LEC 4

• Powder based technologies

• Wire based technologies

DED-LB/M

• Process category (6)

• Process Characteristics:

  • Laser Beam

  • Arc

  • Electron Beam

• Materials:

  • Metal

  • Polymer

  • Ceramics

  • Composites

  
  

• wire comes out of the nozzle tip, it bends away from the straight theoretical direction, cause of it was stored as a spool

• Solution:

  • reduce distance between deposition point and wire guide

  • implementation of wire straightening unit

  • Move or rotate the build plate to match the natural curve of the wire

types of shielding gas:

• Inert Gases (Edelgase, do not react with melt pool):

  • Ar, HE

• Active Gases (react cheically with melt pool)

  • CO2

  • O2

• Mictures:

  • Ar-He

  • Ar-He-Co2

effects of shielding gas:

• protection against oxidation

• reduction of tempering colours

• adaption of surface tension

• heat from the electric arc ionizes the gas atoms

  • atom splitted into positiv Ion and Electron

• Ionized gas creates electrical conductivity

• Continuous flow of electrons and ions maintains the arc to generate high melting hea

• Arc Technologies

  • consumable electrode coupled:

    • Gas Metal Arc Welding (GMAW)

      • most used DED-Arc Process

      • WAAM

  • non consumable electrode decoupled:

    • TIG/ Plasma Welding

• Beam Technologies:

  • uncoupled

    • Laser-/ Electron Beam

Principle:

• wire acts as both the electrode (that creates the arc) and the filler material (that melts to build the part)

• coupled: Wire feed rate is proportional to the welding current

• continous movement:

  • Alternating

  • A -> B, B-> A

  • symmetric layer structure

• discontinous movement:

  • Disposition always starts and ends at same position

  • asymmetric layer structure (one sided raised)

TIG - Welding:

• free arc between tungsten electrode and component

Plasma welding:

• constricted (verengtes) arc between tungsten electrode and component

Principle:

• beam creates localized melt pool

• Wire gets pushed into melt pool

laser metal deposition process:

• lateral & coaxial laser metal deposition process

1. External energy (light or electricity) pumps ground-state electrons up to a higher energy level

2. Incoming photon hits an excited electron

   • Electron drops back to lower Energy level

   • Releases a second identical photon

3. Photons bounce back and forth between to mirrors creating a chain reaction, that increases identical photons

4. Once photon intensity is high enough, photons can pass the partial mirror, building a high intense Laser

• Horizontal offset beween layers

• Rotation of Platform

• Rotation of machinehead

+high depostion rate

+Increased complexity of parts using 5 axis

+larger part size, robust process

+cost savings in wire material

+little material waste (material usage >99.5%)

+Safer Handling (Eliminates health risks associated with inhaling fine metal powders)

-limitated range of usable materials

-more complex process cause of contact depositon

• Arc technologies:

  • non consumable Electrode: Plasma Arc

• Beam technologies:

  • Laser Beam

Feeding mechanisms:

• Disk-Feeder:

  • feeding mechanism: powder disk with spreader

• Bucket wheel feeder:

  • feeding mechanism: bucket wheel (Schaufelrat)

feed rate: controlled over RPM of disk

powder transport: (mostly) with inert gas

Powder focus:

• Inner powder feed: powder focus inside the nozzle

• Outer powder feed: powder focus outside the nozzle

Nozzle Configurations:

• Annual Gap:

  • Continuous 360° ring nozzle around the laser beam delivering powder

  • low deposition rate

  • high geometrical complexity

• Multiple Outlets:

  • Multiple separate nozzles arranged symmetrically around the beam

  • middle depostion rate

  • middle geometrical complexity

• Off-Axis:

  • Single nozzle feeding powder from one side at an angle

  • high depostion rate

  • low geometrical accuracy

+large variability of availble materials

+possible to use multiple different powders at same time

+complicated geometries with out support possible

+contactless process

-safety Risk due to use of fine particles

-material usage of max 80-90%

• Repair of Sintered Tools

• Repair of aero engine components

• Extension of the life time of high quality components

• Improvement of corrosion and wear resistance