MECHENG236 - Additive Manufacturing

Question 1

What is the Material extrusion method

Answer 1

⚫ This method extrudes plastic
through a nozzle and builds each
section by essentially drawing the
shape with the nozzle whilst
extruding beads of plastic for that
layer
⚫ The plastic hardens immediately
after being squirted from the nozzle
and bonds to the layer below
⚫ Process is then repeated for next
layer

Question 2

Material extrusion pros and cons

Answer 2

⚫ Pros:
– Most affordable machines, particularly with ‘desktop’ machines
(though desktop machines are not suitable for manufacturing)
– Prints in standard thermoplastics
– Low cost material available for desktop 3D printers
– Easy to use machines
⚫ Cons:
– Most anisotropic process. Substantial weakness in Z direction
– Poorest surface quality process
– Doesn’t scale well for production. 10 parts takes 10 times longer
than 1 part
– Difficult polymer support material removal, unless they are soluble
– Requires support material for overhangs

Question 3

Material extrusion materials

Answer 3

⚫ Standard materials:
– ABS/ASA
– Polycarbonate
– ABS/Polycarbonate
Blends
– Nylon
– PPSF/PPSU
– ULTEM 9085 and 1010
– PLA
⚫ Special materials:
– Clay filled polymer
– Brick filled polymer
– Wood filled polymer
– Metal filled polymer
– Concrete
– Chocolate
– Polyurethane foam
– Silicone
– Epoxy
– Bio-materials
– HPA/PCL

Question 4

What are Markforged Metal-X &
Desktop Metal methods

Answer 4

Material extrusion-based machine
that uses metal-filled filament.
After printing, polymer is burned
out or chemically debound and
metal is sintered.
Parts can shrink by up to 20%.

Question 5

What is Vat Photopolymerisation (VPP)?

Answer 5

⚫ Traces a UV beam on the surface
of a vat of liquid photopolymer.
⚫ The material solidifies wherever
the UV beam strikes the liquid
⚫ Layer is then lowered a small
distance into the vat and next
layer is traced on top of the first
⚫ The self-adhesive property of the
material causes the layers to
bond to one another

Question 6

Vat Photopolymerisation (VPP) acronyms

Answer 6

SLA, DLP

Question 7

Material extrusion acronyms

Answer 7

FDM, FFF, BAAM

Question 8

Vat Photopolymerisation pros and cons

Answer 8

⚫ Pros:
– Best surface finish of any AM technology (together with
photopolymer jetting)
– Can make clear parts
⚫ Cons:
– Material properties change over time
– Standard resins are relatively brittle (similar to cast acrylic)
– Resin is messy and can be hazardous when removing parts
from machine and when post-processing
– Requires support material for overhangs

Question 9

Vat Photopolymerisation materials

Answer 9

⚫ Wide range of acrylate materials that simulate
the properties of ABS, PC, and PP
⚫ Materials are available that can burn out for
investment casting applications

Question 10

What is Material jetting (MJT) method

Answer 10

Print head deposits material out of either support material nozzle or part material nozzle. UV light cures the material. Builds up the part layer by layer

Question 11

Material jetting pros and cons

Answer 11

⚫ Pros:
– Best surface finish of any AM technology (together with SLA)
– Can make clear parts
– Can make multi-material and full-colour parts
⚫ Cons:
– Material properties change over time
– Elastomeric materials are weak under tension
– Resin is messy and can be hazardous when removing parts
from machine and when post-processing
– Requires support material for overhangs

Question 12

Material jetting materials

Answer 12

⚫ Digital ABS
⚫ Full-colour (C, M, Y, K, clear, support)
acrylate resins
⚫ High-temperature transparent
⚫ Rigid opaque
⚫ Simulated polypropylene
⚫ Rubber-like
⚫ Bio-compatible
⚫ Dental materials

Question 13

What is Powder bed fusion (PBF, P-PBF, M-PBF)

Answer 13

⚫ This method uses a powder which is spread in a layer of the desired thickness
⚫ A laser beam is then passed over the profile of the model slice which cures the powder into a solid in that section
⚫ The tray is then dropped down one level, and the next layer of
powder is spread and the process repeated for the next slice

Question 14

Powder bed fusion (PBF, P-PBF, M-PBF) acronyms

Answer 14

SLS, SLM, LS, DMLS, EBM

Question 15

What is HP Multi Jet Fusion (MJF)

Answer 15

Powder bed fusion with a heat source. Wherever energy
absorbing “ink” gets printed, the material absorbs more heat so
it melts.

Question 16

Powder bed fusion pros and cons

Answer 16

⚫ Pros:
– I estimate around 80%~90% of ‘production’ parts are done with PBF
– Polymer LS produces the strongest AM parts
– Metal PBF produces parts with strength between cast or forged parts
(depending on operator knowledge and/or post-processing treatment)
⚫ Cons:
– LS requires nitrogen atmosphere (usually supplied through on-board
nitrogen generator)
– Metal PBF requires an inert atmosphere (usually nitrogen or argon
depending on material being used)
– Working with metal powders requires precautions
– Requires support material for heat transfer
– Metal PBF requires considerable work to remove support structures

Question 17

Powder bed fusion materials

Answer 17

⚫ Nylon
⚫ GF nylon
⚫ HR nylon
⚫ PP-like nylon
⚫ Alumide (aluminium-
filled nylon)
⚫ Carbonmide
(carbon-filled nylon)
⚫ PEEK
⚫ Stainless steel
⚫ Maraging steel (tool steel)
⚫ Titanium 64
⚫ Aluminum
⚫ Tungsten
⚫ Nickel-based super alloys
⚫ Cobalt chrome
⚫ Copper
⚫ Precious metals, such as
gold

Question 18

What is Binder Jetting

Answer 18

⚫ Printers produce sand-casting molds and cores,
with standard foundry sand.
⚫ Process is applicable to any industry that
produces sand-cast parts.
⚫ Sand-casting process is well established and
understood by many.

Question 19

Binder Jetting pros and cons

Answer 19

⚫ Pros:
– Fast to produce green parts
– Very cost-effective for small parts
⚫ Cons:
– Green parts are very fragile and have to be handled
very carefully
– Part can shrink by up to 20% during the post-sintering
process
– This can make it hard to use BJT on large parts

Question 20

What is Directed energy deposition

Answer 20

Metal powder or wire is deposited from a nozzle and melted
by laser or electron beam, often with multi-axis control.

Question 21

Directed energy deposition pros and cons

Answer 21

⚫ Pro: Can repair worn or broken parts or to add features to an
existing part
⚫ Con: Surface typically requires milling

Question 22

What is Hybrid AM

Answer 22

⚫ Includes both directed energy deposition and multi-axis
CNC machining.

Question 23

Hybrid AM pros and cons

Answer 23

⚫ Pros:
– One of the few technologies that can, in some cases,
produce ready to use metal parts directly from the
machine. Some parts may require thermal stress relief,
even before the entire part is complete.
⚫ Cons:
– Setups are difficult. Requires both multi-axis AM and CNC
programming skills.
– Most of the setup is currently done manually, so it
requires high user knowledge and experience.
– Relatively new technology, so full metallurgical
implications are unknown.

Question 24

Choo

Answer 24

● Application: prototyping, tooling, or series production
● Material requirements
● Mechanical requirements
● Surface finish requirements
● Budget