Lesson 8.7ShapeChapter 8 · Additive manufacturing

Directed energy deposition (DED/LMD)

A laser melts a pool on the part; blown powder adds metal (directed energy deposition)

Directed energy deposition (DED) adds metal by melting it exactly where it lands, like a welding torch that builds instead of joins. In laser metal deposition (LMD), its most common form, a laser melts a tiny pool and blown-in powder becomes new metal. It is the go-to method for repairing costly worn parts and adding features to existing ones.

Photo: Lucie Prokešová, CC BY-SA 4.0, via Wikimedia Commons

laser metal deposition · head cross-section and a repair, 5 stepsTop: a cut through the head as it moves right. Bottom: a typical repair job. Circled numbers match the steps below.

How it works

Melt a small pool. A focused laser beam, typically hundreds of watts to a few kilowatts, melts a spot on the part. This melt pool (a tiny puddle of liquid metal) is a few millimeters wide.
Blow in the powder. Nozzles around the beam blow fine metal powder into the pool. Argon (an inert gas) carries the powder and shields the hot metal from air.
Let the bead freeze. The powder melts into the pool. As the head moves on, the metal behind it cools in a fraction of a second into a bead (a raised track of new metal).
Trace the layer, then step up. A robot or 5-axis machine (one that can also tilt and turn the part) guides the head along each layer's path. Then it rises one layer and repeats.
Machine to size. The surface comes out rippled and slightly oversize, so the part is milled or ground to its final shape. In a repair, this restores the original outline.

Key facts

Materials: Weldable metals: titanium alloys, nickel superalloys (heat-resistant alloys for jet engines), stainless and tool steels, cobalt and copper alloys. Mixing two powders can grade one metal into another
Typical parts: Repaired turbine blades, shafts and molds; wear-resistant coatings; features added to existing parts; near-net-shape blanks (close to final shape, needing only light machining)
Part size: From a few millimeters of repair up to parts over 1 m, limited by the robot or machine reach
Precision: About ±0.5 mm as deposited; final machining brings it to about ±0.05 mm
Surface finish: Rough and rippled as deposited; smooth only after machining
Batch size it suits: One-offs, repairs and small batches
Tooling and machine cost: No tooling. Industrial laser systems typically cost several hundred thousand to over a million dollars
Speed: Typically about 0.1–2 kg of metal per hour: faster than powder-bed fusion, slower than WAAM

Strengths and limits

Strengths

Adds metal to existing parts, so worn parts can be repaired
Builds large parts without a powder bed
Can switch or blend metals within one part
A tilting 5-axis head builds many overhangs without supports

Limits

Rough surfaces: almost every part needs machining afterward
Coarser detail than powder-bed fusion: no fine lattices or tiny holes
Heat causes stress and distortion that must be managed
Costly lasers, and fine metal powder is a fire and breathing hazard

Where it's used

AerospaceRepairing turbine blade tips and blisks (one-piece bladed disks); titanium preforms
Power generationRestoring worn turbine and pump parts
Oil and gasWear- and corrosion-resistant cladding on drilling tools and valves
ToolingRepairing and modifying molds and dies instead of replacing them
Heavy industryRebuilding worn shafts, rollers and gears

How to recognize it

Fine, parallel ripples on the surface, one for each bead laid by a pass of the head.
A boundary line where new metal meets the original part, visible on a cut or polished surface.
Machined faces right next to rough, wavy ones on the same part.
Thick walls with rounded, bead-shaped edges rather than sharp corners.

Compare with

Laser powder bed fusion8.4also melts metal powder with a laser, but in a thin spread layer: finer detail, smaller parts, no repairs.WAAM8.8the same build-up idea with a welding arc and wire: cheaper and faster, but coarser.Arc welding7.1DED is essentially automated welding, stacking beads into a shape instead of filling a joint.

Watch it

3Dnatives · A two-minute beginner's tour of DED, its materials and its uses

AM Media | The Cool Parts Show · An expert compares powder and wire feed and explains why 5-axis heads need no supports

AM Media | The Cool Parts Show · Real repair work: new metal laid on worn blade tips

Vision Miner · The wire-fed version of laser deposition at work

See real photos

Wikipedia: Directed energy deposition — how the powder-fed and wire-fed versions work; few photos
Wikimedia Commons photo search

Remember

DED melts metal exactly where it is added, using a focused heat source and powder or wire.
It shines at repairing and adding to existing parts, and at building large, rough shapes.
Plan for machining: parts come off the machine rippled and slightly oversize.