Lec 15 Flashcards by Jamie Rayson

What is an ideal joint

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

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What does solid state process mean

No melting

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5 examples of solid state processes

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

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What is resistance welding

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

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4 steps of resistance welding (diagram)

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

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Resistance welding diagram cross section

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

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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

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Application of Resistance welding

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

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What is cold welding (diagram)

Pressure applied through rolls or dies to force two materials together

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Adv and Disadv of cold welding

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

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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

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Applications of cold welding

join small workpieces made of soft, ductile metals

Welding wire stock (splicing wire together)

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Ultrasonic welding what are the surfaces exposed to

a static normal force 
oscillating shearing (tangential) stresses

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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

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Freq of oscillation for ultrasonic welding

10 kHz – 75 kHz

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What is ultrasonic welding (diagram)

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

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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

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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

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Ultrasonic welding adv and disadv

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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

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Lap welding of sheet foil and thin wire

packaging with foils

Difference between lap welding and ultrasonic welding

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

Friction welding alternate names

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Stir welding or spin welding

True of false melting at the boundary creates join

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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

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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

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

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

Lec 15 Flashcards

(46 cards)