, abrasion, sterilization if applicable, corrosion exposure, temperature and subsequent finishing. Verify both legibility and the required surface performance after representative exposures. A visually dark mark is not proof of corrosion resistance, and an initial code grade does not demonstrate that the mark will survive its service life.
For coated parts, specify whether marking precedes or follows coating, passivation, polishing or cleaning. Removing a protective layer to improve contrast may change the component’s service surface. Agree acceptable coating penetration, edge location and any subsequent treatment rather than assuming an attractive mark is harmless.
Reading is different from verification
A reader decoding a symbol once answers a narrower question than grading its optical quality under a defined method. Cognex’s Introduction to Barcode Verification distinguishes readers from verifiers and describes grading, calibration and reporting of the optical arrangement. A production-camera read check can be useful, but do not label it standards verification without the applicable equipment, calibration and method. Cognex verification guide, pp. 4–7 and 12
ISO/IEC 29158:2025, Edition 2, March 2025, supersedes the withdrawn 2020 edition. Its scope modifies the ISO/IEC 15415 symbol-quality methodology for direct part marks, including illumination, measurement, grading and reporting. The public scope does not establish a universal minimum grade for every application; state the required method/edition, acceptance grade and verification conditions in the application specification. ISO/IEC 29158:2025 official record
Verify data content separately: symbology, identifier structure, lot/serial value and association to the physical part must be correct. A high optical grade cannot detect that a perfectly printed serial number was assigned to the wrong component. Define how marking data, program selection and part identity are checked together.
Original bounded symbol-footprint example
GS1’s DataMatrix Guideline, Release 2.5.1, ratified January 2018, specifies a quiet zone at least one module wide around a GS1 DataMatrix. Use that geometry here without adopting its historical reference to an older DPM grading document as the current edition. GS1 guideline, printed p. 36
Assume a selected 20 × 20-module symbol with 0.20 mm module width. This is a footprint example, not a claim that an unspecified payload fits that symbol:
symbol side = 20 × 0.20 = 4.00 mm
side including 1-module quiet zone each side = (20 + 2) × 0.20 = 4.40 mm
On an invented 5.00 mm square usable area, centering leaves 0.30 mm additional margin per side, outside the required quiet zone. A 24 × 24-module symbol at the same module width instead needs 5.20 mm, exceeding that area by 0.20 mm overall.
Confirm application sizing rules, curvature and the reader or verifier arrangement on the actual surface.
Manufacturing handoff and acceptance
Provide the drawing/model revision, marking location and orientation, keep-out areas, human-readable content, encoded data rules and final surface condition. Identify the approved material/coating, laser/program revision, fixturing/focus strategy, cleaning and downstream operations. State depth or surface-change limits where function requires them.
Separate appearance, content correctness, optical verification and service durability into explicit acceptance requirements. Inspect at the required delivered stage, retaining representative before/after exposure results for critical uses. A photo, a single successful scan or a vendor’s generic “permanent” description does not define all four outcomes.
The GS1 PDF prints its January 2018 release; ISO’s current record prints March 2025. The manufacturer web pages and Cognex PDF have no separately verified technical issue date here; the TruMark brochure prints 202606. Their older standards references do not supersede the current ISO record. No generic laser-power or scan-speed recipe is prescribed.