lecture 04_joining process & equipments (fusion welding)

7/30/2019 Lecture 04_Joining Process & Equipments (Fusion Welding)

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Lecture 4

JOINING PROCESS & EQUIPMENT

(FUSSION WELDING PROCESSES)


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Joining and assembly of two or more parts so that they can functionreliably.

Ex. Pens, bicycles, chairs, cars, etc.

Aspect of manufacturing:1. Impossible to manufacture as a single product e.g chairs, computers,

etc.2. More economical to manufacture as individual components, which are

then assembled e.g3. For maintenance or replacement purposes e.g. car accessories and

engines.4. Different materials due to different properties requirement e.g.

cooking pots and pans.5. Ease and less costly of transportation e.g. bicyle.

INTRODUCTION

JOINING PROCESS & EQUIPMENT 1

@jurie 2007 Lecture 4


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1 - Welding.

2 - Soldering & brazing.

3 - Mechanical fastening.4 - Adhesive bonding.




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INTRODUCTION



Joining Processes

Welding Adhesive BondingMechanical

Fastener

Fusion Brazing & Soldering Solid State

Chemical Electrical Electrical Chemical Mechanical

Oxyfuel

ThermitArc

Resistance

Electron Beam

Laser Beam

ResistanceDiffusion

ExplosionCold

Friction

Ultrasonic

Fastening, Seaming

Crimping, Stitching


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1. Processes in which two pieces are joined together bythe application of heat, which then melts and fusesthe interface.

2. Heat required obtained from electrical energy.

3. The process involves either a consumable or a nonconsumable electrode.

4. Filler metals (which are metals added to the weldarea during welding) may or may not be used.

WELDING




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FUSION WELDING



- Defined as the melting together & coalescing of materials.

- Heat usually supplied by chemical or electrical means.

- Filler metals may or may not be used.

- Comprised of consumable & non-consumable electrode arc welding and high energy

beam welding processes.

SOLID STATE WELDING- Joining takes place without fusion.

- No liquid (molten) phase involved in the joint.

WELDING


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BRAZING AND SOLDERING- Brazing: uses filler metals & involves with lower temperature compare to welding.

- Soldering: also uses similar filler metals (solders) & involves even lower temperature.

ADHESIVE BONDING- Requiring strength, sealing, thermal & electrical insulating, vibration damping, and

resistance to corrosion between dissimilar metals.

MECHANICAL FASTENING

- Involved with traditional methods of joints by using fastenersbolts, nuts & rivets.


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WELDINGFUSION WELDING PROCESSES

1) Oxyfuel-Gas Welding.

2) Pressure-Gas Welding.

3) Arc-Welding

a) Nonconsumable electrode.

i) Gas tungsten-arc welding.ii) Plasma-arc welding.

iii) Atomic-hydrogen welding.

b) Consumable electrode.

i) Shielded metal-arc welding.

ii) Submerged-arc welding.

iii) Gas metal-ac welding.iv) Flux-cored arc welding.

v) Electrogas welding.

vi) Electroslag welding.

4) Electron-Beam Welding.

5) Laser-Beam Welding.




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SOLID-STATE WELDING PROCESSES

1) Cold Welding.2) Roll Bonding/Welding.

3) Ultrasonic Welding.

4) Friction Welding.

a) Inertia friction welding.

b) Linear friction welding.

c) Friction stir welding.5) Resistance Welding.

a) Resistance spot welding.

b) Resistance seam welding.

c) High-frequency resistance welding.

d) Resistance projection welding.

e) Flash welding.

f) Stud welding.

g) Percussion welding.

6) Explosion Welding.

7) Diffusion Bonding.




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FUSION WELDING PROCESS

1) OXYFUEL-GAS WELDING (OFW)

- OFW uses a fuel gas combined with oxygen to produce flame.

- Function of the flameact as a source of the heat to melt the metals at the joint.

- Common gas welding process uses acetylene (oxyacetylene gas weldingOAW).

- Application: structural sheet metal fabrication, automotive bodies, and various repair

work.


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- OAW process utilizes the heat generated by the combustion of acetylene gas (C2H2)

in a mixture of oxygen.

- These primary combustion process, occurs in the inner core of the flame, involves the

reaction of:

C2H2 + O2 ----------> 2CO + H2 + Heat (1/3 total heat generated in the flame)

- The secondary combustion process involves further burning of hydrogen and carbon

monoxide:

2CO + H2 + 1.5O2 ------------>2CO2 + H2O + Heat (2/3 of the total heat)




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(a) General view of oxy torch.

(b) cross-section of a torch used in

oxyacetylene welding. The acetylenevalve is opened first; the gas is litwith a spark lighter or a pilot light;then the oxygen valve is opened andthe flame adjusted.

(c) Basic equipment used in oxyfuel-gas

welding. To ensure correct

connections, all threads on acetylenefittings are left-handed, whereasthose for oxygen are right-handed.Oxygen regulators are usually painted

green, acetylene regulators red.

Torch Used in Oxyacetylene Welding




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Flame types

1. Neutralratio 1: 1, no excess oxygen

2. Oxidizinggreater oxygen supply (excess oxygen), harmful for steel due to

oxidizes. Only suit for nonferrous metal e.g copper & copper based alloys.

3. Carburizinginsuffient of oxygen (excess acetytelene), low temperature, thus suit

for applications requiring low heat e.g. brazing, soldering, flame hardening.

Filler metals

1. To supply additional metal to the weld zone during welding.

2. Filler rods or wire and may be coated by flux.3. The purpose of flux is to retard oxidation of the welded surfaces.




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Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame;

(b) oxidizing flame; (c) carburizing, or reducing, flame. The gas mixture in (a) is basically equal volumes of oxygen

and acetylene.

Oxyacetylene Flames Used in

Welding




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PRESSURE GAS WELDING

- Involved with two components starts by heating the interface.

- Once when the interface begins to melt, the torch is withdrawn.

- A force is applied to press both components together and maintain until the interface

solidifies.

- The joined end with the occurrence of a flash.




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ARC-WELDING PROCESSES

NONCONSUMABLE ELECTRODE

- In arc welding, the heat is obtained from electrical energyby using AC or a DCpower supply.

- The process involved can be either consumable or non-consumable electrode.

- An arc is produced between the tip of electrode and the work piece which need to be

welded.

- The arc produces temperatures 30,0000C.

-The electrode is a tungsten electrode type.

- Need externally supplied shielding gas because of the high temperatures involved in

order to prevent oxidation of the weld zone.

- For this non-consumable electrode welding process, DC is used and the polarity is

important.

- For straight polarity which is also known as direct-current electrode negative (DCEN);

the workpiece is positive (anode), while the electrode is negative (cathode).

- In this case, it will produce welds that are narrow and deep.




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- For reverse polarity which also known as direct-current electrode positive (DCEP); the

workpiece is negative, and the electrode is positive.- In this process, weld penetration is less, and the weld zone is shallower and wider.




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GAS TUNGSTEN-ARC WELDING (GTAW)

- Also known as TIG welding.- Suitable for thin metals.

- This process is expensive because of the cost of inert gas.

- Provides welds with very high quality and surface finish.

- Filler metal is supplied from a filler wire.

- This filler metals are similar to the metal that need to be welded, and flux is not used.

- In this operation, tungsten electrode is not consumed, therefore a constant and stable arc

gap is maintained at a constant current level.

- The shielding gas is usually argon or helium.

- Power supplyeither DC at 200A, or AC at 500A; depending on the metals to be

welded.

- Generally, AC is suitable for aluminum and magnesium.- Thorium or zirconium may be used in the tungsten electrodes to improve the electron

emission characteristics.

- Contamination of the tungsten electrode by molten metal can cause discontinuities in the

weld.

- Therefore, contact between the electrode with the molten metal pool should be avoided.




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Gas Tungsten-Arc Welding(GTAW)



The gas tungsten-arc welding process and its basic equipment,

formerly known as TIG (for tungsten inert gas) welding.


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PLASMA-ARC WELDING (PAW)

- In this welding operation, a concentrated plasma arc is produced and directed towardsthe weld area.

-The arc is stable and the temperature can reaches up to 33,0000C.

- PAW has less thermal distortion, and higher energy concentrationpermitting deeper

and narrower welds.

- Plasma: it is an ionized hot gas composed of nearly equal numbers of electrons and ions.

- This plasma is initiated between the tungsten electrode and the small orifice by a low-current pilot arc.

- Operating current: usually below 100A.

- Filler metal is fed into the arc during the welding process.

- There are two methods of plasma-arc welding:

i) Transferred-arc method

- Workpiece being welded is part of the electrical cuircuit.- The arc transfers from the electrode to the workpiece.

ii) Nontransferred method

- The arc occurs between the electrode and the nozzle.

- The heat is carried to the workpiece by the plasma gas.




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- The welding speeds: from 120 to 1000 mm/min.

- Can be welded with part thickness less than 6mm.



Two types of plasma-arc welding processes: (a) transferred, (b)

nontransferred. Deep and narrow welds can be made by this process at

high welding speeds.


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ARC WELDING PROCESSES: CONSUMABLE ELECTRODE

SHIELDING METAL-ARC WELDING (SMAW)

- Old method, simplest, held manually.

- Most of all industries and maintenance welding currently performed with this process.

- The electric arc is generated by touching the tip of a coated electrode against the

workpiece.

- Need to have a sufficient distance and movement to maintain the arc.- The heat generated, melts a portion of the electrode tip, its coating, and the base metal

in the immediate arc area.

- The molten metal consists of a mixture of the base metal (workpiece), the electrode

metal, and substances from the coating on the electrode; thus this mixture forms the weld

when it solidifies.

- The electrode coating deoxidizes the weld area and provides a shielding gas to protectit from oxygen in the environment.

- The equipment consists of a power supply, cables and electrode holder.

- Power supply: can be either DC or AC, ranges between 50 to 300A.

- For sheet metal welding, DC is preferred because of the steady arc produces.




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Shielded Metal-Arc Welding(SMAW)




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SUBMERGED-ARC WELDING (SAW)

- The weld arc is shielded by a granular flux consisting of lime, silica, manganese oxide,calcium flouride.

- The flux is fed into the weld zone from a hopper by gravity flow through a nozzle.

- The thick layer of flux completely cover s the molten metal and it prevents from spatter

and sparks.

- The flux also acts as a thermal insulator by promoting deep penetration of heat into the

workpiece.

- The consumable electrode is a coil of bare round wire 1.5 to 10 mm in diameter; and

fed automatically through a tube which is called welding gun.

- Electric current: range between 300 to 2000 A.

- Power supply: single or three phase power point; rating up to 440V.

- Due to flux is a gravity fed type; therefore this welding process is limited largely to

welds into flat or horizontal position.

- Circular weld can be made on pipes or cylindersprovided that they are rotated

during welding process.

- Suitable for carbon and alloy steel and stainless steel sheet or plates.

- Welding speeds: as high as 5 m/min.




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Submerged-Arc Welding

(SAW)

Schematic illustration of the submerged-arc welding process and

equipment. The unfused flux is recovered and reused.


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GAS METAL-ARC WELDING (GMAW)

- Also known as metal inert-gas (MIG).

- The weld area is shielded by an effectively inert atmosphere of argon, helium, carbon

dioxide, or other various gas mixtures.

- The temperatures generated are relatively low.

- Suitable only for thin sheets which is less than 6mm.

- The process are economical and can be automated easily.- The consumable bare wire is fed automatically through a nozzle into the weld arc

controlled by wire-feed drive motor.

- There are 3 types of GMAW process:

i) Spray transfer.

ii) Globular transfer.

iii) Short circuiting.




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Gas Metal-Arc Welding (GMAW)



Schematic illustration of the gas

metal-arc welding process and its

basiq equipment, formerly known as

MIG (for metal inert gas) welding.


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SPRAY TRANSFER

- Small size of molten metal droplets from the electrode are transferred to the weld area

at a rate of several hundred droplets per second.

- The transfer is spatter free and very stable.

- Using high DC current and voltages with large diameter of electrodes.

- The electrodes are used with argon or an argon rich gas mixture act as a shielding gas.

GLOBULAR TRANSFER

- Utilizes with carbon-dioxide-rich gases, and globules are propelled by the forces of the

electric-arc transfer of a metal, resulting in considerable spatter.

- High welding current are usedgreater weld penetration and higher welding speed.

SHORT CIRCUITING

-The metal is transferred in individual droplets, as the electrode tip touches the molten weld

metal and short circuits.

- Low currents and voltages are utilized.

- Electrodes are made from small-diameter wire.

- Power required: 2 kW.




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ELECTRON-BEAM WELDING (EBW)

- Can be welded almost any metal; butt or lap welded and the thicknesses up to 150mm.

- The thickness of the workpiece can range from foil to plate.

- Generally, there is no involvement of shielding gas, flux, or filler metal.

- Distortion and shrinkage in the weld area is minimal.

- Heat is generated by high velocity narrow-beam electrons.

- Capacity of electron guns range up to 100 kW.

- The kinetic energy of the electrons is converted into heat as they strike the workpiece.

- Required special equipment to focus the beam on the workpiece, typically in vacuum.

- The higher the vacuum, the more the beam penetrates, and the greater is the depth-to

width ratio, range between 10 and 30.

- Sizes of the welds are much smaller compared to conventional process.

- Parameters can be controlled accurately at welding speeds as high as 12 m/min; this

can be done by using automation and servo motor.




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LASER-BEAMWELDING (LBW)

- Utilizes a high power laser beam as the source of heat.

- The beam can focused onto a very small area, and due to this it has high energy density

and deep penetrating capability.

- This process is suitable for welding deep and narrow joints with depth-to-width ratios

ranging from 4 to 10.

- The laser beam may be pulsed for a application such as the spot welding of thin

materials with power level up to 100 kW.

- Minimum shrinkage and distortion, good strength and generally are ductile and free of

porosity.

- Can be automated to be used on a variety of materials with thicknesses up to 25mm.- Typical metals and alloys welded: aluminum, titanium, ferrous metals, copper.

- Welding speeds: range from 2.5 m/min to as high as 80 m/min for thin metals.




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Advantages of LBW over EBW:

A vacuum is not required, and the beam can be transmitted through air.

Laser beams can be shaped, manipulated, and focused optically by using fiber optics,therefore the process can be automated easily.

The beams do not generate x-rays.

The quality of the weld is better than in EBW with less tendency for incomplete fusion,

spatter, porosity, and less distortion.



Example of Laser

WeldingLaser welding of razor blades.


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Comparison of Laser-Beam and Tungsten-Arc

Welding

Comparison of the size of weld beads in (a) electron-beam or laser-beam

welding to that in (b) conventional (tungsten-arc) welding.


lecture 04_joining process & equipments (fusion welding)

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