LEC4

• Metal Wire/ Powder

• melted by an energy source (laser, electron beam, electric arc)

• moving deposition head with energy source and wire nozzle

• localized melt pool on previous layer/ substrate (Grundplatte)

• motorized wire feeder pushes wire in center of active melt pool

• Inert:

  • Argon

  • Helium

• Active:

  • CO2

  • O2

• Mixtures:

  • Ar-He

• Protecting against oxidation

  • Reducing of tempering colours (following out of oxidation)

• Adaption/ lowering of surface tension

• Ionisation:

  • electric arc ionizes the gas atoms into free electrons and positive ions

  • turns the gas into a conductive plasma column that allows the electrical current to flow continuously

1. Arc Technologies: Consumable Electrode ("Coupled")

• Gas Metal Arc Welding standart WAAM

• metal printing wire serves a dual purpose

• is both the feedstock material and the electrical electrode that creates the arc

2. Arc Technologies: Non-Consumable Electrode ("Uncoupled")

• TIG (Tungsten Inert Gas)

• Plasma welding

• heat generation and the material feeding are completely separate

• permanent, non-melting electrode creates and maintains the electric arc with the substrate

• metal wire is then pushed into that arc from the side as an independent element

3. Beam Technologies ("Uncoupled")

• high-power laser beam/ electron beam focuses down onto the substrate to create a melt pool

• separate wire feeder pushes the wire into the path of the beam from the side

• high electrical voltage between two electrodes

• electrical pressure removes electrons from the surrounding shielding gas (Ions)

• Gas: superheated, electrically conductive plasma column (Leitfäheige Plasmasäule)

• Current (Strom) flows continuously through this plasma bridge(visible electric arc)

• Continuous Movement (Symmetric Layer Structure)

  • torch alternates its printing direction with every layer

  • height differences/ defects at the start/end points cancel each other out

  • highly flat, even, and symmetric print result

• Discontinuous Movement (Asymmetric Layer Structure):

  • torch prints in the exact same direction for every single layer

  • starts and stops at the same ends

  • material errors pile up over time

  • uneven, sloped, or asymmetric print result

• permanent electrode made of tungsten (tip does not melt during printing or welding)

• electric arc is purely the heat source to create the melt pool

• wire feedstock must be pushed into the arc from the side (uncoupled element)

• pure inert shielding gases (Argon)

• extremely precise control over heat input and deposition rate

  • clean, spatter-free, and high-quality printed layers

• advanced evolution of TIG welding

• non-melting tungsten electrode

• Constricted Arc:

  • torch forces the electric arc through a very narrow copper nozzle

• fast deposition rates, narrow walls, and minimal heat distortion of the part

• power source pumps energy into a special gas or crystal, charging up its atom (Atoms in a higher energy level)

• light wave hits a charged atom and forces it to drop its energy

  • creates a perfect clone of the light wave traveling in the exact same direction

• mirrors bounce these cloned light waves back and forth

  • every pass hits more charged atoms -> huge amount of identical light waves

• if light becomes powerful enough, it bursts through a semi-transparent mirror -> high-energy Laser Beam

Energy source:

• fiber-/ disc-/ diode Laser

Beam guiding system:

• flexible fiber:

  • high-tech glass cable that traps the laser light inside and pipes it directly to the robot arm

  • bends easily (allows robot to move freely in any direction)

• mirror

Focusing optic:

• direct optic:

  • system of lenses located right at the end of the torch

  • takes the incoming laser light and focuses it down into a tiny, intense point

  • melt the metal wire exactly where it hits the substrate

• Stubbing:

  • beam to wide at wire tip -> not enough energy to melt

• Correct Adherence:

  • Balanced heat input -> smooth, uniform, stable print track.

• Dripping Condition:

  • Intense heat hits the wire too early -> wire melts up in the air -> drips down in random blobs

• 
  

• Horizontal offset between layers

• Rotation of platform

• Rotation of machine head

• Repairs

• Extending the lifetime of high quality components

• Improvement of corrosion and wear resistance (Verschleißbeständigkeit)

• Near-net shape (part close to its final, no/ small finishing work) manufacturing of high-quality components with design flexibility

• High deposition rate

• Larger part size, robust process

• Cost saving in wire material & little material wastage

• Near-net-shape manufacturing of high-quality components

• Limited range of compatible materials and alloys as compared to powder AM

• Coupled (GMAW):

  • wire carries the current and touches the pool

  • Wire and heat are linked, making the process highly sensitive and difficult to control

• Arc Technologies (Lichtbogen):

  • non-consumable Electrode: Plasma Arc

• Beam Technologies:

  • Beam: Laser Beam

    
    

• Disk-Feeder:

  • feeding mechanism: powder disk with spreader

  • feed rate controlled over rotational speed (RPM) of the disk

  • Powder Transport: (mostly) Inert Gas

• Bucket wheel feeders

  • Feeding mechanism: bucket wheel

  • feed rate controlled over rotational speed (RPM) of the wheel

  • Powder transport: (mostly) inert gas

• Inner Powder Feed:

  • powder focus inside the nozzle

  • powder melts completely before it leaves the nozzle

• Outer Powder Feed:

  • powder focus outside the nozzle

  • focus point where the powder melts is in the air, right before it hits the component

• Annular gap (Ringspalt):

  • powder flows out of a continuous, 360-degree cone shape surrounding the laser beam

• Multiple Outlets:

  • several seperate nozzles

• Off-Axis:

  • single, separate injection nozzle feeds the powder from one specific side into the laser beam

Advantages:

• Powder efficiency >80%

• good shielding of molten pool

  
  

Disadvantages:

very bulky:

• Accessibility at the workpiece

• Limited 3D capability

  
  

Advantages:

• high robustness

Disadvantage:

• Accessibility at the workpiece

• Powder Efficienty (60-70%)

Advantage:

• Accessibility at the workpiece

Disadvantage:

• Powder efficiency 50-70%

Advantages:

• Large Variety of available materials

• Contactless process

• complicated geometries without support possible

• possibility of using 2/ more powders simultaneously

Limitations:

• Saftey/Health Risks due use of fine powders

• Material Efficiency max 80-90%