Joining Processes

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Joining Processes Outline

• Fusion Bonding

– Oxy-fuel welding

– Arc welding

– Resistance welding

– Solid state welding

• Brazing

• Soldering

• Adhesive Bonding

• Mechanical Fastening

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Direct bonding, or fusion bonding, a

bonding process without any additional

intermediate layers. based on

chemical bonds between two surfaces of any

material possible meeting numerous

requirements.

Brazing, process for joining two pieces of

metal that involves the application of heat

and the addition of a filler metal. This filler

metal, which has a lower melting point than

the metals to be joined,

welding• the two metals (or thermoplastic) must be similar.

• copper cannot be welded to steel.

• uses high temperatures to melt and join two metal parts.

• A filler metal is often used as well.

• When properly done, the finished weld is as strong as the surrounding metal.

• But if the welder applies too much heat, it can change the metal’s properties and weaken the weld.

• There are several different types of welding, including

• metal inert gas (MIG), arc, electron beam, laser, and stir friction.

• Welding is also widely used to slice apart large metal structures by melting through them.

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Weld Joints

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alın kaynakküt kaynak

köşe kaynak bindirme bağlantı

kenar bağlantı

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Advantages• Welding provides a permanent joint.• The welded joint can be stronger than the parent materials• Welding is usually the most economical way to join

components in terms of material usage and fabrication costs.• Welding is not restricted to the factory environment. It can

be accomplished ‘‘in the field.’’

Disadvantages• Skilled workers required• Most welding processes are inherently dangerous because

they involve the use of high energy.• Does not allow for convenient disassembly

Oxyfuel Gas Welding

• The main source is heat resulting from the burning of a fuel gas and oxygen (generally in pure form).

• Acetylene is the principal fuel. up to 3480 °C

• No pressure is involved.

• Filler material is used in the form of a wire or rod.

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Welding Torch

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Oxy-Acetylene Flame

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Oxy-Acetylene Flame

• No excess oxygen ratio 1:1 the flame is considered neutral.

• High oxygen oxidizes metal. • Low oxygen is known as

reducing or carburizing flame.

• Desired for low heat apps brazing soldering and flame hardening operations.

• The maximum temperature of the flame is reached at the tip of the inner cone;

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Oxyfuel Gas Welding

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Alternative Gases

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Arc Welding• Uses a carbon electrode and metal workpiece as the heat source for

fusion welding.

• Filler material is added in the form of a metallic wire.

• Labor skill is important.

• The electric energy from the arc thus formed produces temperatures of

5500 °C or higher

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Arc Welding

• An electric arc, or arc discharge, is an electrical breakdown of a gas

• produces an ongoing electrical discharge.

• The current through a normally nonconductive medium such as air produces a plasma;

• plasma may produce visible light.

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Manual Arc Welding

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Arc Welding Types

• Shielded Metal Arc Welding (SMAW)

• Gas Tungsten Arc Welding (GTAW)

• Gas Tungsten Arc Spot Welding

• Gas Metal Arc Welding (GMAW)

• Submerged Arc Welding (SAW)

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Shielded Metal Arc Welding (SMAW)

As the coating on the electrode melts andvaporizes, it forms a protective atmosphere thatstabilizes the arc and protects the molten and hotmetal from contamination.

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Shielded Metal Arc Welding (SMAW)

• The electrode:• Provide a protective atmosphere.• Stabilize the arc.• Act as a flux to remove impurities from the molten metal• Provide a protective slag to accumulate impurities, prevent

oxidation, and slow down the cooling of the weld metal.• Reduce weld-metal spatter and increase the efficiency of

deposition.• Add alloying elements.• Affect arc penetration.• Influence the shape of the weld bead• Add additional filler metal.

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SMAW

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Gas Tungsten Arc Welding (GTAW)TIG Welding, WIG Welding

• Employs a tungsten electrode.

• Uses an inert gas to form a shield around the arc.

• Fillet material can be supplied by a separate wire.

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ADVANTAGES

• suited include high-quality welds

• no weld spatter because no filler metal is

transferred across the arc

• little or no postweld cleaning because no

flux is used.

Drawbacks

• Costs more• Cast irons, wrought irons, and tungsten are

difficult to weld by GTAW

GTAW Torch

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Gas Tungsten Arc Welding (GTAW)

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Gas Tungsten Arc Spot Welding(TIG Spot Welding)

A variation of gas tungsten arc welding is employed for making spot welds between two pieces of metal without the necessity of having access to both sides of the joint.

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Gas Metal Arc Welding (GMAW)• The arc is maintained between an automatically fed, consumable wire

electrode and the workpiece.• Fast and economical since there is no frequent changing of electrodes.• No slag is formed over the weld.

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Inert gas CO2 and Argon mixtures.

Gas Metal Arc Welding (GMAW)

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Submerged Arc Welding (SAW)

• The arc is maintained beneath a blanket of granular flux.

• The flux is deposited just ahead of the electrode.

• Granular flux provides shielding of the molten metal.

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Submerged Arc Welding (SAW)

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Resistance Welding

• Both heat and pressure are utilized to producecoalescence (the joining or merging of elements to form one mass

or whole).

• Heat is the consequence of large currents passing through the workpieces and their interfaces with small electrical resistivities (resistances).

• Very rapid and economical process.

• Widely used in mass production.

• Types of resistance welding:

– Resistance Spot Welding

– Seam Welding

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Resistance Spot Welding (RSW)

• Simplest and most widely used one.

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Temperature in RSW

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Pressure in RSW

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Resistance Spot Welding (RSW)

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Seam Welding

• The seam is actually a series of overlapping spot welds.• Widely used for the production of liquid or pressure tight

vessels such as gasoline tanks, automobile mufflers, or heat exchangers.

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Seam Welding

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Friction Welding

• Mechanical friction is the heat source.

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Friction Welding

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Inertia Welding

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Sample for Friction Welding

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https://www.youtube.com/watch?v=aNbQH8XBgxQ

Eclipse 500 Experimental Aircraft N504EA at TWI

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https://www.youtube.com/watch?v=Yx5SVQTfTzU

Distortion in Welding

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Causes of Distortion

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• Non-Uniform Expansion and Contraction,

• i.e. Shrinkage due to plastic thermal strain, of the

weld metal and base metal

• during the heating and cooling cycle

• Internal stresses formed in base metal due to

removing restraints given to welds by fixed

components surrounding it

• both Welding processes & procedures and Material

properties affect the extent of distortion

Significance of Material Properties

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Influence of Welding Processes & Procedures

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Torch and Arc Cutting

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• OFC-A (Acetylene)

• OFC-N (Natural gas)

• OFC-P (Propane)

• OFC-H (Hydrogen)

Brazing and Soldering

• Very similar processes.

• Composition of brazing and soldering alloys are different than base metal.

• Melting point of these alloys are lower than that of base metal.

• Base metal does not melt during process.

– T (Solder) < 450oC

– T (Brazing) > 450oC

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"What is flux?"

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FLUX: A chemical composition critical to the heat

joining methods of soldering, brazing, and welding that:

1. Chemically: Cleans metals surfaces to assist the

flow of filler metals over base metals. Provides a

protective barrier against re-oxidation and heat scale.

2. Thermally: Assists with heat transfer from heat

source to metal surface.

3. Physically: Helps in the removal of surface metal

oxides.

Brazing and Soldering

• Flux has an important role:

– Dissolves oxides present on the surface,

– Prevents formation of oxides.

• Flux is not a surface cleaner.

• After the process, flux residues

(corrosive!) must be removed.

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Brazing

• Capillary action distributes the braze metal into the joint.

• Braze metal + base metal alloy is formed at the interface.

• Braze metal also penetrates into the grain boundaries of the base metal.

• Braze materials:

– Cu for HSS, WC, Steel

– Cu alloys for brass & Mn bronze

– Ag for Ti

– Ag alloys for Al-Si alloys

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Advantages of Brazing

• Virtually, all metals can be joined.

• If compared to welding, less heating is

required.

– More economical

– Less distortion: thinner and more complex

assemblies can be joined.

• Suitable for automation.

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Soldering

• Solder metals:

– Pb and Tin + small

amount of antimony.

• No coalescence:

– Bond strength is low.

– Affected by adhesion

between the solder-

and parent metal.

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Soldering Samples

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Adhesive Bonding• Adhesives:

– Thermoplastic and thermo-setting resins

– Artificial elastomers

– Ceramics

• Both metals and non-metals can be joined.

• Critical application areas:

– Automotive industry

– Aviation/Aerospace industry

• Structural adhesives do have several components in various forms:

– Liquids, pastes, solids, pellets, cartridges, tapes, films.

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Properties of Adhesives

Gap Filling: https://www.youtube.com/watch?v=jI59rsDwSW8

Mechanical Fastening

• Integral: Components are deformed so they interlock as

a mechanically fastened joint.

– Embossed intrusions

– Edge seams

– Lanced tabs

– Snap-fit joints

• Discrete: Fasteners are separate, individual pieces.

– Bolts, screws, nuts, rivets, staples, wire stitches.

• Shrink and expansion fits

– Interference fit

– Press fits

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Rivets and Stapling

Examples of rivets: (a) solid, (b)

tubular, (c) split, or bifurcated, and

(d) compression.

Examples of various

fastening methods. (a)

Standard loop staple; (b) flat

clinch staple; (c) channel

strap; (d) pin strap.

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Seams & Crimping

Stages in forming a double-lock seam.

examples of mechanical joining by crimping.

Snap Fasteners

Examples of spring and snap-in fasteners to facilitate assembly.

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Design Guidelines for Welding

Design guidelines for welding

Brazing Designs

Examples of good and poor designs for brazing.

Design for Adhesive Bonding

Various

joint

designs in

adhesive

bonding.

good

designs

require

large

contact

areas for

better joint

strength.

Design for Riveting

Design for Riveting