Lec 15 Flashcards
What is an ideal joint
When you go across joint area you dont seen a change in the composition of material properties
What does solid state process mean
No melting
5 examples of solid state processes
Cold welding, ultrasonic welding, friction welding, explosion welding, diffusion welding/bonding
What is resistance welding
The heat required for welding is produced by electrical resistance across two components to be joined
Spot welding most common
4 steps of resistance welding (diagram)
Pressure applied current on current off pressure on pressure released (electrode weld nugget lap joint)
Resistance welding diagram cross section
2x Electrode electrode tip weld nugget indentation sheet separation heat affected zone
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
Application of Resistance welding
Sheet metal fabrication
automotive body assembly
(places where joint strength is not critical)
What is cold welding (diagram)
Pressure applied through rolls or dies to force two materials together
Adv and Disadv of cold welding
Not particularly strong - produces brittle inter metallic compound but used for putting on cladding
No heat is generated
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
Applications of cold welding
join small workpieces made of soft, ductile metals
Welding wire stock (splicing wire together)
Ultrasonic welding what are the surfaces exposed to
a static normal force oscillating shearing (tangential) stresses
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
Freq of oscillation for ultrasonic welding
10 kHz – 75 kHz
What is ultrasonic welding (diagram)
Force mass coupling system tip Workpiece anvil direction of vibration transducer dc polarization supply ac power supply
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
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
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
Applications of lap welding
Lap welding of sheet foil and thin wire
packaging with foils
Difference between lap welding and ultrasonic welding
The welding tip is replaced with a rotating disk to perform seam welding
Friction welding alternate names
Stir welding or spin welding
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)
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
What does the shape of the weld joint depend on, friction welding
rotational speed and axial pressure applied
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
Friction welding weld zone shape diagrams
High pressure or low speed
Low pressure or high speed
Optimum
Stationary workpiece friction welding steps x3
Workpiece stationary
rotating tool force onto joint are
material plastically deforms and fuses together
Diagram of station workpiece friction welding
Tool pressure direction o the weld joint advancing side retreating side tool shoulder probe weld zone
Advantages of friction welding
Does not require consumable electrodes shield
Strong joint
Applications of friction welding
Joins wide variety of materials, in particular solid or tubular parts to provide good strength joint
What is explosive welding
Pressure is applied by detonating a layer of explosive that has been placed over one of the components being joined
Explosive welding diagram 6 steps
- Plain metal inspection
- Grind mating surfaces
- Assembly backed cladder explosive (space between plates and explosive powder
- Explosion (jet, detonation front, collision point, metallurgical weld line)
- Flattening and cutting
- Testing and inspection
Explosive welding setup
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
Explosive welding basic steps
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
Why must the sheets be cleaned before explosive welding
Contaminator are included in the join making it weak
Type of interface created by explosive welding
Wavy
Advantages of explosive welding
High strength
numerous combinations of dissimilar metals
Applications of explosive welding
High strength joints between aluminium, copper and stainless steel
Corrosion resistant claddings on mild steel substrates
What is diffusion welding
Occurs when surfaces are held in contact under sufficient pressure and time at elevated temperature
The bonding mechanism is atomic diffusion
Under what condition what will atomic diffusion promote
Low pressure and elevated temperature
void shrinkage and grain boundary migration to form a metallurgical bond
What does elevated temperature mean in diffusion welding
Not melting point - just high enough for atoms from both metals to join and form bonds
What does the quality of bond depend on for diffusion welding
Condition of the materials
Pressure
Temperature & time at temperature
Advantages of diffusion welding
Dissimilar metals
Furnaecs with inert/protective atmospheres can be used to produce high quality joints (nitrogen)
Applications of diffusion welding
Titanium welding in aeropsace
Shape of parts able to be joined by diffusion weldin
Complex parts with complex internal geometries not possible with other joining techniques
