Direct Metal Laser Sintering (DMLS)
Direct metal laser sintering fuses metal powder layer by layer with a laser, building dense metal parts anchored to a supported build plate.
- Part
- Forming
- Revised
- 2026-08-11
At a glance
- Family
- Additive Manufacturing
- Typical tolerances
- About ±0.004 in (±0.1 mm) on features up to 1 in (25 mm), then roughly ±0.2% of nominal. Suppliers commonly quote ±0.003 in (±0.076 mm) plus ±0.001 in/in for well-controlled geometry; machined features are far tighter.
- Surface finish
- Ra 200–500 µin (5–13 µm) as built on vertical walls; down-facing supported surfaces reach Ra 800–1,200 µin (20–30 µm). Bead blasting, tumbling, machining, or polishing are used where finish matters, particularly for fatigue-critical surfaces.
- Typical volumes
- 1–500 parts; economical wherever the geometry cannot be machined or cast
- Lead time
- 5–15 business days. The print itself is typically 1–4 days, with stress relief, plate removal, support removal, and any machining or HIP adding most of the balance.
- Materials
- Metal
What it is
Direct metal laser sintering (DMLS) is laser powder bed fusion of metal: a fiber laser of 200–1,000 W fully melts 0.0008–0.0024 in (20–60 µm) layers of 15–45 µm alloy powder under argon or nitrogen, building parts anchored to a solid substrate plate. Finished density is typically above 99.5%, with mechanical properties at or above cast values and, after hot isostatic pressing, approaching wrought.
The production alloy set is small but useful: AlSi10Mg, Ti-6Al-4V and Ti-6Al-4V ELI, 316L and 17-4 PH stainless, maraging steel, Inconel 625 and 718, and CoCrMo. Typical build envelopes are around 10 × 10 × 13 in (250 × 250 × 325 mm), with large-frame machines reaching 400–800 mm in each axis.
Accuracy runs roughly ±0.004 in (±0.1 mm) on the first inch. DMLS earns its cost where geometry cannot be machined or cast — conformal cooling channels, topology-optimized brackets, internal lattices, and consolidated assemblies — at volumes of 1 to a few hundred parts.
How it works
- Prepare the build. Parts are oriented, supported, and sliced. Supports here are structural and thermal: they anchor the part against the enormous residual stresses of solidification and conduct heat away from downward-facing surfaces.
- Inert the chamber. The chamber is purged with argon (reactive alloys such as titanium and aluminum) or nitrogen (steels), typically to below 0.1% residual oxygen. Oxygen pickup embrittles titanium and causes spatter and porosity in any alloy.
- Recoat. A blade or roller spreads a 0.0008–0.0024 in (20–60 µm) layer of powder, with 0.0012–0.0016 in (30–40 µm) the common production setting.
- Melt. The laser scans the cross-section with a 0.003–0.004 in (70–100 µm) spot at scan speeds of roughly 0.5–3 m/s and hatch spacing near 0.003–0.006 in (0.08–0.14 mm). Scan strategies split the layer into stripes or islands and rotate the hatch direction each layer to break up residual stress. Typical build rate is 5–20 cm³/h.
- Repeat to full height. Build time is set almost entirely by Z height and cross-sectional area, not by part count.
- Stress relieve on the plate. The part is heat-treated before it leaves the substrate, or it will spring and distort the moment it is cut free. Typical cycles are around 800 °C (1,470 °F) for 2 hours in argon or vacuum for Ti-6Al-4V, roughly 300 °C (570 °F) for 2 hours for AlSi10Mg, and 550–650 °C (1,020–1,200 °F) for austenitic stainless.
- Separate and finish. The part is cut from the plate by wire EDM or bandsaw, supports are removed by hand or by machining, and critical features are machined. Fatigue-critical aerospace and medical parts are hot isostatically pressed — for Ti-6Al-4V, commonly around 900 °C (1,650 °F) at 15 ksi (100 MPa) for 2 hours — to close internal porosity.
Design guidelines
Overhang angle
Surfaces below about 45° from vertical need support. Unsupported downskins do not merely sag — they sit on loose powder, which conducts heat an order of magnitude worse than solid metal, so the melt pool runs hot and the surface comes out rough and dross-covered. Design self-supporting angles wherever you can; every support you delete is money saved twice, at build time and at removal.
Holes and internal channels
Round horizontal holes above about 0.3 in (8 mm) diameter sag at the crown. Redraw them as teardrops or diamonds and they self-support to much larger sizes. Vertical holes are unrestricted. Every internal channel needs at least one powder evacuation port of 0.08–0.12 in (2–3 mm) or larger; trapped powder in a closed cavity is permanent.
Wall thickness
0.016 in (0.4 mm) is the process minimum; use 0.040 in (1 mm) for structure. Keep sections as uniform as practical — abrupt changes in cross-section concentrate residual stress and are the usual cause of a build peeling off its supports mid-print.
Machining allowance
Add 0.020–0.040 in (0.5–1.0 mm) of stock to any surface that must be flat, round, or held to a fit. Bearing bores, sealing faces, and datum surfaces should always be machined after stress relief — see the ISO 286 fits and tolerances chart for what those fits require.
Threads
Do not build threads. Print a pilot hole with machining stock and tap it; the tap drill chart gives pilot diameters. As-built threads are dimensionally poor and their roots concentrate the stress that additive metal is least good at resisting.
Orientation for properties
Fatigue and tensile properties are direction-dependent: Z-direction ductility is usually the lowest, and as-built surface roughness is itself the dominant fatigue initiator. Orient critical loads in the build plane and machine or polish highly stressed surfaces.
Fillets and stress
Fillet every internal corner at 0.04 in (1 mm) or more. Sharp re-entrant corners in a process that solidifies under steep thermal gradients are crack initiators.
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Overhang from vertical | 40° | 45° | Downskin sits on powder, not metal |
| Wall thickness | 0.040 in (1.0 mm) | 0.016 in (0.4 mm) | Thin walls distort and warp |
| Horizontal hole | Teardrop profile | 0.3 in (8 mm) round | Crown of a round hole sags |
| Powder escape port | 0.16 in (4 mm) | 0.08 in (2 mm) | Trapped powder cannot be removed |
| Machining stock | 0.040 in (1.0 mm) | 0.020 in (0.5 mm) | Distortion after cut-off must be cleaned up |
| Internal fillet | 0.08 in (2 mm) | 0.04 in (1 mm) | Sharp corners crack under residual stress |
| Layer thickness | 0.0012 in (30 µm) | 0.0008 in (20 µm) | Halving the layer doubles build time |
Cost drivers
Build height is the first cost driver: machine time scales with layer count, so a part standing 8 in (200 mm) tall costs far more than the same volume lying flat, even though it uses identical powder. Cross-sectional area matters second, since it sets scan time per layer.
Powder is expensive and alloy-dependent — titanium and nickel superalloy powders cost several times what stainless does per kilogram — and only powder that is sieved and requalified can be reused, so contamination or a cross-alloy mistake writes off a full charge.
Post-processing is the cost most people underestimate. Stress relief, plate cut-off by wire EDM, manual support removal, HIP where required, and CNC finishing of critical features routinely total more than the print itself.
Volume breakpoints: DMLS is competitive from 1 part upward for geometry that cannot be made otherwise. Against machining, it wins below roughly 50–100 parts for complex shapes and loses immediately on simple prismatic ones. Against investment casting, the crossover is typically a few hundred parts, where pattern tooling amortizes.
- Reduce build height before anything else — reorient rather than redesign if you can.
- Design for self-supporting angles above 45° and teardrop holes; support removal is manual labor.
- Hollow and lattice bulk sections; you pay for every cubic centimeter melted.
- Nest several parts on one plate — the stress relief cycle and plate cut-off are shared.
- Machine only what must be machined, and say so explicitly on the drawing rather than applying a blanket tolerance.
Questions
6 questionsWhat tolerance can DMLS hold?
Roughly ±0.004 in (±0.1 mm) up to 1 in (25 mm), then about ±0.2% of the dimension. Some suppliers quote ±0.003 in plus ±0.001 in/in on well-supported geometry. Any feature that needs a fit, a seal, or a datum should be printed with 0.020–0.040 in (0.5–1.0 mm) of stock and machined.
What is the minimum overhang angle for DMLS?
About 45° from vertical. Below that, the melt pool sits on loose powder rather than solid metal, which conducts heat far more poorly, so the surface comes out rough and dross-covered and the part risks curling off its supports. Teardrop and diamond hole profiles avoid supports entirely.
Why do DMLS parts need stress relief before removal from the build plate?
Each melt track solidifies and contracts against already-solid material below it, locking in large residual stresses. Cutting the part free before heat treatment releases those stresses all at once and the part springs out of tolerance. Stress relief is performed with the part still bolted to the plate.
How dense are DMLS parts?
Above 99.5% of theoretical density with correctly developed parameters, and mechanical properties at or above cast values. Hot isostatic pressing — around 900 °C (1,650 °F) at 15 ksi (100 MPa) for Ti-6Al-4V — closes residual porosity and is standard practice for fatigue-critical aerospace and medical parts.
Is DMLS the same as SLM?
In practice, yes. Both are laser powder bed fusion, both fully melt the powder, and both build under inert gas. DMLS began as an EOS trade name and SLM as a competing one; the ISO/ASTM term for the family is laser powder bed fusion (PBF-LB/M).
When does DMLS beat machining or casting?
When the geometry cannot be made another way — conformal cooling channels, internal lattices, topology-optimized load paths, or an assembly consolidated into one piece — and at quantities below roughly 50–100 for complex parts. For simple prismatic geometry, machining is cheaper at any quantity.