Joints and Manufracturing methods Flashcards
1
Q
What type of polymers are generally used for rotation moulding
A
Thermoplastics
2
Q
What sort of components are usually produced from rotation moulding (Size and shape)
A
Large Hollow components
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
4
Q
What are examples of parts that are manufactured using rotation moulding
A
Bins Children's play houses storage tanks Canoes Traffic Cones
5
Q
What are advantages of rotation moulding
A
No weld lines
No residual stresses
Cheaper than injection moulding
Less design constraints
6
Q
Disadvantages of rotation moulding
A
Labour Intensive
Long Cycle times
Sometimes parts require 2 moulding steps
7
Q
What are the key material properties to consider for rotation moulding
A
Thermal conductivity
Heat Deflection Temperature
Specific heat capacity
Melt temperature
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
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
10
Q
What are the 2 types of metal extrusion
A
Direct and indirect
11
Q
What must be used to create hollow shapes using extrusion
A
A bridge
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
13
Q
Why may dies used in metal extrusion need to be replaced overtime
A
Wear on the surfaces which will effect tolerances
14
Q
What is the equation for extrusion force
A
F = AoKln(Ao/Af)
15
Q
What is the extrusion ratio and what is a typical range of values
A
Extrusion ratio = Ao/Af
10-100
16
Q
In hot extrusion what temperature is the material heated to
A
60-70% of melt temperature
17
Q
What is needed to extrude 2 metals at once
A
Cladding and a coaxial billet
18
Q
What are the easiest metals to extrude
A
Aluminium, Copper and lead
19
Q
How is bending of parts during extrusion fixed
A
Using a hydraulic stretcher
20
Q
What is a dummy block used for in metal extrusion
A
Gets rid of the oxidised layer
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
22
Q
Name 5 types of joints
A
Butt Corner Edge Lap T
23
Q
What are the 4 weld positions
A
Flat
Horizontal
Vertical
Overhead
24
Q
In soldering and brazing does the parent metal melt
A
No
25
In fusion welding does the parent metal melt
No
26
What are some benefits of welding
```
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
```
27
What is the difference between soldering and brazing
Brazing occurs at a higher temperature than soldering but a lower temperature than fusion welding.
28
What are advantages of the parent metal not melting
Less warping, decreased heat effected zone and less residual stresses
29
In Brazing what is the joint strength dependant on
The bond between the parent and filler metal
30
What is the process of brazing
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
31
What is the purpose of fluxes used in brazing
It prevents oxidation and removes oxide film from surfaces
32
What is the difference between brazing and braze welding
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
33
Does braze welding occur at higher or lower or higher temperatures than fusion welding
Lower temperatures
34
What is braze welding usually used for
Repair
35
What temperatures do solder materials melt at
Bellow 723K
36
What are the 2 main types fusion welding
Gas or arc welding
37
What are the 2 main types of Gas fusion welding
Oxyfuel Gas welding (Filler welding)
| Pressure gas welding (No filler rod)
38
What are the 2 types of arc welding
Consumable electrode
| Non consumable electrode
39
In Oxygas welding where does the heat to melt the meatal come from
Combustion
40
What are the most common gasses used in Oxygas welding
Oxygen and acetyl
41
What are advantages of oxygas welding
It is portable, can be used to create very fine parts
42
What are disadvantages of oxygas welding
Requires skilled operators and there is a danger associated with it
43
What are the 3 types of flame used in Oxygas welding
Neutral flame
Oxidising flame
Reducing flame
44
Which of the 3 flame types of oxygas welding burns with the highest welding temperature
Oxidising flame
45
The oxidising flame causes oxidation what metals is this beneficial for and what metals is this a negative for
Creates a protective layer for copper
| But is a bad thing for steel
46
On Oxygas welding what function does a flux covering provide
Flux covering prevents oxidation on the surface weld by creating a gaseous shield around the weld zone
47
What is a pressure gas welding
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
48
What is the difference between the start and end products of pressure gas welding
The final product has a reduced overall length and a flash is produced
49
Describe the process of consumable electrode arc welding
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
What are some examples of consumable electrode arc welding
Shielded metal, submerged, gasmetal, flux covered
51
What is the main benefit of consumable electrode arc welding
This type of welding can be done overhead.
52
What is consumable electrode arc welding usually used for
Construction and maintenance
53
Describe submerged arc welding
Very automatable form of welding
| speeds up to 5m/min with high quality
54
What was Gas metal arc welding previously known as
MIG
55
Does gas metal arc welding use a consumable or non consumable electrode
Consumable
56
Is Gas metal arc welding continues or discontinues
Continues
57
What are the 3 types of metal transfer in gas metal arc welding
Spray transfer
Globular transfer
Short circuit, electrode touches metal plate
58
What is the difference between gas metal arc welding and flux core arc welding
In flux core arc welding the electrode is hollow and flux is in the centre of the electrode (provides a more stable arc)
59
Why must slag be removed from a weld surface
To allow a 2nd weld pass to be made
60
In Non consumable electrode arc welding what is used to provide filler material
A filler rod
61
What is non consumable electrode arc welding usefull for
Welding of thin steel parts
62
What is a joint without a filler metal known as
autogenous joint
63
Why do residual stresses form as a result of weld heating
Localised heating causes differential shrinkage that then leads to distortion and warpage
64
Why may cracks in the heat affected zone form
Due to the changed microstructure may have a reduced ductility and a degree of hardening
65
What factors effect how heating will effect the heat effected zone
The rate of heating, Max temperature, length of time at max temperature, rate of cooling
66
What is the size of grains that form in the heat affected zone dependant on
Welding process
| Filler material used
67
What are advantages and of single pass welded joints
Better for thinner parts, more economical
68
What are disadvantages of single pass welds
Weaker mechanical properties due to rapid cooling and hard microstructure
69
What are advantages of multi pass welding
Better for thicker structures, potential for sower cooling and annealing effects, in general better weld quality
70
What are disadvantages of multi pass welding
More time consuming, can create a non homogenous microstructure
71
What is the weldability of a metal determined by
Physical properties of the parent metal and the desired mechanical properties of the joint
72
How does the melting point of a metal affect the weldability
A lower melting point means that the weld can be carried out a lower temperatures therefor lower cost
73
How does a materials boiling point affect its weldability
When a material melts it gives of toxic fumes
74
How does thermal conductivity affect the weldability of a metal
The higher the thermal conductivity the faster the weld will cool so a higher rate of cooling is required so a higher cost
75
How can the problems associated with a high thermal conductivity be combated
pre heating the metal to reduce the temperature gradient
76
What is linear expansion
Measure of increase per unit length per degree temperature increase
77
What effect does linear expansion coefficient have on l weldability
High values can create warping issues and can cause problems when welding materials with different coefficients
78
Why is overhead welding so hard
The weld material will try and pull away from the parent material
79
To combat the problems with overhead welding what mechanical property is desired for overhead welding
A high thermal conductivity so the weld will solidify quickly
80
What are the mechanical properties of a metal governed by
Chemical composition of the metal, surface treatments and heat treatments
81
Why is ductility a good attribute for a welded joint
It reduces the joints likelihood to crack
82
What are some problems associated with welding (7)
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
What are the 2 most important considerations when welding steel
Hardenability
| Susceptibility of hardened material to cracking
84
If the Carbon Equivalent % is less that 0.04 what processes are required
Pre heating
Higher heat input
Low hydrogen filler material
85
Why do full phase changes not often occur in welding
The cooling is to rapid
86
What temperature will a material be pre heated to before welding
Usually about 300C
87
How does heat treatment affect welding
Reduced temperature gradients means that the heat transfer is reduced so phase changes can now occur
88
What are post heat treatments useful for
Reducing residual stresses
89
What are the 2 methods for post heat treatment
Normalising and Annealing
90
Which of the 2 post heat treatment methods is preferred
Normalising
91
Does annealing involve heating above or bellow 723C
Bellow
92
What does annealing enable
```
Recovery 7 recrystallisation (New grains form)
Grain growth (Bad)
```
93
What are the benefits of annealing
Increased ductility, reduces residual stresses, and can create a specific microstructure
94
Does normalising take place above or bellow 723C
Above
95
When is normalising usually used
After severe distortion, such as rolling
96
What are the benefits of normalising
Eliminates residual stresses
97
What are the problems caused when welding aluminium
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
What are some typical weld defects found in fusion welds
Lack of fusion, cracking, Porosity, lack of penetration
99
What are the 2 types cracking in fusion welds
Solidification or Hydrogen and reheat
100
What can cracking on the HAZ be prevented by
Pre and Post heating
101
What is porosity caused by
Trapped gas, slag or impurities
102
What are the 2 types porosity
Surface or creator
103
What are types weld distortions occur in butt welds
Transverse shrinkage, Angular distortion, Longitudinal shrinkage
104
Distortion in welding is inevitable so how to designers make account for this
Specify Larger dimensions and fine machining after
105
What are some non-destructive methods of weld testing
Ultrasonic
Visual
Radiographic
106
What is an adhesive bond
A rigid or semi rigid interface without the use of mechanical fastenings used for similar or dissimilar materials
107
What are the 3 main types of adhesives
Natural
Inorganic
Synthetic
108
What are limitations of adhesives
Vapours
High temperature applications
Surface preparation
Curing times
109
What are advantages of adhesive bonding over welding
```
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
What type of polymers can be welded
Thermoplastics
111
What are the 3 types of heating mechanisms used for polymer welding
Mechanical movements
External heat
Electromagnetism
112
Describe ultrasonic welding
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
Describe Friction spin welding
One part is stationary and one rotates and they are forced together
114
What are benefits of friction spin welding
Simple, reproducibility, little end prep
115
What are disadvantages for friction spin welding
Residual stresses
116
What loads can adhesive joints not be subjected to
Peel or cleavage
117
Describe hot gas welding
similar to oxy gas welding but hot gas is used instead of flame
118
What gasses are used for hot gas welding
Air
O2
N
CO2
119
Describe implant resistance welding
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
