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Additive Manufacturing > Processes overview > Flashcards

Processes overview Flashcards

1
Q

Describe Material Extrusion.

A

A material is selectively dispensed through a nozzle or orifice.

Fused Deposition Modeling (FDM)

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2
Q

What materials are used for MEAM?

A

Polymers: ABS, PLA, PETG

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3
Q

What are the advantages of MEAM?

A

cheapest and most common AM tech

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4
Q

Describe Vat Photopolymerisation.

A

Liquid photopolymer in a vat is selectively cured by light-activated polymerization.

Top down or bottom up.

Laser or projector used.

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5
Q

What materials are used in VAT polymerisation?

A

Liquid photopolymers: epoxy/acrylic non polymerised liquid.

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6
Q

Compare projector to laser image projection in VAT polymerisation.

A

Projector:
- Faster (laser moves around whole shape)
- Less moving parts

Laser:
- More detailed
- can change resolution
- Larger range light spectrum.

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7
Q

Compare top down to bottom up image projection in VAT polymerisation.

A

Bottom up:

Advantages:
- Accurate layer thickness control
- No sweeper
- part height not limited
- smaller vats used

Disadvantages:
- sticking
- Peeling process

Top down:

Advantages:
- Higher resolution
- No peeling process required

Disadvantages:
- Resin surface charecteristics can affect the quality of the part.
- Slower due to recoating process
- part thickness determined by the viscocity of the resin.

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8
Q

What are the advantages of VAT polymerisation?

A

Accurate, good surface finish, large build sizes available, low thermal energy input.

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9
Q

What are the disadvantages of Vat polymerisation?

A

Curling of large flat surfaces - prevents sweeper from sweeping.

Toxic materials

UV light ages parts

Parts need cleaning and the post curing.

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10
Q

Describe Powder Bed Fusion

A

Thermal energy selectively fuses regions of a powder bed.

Selective Laser Sintering (SLS) or Selective Laser Melting (SLM)

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11
Q

What materials are used for SLS and SLM?

A

SLS - Polymer powder (nylon, polystyrene, PEEK)

SLM - Metal powder ( stainless steel, aluminium, Ti alloy)

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12
Q

What are the pros of SLS?

A

Similar properties to injection moulded parts

Supports not needed

minimal post processing required

tough parts

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13
Q

What are the pros of SLM?

A
  • materials used are common
  • bespoke geometries possible
  • dense metallic components
  • any unfused powder can be reused
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14
Q

What are the cons of SLS?

A

Distortion in parts

High thermal energy input

dust and particle control

rough surface finish

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15
Q

What are the cons of SLM?

A

Distortion in parts

High thermal energy input

dust and particle control

rough surface finish

Supports to allow heat escape required

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16
Q

Describe Material Jetting

A

Droplets of build material are selectively deposited.

  • Ink Jet Printing.
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17
Q

What actuation methods are used for material jetting? compare them

A

thermal:
pros
- Cheaper print heads
cons
- material gets burnt on print head reducing performance and lifetime
- Thermal cycling of print material can affect its properties

piezoelectric:
pros
- wider range of materials can be printed
- More viscous materials can be printed.

18
Q

What materials are used in material jetting?

A

Polymers and waxes, Metals and Ceramics, UV cured materials.

19
Q

What are the pros of material jetting?

A

dissolvable supports

multi material parts

smooth surfaces

fast process

20
Q

What are the cons of material jetting?

A

Material properties are limiting, sometimes too weak

21
Q

Describe Binder Jetting

A

A liquid bonding agent is selectively deposited to join powder materials. Similar to powder bed fusion.

2 types: visual and large scale visual/ mechanical

22
Q

What materials are used in the two types of binder jetting?

A

Visual = Cornstarch or plaster powder

Large scale/mechanical = polymer metal or ceramic powder

23
Q

What are the pros of binder jetting?

A

visual and mech properties:

Fast

low cost

low waste

mech properties only:

low temp - less energy

better mech properties than pbf

New process so less old systems.

24
Q

What are the cons of binder jetting?

A

visual models:

  • not functional parts
  • limited materials
  • low strength and poor surface quality

Mech properties:

quite a few post processing steps required

25
Q

What is infiltrant?

A

Post process of binder jetting. applied to part after printing to improve mechanical properties

26
Q

Describe Directed Energy Deposition

A

Focused thermal energy is used to fuse powder or wire material by melting as the material is being deposited.

Laser Engineered Net Shaping (LENS).
Electron Beam Additive Manufacture (EBAM)

27
Q

What materials are used in DED?

A

Metal powder or wire

occasionally polymers or ceramics.

28
Q

What are the pros of LENS over EBAM?

A
  • No vacuum required (Cheaper setup, larger parts possible).
  • More precise

No x-rays generated during process

29
Q

What are the pros of EBAM over LENS?

A
  • Better weld penetration
  • Dissimilar materials possible.
  • No risk of gas contamination
  • Electron is more electrically efficient
  • Faster material deposition rate.
30
Q

What are the pros of DED?

A
  • Fine microstructure means higher hardness than wrought parts.
  • Control of microstructure possible
  • High density parts
  • Functionally graded metals
  • Faster deposition than powder bed fusion
31
Q

What are the cons of DED?

A
  • Requires inert atmosphere or vacuum environment
  • Poor resolution and surface roughness
  • Part complexity limited compared to powder bed process.
32
Q

What are the two types of sheet lamination?

A

Laminate object manufacture (LOM) - sheets of material bonded together.

Ultrasonic additive manufacturing (UAM) - metal sheets ultrasonically welded together before being CNC machined to shape.

33
Q

What materials are used in LOM?

A

Papers and polymers

34
Q

What materials are used in UAM?

A

Metal sheets.

35
Q

What are the benefits of LOM?

A
  • Cheap materials
  • Simple setup and operations
  • Nesting of multiple parts
36
Q

What are the cons of LOM?

A
  • Support removal can damage part, also time consuming
  • Sealing of part required to prevent moisture ingress, Can distort the part.
  • Difficult to produce enclosed volumes.
  • Lack of material choice
  • Wasteful process for materials
  • Less complex part geometry than most other am processes.
37
Q

What are the pros of UAM?

A
  • Process occurs well below metal melting point
  • Bonds dissimilar materials
  • Process can be paused without creating weaknesses or errors.
  • High accuracy
  • No powder
  • No vacuum needed
  • Quite fast
  • no support structures
38
Q

What are the cons of UAM?

A
  • Expensive system
  • Limited material choice
  • Cant print complex shapes
39
Q

What are the main types of physical model in AM?

A

Geometric: Validate geometry and assembly, materials not so important

Design concept: Full size or scaled they enhance communication between partners. Good for checking concept / aesthetics etc., accuracy not important.

Functional: Allows some testing that is similar to the market function of the part, similar or same material properties are desirable

Technical: Have all the functional features, manufacturing process may be slightly different

40
Q

What is the equation for cure depth?

A

Cd = Dp ln(E/E1)

Cd = cure depth

Dp = penetration depth

E = energy

Ec = Critical Exposure

41
Q

Whats the equation for volumetric extrusion?

A

VE = w * H * f

VE = Volumetric extrusion rate

w = nozzle diameter

H = layer height

f = nozzle movement speed

42
Q

What are the equations for jettability?

A

Oh = (We)^-2 * Re

Oh = n/(pLo)^-2

Oh = jettability between 1 & 10

We = Weber number
Re = Reynolds number

n = viscosity
p = density
L = nozzle diameter
o = surface tension

Additive Manufacturing (9 decks)

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