8. Powder Bed Fusion

Question 1

Describe powder bed fusion.

Answer 1

Thermal energy either sinters or melts regions of a powder bed.

Question 2

What are the 2 types of powder bed fusion?

Answer 2

Selective Laser Sintering (SLS)

Selective Laser Melting (SLM)

Question 3

What heat sources are used for SLS and SLM?

Answer 3

• Infrared heater to heat close to sintering temp
• Laser to selectively heat loose particles even more.

Question 4

What are the stages of selective laser sintering?

Answer 4

1. Unsintered particles in heated state
2. Laser provides additional heat. this causes necking.
3. Grain boundaries form, Porosity reduces.
4. Powder fused, pores in material are smaller.

Question 5

What materials are used for SLS?

Answer 5

Polymers - Nylon, Polystyrene, PEEK

Question 6

What are the advantages of sintering?

Answer 6

• Produces parts with similar properties to injection moulded parts.
• Minimal post processing - No supports are required
• Less H & S issues than VAT polymerisation.

-Complex geometries are possible

• Nesting of multiple parts in bed possible.

Question 7

What are the cons of selective laser sintering?

Answer 7

• Distortion occurs in parts, this requires compensation.
• Higher energy requirement than most other processes.
• Rough surfaces on parts
• Dust and particle health and safety.

Question 8

What is the key difference between SLS and SLM?

Answer 8

Parts are melted not sintered, requiring more energy.

Question 9

What are the stages of SLM?

Answer 9

1. Particles in heated state
2. Laser heats particles to melting point.
3. Powder is now fused. Rapid cooling occurs and grain boundaries are formed.

Question 10

What materials are used for SLM?

Answer 10

Metals:

• Stainless steel
  -Aluminium alloy
  -Cobalt chrome

Question 11

What are the advantages of SLM?

Answer 11

• Common materials used.
• Parts can be heat treated
• Complex geometries
• Dense components produced.
• Unused powder can be reused.

Question 12

What are the cons of SLM?

Answer 12

-Distortion occurs and must be compensated for.

• High energy input required.
• Dust and particle health and safety.
• Rough surfaces.
• Heat dissipation structures are required sometimes.

Question 13

What is the main concern with fine powder?

Answer 13

Fire risk.

Question 14

Compare SLS and SLM.

Answer 14

SLS - sintering only, polymer powders only, no support structures required.

SLM - Melting, metal powder only, support structures to dissipate heat.

Both methods produce tough components and require expensive machines. Parts can be post treated to improve mech properties.