In powder-bed fusion (PBF), a thin powder layer is spread across a build surface and selected regions are fused by a scanning energy source. The platform then moves and the cycle repeats.

For a beam with power $P$ moving at scan speed $v$, a simple line-energy measure is

$$E_l=\frac{P}{v}.$$

If $P=200\ \mathrm W$ and $v=800\ \mathrm{mm/s}$,

$$E_l=0.25\ \mathrm{J/mm}.$$

Line energy alone does not determine the process: layer thickness, hatch spacing, beam size, powder packing and thermal history also matter.

If delivered energy is too low, neighboring particles or tracks may not fuse completely, producing lack-of-fusion porosity. Excessive local energy can create unstable melt behavior, evaporation or deep narrow melt regions. Repeated heating and cooling can also generate residual stress and distortion.

Unfused powder supports some surrounding geometry, but metal PBF can still require solid supports for heat flow, anchoring and distortion control.

The resulting microstructure can differ strongly from wrought or cast material because solidification occurs rapidly under directional thermal gradients. Build orientation and scan strategy can therefore affect both geometry and properties.

PBF is not simply 'melting a powder drawing'. It is a repeated thermal-manufacturing process whose local energy delivery, powder state and heat flow determine consolidation and final performance.