Lecture 15 - Resistance and Solid State Welding

Question 1

Types of welding processes

Answer 1

Resistance welding
Cold welding
Ultrasonic welding
Friction welding
Explosion welding
Diffusion welding / bonding

Question 2

Resistance welding definition

Answer 2

Heat required for welding produced by electrical resistance across 2 components
Resistance spot welding most common

Question 3

Advantages, disadvantages and applications of resistance welding

Answer 3

Doesn’t require consumable electrodes, shielding gases and flux
easy and fast

complex and expensive equipment

sheet metal fabrication
automotive body assembly

Question 4

Cold welding

Answer 4

Pressure applied to workpiece wither through dies or rolls
Plastic deformation takes place
at least one component must be ductile
Prior to welding, interface thoroughly cleaned
Produces weak brittle joint
Best bond obtained between 2 similar materials

Joins small workpieces made of soft, ductile materials

Question 5

Applications of cold welding

Answer 5

Weldign wire stock (splice wire together)

Some electrical connections work in same way

Question 6

Ultrasonic welding

Answer 6

Surfaces of two components subjected to static normal force and oscillating shearing stresses
Shearing stresses applied by tip of transducer
Frequency of oscillations generally between and 10kHz and 75 kHz
Proper coupling between transducer and tip important for efficient operation
Temperature generated in weld zone usually 1/3 -1/2 melting point of metals joined so neither melting nor fusion takes place

Question 7

What are advantages of plastic deformation caused by shearing stresses in ultrasonic welding

Answer 7

allowing good contact
producing strong solid-state bond
breaks up oxide films and contaminants

Question 8

Advantages and applications of ultrasonic welding

Answer 8

in certain situations temp generated sufficiently high to cause metallurgical changes in weld zone

versatile and reliable
can be used with wide variety of materials
- dissimilar metallic workpieces
- non-metallic workpieces

used for joining plastics
lap welding of sheet, foil, and thin wire (automotive and electronics industries)
packaging with foils

welding tip replaced with rotating disk to perform seam welding

Question 9

Friction welding (stir welding spin welding)

Answer 9

No melting occurs even though heat generated through friction
Technically a forging process

Question 10

Friction welding method 1

Answer 10

One component remains stationary
Other component placed in chuck and rotated at constant high speed
Both components brought into contact under increasing force

Pressure at interface and resulting friction produces sufficient heat for strong join to form

Question 11

Friction Welding - weld zone

Answer 11

Confined to narrow region whose size depends on:
amount of heat generated
thermal conductivity of materials
mechanical properties of materials at elevated temperature

Shape of welded joint depends on rotational speed and axial pressure applied
High pressure or low speed - large at surface, thin at centre
Low pressure or high speed - large in centre, small at surface
Optimum - flat weld

Question 12

Friction loading method 2

Answer 12

Workpiece stationary
Rotating tool forced onto joint area
material plastically deforms and fuses together

Question 13

Advantages and applications of friction welding

Answer 13

Does not require consumable electrodes, shielding gases or flux

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

Question 14

Explosive welding

Answer 14

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

Bottom sheet of metal positioned on rigid base/anvil
Top sheet inclined to it with small open angle between surfaces to be joined
Explosive material placed on top of two layers of metal

Detonated in progressive fashion beginning where surfaces touch
Compressive stress wave sweeps across surface of plates
Surface films liquefied or scarfed off the metals and jetted out of interface
Clean metal surfaces are joined together under high contact pressure

Kinetic energy of plate striking mating component causes wavy interface

Question 15

Advantages and applications of explosive welding

Answer 15

Bond strength is high
Ability to join numerous combinations of dissimilar metals

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

Question 16

Diffusion welding / Bonding

Answer 16

Occurs when surfaces held in contact under sufficient pressure and time at elevated temperature

Bonding mechanism is atomic diffusion

Under low pressure and elevated temp atomic diffusion promotes
void shrinkage
grain boundary migration to form metallurgical bond

Quality of bond depends on
Conditions of material
pressure
temperature and time at temperature

Question 17

Advantages and applications of diffusion welding / bonding

Answer 17

Ability to join dissimilar metals
furnaces with inert/protective atmospheres can be used to produce high quality joints

titanium welding in aerospace industry