Three Ways to Mark: Etching, Engraving, and Annealing

Material by Material: Where to Start

Stainless Steel

Stainless is the most common material we mark, but it's also where I see the most mistakes. Engraving or etching removes the chromium oxide layer, which can lead to corrosion. Annealing is the better choice. It preserves the surface and gives a dark, high-contrast mark. [11†L15-L18]

For annealing, start with a MOPA fiber laser at 50-100W, Q-pulse around 100 ns, frequency 30-60 kHz, and speed roughly 300 mm/s. [20†L35-L36] For standard marking on stainless steel 304, a research study found good results with 15W laser power, 50 kHz pulse frequency, and 35 mm/s scanning speed. [10†L24-L26] A practical baseline for a 20W fiber machine is power 70-80%, speed 300-500 mm/s, frequency 20-30 kHz, then test and adjust. [18†L10-L11]

If your customer wants colored marks (blue, purple, bronze), that's possible with a MOPA laser. The color comes from thin‑film interference at different oxide thicknesses. It takes fine parameter tuning, but once you dial it in, the results are impressive. [12†L50-L52][20†L28-L35]

Aluminum

Aluminum is tricky. Bare aluminum is highly reflective, which makes it hard for the laser to couple energy into the surface. Most shops mark anodized aluminum instead, which works beautifully. [13†L42-L44]

On anodized aluminum, the laser vaporizes or bleaches the dye in the anodized layer, leaving a crisp white mark. Too much power will create a yellow "halo" around the mark. Too little, and you get a faint gray. [15†L19-L24]

For black marks on anodized aluminum, you need a MOPA laser. The standard recommendation is a 20W MOPA source. Slower speeds create a deeper effect suitable for black; faster speeds give lighter marks suitable for white. [15†L48-L50]

For bare aluminum, use a fiber laser with parameters tuned for oxidation marking. Expect a light gray or white result unless you use additives. [13†L25-L28]

Titanium

Titanium is used for medical implants and aerospace components. Annealing is the preferred method here too, because it doesn't compromise the material's fatigue life. The process creates a dark oxide layer that's highly durable. [22†L45-L49]

Use a fiber laser with moderate power and a focus spot size appropriate for your detail requirements.

Plastics and ABS

Plastic is where things can go wrong fast. Too much power and you'll burn or melt the surface. ABS is safe to mark, but you need to go light to avoid a burn tint. A good starting point for ABS is speed 300 mm/s, power 25%, frequency 35 kHz. [16†L30-L31]

A UV laser is the best choice for plastics. It breaks the surface photochemically rather than thermally, so there's no melting or burning. [17†L31-L34]

Avoid marking PVC or vinyl. The chlorine gas they release is toxic and damages your laser equipment. [17†L19-L21]

The Core Parameters: What They Control

Power sets the intensity of the laser beam. Higher power means deeper marks. Too high, and you'll get a yellow halo on anodized aluminum or burn plastic. Too low, and the mark will be faint. [15†L47-L48]

Speed is how fast the laser head moves. Slower speed means more heat input. Fast speed gives lighter marks, slow speed creates deeper effects. [9†L7-L8]

Frequency is the number of pulses per second (kHz). Lower frequencies give more "punch" per pulse, which is good for blasting away anodized dye. Higher frequencies produce smoother marks but less contrast. [15†L50-L50]

Depth control follows a simple logic: higher power, lower speed, and lower frequency all increase depth. But going too far will damage the material. [18†L9-L10]

For deep engraving on metal, you can also use multiple passes. One pass at moderate power, then another to clean it up, often works better than one high-power pass. [9†L9-L10]

Focus is often overlooked. The focal point must be precisely on the surface. Even 0.1mm out can make a mark unreadable. Some machines have auto-focus systems with 0.01mm accuracy—use them. [19†L44-L47]

Always Run a Test Matrix

No matter how many times I've marked a material, I still run a test matrix on a scrap piece at the start of each job. Set up a small grid with varying power, speed, and frequency. Run the test. Look for the combination that gives the best contrast, edge definition, and depth.

This takes five minutes and saves me from burning a batch of real parts.

Which Laser to Buy

For a machine shop, start with a MOPA fiber laser (20W to 100W depending on your volume). It handles metals well and gives you the flexibility to do annealing, color marking, and deep engraving. [19†L19-L23]

If you mark a lot of plastics, add a UV laser. The cold marking process eliminates burning and melting. [17†L34-L35]

Avoid trying to use a CO₂ laser on bare metal. It won't work unless you use a marking spray, which adds time and consumable cost. [11†L38-L44]

Standards and Readability

For traceability marks, the mark needs to be readable by humans and machines.

• Aerospace requires marks that stay readable after decades in harsh conditions. The AS9100 standard requires validation of the marking process. MIL-STD-130 requires UID (unique identification) codes, typically data matrix. [21†L12-L14][21†L21-L25]

• Medical devices require UDI (unique device identification) marking. The process must be validated per ISO 13485 with IQ/OQ/PQ. Marks must remain readable through sterilization and years of use. [8†L36-L38]

• Readability verification uses 2D barcode verifiers that provide grades based on the AIM DPM standard, also known as ISO/IEC TR 29158. [22†L6-L8]

Readability grades are scored from A to F. Aerospace customers often require A or B grades. If your mark scores lower, you need to adjust parameters and try again.

Common Problems and Fixes

Mark is too faint (low contrast) : Increase power, decrease speed, or adjust frequency. For anodized aluminum, try increasing frequency. [15†L48-L50]

Yellow halo around the mark : Too much power on anodized aluminum. Reduce power and increase speed.

Burn marks on plastic : Reduce power and increase speed. Switch to a UV laser if the problem persists. [16†L30-L31]

Mark is shallow and needs more depth : Increase power, decrease speed, decrease frequency, or increase passes. Deep engraving may require a higher-power laser (e.g., 100W). [18†L9-L10][19†L32-L33]

Mark is inconsistent across the part : Check your focus. The part may not be flat or you may be out of the focal zone. Also check for the laser's optimal marking area (usually in the center of the field).

Post-Marking Care

After marking, blow off any residue with clean air. For critical parts, clean with IPA to remove any debris. On stainless steel, if you've used a method that removed the oxide layer, you may need to passivate the marked area to restore corrosion resistance. [12†L47-L48]

The Bottom Line

Laser marking is a core capability for any precision machine shop. But it's not "set it and forget it." Each material and each marking method needs its own parameter set. The tools are precise—lasers can engrave down to 0.001mm level. [19†L28-L31] Use them right, and you'll get marks that outlast the part.

The short version: Use annealing for stainless and titanium to preserve corrosion resistance. Use etching for high-volume serialization. Use engraving for parts that will see wear. Test on scrap. Verify readability. And when in doubt, run a test matrix.

Have you dialed in a laser marking process that works really well? Or run into a problem I haven't covered? I'd like to hear your experiences.