Lesson 8.4ShapeChapter 8 · Additive manufacturing

Laser powder bed fusion (metal, SLM/DMLS)

A laser melts thin layers of metal powder (powder bed fusion)

Laser powder bed fusion (LPBF) melts fine metal powder with a laser, one thin layer at a time, to build fully dense metal parts. Machine makers call it SLM (selective laser melting) or DMLS (direct metal laser sintering). It matters because it makes metal shapes no cutting tool or mold could, such as rocket engine parts with cooling channels inside.

Photo: Matti Blume, CC BY-SA 4.0, via Wikimedia Commons

Metal powder bed fusion chamber in cross-section: argon flow, laser, blade, supports and build plateCircled numbers match the steps below; steps 3 to 5 repeat thousands of times.

How it works

Slice and add supports. Software slices the model into very thin layers and adds supports (thin metal struts). They anchor overhangs to the build plate and draw heat away so the part does not warp.
Fill with argon. The chamber is sealed and flushed with argon or nitrogen, inert gases that keep hot metal from oxidizing. A steady gas flow sweeps smoke and spatter (tiny hot droplets) out of the laser's path.
Spread a layer. The supply piston rises, and a recoater blade spreads metal powder over the build plate, typically 0.02–0.06 mm thick.
Melt the slice. A fiber laser, typically 200–1,000 W, traces the slice. It melts the powder into a tiny melt pool that freezes almost instantly, welding onto the layer below.
Lower and repeat. The build plate drops by one layer and the cycle repeats, often thousands of times over one or more days.
Finish the part. While still on the plate, parts get a stress-relief heat treatment (slow heating that relaxes locked-in stresses). Then they are cut off, supports are removed, and many go on to HIP (hot isostatic pressing, lesson 9.3) and machining.

Key facts

Materials: Titanium alloys (Ti-6Al-4V), stainless and tool steels, nickel superalloys (Inconel), aluminum (AlSi10Mg), cobalt-chrome, copper alloys
Typical parts: Rocket engine injectors, turbine and fuel-system parts, medical implants, dental crowns, molds with cooling channels, heat exchangers
Part size: Typically 25–40 cm per side; the largest machines exceed 1 m
Precision: About ±0.1 mm as printed; critical faces are machined afterwards
Surface finish: Matte and slightly rough, like fine sandpaper; rougher on down-facing surfaces; often blasted, polished or machined
Batch size it suits: 1 to a few thousand parts a year; best when each part is complex and valuable
Tooling and machine cost: No tooling; machines cost several hundred thousand to a few million dollars
Speed: Slow: builds often take one to several days

Strengths and limits

Strengths

Shapes impossible to machine or cast: inner channels, lattices, organic forms
Fully dense metal, comparable to cast or wrought metal after heat treatment
Several parts merged into one, saving assembly and weight
Light designs from topology optimization (software that removes unneeded material)

Limits

Very expensive machines, powder and post-processing
Needs supports, which must be cut or machined off
Locked-in heat stresses can warp parts or crack them off the plate
Slow, with rough surfaces that often need machining

Where it's used

SpaceRocket engine injectors, combustion chambers, turbopump parts
AerospaceJet engine fuel nozzles, brackets, heat exchangers
MedicalHip cups and spinal implants with porous surfaces, custom implants
DentalCobalt-chrome crowns, bridges and denture frames
ToolingInjection molds with conformal cooling (channels that follow the part's shape)
MotorsportLight brackets, uprights, exhaust and hydraulic parts

How to recognize it

A matte, slightly grainy gray metal surface, often with faint layer lines.
Small scars or rough patches on down-facing surfaces, where supports were removed.
A flat, often machined base where the part was cut off the build plate.
Organic shapes, lattices or inner channels that no drill or mold could produce.

Compare with

Selective laser sintering8.3the same powder-bed idea with nylon; no supports needed, but plastic parts only.Binder jetting8.5glues metal powder instead of melting it, then sinters it in a furnace; cheaper per part, but parts shrink.Directed energy deposition8.7feeds powder or wire into a laser melt pool; builds or repairs bigger parts, with coarser detail.

Watch it

RAPID DIRECT · The full SLM workflow, explained for beginners

Billy Wu · Close-up footage of a part being built

3D Distributed · A machine at work: laser, sparks and recoater

NASA's Marshall Space Flight Center · Printed rocket engine parts at NASA

See real photos

Wikipedia: Selective laser melting — process schematic and photos of printed metal parts
Wikimedia Commons photo search

Remember

LPBF melts metal powder with a laser in inert gas, building fully dense parts layer by layer.
It makes complex, light metal parts no other process can, but slowly and at high cost.
Supports, heat treatment, cutting off the plate and often machining are part of every job.