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Materials and manufacturing 3 > Joints and Manufracturing methods > Flashcards

Joints and Manufracturing methods Flashcards

1
Q

What type of polymers are generally used for rotation moulding

A

Thermoplastics

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2
Q

What sort of components are usually produced from rotation moulding (Size and shape)

A

Large Hollow components

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3
Q

Describe the steps in rotation moulding

A

Polymer is placed into a warm mould
Mould is heated while it is rotated about 2 axis and the mould is built up in successive layers
Mould is cooled by air or water (cooled bellow thermal deflection temperature)
Part is removed

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4
Q

What are examples of parts that are manufactured using rotation moulding

A 
Bins
 Children's play houses
 storage tanks
 Canoes
 Traffic Cones
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5
Q

What are advantages of rotation moulding

A

No weld lines
No residual stresses
Cheaper than injection moulding
Less design constraints

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6
Q

Disadvantages of rotation moulding

A

Labour Intensive
Long Cycle times
Sometimes parts require 2 moulding steps

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7
Q

What are the key material properties to consider for rotation moulding

A

Thermal conductivity
Heat Deflection Temperature
Specific heat capacity
Melt temperature

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8
Q

Why is thermal conductivity so important for Rotation moulding

A

As the polymer is deposited in layers the heat needs to be transferred trough the layers to melt the next layer

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9
Q

What is the basic process of metal extrusion

A

Forcing a chunk of metal through a die using a ram to create a new shape

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10
Q

What are the 2 types of metal extrusion

A

Direct and indirect

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11
Q

What must be used to create hollow shapes using extrusion

A

A bridge

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12
Q

How can the Gap in an extruded part caused by the bridge be fixed

A

Closed by either applying pressure (2nd die) or welding the part

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13
Q

Why may dies used in metal extrusion need to be replaced overtime

A

Wear on the surfaces which will effect tolerances

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14
Q

What is the equation for extrusion force

A

F = AoKln(Ao/Af)

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15
Q

What is the extrusion ratio and what is a typical range of values

A

Extrusion ratio = Ao/Af

10-100

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16
Q

In hot extrusion what temperature is the material heated to

A

60-70% of melt temperature

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17
Q

What is needed to extrude 2 metals at once

A

Cladding and a coaxial billet

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18
Q

What are the easiest metals to extrude

A

Aluminium, Copper and lead

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19
Q

How is bending of parts during extrusion fixed

A

Using a hydraulic stretcher

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20
Q

What is a dummy block used for in metal extrusion

A

Gets rid of the oxidised layer

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21
Q

What is the definition of welding

A

Welding is a joining process that produces a coalescence of materials by heating them to the weld temperature with or without pressure, and with or without a filler material

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22
Q

Name 5 types of joints

A 
Butt
Corner
Edge
Lap
T
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23
Q

What are the 4 weld positions

A

Flat
Horizontal
Vertical
Overhead

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24
Q

In soldering and brazing does the parent metal melt

A

No

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25
Q

In fusion welding does the parent metal melt

A

No

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26
Q

What are some benefits of welding

A 
Allows different grades of materials to be joined
Materials to be joined with on overlap 
No fretting or loosening 
Leak proof joint
Lighter joints due to no bolts
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27
Q

What is the difference between soldering and brazing

A

Brazing occurs at a higher temperature than soldering but a lower temperature than fusion welding.

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28
Q

What are advantages of the parent metal not melting

A

Less warping, decreased heat effected zone and less residual stresses

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29
Q

In Brazing what is the joint strength dependant on

A

The bond between the parent and filler metal

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30
Q

What is the process of brazing

A

2 parent set beside each other with a small gap in-between, and the brazing filler and flux are put in the gap and the filler is heated and melted and is drawn into the joint by capillary action

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31
Q

What is the purpose of fluxes used in brazing

A

It prevents oxidation and removes oxide film from surfaces

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32
Q

What is the difference between brazing and braze welding

A

Brazing welding does not use capillary action, instead the joint is prepared in the same manner as fusion welding. The oxyacetylene torch is used to melt the filler material and deposit it at the weld site

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33
Q

Does braze welding occur at higher or lower or higher temperatures than fusion welding

A

Lower temperatures

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34
Q

What is braze welding usually used for

A

Repair

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35
Q

What temperatures do solder materials melt at

A

Bellow 723K

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36
Q

What are the 2 main types fusion welding

A

Gas or arc welding

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37
Q

What are the 2 main types of Gas fusion welding

A

Oxyfuel Gas welding (Filler welding)

Pressure gas welding (No filler rod)

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38
Q

What are the 2 types of arc welding

A

Consumable electrode

Non consumable electrode

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39
Q

In Oxygas welding where does the heat to melt the meatal come from

A

Combustion

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40
Q

What are the most common gasses used in Oxygas welding

A

Oxygen and acetyl

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41
Q

What are advantages of oxygas welding

A

It is portable, can be used to create very fine parts

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42
Q

What are disadvantages of oxygas welding

A

Requires skilled operators and there is a danger associated with it

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43
Q

What are the 3 types of flame used in Oxygas welding

A

Neutral flame
Oxidising flame
Reducing flame

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44
Q

Which of the 3 flame types of oxygas welding burns with the highest welding temperature

A

Oxidising flame

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45
Q

The oxidising flame causes oxidation what metals is this beneficial for and what metals is this a negative for

A

Creates a protective layer for copper

But is a bad thing for steel

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46
Q

On Oxygas welding what function does a flux covering provide

A

Flux covering prevents oxidation on the surface weld by creating a gaseous shield around the weld zone

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47
Q

What is a pressure gas welding

A

2 components are heated at their interface using a gas torch until it starts to melt. Then the 2 components are pressed together and the pressing force is maintained until the interface solidifies

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48
Q

What is the difference between the start and end products of pressure gas welding

A

The final product has a reduced overall length and a flash is produced

49
Q

Describe the process of consumable electrode arc welding

A

localised heating and melting of material and controlled solidification of molten weld pool using a electrode that is consumed to provide the weld filler metal.

50
Q

What are some examples of consumable electrode arc welding

A

Shielded metal, submerged, gasmetal, flux covered

51
Q

What is the main benefit of consumable electrode arc welding

A

This type of welding can be done overhead.

52
Q

What is consumable electrode arc welding usually used for

A

Construction and maintenance

53
Q

Describe submerged arc welding

A

Very automatable form of welding

speeds up to 5m/min with high quality

54
Q

What was Gas metal arc welding previously known as

A

MIG

55
Q

Does gas metal arc welding use a consumable or non consumable electrode

A

Consumable

56
Q

Is Gas metal arc welding continues or discontinues

A

Continues

57
Q

What are the 3 types of metal transfer in gas metal arc welding

A

Spray transfer
Globular transfer
Short circuit, electrode touches metal plate

58
Q

What is the difference between gas metal arc welding and flux core arc welding

A

In flux core arc welding the electrode is hollow and flux is in the centre of the electrode (provides a more stable arc)

59
Q

Why must slag be removed from a weld surface

A

To allow a 2nd weld pass to be made

60
Q

In Non consumable electrode arc welding what is used to provide filler material

A

A filler rod

61
Q

What is non consumable electrode arc welding usefull for

A

Welding of thin steel parts

62
Q

What is a joint without a filler metal known as

A

autogenous joint

63
Q

Why do residual stresses form as a result of weld heating

A

Localised heating causes differential shrinkage that then leads to distortion and warpage

64
Q

Why may cracks in the heat affected zone form

A

Due to the changed microstructure may have a reduced ductility and a degree of hardening

65
Q

What factors effect how heating will effect the heat effected zone

A

The rate of heating, Max temperature, length of time at max temperature, rate of cooling

66
Q

What is the size of grains that form in the heat affected zone dependant on

A

Welding process

Filler material used

67
Q

What are advantages and of single pass welded joints

A

Better for thinner parts, more economical

68
Q

What are disadvantages of single pass welds

A

Weaker mechanical properties due to rapid cooling and hard microstructure

69
Q

What are advantages of multi pass welding

A

Better for thicker structures, potential for sower cooling and annealing effects, in general better weld quality

70
Q

What are disadvantages of multi pass welding

A

More time consuming, can create a non homogenous microstructure

71
Q

What is the weldability of a metal determined by

A

Physical properties of the parent metal and the desired mechanical properties of the joint

72
Q

How does the melting point of a metal affect the weldability

A

A lower melting point means that the weld can be carried out a lower temperatures therefor lower cost

73
Q

How does a materials boiling point affect its weldability

A

When a material melts it gives of toxic fumes

74
Q

How does thermal conductivity affect the weldability of a metal

A

The higher the thermal conductivity the faster the weld will cool so a higher rate of cooling is required so a higher cost

75
Q

How can the problems associated with a high thermal conductivity be combated

A

pre heating the metal to reduce the temperature gradient

76
Q

What is linear expansion

A

Measure of increase per unit length per degree temperature increase

77
Q

What effect does linear expansion coefficient have on l weldability

A

High values can create warping issues and can cause problems when welding materials with different coefficients

78
Q

Why is overhead welding so hard

A

The weld material will try and pull away from the parent material

79
Q

To combat the problems with overhead welding what mechanical property is desired for overhead welding

A

A high thermal conductivity so the weld will solidify quickly

80
Q

What are the mechanical properties of a metal governed by

A

Chemical composition of the metal, surface treatments and heat treatments

81
Q

Why is ductility a good attribute for a welded joint

A

It reduces the joints likelihood to crack

82
Q

What are some problems associated with welding (7)

A

Localised heating and rapid cooling
Non equilibrium solidification
Thermomechanical influence on HAZ
Loss of strength in HAZ
Defects caused by contamination of molten metal
Defects caused by oxidation of molten metal
Residual stresses caused by thermal expansion and contraction

83
Q

What are the 2 most important considerations when welding steel

A

Hardenability

Susceptibility of hardened material to cracking

84
Q

If the Carbon Equivalent % is less that 0.04 what processes are required

A

Pre heating
Higher heat input
Low hydrogen filler material

85
Q

Why do full phase changes not often occur in welding

A

The cooling is to rapid

86
Q

What temperature will a material be pre heated to before welding

A

Usually about 300C

87
Q

How does heat treatment affect welding

A

Reduced temperature gradients means that the heat transfer is reduced so phase changes can now occur

88
Q

What are post heat treatments useful for

A

Reducing residual stresses

89
Q

What are the 2 methods for post heat treatment

A

Normalising and Annealing

90
Q

Which of the 2 post heat treatment methods is preferred

A

Normalising

91
Q

Does annealing involve heating above or bellow 723C

A

Bellow

92
Q

What does annealing enable

A 
Recovery 7 recrystallisation (New grains form)
Grain growth (Bad)
93
Q

What are the benefits of annealing

A

Increased ductility, reduces residual stresses, and can create a specific microstructure

94
Q

Does normalising take place above or bellow 723C

A

Above

95
Q

When is normalising usually used

A

After severe distortion, such as rolling

96
Q

What are the benefits of normalising

A

Eliminates residual stresses

97
Q

What are the problems caused when welding aluminium

A

Aluminium has a low melting point but a high heat input is required as AlO3 has a high melting point, the AlO3 has to be removed first

98
Q

What are some typical weld defects found in fusion welds

A

Lack of fusion, cracking, Porosity, lack of penetration

99
Q

What are the 2 types cracking in fusion welds

A

Solidification or Hydrogen and reheat

100
Q

What can cracking on the HAZ be prevented by

A

Pre and Post heating

101
Q

What is porosity caused by

A

Trapped gas, slag or impurities

102
Q

What are the 2 types porosity

A

Surface or creator

103
Q

What are types weld distortions occur in butt welds

A

Transverse shrinkage, Angular distortion, Longitudinal shrinkage

104
Q

Distortion in welding is inevitable so how to designers make account for this

A

Specify Larger dimensions and fine machining after

105
Q

What are some non-destructive methods of weld testing

A

Ultrasonic
Visual
Radiographic

106
Q

What is an adhesive bond

A

A rigid or semi rigid interface without the use of mechanical fastenings used for similar or dissimilar materials

107
Q

What are the 3 main types of adhesives

A

Natural
Inorganic
Synthetic

108
Q

What are limitations of adhesives

A

Vapours
High temperature applications
Surface preparation
Curing times

109
Q

What are advantages of adhesive bonding over welding

A 
Cheaper, 
no distortion at low temperature 
Larger variety of materials that can be used 
Vibration dampening 
Less weight added 
Good surface finish
Uniform stress distribution
110
Q

What type of polymers can be welded

A

Thermoplastics

111
Q

What are the 3 types of heating mechanisms used for polymer welding

A

Mechanical movements
External heat
Electromagnetism

112
Q

Describe ultrasonic welding

A

Pressure is applied to the top and bottom of a joint and vibration is applied and the material is heated due to surface and intermolecular friction

113
Q

Describe Friction spin welding

A

One part is stationary and one rotates and they are forced together

114
Q

What are benefits of friction spin welding

A

Simple, reproducibility, little end prep

115
Q

What are disadvantages for friction spin welding

A

Residual stresses

116
Q

What loads can adhesive joints not be subjected to

A

Peel or cleavage

117
Q

Describe hot gas welding

A

similar to oxy gas welding but hot gas is used instead of flame

118
Q

What gasses are used for hot gas welding

A

Air
O2
N
CO2

119
Q

Describe implant resistance welding

A

metal is placed in the plastic which is to be bonded then the metal is heated using EM or electrical current and the plastic is melted and a joint is formed

Materials and manufacturing 3 (3 decks)

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