Composites part 1 - f

Question 1

What are the two types of composite manufacturing processes?

Answer 1

• open moulding

- closed moulding

Question 2

What is open moulding?

Answer 2

the gel coat and laminate are exposed to the atmosphere during the fabrication process

Question 3

What is closed moulding?

Answer 3

The composite is processed in a two-sided mould set

Question 4

Examples of open moulding?

Answer 4

• hand lay-up or contact moulding
• spray-up
• filament winding

Question 5

Examples of closed moulding?

Answer 5

• Compression moulding
• pultrusion
• resin transfer moulding
• vacuum bag moulding
• centrifugal casting
• continuous lamination

Question 6

What processes can be used for low volume production?

Answer 6

• hand lay up
• vacuum bag molding
• vacuum infusion processing

Question 7

What processes can be used for medium volume production?

Answer 7

• filament winding
• wet lay-up compression moulding
• resin transfer molding
• centrifugal casting

Question 8

What processes can be used for high volume production?

Answer 8

• compression molding
• pultrusion
• reinforced reaction injection molding
• continuous lamination

Question 9

Discuss the hand lay-up process?

Answer 9

The hand lay-up method is simple and versatile and the most widely used FRP process. The process consists of applying layers of reinforcing material against a single sided mold and working resin into the material with a brush and roller. After a suitable period of time to allow the resin to cure, the molding, with one smooth surface, is removed from the mold and trimmed to size.

Question 10

Can you draw a diagram of the hand lay-up process?

Answer 10

yes or no

Question 11

What are the issues with hand lay-up molding?

Answer 11

• It is slow and highly labour intensive.
• because it depends on the skill of the laminator, the process has the inherent problem of variability in the finished moldings.

Question 12

How can the hand-lay-up process be sped up?

Answer 12

The resin and reinforcement material can be simultaneously applied by spraying on to the surface of the mold. After consolidating with a roller and curing, the molding can be removed and trimmed as before.

Question 13

What is a positive aspect of hand lay-up?

Answer 13

The size and complexity of the moldings that can be produced by this method are endless.

Question 14

What are the different catergories of hand lay-up?

Answer 14

• wet laminating
• pre-preg laminating
• vacuum bagging
• vaccum infusion may also fall into this category

Question 15

What are some applications of spray-up (or chopping) molding?

Answer 15

Boats, tanks, transportation components and tub/shower units in a large variety of shapes and sizes.

Question 16

What are the advantages of spray-up molding?

Answer 16

A chopped laminate has good conformity and is sometimes faster than hand lay-up in molding complex shapes.

Question 17

What are the disadvantages of spray-up molding?

Answer 17

In the spray-up process the operator controls the thickness and consistency, therefore the process is more operator dependent than hand lay-up.

Question 18

What type of moldings is vacuum bag molding used on?

Answer 18

Moldings which are large or of complex shape.

Question 19

What type can the mold be in vacuum bag molding?

Answer 19

either male or female

Question 20

What type of resin system is the vacuum bag technique usually used with?

Answer 20

pre preg resin systems although there are techniques for wet resin systems

Question 21

How does vacuum bag molding work?

Answer 21

Consolidation is achieved by covering the molding with an airtight bag from which the air is removed with a vacuum pump providing up to one atm of pressure.

Question 22

What is required if pressures higher than 1atm are needed in vacuum bag molding?

Answer 22

The whole assembly is placed inside an autoclave or heated pressure vessel.

Question 23

What are the disadvantaged of vacuum bag molding?

Answer 23

• cycle times tend to be long, often several hours
• labor content is high
• process is highly dependent on skill of laminator

Question 24

How does resin transfer molding work?

Answer 24

Dry reinforcement is placed between 2 matched molds. Resin is injected into the cavity and through the reinforcement which is trapped or pinched at the edges of the mold. The effect of the pinching is to provide a path for air to escape but block the passage of resin. There are variations to this which lead to more accurate moldings with less material wastage.

Question 25

What are the advantages of resin transfer molding?

Answer 25

• Accurate fiber management with reproducible moldings.

- With automation, this process is capable of high vol production with cycle times down to minutes using reactive resin

Question 26

How does pultrusion work?

Answer 26

Continuous fibers pulled through resin tank to impregnate fibers with thermosetting resin.
Impregnated fibers pass through steel die that preforms to the desired shape.
Preformed stock passes through a curing die that is precision machined to impart final shape and heated to initiate curing of the resin matrix.

Question 27

How does filament winding work?

Answer 27

Continuous reinforcing fibers are accurately positioned in a predetermined pattern to form a hollow (usually cylindrical) shape.
Fibers are fed through a resin bath to impregnate with thermosetting resin.
Impregnated fibers are continuously wound (typically automatically) into a mandrel. After appropriate number of layers is added, curing is carried out either in an oven or at room temperature. The mandrel is removed to give the final product.

Question 28

Advantages of filament winding?

Answer 28

• Modern machines are capable of winding non-axisymmetric and branched shapes
• Accurate reproducible parts

Question 29

Disadvantage of filament winding?

Answer 29

• Relatively slow