Joining Processes

Welding Brazing Soldering

Riveting Adhesive joining

Classification

• Welding– Fusion

– Solid‐state

• Brazing and Soldering

• Adhesive bonding

• Mechanical fastening

WeldingIt is material joining process in which two or more partsare joined at their contacting surfaces by suitable application of heat and or pressure.In some welding processes, a filler material is added to facilitate coalescence. The assemblage of parts that are joined by welding is called a weldment.

FillerWeldment

MACH3 Shaving System

Source:Gillette Consumer Services

Spot Welding

Laser Welding

www.pzvar.sk

WeldingFUSION WELDING

• Melting together and coalescing materials by means of heat.

• Heat source– Chemical, as in gas welding/oxyfuel welding– Electrical, as in arc welding, resistance weldingSOLID‐STATE WELDING

• Diffusion welding – application of pressure• Ultrasonic welding‐ heat of friction• Friction welding – moderate pressure with oscillation at ultrasonic frequency

Welding Joints 

Butt Joint

Corner Joint

T-Joint

Lap Joint

Edge Joint

Weld Types 

Fillet

Groove

Single filletcorner

Outside Singlefillet corner

Double filletlap joint Double fillet

T‐joint

V groove U grooveDouble V groove

Plug weld Slot weld

Weld Types 

Spot weld Seam weld

Flange weld Surface weld

Arc  Welding

• Developed in mid‐1800s• Uses a consumable or non‐consumable electrode (rod or wire)• Arc is produced between the tip of the electrode and work

piece to be welded• Arc is started by momentarily touching the electrode to the

work piece and then withdrawing it to a short distance ( a fewmm)

• An arc is an electric current flowing betweentwo electrodes through an ionized column ofgas.

• Arc is generated by electrons liberated fromcathode and moving towards the anode

• About 70% of the heat is liberated at the anodeby the striking electrons

• Anode temperature can reach 5000 – 30000o C

• +ve workpiece (straight polarity) melts ~50%faster than –ve workpiece (reverse polarity)

• Both AC and DC welding possible

• AC advantage is low power source cost andbulk considerations

Arc  Welding

Electrodes : Consumable / Non‐consumable

Flux : Used to form oxides or otherunwanted contaminants to facilitate their removal

Arc Shielding: Ar/He gas used to protect theweld

Consumable Electrode

• Shielded metal arc welding (SMAW)

• Submerged arc welding (SAW)

• Gas‐metal arc welding (GMAW)

Shielded Metal Arc Welding

• Oldest, simplest, inexpensive and most versatile 

• Coated electrode

• Coating “fluxes” and “shields”

• Current: 50 – 300 A; Power < 10 kW

• Process best suited for workpiece thicknesses of 3 mm to 19 mm.

• Used in 50% of all industrial (general construction, shipbuilding,  pipeline) and maintenance welding

• Use multiple‐pass techniques for deeper “welds”– Solidified slag can cause corrosion

– Remove slag after each pass

Submerged Arc Welding

• Weld arc is shielded by a granular flux

• Flux: Lime, SiO2, MnO2, CaF2• Flux fed into weld zone by gravity

Submerged Arc Welding

• Thick layer of flux covers molten metal– Prevents oxidation, sparks – Reduces weld metal spatter. Increases deposition efficiency

– Acts as thermal insulator; promotes deep penetration

• Electrode wire: 1.5 – 10 mm• Current: 300 – 2000 A• Limited to welds in a flat or horizontal positionbecause flux is fed by gravity

• Can weld a wide variety of C, alloy andstainless steel sheet or plate often at speedsas high as 5 m/min

• Quality of weld is very high, with good toughness, ductility and uniformity of properties.

• Typical applications– Thick plate welding for shipbuilding and pressurevessels

Gas‐Metal Arc Welding (GMAW)

• Weld area shielded by inert gas: Ar, He, CO2

• Used for welding a variety of ferrous & non‐ferrous metals

• Low temperatures; hence used for thin sections

Non‐Consumable Electrode

• Constant gap and hence constant current maintained because of NC‐electrode

• Arc is stable and easy to maintain

• Types– Gas‐Tungsten arc welding (TIG)

• Shielding gas usually Ar, He or Ar+He

• AC or DC mode of operation– AC preferred for Al and Mg because cleaningaction of AC removes oxide and improves weldquality

• GTAW produces very clean welds since no fluxis employed

• Particularly attractive for reactive metals (Al,Mg and Ti), and high temperature refractorymetals

• W contact with molten pool should be avoided because it can cause discontinuity in the weld

Gas‐Tungsten Arc Welding

Resistance Welding

Force

Force

Electrode

Electrode

Sheets Weld nugget

Resistance Welding

Resistance Welding

Press‐type Resistance Welding

Resistance Seam Welding

Resistance Seam Welding

Resistance Seam Welding

Gas Welding

Gas Welding Torch

Types of Flame• Depends on acetylene‐oxygen ratio• Neutral flame

– Used for most operations

• Oxidizing flame– Harmful for steels.  Excess O2 reacts with C– Used for Cu and Cu‐based alloy because it forms a protective oxide film

• Reducing/Carburizing flame– Lower temperatures– Soldering, Brazing, Flame hardening

Types of Flame

Reducing Flame

Neutral Flame: C2H2: O2= 1:1

Oxidizing Flame

HOHCOCOHCOHHCOOHC

Δ++→++Δ++→+

2222

2222

25.122

• Filler Metals– Bare

– Flux coated

• Metals at high temperatures tend to reactchemically with elements in the air ‐ oxygenand nitrogen.

• Oxides and nitrides destroy the strength andtoughness of the weld joint.

• Flux retards oxidation by– Generating a gaseous shield around the weld zone

– Dissolves and removes oxides in the form of“slag”. Slag protects metal against oxidation as itcools

• Advantages– Low cost

– Portable

– Versatile

– Economical for low quantities

Laser Welding