Laser powder bed fusion. Powder metal 3D printing at full density.

How laser powder bed fusion works.

1. A layer of powder is spread. A recoater draws a layer of spherical, gas atomised metal powder across the build plate. On our machine a layer is typically 40 microns, about half the width of a human hair.
2. The laser melts the cross section. A 1 kilowatt ytterbium fibre laser, focused to a spot around 90 microns across, scans the slice of the part at up to 7 metres per second. The powder melts completely and fuses to the layer beneath. This is a full melt, which is why the parts are dense.
3. The plate drops one layer. The build platform lowers by one layer thickness, fresh powder is spread, and the next slice is melted. The scan pattern rotates 67 degrees between layers so that stresses do not line up.
4. Repeat, for hours or days. A 400 mm tall build is ten thousand layers. The chamber stays flooded with argon throughout so the molten metal never sees oxygen.
5. Cool, unpack, cut, treat. When the build finishes the plate cools under argon, loose powder is recovered and sieved for reuse, and the plate goes to stress relief before the parts are cut off it. Supports come off, and the parts go on to HIP, heat treatment, machining and finishing as the drawing requires.

LPBF, SLM, DMLS: one process, several names.

Laser powder bed fusion is the name in ISO/ASTM 52900, written PBF-LB/M for metal. Selective laser melting (SLM) and direct metal laser sintering (DMLS) are older trade names for the same thing; DMLS is the EOS term and appears on our machine. Despite the word sintering, DMLS on a modern machine melts the powder fully. If a supplier quotes you SLM, DMLS or LPBF they are describing the same process.

Is this powder metallurgy?

Yes and no, and the difference matters when you compare quotes. Powder metallurgy traditionally means pressing metal powder in a die and sintering it in a furnace, or injecting a powder and binder mix into a mould (metal injection moulding) and sintering that. Both start with powder, both end with a part that has shrunk in the furnace and kept some porosity.

Laser powder bed fusion starts with the same kind of powder and skips the sintering. The laser melts each layer into the last, so the part is fully dense when it leaves the machine, has not shrunk, and does not need a die or a mould. Binder jetting and bound metal filament are the additive processes that keep the sinter step, which is why their parts are cheaper per piece and weaker per gram. When a specification calls for powder metal 3D printing, ask which side of that line the supplier is on.

What LPBF does well.

• Internal channels and passages that follow the shape of the part, printed closed and leak tight.
• Thin walls to 0.5 mm, fine lattices and features a cutter cannot reach.
• Assemblies consolidated into one part with no brazed or welded joints.
• Alloys that are hard to machine, like Inconel 718, or hard to cast, like GRCop-42.
• One part through pilot volumes with no tooling and no change to the process between them.

Design rules that keep a build honest.

• Overhangs. Surfaces that lean more than about 45 degrees from vertical need supports or a redesign. Chamfers and teardrop holes are self supporting.
• Holes and channels. Horizontal round holes self support up to roughly 8 mm in diameter; above that, teardrop or diamond them. Internal channels need an exit so powder can be removed.
• Walls. 0.5 mm is achievable; 1 mm is comfortable for a structural wall. Keep thickness consistent to avoid distortion.
• Orientation. Height drives build time; downward facing surfaces are rougher; critical faces should point up or sit vertical.
• Machining stock. Add 0.5 to 1 mm on faces that will be finished to a tight tolerance.
• Residual stress. Every build is stress relieved on the plate before parts are cut free. Design for it: avoid long thin unsupported spans and abrupt section changes.

We check all of this before quoting. If a feature will not build, you hear about it with a proposed fix, not after the plate is unpacked.

The machine.

AME runs an EOS M 400: a single 1 kW ytterbium fibre laser over a 400 × 400 × 400 mm build envelope, under argon, with a scan speed of up to 7 m/s and a focus diameter of about 90 microns. It is the largest commercial metal additive platform in Alabama, and the same machine class the propulsion primes use. One machine, two alloys, run every week, is how you get to know a process.