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Flashcards in Lec 15 Deck (46)
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1

What is an ideal joint

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

2

What does solid state process mean

No melting

3

5 examples of solid state processes

Cold welding,
ultrasonic welding,
friction welding,
explosion welding,
diffusion welding/bonding

4

What is resistance welding

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

5

4 steps of resistance welding (diagram)

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

6

Resistance welding diagram cross section

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

7

Adv and Disadv of Resistance welding

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

8

Application of Resistance welding

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

9

What is cold welding (diagram)

Pressure applied through rolls or dies to force two materials together

10

Adv and Disadv of cold welding

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

11

Cold welding requirements

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

12

Applications of cold welding

join small workpieces made of soft, ductile metals
Welding wire stock (splicing wire together)

13

Ultrasonic welding what are the surfaces exposed to

a static normal force
oscillating shearing (tangential) stresses

14

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

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

15

Freq of oscillation for ultrasonic welding

10 kHz – 75 kHz

16

What is ultrasonic welding (diagram)

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

17

How does ultrasonic welding work

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

18

Temperature generated during ultrasonic welding

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

19

Ultrasonic welding adv and disadv

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

Applications of lap welding

Lap welding of sheet foil and thin wire
packaging with foils

21

Difference between lap welding and ultrasonic welding

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

22

Friction welding alternate names

Stir welding or spin welding

23

True of false melting at the boundary creates join

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

Friction welding diagram spinning the workpiece
4 step process

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

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

rotational speed and axial pressure applied

26

Friction welding weld zone factors x3

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

Friction welding weld zone shape diagrams

High pressure or low speed
Low pressure or high speed
Optimum

28

Stationary workpiece friction welding steps x3

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

29

Diagram of station workpiece friction welding

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

30

Advantages of friction welding

Does not require consumable electrodes shield
Strong joint