Polymer Processing

Question 1

Describe Blow moulding

Answer 1

a hollow parison is lowered into a mould
copressed air forces it outwards to become the shape of the mould
is it then cooled into the final shape

Question 2

Describe blow film moulding

Answer 2

a hollow parison is extrude using an extrusion machine, compressed air is pushed through it as it is drawn upwards by a pair of rollers. it streches outwards into a thin film which is collected and cooled into a roll of film

Question 3

Describe injection moulding

Answer 3

polymer granules and diposited onot an achemedes screw with surrounding heating elements, melting it and drawing in along the screw.
a piston applied pressure to the molten polymer forcing it into a mould where it cools

Question 4

Describe Fused deposition modelling

Answer 4

1) A spool of themoplastic wire is continuously supplied to a nozzle

2) The nozzle heats up the wire and extrudes a hot, viscos strand

3) A computer controls the nozzle movement along the x- and y-axes

4) the polymer cools into the correct shape

Question 5

what factors affect Fused Deposition modelling design

Answer 5

Support structures are needed to hold up overhangs
wall thickness,
infill patterns and density

Question 6

Why does delta dynamic-Z deposition create stronger shapes than cartesian depostition?

Answer 6

the layers follow the contors of the shape instead of stacking vertically reducing stress concentration and preventing layers splitting

Question 7

Describe Sterolithography

Answer 7

a bath of thermoset bolymer is suspended above a UV laser.
the laser is controlled by a set of optics and causes the thermoset to cure
the set thermoset is moved upwards allowing the next layer to be cured below

Question 8

What is the difference between fixed surface (bottom up) and free surface (top down) Stereolithography?

Answer 8

cured thermoset is moved upwards out of the uncured bath in free surface whereas it is moved downwards in the bath during fixed surface

Question 9

What are the advantages and disavantages of Fused deposition modelling FDM?

Answer 9

ADV:Economical, Easy to build DIY kits , A wide range of materials
DIS:limited to
thermoplastics for most of cases, Surface finish ( FDM < SLA ), Lower bonding strength between layers

Question 10

What are the advantages and disavantages of Stereolithography SLA?

Answer 10

ADV:Fast, Good resolution, Minimal need for support material
DIS: Expensive equipment,
Expensive materials,
Material limited to photosensitive resins