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MEC130 2 4 8 10 15 > Lec 15 > Flashcards

Lec 15 Flashcards

1
Q

What is an ideal joint

A

When you go across joint area you dont seen a change in the composition of material properties

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2
Q

What does solid state process mean

A

No melting

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3
Q

5 examples of solid state processes

A 
Cold welding, 
ultrasonic welding, 
friction welding, 
explosion welding, 
diffusion welding/bonding
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4
Q

What is resistance welding

A

The heat required for welding is produced by electrical resistance across two components to be joined
Spot welding most common

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5
Q

4 steps of resistance welding (diagram)

A 
Pressure applied
current on
current off pressure on
pressure released
(electrode weld nugget lap joint)
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6
Q

Resistance welding diagram cross section

A 
2x Electrode
electrode tip 
weld nugget
indentation
sheet separation
heat affected zone
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7
Q

Adv and Disadv of Resistance welding

A

Does not require consumable electrode shielding gas or flux
easy and fast
BUT
Complex and expensive equipment
Copper electrodes will wear down
Will only work for poor conducting materials ie steel

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8
Q

Application of Resistance welding

A

Sheet metal fabrication
automotive body assembly
(places where joint strength is not critical)

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9
Q

What is cold welding (diagram)

A

Pressure applied through rolls or dies to force two materials together

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10
Q

Adv and Disadv of cold welding

A

Not particularly strong - produces brittle inter metallic compound but used for putting on cladding
No heat is generated

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11
Q

Cold welding requirements

A

It is necessary that at least one, but preferably both mating parts be ductile
Prior to welding, the interface is thoroughly cleaned
best with two similar metals

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12
Q

Applications of cold welding

A

join small workpieces made of soft, ductile metals

Welding wire stock (splicing wire together)

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13
Q

Ultrasonic welding what are the surfaces exposed to

A 
a static normal force 
oscillating shearing (tangential) stresses
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14
Q

where are the shearing stresses applied by in ultrasonic welding and what is required for efficient operation

A

Tip of a transducer

Proper coupling between the transducer and the tip is important for efficient operation

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15
Q

Freq of oscillation for ultrasonic welding

A

10 kHz – 75 kHz

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16
Q

What is ultrasonic welding (diagram)

A 
Force 
mass
coupling system
tip
Workpiece
anvil
direction of vibration
transducer dc
polarization supply
ac power supply
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17
Q

How does ultrasonic welding work

A

The shearing stresses cause plastic deformation at the interface of the two components
Allowing good contact
Producing a strong solid-state bond
It breaks up oxide films and contaminants

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18
Q

Temperature generated during ultrasonic welding

A

The temperature generated in the weld zone is usually 1/3 – 1/2 of the melting point of the metals joined
Neither melting nor fusion takes place

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19
Q

Ultrasonic welding adv and disadv

A

temperature generated CAN be sufficiently high to cause metallurgical changes in the weld zone

Versatile and reliable 
Can be used with a wide variety of materials
DISSIMILAR metallic workpieces
Non-metallic workpieces plastics
Dont need to clean so well
20
Q

Applications of lap welding

A

Lap welding of sheet foil and thin wire

packaging with foils

21
Q

Difference between lap welding and ultrasonic welding

A

The welding tip is replaced with a rotating disk to perform seam welding

22
Q

Friction welding alternate names

A

Stir welding or spin welding

23
Q

True of false melting at the boundary creates join

A

False Although heat is generated through friction at the interface of the two components being joined no melting occurs
Process is technically a forging process (plastic deformation)

24
Q

Friction welding diagram spinning the workpiece

4 step process

A

One component remains sationary
Other is placed in a chuck/collet and is rotated at constant high speed
two components to be joined are brought in contact under increasing force
flashing removed by grinding

25
Q

What does the shape of the weld joint depend on, friction welding

A

rotational speed and axial pressure applied

26
Q

Friction welding weld zone factors x3

A

a narrow region whose size depends on:
The amount of heat generated
The thermal conductivity of the materials
The mechanical properties of the materials at elevated temperature

27
Q

Friction welding weld zone shape diagrams

A

High pressure or low speed
Low pressure or high speed
Optimum

28
Q

Stationary workpiece friction welding steps x3

A

Workpiece stationary
rotating tool force onto joint are
material plastically deforms and fuses together

29
Q

Diagram of station workpiece friction welding

A 
Tool pressure 
direction o the weld
joint 
advancing side
retreating side
tool shoulder
probe 
weld zone
30
Q

Advantages of friction welding

A

Does not require consumable electrodes shield

Strong joint

31
Q

Applications of friction welding

A

Joins wide variety of materials, in particular solid or tubular parts to provide good strength joint

32
Q

What is explosive welding

A

Pressure is applied by detonating a layer of explosive that has been placed over one of the components being joined

33
Q

Explosive welding diagram 6 steps

A
  1. Plain metal inspection
  2. Grind mating surfaces
  3. Assembly backed cladder explosive (space between plates and explosive powder
  4. Explosion (jet, detonation front, collision point, metallurgical weld line)
  5. Flattening and cutting
  6. Testing and inspection
34
Q

Explosive welding setup

A

The bottom sheet of metal is positioned on a rigid base/anvil
The top sheet is inclined to it with a small open angle between the surfaces to be joined

35
Q

Explosive welding basic steps

A

1 An explosive material is placed on top of the two layers of metal
2 It is detonated in a progressive fashion beginning where the surfaces touch
3 A compressive stress wave sweeps across the surface of the plates
4 Surface films are liquefied or scarfed off the metals and are jetted out of the interface
5 The clean metal surfaces are joined together under high contact pressure

36
Q

Why must the sheets be cleaned before explosive welding

A

Contaminator are included in the join making it weak

37
Q

Type of interface created by explosive welding

A

Wavy

38
Q

Advantages of explosive welding

A

High strength

numerous combinations of dissimilar metals

39
Q

Applications of explosive welding

A

High strength joints between aluminium, copper and stainless steel
Corrosion resistant claddings on mild steel substrates

40
Q

What is diffusion welding

A

Occurs when surfaces are held in contact under sufficient pressure and time at elevated temperature
The bonding mechanism is atomic diffusion

41
Q

Under what condition what will atomic diffusion promote

A

Low pressure and elevated temperature

void shrinkage and grain boundary migration to form a metallurgical bond

42
Q

What does elevated temperature mean in diffusion welding

A

Not melting point - just high enough for atoms from both metals to join and form bonds

43
Q

What does the quality of bond depend on for diffusion welding

A

Condition of the materials
Pressure
Temperature & time at temperature

44
Q

Advantages of diffusion welding

A

Dissimilar metals

Furnaecs with inert/protective atmospheres can be used to produce high quality joints (nitrogen)

45
Q

Applications of diffusion welding

A

Titanium welding in aeropsace

46
Q

Shape of parts able to be joined by diffusion weldin

A

Complex parts with complex internal geometries not possible with other joining techniques

MEC130 2 4 8 10 15 (6 decks)

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