Composite Processes

Question 1

Describe the hand lay-up process

Answer 1

Apply release agent to cleaned mould
Apply gel coat
Lay one ply of prepared reinforcement
Apply matrix to fibres and work in
Cure

Question 2

Why is a glass fibre veil added to a mould after the gel coat

Answer 2

Stops fibres blooming into gel coat

Question 3

Give composite mould types and their advantages

Answer 3

Composite - cheap & thermal expansion match
Metal - more durable, can withstand higher temps and pressures
Plaster/wood - very cheap, for prototyping

Question 4

What are the advantages of hand lay up

Answer 4

Low initial costs
Versatile
Simple

Question 5

What are the disadvantages of hand lay up

Answer 5

Low fibre fraction
High void fraction
High labour costs
Slow
Poor consistency
Only one moulded side
Safety issues

Question 6

Describe the spray lay-up process

Answer 6

Mould prepared and gel coat applied
Fibres chopped and fed with resin into gun
Mixture fired into mould
Rolled to consolidate
Cure

Question 7

What are the advantages of spray lay-up

Answer 7

Faster than hand lay-up
Reduced labour costs
Better quality consistency

Question 8

What are the disadvantages of spray lay-up

Answer 8

Higher initial cost that hand lay-up
Very low fibre fraction
Short fibres

Question 9

Describe the compression moulding process

Answer 9

Fibres and resin (and filler) come in sheet or bulk putty
Placed in two-part cavity mould
Moulds pressed and voids compressed
Part cured in press
Viscosity of compound important to fill mould but also carry fibres

Question 10

What are the advantages of compression moulding

Answer 10

Any geometry possible
Two good surfaces
Can be automated
Good quality consistency

Question 11

What are the disadvantages of compression moulding

Answer 11

Low fibre fraction
Can’t mould holes
Medium capital investment
Very limited size

Question 12

Descirbe the filament winding process

Answer 12

Continuous reinforcement wound onto a rotating mandrel
Can be left dry as an RTM preform
Usually passed through a resin bath
Can also wind prepreg tapes onto mandrel
Then part cured

Question 13

Why is tension important in filament winding

Answer 13

Too low tension - not enough compaction
Too high tension - tows migrate inwards and create resin rich areas

Question 14

What are the winding types and what properties do they give

Answer 14

Hoop winding - 90deg to mandrel - slow but excellent radial properties
Helical winding - tows laid with gaps which meet after several revolutions - excellent torsional and bending properties
Polar winding - mandrel rotated end-over-end - excellent longitudinal/axial properties
Can combine winding types for mix of properties