Metal 3D Printing
Also: DMLS, direct metal laser sintering, SLM, selective laser melting, laser powder bed fusion, LPBF, L-PBF, PBF-LB/M, DMLM, metal additive manufacturing, metal AM
Metal 3D printing (laser powder bed fusion, DMLS) makes dense titanium, stainless, Inconel and AlSi10Mg parts with internal channels, HIPed and machined.
36 shops tagged Metal 3D printing among 771 3D printing companies in the Noramark directory
Laser powder bed fusion (LPBF) spreads a layer of metal powder 30-60 µm (0.001-0.002") thick across a build plate, melts the cross-section of each part with one or more fiber lasers, lowers the plate and repeats, all under argon or nitrogen. DMLS, SLM and DMLM are machine makers' names for the same process. Parts are welded to the plate and held by support structures that anchor down-facing surfaces and carry heat away. Well-tuned parameters give parts above 99.5% dense, with static strength comparable to cast or wrought metal of the same alloy after heat treatment.
The process earns its cost where machining and casting struggle: conformal cooling channels, manifolds with internal passages, heat exchangers, lattice-filled or topology-optimized brackets, and assemblies consolidated into one part. Fuel nozzles, turbine and rocket engine hardware, orthopedic implants and injection-mold inserts are established applications. It also makes one-off and low-volume titanium and nickel alloy parts without waiting for forging dies or a casting pattern.
A printed metal part is not finished when it leaves the machine. The usual routing is stress relief on the plate, removal by wire EDM or bandsaw, support removal, hot isostatic pressing (HIP) for fatigue-loaded parts, the alloy's heat treatment, bead blasting, and machining of every surface that needs better than ±0.1-0.2 mm (±0.004-0.008") or a sealing finish. Parts that skip stress relief distort when cut free, as-built surfaces are rough enough to cut fatigue life, and properties differ between the build direction and the layer plane. Budget for the whole chain on the quote.
At a glance
| Typical tolerances | Standard ±0.2 mm (±0.008") on small features, or about ±0.2% on larger dimensions, as-built after stress relief; ±0.1 mm (±0.004") with care on small, well-supported parts. Bores, sealing faces, bearing fits and threads are printed with 0.5-1 mm (0.020-0.040") of stock and machined to ±0.025 mm (±0.001"). Flatness and straightness of long, thin sections are the weak points, because residual stress bends them when they come off the plate. |
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| Size limits | Common machines build within about 250 x 250 x 300 mm (10 x 10 x 12"); 400 x 400 x 400 mm (16 x 16 x 16") machines are widespread at larger shops, and a few U.S. shops run 600 mm (24") class machines with build heights near 1 m (40"). Minimum wall about 0.4-0.5 mm (0.016-0.020"), with 1 mm (0.040") a safer design value; holes and channels under about 1 mm (0.040") tend to fill with sintered powder, and every internal passage needs an opening to clear the powder. |
| Surface finish | As-built 6-12 µm Ra (240-470 µin) on vertical walls and up-facing surfaces; 15-25 µm Ra (600-1,000 µin) on down-facing and supported surfaces. Bead blasting evens this to about 3-6 µm Ra (120-240 µin); machined faces reach 0.8-1.6 µm Ra (32-63 µin); polishing, electropolishing or abrasive flow machining improves visible surfaces and internal channels. |
| Lead time | Prototype parts in 1-2 weeks as-built with stress relief and support removal; 3-6 weeks when HIP, heat treatment, machining and inspection are added (HIP runs are batched and can add one to two weeks). Qualified production depends on a frozen build file, witness coupons and first article inspection. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
The qualified workhorses are Ti-6Al-4V (Grade 5, and Grade 23 ELI for implants), 316L and 17-4 PH stainless, and Inconel 718 and 625, with 15-5 PH, maraging steel (1.2709), cobalt-chrome, Hastelloy X and copper alloys such as CuCrZr and GRCop-42 at specialist shops. Aluminum prints as AlSi10Mg (plus a few proprietary high-strength alloys), a casting-type composition: 6061, 7075 and 2024 hot-crack under the laser. AlSi10Mg is usually stress relieved around 300 °C (570 °F), which trades some as-built strength for ductility; it suits housings, brackets and heat exchangers, not fatigue-critical structure where 7075 would be specified. As-printed 17-4 PH can hold retained austenite, depending on the powder and atmosphere, so it is solution treated before aging to H900 or H1025. Free-machining grades and high-carbon tool steels are not printed.
What drives the cost
- Build height and laser time: every layer takes time whether the plate holds one part or twenty
- Support volume, and the hand labor to remove supports and blend their witness marks
- Alloy: titanium and nickel alloy powders cost several times 316L, and reactive powders need extra handling
- Post-processing: stress relief, wire EDM off the plate, HIP, heat treatment and machining of critical features
- Nesting: how many parts share one build plate
- Inspection and documentation: powder certs, witness tensile coupons, CT scanning, first article inspection
When to use it
- Internal passages, conformal cooling, manifolds and heat exchangers that cannot be drilled or cast
- Consolidating a multi-piece brazed or welded assembly into one part
- Low volumes of complex titanium, nickel alloy or stainless parts, without waiting for forging dies or casting patterns
- Lightweight lattice and topology-optimized structures
- Injection-mold inserts with conformal cooling channels, in maraging steel
When not to
- Parts a mill can cut from bar in one or two setups: machining is faster, cheaper and more accurate
- Volumes in the thousands: investment casting or die casting win once the tooling is amortized
- Large, thin, flat plates, which distort under residual stress
- Fatigue-critical parts without HIP, machined or polished surfaces and a qualified process
- Alloys outside the shop's qualified parameter sets, such as 6061 or 7075 aluminum
Design tips
- Keep down-facing surfaces at 45° or steeper from the build plate, or accept supports and the finishing they need on those faces.
- Make horizontal holes larger than about 6-8 mm (0.25-0.30") teardrop or diamond shaped so they print without internal supports, which cannot be removed.
- Leave 0.5-1 mm (0.020-0.040") of machining stock on bores, sealing faces and threads, and give the machinist datums that survive printing.
- Add powder escape holes to every closed cavity and channel, and say how clean the passages must be.
- Call out the alloy to its AM specification where one exists (ASTM F2924 or F3001 for Ti-6Al-4V, F3055 for 718, F3056 for 625, F3184 for 316L) and state the post-processing: stress relief, HIP and heat-treat condition.
- Ask for witness tensile coupons from the same build when properties matter.
- Avoid abrupt changes in section and long, thin, unsupported features; they concentrate residual stress and curl.
Frequently asked questions
- How accurate is metal 3D printing?
- As-built laser powder bed parts hold about ±0.1-0.2 mm (±0.004-0.008") on small features and roughly ±0.2% on larger dimensions, after stress relief. Surfaces that need better, such as bores, seal faces and threads, are printed with stock and machined to ±0.025 mm (±0.001") like any other blank.
- Are metal 3D printed parts as strong as machined parts?
- In static strength, largely yes: stress-relieved, HIPed and heat-treated Ti-6Al-4V and Inconel 718 meet or approach the tensile minimums of wrought material. Fatigue strength is lower unless the part is HIPed and its critical surfaces are machined or polished, and properties vary with build direction, so qualified parts are tested with coupons from the same build.
- Do metal 3D printed parts need HIP?
- Not always. HIP closes internal porosity and lack-of-fusion voids, which raises fatigue life and ductility; it is standard for aerospace, medical and pressure-critical parts and optional for prototypes, fixtures and statically loaded brackets. It does not close porosity that breaks the surface, and it adds cost and one to two weeks.
- DMLS vs SLM: what is the difference?
- Nothing that matters to a buyer. DMLS, SLM and DMLM are trade names for laser powder bed fusion, and all of them fully melt the powder. Compare shops by build size, qualified alloys, in-house post-processing and inspection rather than by the name of the machine.
