week 4: additive manufacturing

Question 1

what are the rapid prototyping technologies

Answer 1

• fused filament fabrication (FFF)
• stereolithography (SLA)
• selective laser sintering (SLS)
• electron beam melting (EBM)
• laminated object manufacturing (LOM)
• 3D printing

Question 2

fused filament fabrication

Answer 2

• extruder moves in 2 directions over a table
• table can be lowered or raised
• filament (typically thermoplastic) extruded through a small orifice of a heated die
• controlled motion of extrusion head in relation to table and switching head on and off to achieve complex geometries

Question 3

stereolithography

Answer 3

• liquid polymer cured selectively into solid
• platform put into a vat of the polymer and raised so only a thin layer covers it
• UV laser traces the shape of the bottom layer of the component to cure polymer
• process repeated

Question 4

selective laser sintering and electron beam melting

Answer 4

• nonmetallic or metallic powder is sintered using a laser (SLS) or electron beam (EBM)
• thin layer of powder deposited on build area
• beam scans the shape of the layer to sinter powder in solid
• build area lowered and process repeated
• SLS most common for plastics
• EBM used for titanium and cobalt chrome alloys

Question 5

laminated object manufacturing

Answer 5

• layers of material (vinyl, plastic or paper) cut using computer controller machines then stacked
• stacking manual or automatic
• cross hatch pattern usually cut into parts for removal

Question 6

3D printing

Answer 6

• head deposits binder onto layer of polymer, ceramic or metal powder
• bed of build area then lowered and new layer of powder deposited and fused by binder
• process repeated

Question 7

what are the types of composites

Answer 7

-reinforced plastics (polymer matric composites (PMC) and fiber reinforced plastics (FRP)) - high specific strength

• metal matrix composites (MMC) - high toughness, ductility and resistance to high temps but difficult to manufacture
• ceramic matrix composites (CMC) - highest resistance to temps and corrosive environments

Question 8

techniques used for manufacturing PMCs

Answer 8

• fibre impregnation
• moulding of reinforced plastics
• filament winding
• pultrusion
• pulforming

Question 9

describe spray layup and hand layup (contact moulding)

Answer 9

• single mould is used
• simplest method is hand layup
• materials placed in proper order
• brushed and shaped by hand with roller
• squeezing action of roller expels trapped air
• moulding done by spraying materials to mould
• both resin and chopped fibres sprayed
• rolling deposited materials may be necessary

Question 10

filament winding description

Answer 10

• resin and fibres combined at time of curing to develop composite structure
• axisymmetric parts and non symmetric parts are produced on a rotating mandrel
• reinforced filament, tape or roving is wrapped continuously
• reinforcements are impregnated by passing through polymer bath

Question 11

what are the two categories of welding

Answer 11

• fusion welding (base material is heated to melting)
• solid state welding (parts joined under pressure or a combination of pressure and heat)

Question 12

what are the three techniques of fusion welding

Answer 12

• resistance ( combo of heat and pressure - heat from electrical resistance of current flow at interface)
• oxyfuel gas welding ( fuel mix with oxygen are burned to generate the required heat and melt the material)
• arc welding ( use of electric arc - discharge of current across gap in circuit)