Lecture 10-powder bed fusion

Question 1

Define Powder bed fusion

Answer 1

thermal energy selectively fuses regions of a powder bed.

Question 2

What are the 3 Powder bed fusion methods

Answer 2

SLS-Selective laser sintering
SLM-Selective laser melting
Binder jetting

Question 3

Describe SLS

Answer 3

Powder bed is heated with IR heaters to near sintering temperature

Laser is then used to selectively sinter loose powder

Question 4

Why is sintering not melting

Answer 4

Sintering is NOT melting as the particles simply neck together and and form grain boundaries. while reducing pore sizes.

Question 5

Does SLS need supports

Answer 5

No the powder bed acts as the support

Question 6

SLM

Answer 6

Same as sintering but more energy is used to actually melt the powder and flow, rapid cooling occurs and grain boundaries are formed and the powder is fused.

Question 7

Describe Binder sintering

Answer 7

Polymer coated particles are sintered
The “green” part is then placed in furnace and polymer is burned off
Part is then infiltrated with lower temp alloy to complete part

Question 8

Materials

Answer 8

Polymer
Nylon
PEEK
Polystyrene

Metals
Stainless steel
Titanium/Alloy

Question 9

Pros of sintering

Answer 9

• Parts produced have properties similar to injection moulded material

• Un-fused powder acts as the support mechanism – therefore no support
structures

• There are fewer H&S issues than with Vat Photopolymerisation processes
• Parts are tough and therefore suitable for functional testing

• Unused polymer powder material can be re-cycled and used in the build
process

• You can fill the whole build volume with parts

• Minimal post-processing (for polymers) – requires unsintered powder remova
l
• Highly complex bespoke geometries are achievable

Question 10

Cons of sintering

Answer 10

• Distortion occurs in materials that must be compensated for (not all distortion
can be compensated)

• Higher energy input than most other processes due to the need for:
– Powder materials
– Inert atmosphere
– Heated build volume
– Thermal energy source for fusing

• Stresses may be set up during the cooling of parts
• Dust and particle control (more on this later)
• Build volume pre-heat and then post build cool down can take many hours
• Parts have rough surfaces

Question 11

Pros of melting

Answer 11

• Allows the use of common engineering metals with no
exotic additives required

• Produces dense (typically 80-98%) metallic components
• Un-fused powder is fully recyclable

• Parts can be heat treated as standard metallic engineered
components

• Highly complex bespoke geometries are achievable

Question 12

Cons of Melting

Answer 12

Distortion occurs in materials that must be compensated for (not all distortion
can be compensated)

Parts have rough surfaces

• Higher energy input (even higher than sintering) than most other processes
due to the need for:
– Powder materials
– Inert atmosphere
– Heated build volume
– Thermal energy source for fusing

• Dust and particle control (more on this later)

Question 13

Problems with powders

Answer 13

Health problems from inhalation

Powder can react quickly due to its surface area and can be fire risk

Question 14

Sintering nylon 12 is the most common manufacture for commercial applications as ?

Answer 14

It absorbs very little moisture
Nylon 12 retains excellent impact and non-impact strength even below freezing

resistance to chemicals

exceptionally strong resistance to cracking under stress

Nylon 12 has a very low coefficient of friction.

It dampens noise and vibration.

It is highly processable.

Question 15

Exam

d) Explain how binder sintering (also known as indirect sintering) works.

Answer 15

lecture notes