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MPM052 - Composite and nano-composite material > Lecture 9 - Manufacturing > Flashcards

Lecture 9 - Manufacturing Flashcards

1
Q

When you manufacture you want 3 steps to be one, which?

A
  1. Wetting
  2. Forming/shaping
  3. Drainage
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2
Q

What is the most common to use when talking about PMCs?

A

Thermosets, 75%

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3
Q

What is the principle for curing?

A

uncured liquid + curing agent = solid thermosetting polymer

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4
Q

What happens under the curing?

A

Crosslinking

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5
Q

What is hydrodynamics?

A

It could be turbulence

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6
Q

describe what happens from pure viscous liquid to solid material?

A

Pure viscous liquid → Curing (heat, pressure, radiation, curing agent, + combinations) which leads to crosslinking with covalent bonds → solid material

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7
Q

What happens to the viscosity and elasticity when curing?

A

Thet increases

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8
Q

What happens to De when curing?

A

It increases

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9
Q

What are the stages when curing?

A

Viscous liquid → gel → Solid

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10
Q

What is molecular gelation?

A

Covalent bonds connect across the resin to form a 3D network (gel point)

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11
Q

What is vitrification?

A

Molecular motion is being hindered

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12
Q

What is G’ and G’’?

A 
G' = Storage modulus
G'' = Loss modulus
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13
Q

what happens when you increase the temperature in terms of curing?

A

You get a higher degree of curing

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14
Q

What happens with the viscosity if you

a) Increase the shear rate
b) Add fillers e.g calcium carbonate

A

a) Viscosity decrease

b) Viscosity increase

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15
Q

When are voids formed?

A

During processing of the non-solidified matrix

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16
Q

What does voids originate from?

A
  • Incomplete impregnation, wetting-out fibers
  • Resin cavitation during deformation
  • Air or vapors entrapment (from resin viscosity control, relative values of fiber and resin surface energies, moisture, chemical contaminants in the resin, styrene monomer, they may remain dissolved in the resin mix and volatilize during elevated temperature curing)
  • Too high viscosity
  • Emulsification, when fibers are pulled through the liquid resin
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17
Q

What are the 3 thermoset composite processing techniques, give some examples of subcategories?

A
  1. liquid resin impregnation
    • (wet) hand lay-up and spray lay-up (also referred to as contact moulding)
    • filament winding
    • pultrusion
    • Resin Transfer Moulding (RTM)
    • Vacuum Infusion Process (VIP) (also referred to as Vacuum Injection Moulding)
  2. pressurized consolidation of prepregs
    • directional pressing in a hydraulic press - autoclave moulding
    • vacuum bagging
    • prepreg lay-up
  3. pressurized consolidation of other moulding compounds - compression moulding (SMC, BMC)
    • compression moulding (SMC, BMC)
    • Reaction Injection Moulding (RIM)
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18
Q

Which surface is the best? The one facing the mould or the free surface?

A

Facing the mould

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19
Q

What are the pros and cons for hand layup and spray layup?

A

Pros: very large parts can be manufactured. Cons: the method is labour consuming, difficulty in obtaining high, reproducible quality and high fibre volume fraction.

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20
Q

Why does shrinkage occur during curing?

A

Curing shrinkage occurs because of the re-arrangement of polymer molecules into a more compact mass, as the curing proceeds. Addition of fibres or fillers reduces the volumetric shrinkage of a resin. In the case of UD fibres, reduction in shrinkage in the longitudinal direction is higher than in the transverse direction.

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21
Q

Why do you want shrinkage while curing?

A

It can be desirable for easy mould release.

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22
Q

How can you remove voids in the pre-moulding stages?

A

• degassing the liquid resin
• applying vacuum during the moulding process
• allowing the resin mix to flow freely in the mould, which helps in carrying the air
and volatiles out through the vents in the mould.

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23
Q

What can spray lay-up be called as well?

A

Contact moulding

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24
Q

What are the 2 main approaches to thermoplastic composite processing?

A

• injection moulding
• hot and cold pressing
- compression moulding (GMT)
- prepreg lay-up.

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25
Q

Describe the Hand lay-up and spray-up process

A

For thermosetting composites, CSMs, woven rovings and other fabrics are placed on the mould and impregnated with resin by painting and rolling. Layers are built up until design thickness is achieved.

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26
Q

What is the difference between spray and hand lay-up?

A

Spray-up is less labour and time consuming, and in this case short reinforcing fibres and lower viscosity polyester grades are used.

27
Q

What are the pros and cons with spray and hand lay-up?

A

An obvious advantage is that very large parts can be manufactured, and the disadvantage is that the method is labour consuming. Further disadvantages are difficulty in obtaining high, reproducible quality and high fibre volume fraction.

28
Q

What applications uses spray and hand lay-up?

A

automobile, truck and bus components; boat hulls; windmill blades, storage tanks and vats, bathroom interiors and pools

29
Q

What are the three conceptually different ways in which a mould of a given shape can be fabricated?

A
  • direct manual fabrication (common in boat and shipbuilding; low cost, economically feasible for manufacturing prototypes, one-of-a-kind components, short series; disadvantages are rather low geometric precision and low durability)
  • use of a master model (common in aerospace applications; high degree of precision may be maintained and several identical moulds can be produced, however fabrication can be time consuming and cost can be high)
  • direct machining from a block of material (materials used with this approach include wood, expanded polymer foams, syntactic foams, high grade tool steels, monolithic carbon and others; where steel moulds are used there is usually a need for closed moulds; metal moulds are very expensive, they are durable and tolerate high pressures and temperatures, and thus are the norm in compression moulding, injection moulding and pultrusion).
30
Q

Describe how filament winding works

A

In a filament winding process, resin (thermosetting or thermoplastic) impregnated fibres (sometimes prepreg sheets) are wrapped around a rotating mandrel to produce axisymmetric or non-axisymmetric hollow parts.
A large number of rovings are pulled from a series of creels into a liquid resin bath containing the catalyst and other ingredients. Next, the impregnated fibres are pulled through a wiping device to remove excess resin and to control the thickness of coating. Now the fibres are placed on the mandrel.
In another type of filament winding the mandrel is stationary and whirling arm winds the roving. Polar winding is also used.

After winding a number of layers to generate the desired thickness, the filament-wound part is generally cured on the mandrel. The mandrel is then removed from the cured part(collapsable, segmented or inflatable mandrels are used). In some cases the mandrel can stay inside the manufactured part.

31
Q

What are common defects of filament windings and why do they occur?

A

voids, delaminations and fibre wrinkles. Voids may appear because of poor fibre wet-out, emulsifying of the resin bath, excessive resin squeeze-out from inner layers by too high fibre tension, excessive time lapse between two consecutive layers of winding. Wrinkles result from improper winding tension and misaligned rovings.

32
Q

What is the main advantage with filament winding?

A

The main advantage is a high performance, reproducible product. This is supported by computer control of fibre tension and accurate winding angles.

33
Q

What applications do you use filament winding for ?

A

Among applications are pipes, drive shafts, pressure vessels, helicopter blades, military launching tubes, masts.

34
Q

Describe pultrusion.

A

Pultrusion is a continual process where impregnated fibres are passed through a heated mould/die for producing long, mainly prismatic components like solid rods, hollow tubs, flat sheets, various beams (angles, hat-sectioned etc.).

fibres and mats are pulled from creels into the precatalyzed resin bath, and then pulled through series of preformers (in order to distribute fibre evenly, squeeze out excess resin, and carefully form the cross-section). Then they are pulled through a long heating (gradual tapering) die where lateral pressure improves resin infiltration and wet-out), and curing takes place.

35
Q

What applications do you produce with pultrusion?

A

structural beams, hollow tubes, flat sheets, mobile phone antennas, sporting equipment and other.

36
Q

What does RTM mean?

A

Resin Transfer Moulding

37
Q

Explain Resin Transfer Moulding

A

The RTM is a two-stage process. First, a pre-form consisting of fibres and possibly a foam core, even metal inserts, is prepared (pressed) in the general shape of the finished part. A binder is used to preserve integrity of the preform. Second, the pre-form is placed in a closed mould and the liquid resin is injected under pressure. The resin and curing agent are premixed before injection into mould, and a low viscosity mix then injected into the mould at relatively low pressure (0.1 to 1 MPa), at room or elevated temperatures. Due to low pressures and temperatures moulds can be inexpensive.

38
Q

What applications uses RTM as manufacturing process?

A

boat hulls, tennis rackets, marine propellers, crash helmets and relatively large body parts for the automotive industry are made in this way

39
Q

Liquid Composite Moulding (LCM) is a generic name for a number of processes involving injection of resin into a pre-form of dry fibres. Name two!

A

Resin Transfer Moulding (RTM)(less known as Resinject, VARI or TERTM) and Reaction Injection Moulding (RIM).

40
Q

What is cavitation?

A

Propeller. When the water around the propeller is exposed to low pressure and high velocity this forms bubbles that implode when they reach zones with higher pressure.. This leads to shockwaves that damage the propeller.

41
Q

What is special with RTM?

A

In Resin transfer moulding all sides will have a nice surface

42
Q

Describe Vacuum Infusion Moulding (VIM)

A

A stack of dry fibres is placed between a rigid mould half and a flexible and airtight bag. The bag is sealed to the mould, except at certain positions being open for resin inlets and outlets. Liquid resin is then forced into the stack by reduction of the pressure at the outlets, while keeping the pressure atmospheric at the resin inlets. The flow-enhancing layer facilitates the infusion by allowing the resin to spread quickly over the lateral extent of the part.

43
Q

Is VIM suitable for high-quality manufacturing of large or small-scale?

A

Large scale, up to 1000 m2

44
Q

What are the advantages with VIM?

A

Advantages of this process are:
• possibility to produce large surface area components
• increased fibre to resin ratio
• stronger laminate
• low void content
• reduced volatile organic compounds (VOC) emissions

45
Q

What are common applications of VIM?

A

boats, yacht hulls, offshore structures, vehicle body panels, wind turbine rotor blades and others.

46
Q

describe vacuum bag, pressure bag, autoclave moulding

A

The entire assembly is placed inside a preheated autoclave where a sequence of vacuum
and pressure + temperature is applied to consolidate the laminate.
Typically:
• apply vacuum and slowly increase temp. to 130°C
• dwell at 130°C (with vacuum on); when viscosity is at minimum switch on
pressure (~7 bar) for about 60 min; during this time excess resin flows out
• further increase temperature to 175°C and cure for 2 h
• slowly cool and switch of vacuum and pressure.

47
Q

What is a autoclave?

A

An autoclave is a pressure chamber used to carry out industrial processes requiring elevated temperature and pressure different from ambient air pressure.

48
Q

What applications are common for Vacuum bag, pressure bag, autoclave moulding?

A

aerospace industry (low productivity not an issue), high-performance racing vehicles and yachts, aircraft control surfaces and skins, sport equipment, etc.

49
Q

What kind of fibers are used in Vacuum bag, pressure bag, autoclave moulding

A

Usually prepregs

50
Q

What are the pros with compression moulding?

A

ability to produce in one-go, at a low cost, large series of complex geometry parts.

51
Q

What applications are common for compression moulding?

A

One-piece car grilles, wheels, bumpers, leaf springs, and others are typical examples of processing by compression moulding.

52
Q

Describe compression moulding.

A

Two movable mould halves press the application to the desired shape.

53
Q

What are the advantages with compression moulding?

A

its ability to produce in one-go, at a low cost, large series of complex geometry parts.

54
Q

What do you usually produce with compression moulding?

A

One-piece car grilles, wheels, bumpers, leaf springs, and others are typical examples of processing by compression moulding.

55
Q

What does RIM stand for?

A

(Reinforced) Reaction injection moulding

56
Q

Describe Reaction injection moulding

A

In the RIM process two resins are mixed and injected into a mould

57
Q

What is the major difference between RIM and RTM?

A

The major differences between RIM and RTM is that with RTM the resin and curing agent are premixed before injection into mould, low pressure is used, whereas with RIM the liquid resin and curing agent are mixed by impingement as they are injected into the mould, thus high pressure is needed. RIM tends to be faster but gives worse mechanical properties.

58
Q

What 2 types of RIM is available?

A

Reinforced Reaction Injection Moulding (RRIM) using discontinuous and short fibres, and Structural Reaction Injection Moulding (SRIM) using long fibre pre-form. In the RRIM process milled fibres or glass flakes are added before injecting. In SRIM the reinforcement is first placed in the mould (just as in RTM) and following mould closure the highly reactive impingement-mixed resin is injected into the mould to impregnate the reinforcement.

59
Q

What do you produce with RIM?

A

automotive bumpers, air spoilers, and fenders

60
Q

What are the pros and cons with RIM?

A

Pros: RIM tends to be faster, Cons: gives worse mechanical properties.

61
Q

What manufacturing techniques do you use for thermoplastic composites?

A
  1. Injection moulding

2. Hot and cold pressing

62
Q

What is the difference between thermoplastic and thermosets when it comes to injection moulding?

A

In thermoset injection moulding the injection chamber is cooled and the mould heated, whereas in thermoplastic injection moulding it is the opposite. Furthermore, the processing screws used for thermoplastics are generally longer than those used for thermosets, and the compression ratio tends to be higher. However, the main use is for thermoplastic matrices.

63
Q

Describe injection moulding

A

For composites processing, the polymer is mixed with short cut fibres to form pellets (or granulates) few mm in length, which are fed into the hopper of the injection moulding machine, and injected into a mould in the same manner as conventional, neat thermoplastics.

64
Q

What is the main problems with injection moulding when it comes to fibers?

A

Intensive fibre breakage takes place and, as a result, a strong fibre length distribution has to be expected. Due to varying conditions of flow in the mould there is a strong fibre orientation distribution, and hence different anisotropy in different places of the part. It should be also noted that the wear on the machine is high due to the abrasive action of some fibres.

MPM052 - Composite and nano-composite material (12 decks)

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