DMLS vs. SLM vs. LPBF
DMLS, SLM and LPBF name one laser powder-bed process. What differs between machines, why alloy and heat treatment decide the part, and how to specify it.
Three names, one laser powder-bed process
A fiber laser melts a 20–60 µm layer of metal powder onto the layer below, inside an argon or nitrogen chamber, until the part stands on its build plate. Every metal printer in this family does exactly that; the acronym on the brochure is the brand of the machine.
DMLS
EOS trade name
Direct Metal Laser Sintering. The word “sintering” is a leftover from the 1990s bronze-nickel powders; modern DMLS parts are fully melted and more than 99 % dense.
SLM
Nikon SLM Solutions trade name
Selective Laser Melting. Coined to stress full melting when DMLS still meant partial sintering; used generically in Europe and Asia and by several other machine builders.
PBF-LB/M
The standard name
Laser-beam powder-bed fusion of metals in ISO/ASTM 52900, written LPBF in papers and L-PBF by some suppliers. Every ASTM F42 alloy specification uses this name.
Renishaw, Trumpf, Velo3D, Farsoon and Colibrium Additive (formerly Concept Laser, brand LaserCUSING) build the same process; 3D Systems calls it DMP. A buyer who asks for “DMLS parts” and one who asks for “SLM parts” receive the same thing from the same supplier. They do not receive the same part twice unless both name the alloy, the specification and the heat treatment.
Two processes often confused with this family are not part of it: binder jetting glues powder and sinters it later, at lower density and with 15–20 % shrinkage; electron-beam melting (EBM) uses an electron gun in vacuum with a hot bed and coarser layers. This guide covers laser powder-bed fusion only.
What actually differs between machines
The physics is shared; the hardware is not. These are the parameters a supplier chooses when it buys a machine, and what each one changes for the part on your drawing.
| Parameter | Typical range | What it changes for your part |
|---|---|---|
| Laser count | 1 on entry machines; 2, 4, 8 or 12 on production systems | Build speed, so price per part on large builds. Multi-laser overlap zones need qualified parameters on a critical part. |
| Laser power | 200–500 W standard; 700–1,000 W for aluminum and copper | Melts reflective alloys and thicker layers; does not raise density on a qualified parameter set. |
| Spot size | 50–100 µm | The finest wall and edge a machine can draw: 0.4 mm on most, 0.2 mm only on small-spot machines. |
| Layer thickness | 20–60 µm; 30 µm default, 60 µm for bulky aluminum | Thinner layers sharpen features and down-facing surfaces at the cost of build time; properties barely move. |
| Inert gas | Argon for titanium, aluminum and nickel; nitrogen acceptable for stainless steels | Oxygen pickup lowers titanium ductility. F2924 limits oxygen; ask for the chamber level on Ti-6Al-4V. |
| Plate preheat | None or 80–200 °C on most; up to 500 °C for crack-prone alloys | Less residual stress and warp on tall or thin parts. Without preheat, stress relief before support removal is not optional. |
| Build volume | 100 mm cubes to 250 × 250 × 325 mm mainstream to 600 × 600 × 600 mm | Whether the part prints in one piece and how many nest in a build; the 250 mm class carries most bureau work. |
| Powder handling | Sieving, refresh ratio, lot traceability | Reuse is normal; what matters is a documented refresh ratio and a certificate naming the lot. |
None of these rows is decided by the acronym. Two machines labelled DMLS can differ more from each other than a DMLS machine and an SLM machine of the same class.
Alloy and post-processing matter more than the acronym
The five alloys most service bureaus stock each have a specification written for laser powder-bed fusion and a heat treatment that sets the properties. Those two lines on the drawing decide the part; the machine brand decides nothing you can measure.
| Alloy | Specification | Heat treatment that sets the properties | Not decided by the acronym |
|---|---|---|---|
| 316L stainless | ASTM F3184 | Stress relief; solution anneal or HIP when ductility or fatigue matter | Corrosion performance depends on surface state and passivation, not on DMLS versus SLM. |
| 17-4PH stainless | ASTM A564 Type 630 chemistry; heat treatment per AMS 2759/3 | Solution treat and age — H900 for strength, H1025 or H1150 for toughness | As-built 17-4PH holds retained austenite; without a named age condition two suppliers deliver different strengths. |
| Ti-6Al-4V | ASTM F2924 (Grade 5); F3001 for ELI Grade 23 | Stress relief at 650–800 °C in vacuum or argon; HIP for fatigue-critical parts | Oxygen pickup and porosity, controlled by the gas and the parameter set, decide ductility and fatigue life. |
| AlSi10Mg | ASTM F3318 | Stress relief at about 300 °C; T6 trades strength for ductility and conductivity | As-built strength is high and brittle; name the condition you actually want on the drawing. |
| Inconel 718 | ASTM F3055; heat treatment per AMS 5662 / 5664 | Solution and double age; HIP recommended for pressure parts | Creep and fatigue at temperature depend on the age cycle and porosity, not on the machine brand. |
Thermal post-processing of powder-bed parts is specified generically in ASTM F3301. The metal 3D printing service page lists indicative as-built tensile ranges for each alloy; the DMLS design guide covers the geometry rules.
How to specify it on a drawing
Write the drawing so that any qualified laser powder-bed supplier builds the same part. That means naming outcomes and standards, not the machine.
- Name the alloy and its specification. “Ti-6Al-4V per ASTM F2924” or “316L per ASTM F3184”. This fixes chemistry, minimum properties and the test method without naming a machine.
- Name the heat treatment and condition. “Stress relieved”, “H900 per AMS 2759/3”, “solution treated and aged per AMS 5662”, “HIP per ASTM F3301”. The condition sets strength, ductility and fatigue; leave it out and two suppliers will ship two different parts.
- Call the process by its standard name, if at all. “Laser powder-bed fusion (PBF-LB/M) per ISO/ASTM 52900”. Writing “DMLS” or “SLM” on a drawing excludes qualified suppliers who use the other brand for no technical gain.
- Mark machined features and their datums. As-built accuracy is ±0.1–0.2 mm with Ra 6–12 µm; bores, threads and sealing faces need a machining symbol, a finish and 0.5–1 mm of stock in the model.
- State density and inspection. “Relative density ≥ 99.5 %, verified by Archimedes on a witness coupon” or CT on the part itself for pressure-critical channels. Exterior CMM cannot prove an internal path.
- Ask for the certificate, not the brand. Powder lot, machine and parameter identification, build orientation, heat-treatment chart and test results on a material certificate per the specification. That is the evidence a brand name never gives you.
Example title-block note: “Additive manufacture, PBF-LB/M per ISO/ASTM 52900. Material Ti-6Al-4V per ASTM F2924. Stress relieve before support removal; HIP per ASTM F3301. Features marked ▽ machined after heat treatment. Material certificate and density report required.”
Frequently asked questions
Is DMLS the same as SLM?
Yes, for the part. Both names describe a laser melting metal powder layer by layer in an inert chamber. DMLS is the EOS trade name, SLM is the Nikon SLM Solutions trade name, and ISO/ASTM 52900 calls the process PBF-LB/M. Differences you can measure come from the alloy, the parameter set and the heat treatment.
Does DMLS really sinter the metal?
No. The name dates from 1990s bronze-nickel powders that were partially sintered. Modern DMLS fully melts the alloy and reaches more than 99 % relative density, the same as SLM. Only binder jetting and bound-powder filament processes sinter metal today.
Is LPBF better than DMLS or SLM?
LPBF is not a third process; it is the generic name for the same one. Choosing “LPBF” on a drawing simply avoids naming a machine brand and keeps every qualified supplier eligible to quote.
What should I write on a drawing instead of DMLS?
The alloy and its specification (for example Ti-6Al-4V per ASTM F2924), the heat treatment and condition, HIP if required per ASTM F3301, which features are machined and to what tolerance, and the density and certificate you expect. Optionally the process by its standard name, PBF-LB/M per ISO/ASTM 52900.
Which is more accurate, DMLS or SLM?
Neither as a class. As-built accuracy on any laser powder-bed machine is about ±0.1–0.2 mm and Ra 6–12 µm, set by spot size, layer thickness and thermal distortion rather than the brand. Machine the features that need better and specify them as machined.
Sources and further reading
- ISO/ASTM 52900 — Additive manufacturing: general principles, fundamentals and vocabularyDefines powder bed fusion and the PBF-LB/M designation used in place of trade names.
- ASTM F3184 — Additive manufacturing of stainless steel alloy UNS S31603 with powder bed fusionChemistry, minimum properties and test methods for laser powder-bed 316L.
- ASTM F2924 — Additive manufacturing of Ti-6Al-4V with powder bed fusionGrade 5 titanium: oxygen limits, minimum tensile properties after heat treatment.
- ASTM F3055 — Additive manufacturing of nickel alloy UNS N07718 with powder bed fusionInconel 718 chemistry and property classes by heat-treatment condition.
- ASTM F3318 — Additive manufacturing of aluminum alloy AlSi10Mg with laser-based powder bed fusionCondition classes for as-built, stress-relieved and heat-treated AlSi10Mg.
- ASTM F3301 — Thermal post-processing of metal parts made via powder bed fusionStress relief, HIP and heat treatment specified independently of the machine.
- EOS — DMLS metal 3D printingTrade-name owner; machine and material process data are published per system.
- Nikon SLM Solutions — Selective Laser MeltingTrade-name owner; multi-laser machine range.
Specify the details that make the part work.
Upload your CAD and drawing with the material, quantity, finishing and critical dimensions. Confirm the manufacturing route before production.