Gas Flow Velocity Calibration in Tool Steel Powder Bed Fusion
Calibrating cross-flow velocity to 2.2-2.8 m/s prevents laser plume attenuation and condensate redeposition in tool steel powder bed fusion.
Laser Plume Attenuation
Meaning
Optical energy loss occurs when a laser beam travels through the vaporized metal and spatter generated during additive manufacturing. Understanding laser plume attenuation is vital for predicting the actual energy delivered to the powder bed. When the laser plume absorbs or scatters the laser beam, the effective melting power is reduced.
This reduction varies with the density of the metal vapour, creating inconsistent melt pool dimensions if the plume is allowed to linger.
Melting Defect
Vaporized metal acts as an aerosol that blocks a portion of the incoming laser radiation. Excessive laser plume attenuation results in insufficient energy density at the powder surface, which prevents complete consolidation. This leads to the formation of lack-of-fusion defects that compromise the mechanical performance of the finished component.
Flow Optimization
Inert gas sweeps the plume away from the optical path to maintain consistent laser power transmission. Managing laser plume attenuation requires a continuous, high-velocity gas stream that operates across the entire build area. Inadequate gas flow allows the dense plume to accumulate directly above the melt pool.
Sensor Monitoring
Photodiode sensors monitor the emission intensity and scattering of the laser beam to track changes in the optical path. These real-time measurements assist in evaluating the effectiveness of the gas flow system. Systems that maintain low, stable attenuation values ensure consistent weld track geometry throughout long production runs.