VL VI - PBF

Definition Powder bed fusion

AM Process in which thermal energy selectively and layer wise fuses powder bed

Powder bed can consist of plastic or metal powders

Whats PBF-LB/M

Powder bed fusion of metals using laser beam

Whats PBF-EB/M

Powder bed fusion of Metals using Electron beam

Pros PBF

• High Maturity

• High dimensional accuracy

• Complex geometries

• High material performance

• Wide range of materials availible

• High material utilization (95 - 99%)

Cons PBF-M

• High cost

• Low build rates

• Powders can be harmful

• Post processing needed

• Energy intensive process

Beam source PBF-LB/M

Fiber Laser

Fiber Lasers Pros and characteristics

• Fiber lasers gives better narrowing

• high beam quality M² < 1,3 (1,1-1,3)

• Inner fiber doped with rare earth ions

• Wavelength {lambda} = 1064nm - 1080nm

Whats a Galvanometer scanner

• Highly dynamic electro-optical component

• use a rotatable low-inertia mirror

• position a laser beam with high precision and repeatability

• name derived from motor type

Whats used to deflect the beam in PBF-LB

Galvanometer scanner

Rotation speed and velocity of Galvanometer scanner

• Rotation: up to 30 rad/s

• Velocity: up to 10m/s

Galvanometer challenges and solution

• enable 2D deflections, 2 axes with no commen center of rotation

  • Compensation by an adapted control

• Rotation creates almost a focussphere when using simple lens

  • Prefocused system (moveable lens)

  • Flat field objective (f-theta lens)

Different Powder Dosing mechanisms PBF

• Powder Tank

• Dosing platform

Whats a powder Tank

Powder is conveyed from above through a powder tank

Whats a Dosing platform

Powder is conveyed from the bottom to the top

Different Powder Coating mechanisms

Established:

• Knife

• Brush

• rubber lip

Research

• Roller

• Sprinkling

• Lift off the blade

Why is a Knife Coating mechanism bad

Knife can be damaged by the part during coating

Meltpool Lifetime PBF

50 mikroseconds

Absorbtion rate of Laser beam in powder layer

Ca. 80%

Absorbtion rate of Laser beam in substrate (metal block)

ca 50% with a peak at the beginning due to deeper penetration and higher absorbtion

Prerequisite for a stable process

Uniform, reproducible and complete powder layers

Process Atmosphere PBF

Flooded with inert gas like Argon

Why use a Process atmosphere for PBF

Gas carries metal vapor dischrage, spatter and ejections away, so i doesnt interact with laserbeam

In which direction should the inert gas flow

In a way, that spatter, etc. is transported away from the print

What does increased shielding gas flow lead to

• Increased penetration and instability

• Decreased porosity

• Better removal of vapor plume

• less interaction LB and vapor plume

Why is Helium better than Argon

• Reduction of spatter

• increase of vapour plume speed

• modification of vapour composition

• smaller nanoparticles due to higher conductivity

• promoted denudation phenomena, because of higher gas flow speed