LEC 5 - 2

• Defintion:

  • AM process in which a liquid Binder is deposited to join selectively powder materials of the powder bed

• Type of Material: Metallic+ Composites

• State of Fusion: thermal + chemical reaction bonding

• Feedstock: Powder Bed + Liquid

• Material Distribution: Recoater + Print head

• Basic AM principle: solvent reacting curing

  (Lösungsmittel aushärten)

• Produced by AM: Greenpart

  • Composition material parts are joined by polymeradhesion

• Consolidation by secondary process: Furnace Sintering

+no need of support structures

+huge parts are printable

+wide range of materials available

-Post process needed

-Mechanical Properties dependend on chosen Binder

-Powders can be harmful

1. Material preparation of the powder

2. Printing

   • Powder coating

   • Binder Printing

   • Heating

     -> Green part

3. Curing:

   • Drying and Curing

   • Strengthen the green part for better handling

     -> cured part

4. Debinding:

   • Single heat treatment

   • Debinding

     -> brown part

5. Sintering:

   • Densification of part

   • Shrinkage to final geometry

     -> Final Part

Steps till Curing are done repetively during build phase

Debinding and Sintering are steps which are only done once after print is finished

Material:

• Powder

  • any powder can be proceed

• Binder

  • Water + glycerol

  • Solvent

  • Liquid

• plastic powder: 80:20 ratio, sand: 40:60 ratio

• Machine:

  • Cleaning cycle

  • Binder washing intervall

  • Heating power

  • Heating time

• Process:

  • Feed to power ratio

  • Layer thickness

  • Binder saturation

  • Roll speed

• Heading conditions:

  • Sintering/ Debinding atmosphere

  • Sintering temperature/ time

  • Curing temperature/ time

  • Debinding temperature/ time

  • Heating rate

• Powder:

  • Particle shape

  • Composition

  • Particle size

  • Flowanbility

  • Humidity

Right is:

• 1

• 4

• Stainless steel

• Titanium-alloys

strongly influences the

• process

• part requirements

• economics

• fills out void space between the particles in each layer & creates desired space

Requirements:

• Rheology for infiltration & printing

• Stability to be deposited with a printhead

• Wetting the powder

types of binder:

• Acid based binder

• Metal salts binder

• Aqueous-based binder

• initial contact

  • Binder droplet lands on the powder bed.

• spreading:

  • Binder spreads over the powder surface

  • Better spreading = larger contact area = better particle bonding

  • measures for enhancing wetting behaviour:

    • increase surface tension of solid

    • Decrease surface tension of liquid

• Imbition:

  • liquid binder pulled into empty pore between powders

• Drainage:

  • Binder flows from highly saturated regions to nearby dry regions.

• Saturation (Sättigung):

  • Percentage of the pore volume filled with binder

  • Under saturation:

    • powder can drop from green part (to less binder)

    • poor surface finish/ dimensional accuracy

  • Over saturation:

    • Binder flows outside the intended printing area (bleeding).

    • poor surface finsih/ dimensional accuracy

• Layer thickness:

  • minimum thickness of material layer

• Powder spread & print speed

• Saturation level:

  • Percentage of the pore volume filled with binder

  • undersaturation:

    • powder can drop from green part

    • poor surface finish/ dimensional accuracy

  • oversaturation:

    • Binder flows outside the intended printing area (bleeding).

    • poor surface finish/ dimensional accuracy

• Feed to powder ratio:

  • ratio comparing the volume of fresh powder supplied (fed) in front of the spreading mechanism (roller or blade) to the actual layer thickness being created

• Part Orientation

• Curing Cycle:

  • dry liquid binder

  • bound powder particles firmly together

  • greenpart

• Depowdering:

• Burn out/ Debinding:

  • same oven then Sintering

  • polymeric binder is pyrolyzed

• Infiltration:

  • Densyfication using an alloy with lower melting temperature

• Sintering:

  • densyfication method for binder jetted parts