A serial number that looks perfect on the bench can be gone after galvanizing. A laser-marked Data Matrix code that scans fine can turn grey after heat treatment. Most marking problems start after the mark is made.
To permanently mark metal, cut or press the mark into the surface with a fiber laser marking machine, a dot peen marker, a steel stamp or an electrochemical etcher. Then choose by what happens next: paint and zinc bury shallow marks, and heat fades laser color marks.
This guide compares seven methods by depth, speed and cost. It shows which marks survive paint, galvanizing, blasting and heat, and which methods suit rough, hard or thin parts. It ends with a simple test for when to buy a machine.
Not sure which fits? Send us your part and what happens to it next, and we will suggest a method.
A note on bias: I work for HeatSign. We build both fiber laser marking machines and dot peen marking machines, so we have no reason to push one. Facts on coatings, standards and tests come from public sources listed at the end.
What are the ways to permanently mark metal?
There are seven common ways: fiber laser marking, dot peen marking, steel stamping, electrochemical etching, scribing, inkjet or paint markers, and metal tags. The first five change the metal itself. Ink and paint are temporary, and tags can fall off.
Method | How it marks | Typical depth | Equipment cost |
|---|---|---|---|
Fiber laser marking machine | A laser beam darkens or removes a thin layer. Nothing touches the part. | Surface marks about 0.025–0.08 mm; engraving goes deeper with more passes | Our desktop machines: $1,950–5,000 |
Dot peen marking machine | A hard pin dents a line of dots into the surface | About 0.03–0.5 mm; over 0.5 mm is already deep. Our pneumatic markers reach about 1 mm at most. | Our machines: $1,500–2,850 |
Steel stamps (hand or press) | A hammer or press drives steel letters in | About 0.3–0.5 mm by hand | A 36-piece letter and number set: about $150 |
Electrochemical etching | An electric current and a salty liquid (electrolyte) eat away metal through a stencil | Up to about 0.05 mm | Kits: about $130–350 |
Scribing | A hard stylus (a pointed tip) scratches the shape into the surface | Up to about 0.25 mm | Usually an option on a dot peen or CNC (computer-controlled) machine |
Inkjet or paint marker | Ink or paint sits on top of the metal | None | Pens cost a few dollars |
Metal tag or nameplate | A separate plate is riveted, wired or welded on | Depends on how the tag is marked | Per tag |
Depths: NASA-STD-6002D, a UK steel construction guidance note and maker data. Prices: our public product pages and US tool dealers.
Four terms used on this page
- Direct part marking (DPM)
- Marking the part itself, not a label stuck on it.
- Data Matrix code
- A small square barcode, a bit like a QR code, used to track parts.
- Annealing mark
- A dark color mark made by laser heat. It removes almost no metal.
- Intrusive mark
- Any mark that cuts, dents or dissolves the surface. Dot peen, stamping, etching and laser engraving are all intrusive.
Where a fiber laser marking machine wins
A laser marker never touches the part. It writes the smallest text and barcodes, needs no pins or stencils, and costs almost nothing to run. In a German study on cast parts, a Data Matrix code took about 4 seconds by laser and about 10 seconds by dot peen.
The same study scored laser marks highest on every cast surface tested. For finished, machined or hardened parts, a laser is usually the first choice. See our fiber laser marking machines.
Where a dot peen marking machine wins
A dot peen marker makes a physical dent. Deep dents survive thick coatings and rough handling, and the machine costs less to buy. Pins wear and need changing every few months, but they are cheap.
Both are preferred methods in the US military marking standard (MIL-STD-130), which calls automated marking such as dot peen and laser “the preferred method”.
Which marks survive paint, galvanizing, blasting and heat?
Dents survive coatings; color marks do not. A dot peen or stamped mark stays readable when it is several times deeper than the coating that goes over it. A laser color mark is lost in galvanizing and fades in heat, while an engraved laser mark keeps its shape.
What happens next | Fiber laser marking | Dot peen marking | Other methods |
|---|---|---|---|
Paint, powder coat or e-coat (electrocoat paint) | Mark after painting by burning through the paint, or mark larger Data Matrix codes before painting. | Survives when the dent is several times deeper than the coating | Stamps follow the same rule. Ink and paint pens are covered. |
Hot-dip galvanizing | Color marks are lost in the acid clean before galvanizing. Mark on the zinc afterwards. | Deep pneumatic dot peen marks stay readable | Deep stamps stay readable. Oil-based markers leave bare spots. |
Shot or sand blasting | Normal Data Matrix codes are erased. Larger, engraved codes made in several passes survive. | Deep dents survive better than shallow ones | Electrochemical marks were mostly wiped out in testing |
Heat treatment | Color marks fade. Engraved marks keep their shape. | The dent stays. Heat oxide (a dark film) lowers contrast. | Stamps stay. Ink burns off. |
Outdoors | On stainless, use the lowest heat that gives contrast; too much heat can lead to rust | Dents on carbon steel can rust; protect them like the part | Etching “tends to rust the part”, one machinist reports |
How deep to go for each coating, with the numbers, is in how deep to mark before painting or galvanizing.
Will your part be painted, blasted or galvanized?
Tell us the coating and its thickness. We will suggest a mark depth or laser settings that last.
Makers disagree here. Some dot peen makers say their marks always survive galvanizing; some laser makers say dot peen marks rarely do. Both are partly right. Compare the mark depth with the coating thickness, and you have your answer.
A US welder put it plainly on a welding forum: an oil-based paint mark left on steel “will show up as a shadow under the galv”.
Heat is where the type of laser mark matters. A dark annealing mark is only a thin color layer, and it fades in high heat. An engraved laser mark removes metal, like the deep mark on this stainless part, and keeps its shape through heat.
So for parts that go to heat treatment, ask for an engraved laser mark, not a color mark.
What published tests found
- Cast aluminum parts (Fraunhofer IGCV, Germany): laser, dot peen and electrochemical marking were tested on 60 sand, gravity and die-cast parts. Laser scored highest on every surface. Dot peen came close on rough sand castings. Electrochemical marks passed only on smooth die-cast faces.
- After blasting and T6 heat treatment, a common hardening step (same study): all three lost quality. Ten seconds of sand blasting wiped out most electrochemical marks.
- Laser-marked Data Matrix codes after processing (a North American laser maker): normal ones did not survive shot blasting. Larger engraved ones made in several passes did, and engraved codes on A356 cast aluminum stayed readable after T4 and T6 heat treatment.
- Steel bridges (UK Steel Construction Institute): shop paint and marker pens “can only be regarded as temporary”. Each part needs a permanent mark before it leaves the shop.
How do you mark rough, hard, curved or thin metal parts?
Use a fiber laser marking machine or a dot peen marker on rough cast surfaces; electrochemical etching needs a smooth face. Use a laser on hardened steel, thin walls and small curved parts. On safety-critical parts, keep marks shallow, no deeper than one tenth of the wall.
Surface | Best methods | Why |
|---|---|---|
Rough castings and forgings | Fiber laser marker or dot peen marker | Both scored well on sand castings in the Fraunhofer test. Etching failed on rough faces. |
Mill scale or rust | Dot peen | The pin goes through scale. A laser needs a cleaner surface or a primer first. |
Hardened steel, tools, bearings | Fiber laser marker | The laser does not touch the part, so hardness does not matter. NASA asks users to watch pin wear closely above 35 HRC (fairly hard steel on the Rockwell hardness scale). |
Tubes, shafts and rings | Fiber laser marker with a rotary axis, or a rotary dot peen marker | Flat areas mark best. On round parts, keep marks small or turn the part. |
Thin walls and safety-critical parts | Fiber laser marker or electrochemical etching | Shallow marks with no impact. NASA limits depth to one tenth of the wall. |
What the standards say
- NASA-STD-6002D: non-intrusive marking is recommended for safety-critical parts. Intrusive marks there “shall be documented and approved”. Marks should be no deeper than one tenth of the part’s thickness.
- MIL-STD-130: steel stamps only on parts that “will not deform” under the blow; dot peen on parts that would.
Does stamping weaken steel? A sharp stamp leaves a notch where cracks can start (a stress raiser), so rail and aerospace users prefer round-bottom or dot stamps. Yet a fatigue study in the AISC Engineering Journal found automatically stamped steel still met the top rating for resistance to cracking under repeated loads (fatigue). Choose a low-stress character shape and keep marks away from high-stress areas.
For oily, rusty and coated stock, see marking oily, rusty or coated metal: laser vs dot peen. Have a hard, thin or cast part? Send us a photo of it.
Which metal marking method fits your part?
Machined, hardened or thin parts that need Data Matrix codes suit a fiber laser marking machine. Castings, forgings and parts that will be painted or galvanized suit a pneumatic dot peen marker. Large or installed parts suit a handheld dot peen or portable fiber laser marker.
Your part | Method | Why |
|---|---|---|
Machined parts with Data Matrix codes or small text | Desktop fiber laser marking machine | Smallest, sharpest text and barcodes; no contact |
Hardened tools, molds and bearings | Fiber laser marking machine | Hardness does not matter |
Thin-wall or delicate parts | Fiber laser marking machine | No impact, no distortion |
Parts moving on a production line | Flying fiber laser marking machine | Marks without stopping the line |
Logos, black marks on aluminum, color on stainless | MOPA fiber laser marking machine | Adjustable pulse for contrast and color |
Castings, forgings, raw bar and plate | Pneumatic dot peen marker (or fiber laser marker) | Dot peen goes through scale; laser for cleaner faces |
Parts to be painted or galvanized | Deep pneumatic dot peen; mark a sample and send it through your coating first | Depth beats coating thickness |
Large, heavy or installed parts | Handheld dot peen or portable fiber laser marker | Take the marker to the part |
A few parts a day, text only | Steel stamps or an etching kit | Lowest cost to start |
Many shops end up with both: a fiber laser marking machine for finished parts and a dot peen marker for raw stock and parts that go out for coating.
The nameplate in the photo was marked by a fiber laser marking machine. For black marks on anodized aluminum or color on stainless, see laser engraving metal: bare, painted and coated surfaces. Choosing a machine for stainless parts? See laser engraver for stainless steel: which machine fits your parts. For barcodes and audits, see our part marking buyer’s guide.
Finished parts and barcodes: desktop fiber laser marking machine20–60 W. Data Matrix, serial numbers and logos. $1,950–5,000.See the desktop laser marker → 
Large parts, laser quality: portable fiber laser marker1.5 kg handheld head, optional battery. $1,950–3,800.See the portable laser → 
Deep marks before coating: pneumatic dot peen markerUp to about 1 mm deep. Rotary axis available. $1,500–2,800.See the pneumatic marker → 
Large parts, no air supply: handheld dot peen markerMains or battery power. $1,600–2,850.See the handheld marker →When should you replace hand stamps or paint pens with a machine?
Switch when a customer asks for Data Matrix codes, when marks vanish under paint or zinc, or when hand marking takes real labor time. In our example, saving 45 seconds a part at $25 an hour, a $2,000 marker pays back in about 6,400 parts.
- A customer asks for barcodes or grades. Hand stamps cannot make a Data Matrix code. A fiber laser marker or dot peen marker can.
- Serial numbers must never repeat. A machine counts for you and can read numbers from a spreadsheet.
- Marks disappear after coating. A machine gives the same depth every time.
- Parts come back for rework. Crooked or shallow hand stamps get rejected.
- Volume is going up. Hand marking time grows with every part.
The tag in the photo carries a serial number and a barcode marked by a fiber laser marking machine. A machine reads the next number from a file, so the same number never comes up twice.
A payback example you can redo with your numbers
Say a worker stamps a 12-character serial number by hand in about 60 seconds, and labor costs $25 an hour. Change the numbers to match your shop.
Item | Hand stamping | Dot peen or fiber laser marker |
|---|---|---|
Time per part | About 60 s | About 15 s, including loading |
Labor per part | About $0.42 | About $0.10 |
Saving per part | — | About $0.31 |
Payback on a $2,000 machine | — | About 6,400 parts (2,000 ÷ 0.31); at 30 parts a day, about 10 months of working days |
Inkjet and stamps have running pains too. One machinist on a trade forum switched to laser after years of “ink, solvent, blue and black fingers, blocked jets”. To compare makers and prices, see metal marking machine manufacturers compared.
Want real numbers? Send us the part, the characters and your daily volume, and we will tell you the cycle time.
How do structural steel fabricators mark beams and plates?
Structural shops treat paint and marker pen as temporary. Each beam or plate gets a permanent mark before it leaves the shop, usually a hydraulic stamp on the beam saw-and-drill line or a portable dot peen marker. Galvanized members need deep marks that the zinc cannot fill.
On many beam lines, the marks come straight from the design model. Design software such as Tekla exports files (DSTV or NC1) that the shop’s computer-controlled steel machines read. These files carry the hole positions and the “hard stamp” text, such as the job and piece number.
Parts marked after the line, in the yard or on site, need a portable marker. A handheld dot peen marker needs no air supply. The beam in the photo was marked through red primer.
EN 1090 in Europe and AISC practice in the US both expect parts to be traceable. For fabrication shop setups, see marking machines for steel fabrication.
Metal Marking FAQ
Is a paint marker or Sharpie permanent on metal?
No. MIL-STD-130 lists ink and rubber stamps as temporary marks. On parts going for galvanizing, oil-based markers must be removed first, or they leave bare spots in the zinc.
Does stamping or dot peen weaken metal?
A sharp stamp can leave a notch where cracks can start (a stress raiser), so use round-bottom or dot characters and keep marks away from high-stress areas. On safety-critical parts, follow the drawing; NASA asks for intrusive marks there to be approved.
Can you laser mark metal after galvanizing or painting?
Yes. A fiber laser marking machine can mark the zinc, or burn through paint to show bright metal. The mark is then shallow, so it suits parts that need no further coating.
How deep should a permanent mark on metal be?
It depends on what comes next. Bare parts need only about 0.03–0.1 mm. Parts going for hot-dip galvanizing need a deep dot peen or stamped mark. Thin walls should stay under one tenth of the thickness.
What is the cheapest way to permanently mark metal?
Steel stamps, at about $150 a set, or an electrochemical etching kit at about $130–350. Above a few dozen parts a day, a machine usually costs less per part.
Dot peen or laser: which is better for metal parts?
Use a fiber laser marking machine for finished, hardened or thin parts and small barcodes. Use dot peen for rough, scaled or coated parts and deep marks. See laser vs dot peen vs stamping for deep marks.
Decide what happens to the part after marking, then pick the method. Most shops need a fiber laser marker, a dot peen marker or both, not every method on this page.
Sources
- Fraunhofer IGCV, comparative evaluation of marking methods on cast parts, International Journal of Metalcasting
- American Galvanizers Association, marking parts for galvanizing
- Steel Construction Institute, guidance note GN 5.05 on marking steel
- NASA, NASA-STD-6002D, applying data matrix identification symbols
- MIL-STD-130, Identification marking of US military property
- ISO 1461 and ASTM A123, hot-dip galvanized coatings
- AISC Engineering Journal, fatigue of stamped steel
- Laser and dot peen maker application notes. We do not link to other companies’ sites.
