LEC 5 - 1

• Definition:

  • AM process in which material is selectively dispensed through a nozzle or orifice (Öffnung)

• Type of Material: Composite (metall filler + polymer binder)

• State of Fusion: thermal reaction bonding

• Material Distribution: Depostion Nozzle

• Basic AM principle: Extrusion of melted material

• Produced by AM: Greenbody

  • Composite material part joined by Polymeradhesion

• Consolidation by secondary step: Furnace Sintering

+easy to use

+equipment usually not expensive

+variety of materials

-Need of support structures

-high surface roughness compared to other AM techniques

-Anisotropy of properties

• Plunger-based:

  • plunger (Kolben) pushes pre-heated Melt through an Orifice

• Filament-based:

  • rotating gears (Zahnrad) push a filament through a heated nozzle

• Screw-based:

  • rotating screw (Schraube) melts and mixes materials before deposition through nozzle

-MEX:

• AM Steps:

  • Feed stock material gets heated

  • Fusion/ Melting

  • Extrusion and cooling after deposition

  • Solidification

• Secondary Steps:

  • Green part / body

    • furnace sintering

  • Consolidation (Verdichtung)

• Binder Systems: polymeric component

  • Main binder Component:

    • 50-90% of the Volume

    • removed first during debinding step

  • Backbone:

    • 0-50% of the Volume

    • holds together shape of the greenpart when main binder is removed

    • thermally decomposes right before sintering begins, just as powder particles start fusing together

  • Additives:

    • 1-10% of the volume

    • ensure uniform distribution of filler powder throughout the binder matrix

    • preventing agglomeration and phase seperation

• Fillers

  
  

• Ceramic fillers:

  • Silicon nitrate

  • Titanium dioxide + MgO

• Metall fillers:

  • Stainless steel

  • Titanium

• mechanical properties of the filament

• flow properties of feedstock

• processing conditions

• geometry of the filament

• design of printing head

• Buckling (Nachgeben) of the filament

  • Extrusion pressure > critical buckling stress

• Risk area of buckling:

• concept models:

  • .STL File

• Unprocessed Material:

  • Mechanical Properties

  • Density

• System:

  • Nozzle temperature

  • Nozzle diameter

  • Envelope temperature (Bauraumtemperatur)

  • Wear resistancy (Verschleißfestigkeit) of extruder

• Environmental factors:

  • Humidity

  • Temperature

• Build orientation:

  • x-/ y-/ z-direction

• Working parameters:

  • contur width

  • part x/y/z-shrinkage factor

  • layer thickness

  • raster width

  • air gap

  • raster angle

• Build orientation:

  • Direction along part is grown (typicall z-direction)

• Bead width:

  • width of extrusion track; 0.3-1mm

• layer slice thickness:

  • height of ectrusion track; (z-direction)

• Contouring:

  • extrusion tracks along the part edges; 1-2

• Raster Orientation:

  • The angle/direction at which the internal infill extrusion tracks are deposited relative to the main axis

• Air gap:

  • space between two extrusion tracks of the same layer

  • default = 0; tracks just touch

  • positive gap: tracks dont touch/ rapid build

  • negative gap: tracks do overlap/ dense structure

• Nozzle or liquefier temperature:

  • Equals melt temperature at the exit of the tip of the nozzle

• Envelope temperature:

  • temperature of air / room temperature

• Feed rate/ speed:

  • speed at which filament is driven into the liquefier

• Extrusion rate:

  • length of volume extruded in given time interval

• Travel speed:

  • speed of moving print head

Debinding:

• Definition:

  • The removal of the main primary binder system (polymers/waxes) prior to sintering

• Occuring error:

  • Bloating (Aufblähung)

  • Blistering (Blasenbildung)

  • Surface Cracking

  • Large Internal voids (Porosity)

• debinding techniques:

  • thermal

  • solvent

  • catalytic

Definition:

• final heat treatment that transforms powder particle of the brown body into bulk material (solid part)

Mechanism:

• growing sintering necks between particles, leads in reduction of porosity and overall part shrinkage

Temperature range:

• below melting point of main metals

• typicall around 70-90% melting point temperature of main metals

Wrong is:

• 2

• 4