Electron Beam Melting (EBM)

EBM is a powder bed fusion process that melts metal powder with a high-power electron beam in a vacuum, building fully dense metal parts layer by layer.

Principle

A heated tungsten filament emits electrons, which are accelerated by high voltage (about 60 kV) and focused and deflected by electromagnetic coils. The kinetic energy of the electrons turns into heat when they strike the powder and melts it.

Working

1. The chamber is evacuated (about $10^{-4}$ to $10^{-5}$ mbar), then a little helium is added.
2. A rake spreads a 50 to 100 micron layer of metal powder.
3. The beam first preheats the powder (about 700 C for Ti-6Al-4V), lightly sintering it so it will not blow away and reducing residual stress.
4. The beam then melts the cross-section selectively.
5. The platform lowers, new powder is spread and the cycle repeats.
6. The part cools slowly in vacuum, then loose powder is removed.

Materials

Titanium alloys (Ti-6Al-4V), cobalt-chrome, Inconel, tantalum.

Advantages and limits

Advantages	Limitations
Dense parts, good properties	Only conductive metals
Low residual stress (high temperature)	Rough surface finish
Vacuum prevents oxidation	Costly machine
Fast, high beam power	Powder removal and size limits

Applications

Orthopaedic and dental implants, aerospace parts (turbine blades), lightweight lattice structures.

Exam tip

Mention vacuum, preheating and electron beam source; compare with SLM (laser, inert gas).