UNIT II
WELDING PROCESS
Welding
Welding is defined as an localized
coalescence of metals, where in
coalescence is obtained by heating to
suitable temperature, with or without
the application of pressure and with
or without the use of filler metal.
Fusion Welding Processes Welding Processes
Consumable Electrode
SMAW – Shielded Metal Arc Welding
GMAW – Gas Metal Arc Welding
SAW – Submerged Arc Welding
Non-Consumable Electrode
GTAW – Gas Tungsten Arc Welding
PAW – Plasma Arc Welding
High Energy Beam
Electron Beam Welding
Laser Beam Welding
Different welding processes.
• Fusion Welding, Brazing & Soldering
• Solid State Welding
• Chemical, welding
• Electrical Resistance
• Diffusion, Explosion
• Mechanical
• Cold Friction Ultrasonic
• Oxyfuel gas, hermit welding
• Electron Beam, Laser Beam,Plasma arc welding
GasWelding
Gas welding is a group of welding
processes where in coalescence is
produced by heating with a flame or
flames with or without the application
of pressure and with or without the
use of filler material.
SMAW – Shielded Metal Arc Welding Welding Processes
• Consumable electrode
• Flux coated rod
• Flux produces protective gas around weld pool
• Slag keeps oxygen off weld bead during cooling
• General purpose welding—widely used
Power... Current I (50 - 300 amps)
• Thicknesses 1/8‖ – 3/4‖ Voltage V (15 - 45 volts)
• Portable Power = VI 10 kW
Electric Arc Welding -- Polarity Welding Processes
SMAW - DC Polarity
Straight Polarity Reverse Polarity
(–) (+)
(+) (–)
Shallow penetration Deeper weld penetration
(thin metal)
AC - Gives pulsing arc
- used for welding thick sections
GMAW
• An arc welding process that uses an arc
between a continuous filler metal electrode
and the weld pool to produce a fusion
(melting) together of the base metal
• The process is used with a shielding gas
supplied from an external source without
pressure.
GMAW – Gas Metal Arc Welding (MIG) Welding Processes
• DC reverse polarity - hottest arc
• AC - unstable arc
Gas Metal Arc Welding (GMAW) Torch
• MIG - Metal Inert Gas
• Consumable wire electrode
• Shielding provided by gas
• Double productivity of SMAW
• Easily automated
Groover, M., Fundamentals of Modern Manufacturing,, p. 734, 1996
SAW – Submerged Arc Welding Welding Processes
• 300 – 2000 amps (440 V)
• Consumable wire electrode
Gas Metal Arc Welding (GMAW) Torch
• Shielding provided by flux granules
• Low UV radiation & fumes
• Flux acts as thermal insulator
• Automated process (limited to flats)
• High speed & quality (4 – 10x SMAW)
• Suitable for thick plates http://www.twi.co.uk
GTAW – Gas Tungsten Arc Welding (TIG) Welding Processes
Current I (200 A DC)
(500 A AC)
Power 8-20 kW
• a.k.a. TIG - Tungsten Inert Gas
• Non-consumable electrode
• With or without filler metal
• Shield gas usually argon
• Used for thin sections of Al, Mg, Ti.
• Most expensive, highest quality
Friction Welding (Inertia Welding) Welding Processes
• One part rotated, one stationary
• Stationary part forced against rotating part
• Friction converts kinetic energy to thermal energy
• Metal at interface melts and is joined
• When sufficiently hot, rotation is stopped
& axial force increased
Resistance Welding Welding Processes
Resistance Welding is the coordinated
application of electric current and mechanical
pressure in the proper magnitudes and for a
precise period of time to create a coalescent
bond between two base metals.
• Heat provided by resistance to electrical current (Q=I2Rt)
• Typical 0.5 – 10 V but up to 100,000 amps!
• Force applied by pneumatic cylinder
• Often fully or partially automated
- Spot welding
- Seam welding
Resistance Welding Welding Processes
• Heat provided by resistance to electrical current (Q=I2Rt)
• Typical 0.5 – 10 V but up to 100,000 amps!
• Force applied by pneumatic cylinder
• Often fully or partially automated
- Spot welding
- Seam welding
Diffusion Welding Welding Processes
• Parts forced together at high temperature
(< 0.5Tm absolute) and pressure
• Heated in furnace or by resistance heating
• Atoms diffuse across interface
• After sufficient time the interface disappears
• Good for dissimilar metals
• Bond can be weakened by surface impurities
Kalpakjian, S., Manufacturing Engineering & Technology, p. 889, 1992
Soldering & Brazing Metal Joining Processes
Soldering & Brazing
• Only filler metal is melted, not base metal
• Lower temperatures than welding
• Filler metal distributed by capillary action
• Metallurgical bond formed between filler & base metals
• Strength of joint typically
– stronger than filler metal itself
– weaker than base metal
– gap at joint important (0.001 – 0.010‖)
• Pros & Cons
– Can join dissimilar metals
– Less heat - can join thinner sections (relative to welding)
– Excessive heat during service can weaken joint
LASER BEAM WELDING
High Energy Density Processes
Laser Beam Welding (LBW)
shielding
gas nozzle
(optional)
Laser beam
Plasma plume
Molten
Plasma material
keyhole
workpiece motion
Keyhole welding
High Energy Density Processes
Focusing the Beam
Heat Surface Welding Cutting
treatment modification
Advantages
• Single pass weld
12 penetration up to 3/4”
6 kW CO2 in steel
Weld penetration, mm
10
2 kW Nd:YAG • High Travel speed
8 • Materials need not be
6 conductive
• No filler metal required
4
• Low heat input produces
2 low distortion
0 • Does not require a
1 3 5 7 vacuum
Welding speed, m/min
0.1.1.2.1.T4.95.12
Soldering Metal Joining Processes
Soldering
Solder = Filler metal
• Alloys of Tin (silver, bismuth, lead)
• Melt point typically below 840 F
Flux used to clean joint & prevent oxidation
• separate or in core of wire (rosin-core)
Tinning = pre-coating with thin layer of solder
Applications:
• Printed Circuit Board (PCB) manufacture
• Pipe joining (copper pipe)
• Jewelry manufacture
• Typically non-load bearing
Easy to solder: copper, silver, gold
Difficult to solder: aluminum, stainless steels
(can pre-plate difficult to solder metals to aid process)
PCB Soldering Metal Joining Processes
Manual PCB Soldering
• Soldering Iron & Solder Wire
• Heating lead & placing solder
• Heat for 2-3 sec. & place wire
opposite iron
• Trim excess lead
PCB Reflow Soldering Metal Joining Processes
Automated Reflow Soldering SMT = Surface Mount Technology
• Solder/Flux paste mixture applied to PCB using screen
print or similar transfer method
• Solder Paste serves the following functions:
– supply solder material to the soldering spot,
– hold the components in place prior to soldering,
– clean the solder lands and component leads
– prevent further oxidation of the solder lands.
Printed solder paste on a printed circuit board (PCB)
• PCB assembly then heated in ―Reflow‖ oven to melt solder and
secure connection
Brazing Metal Joining Processes
Brazing
Use of low melt point filler metal to fill thin gap
between mating surfaces to be joined utilizing
capillary action
• Filler metals include Al, Mg & Cu alloys (melt
point typically above 840 F)
• Flux also used
• Types of brazing classified by heating method:
– Torch, Furnace, Resistance
Applications:
• Automotive - joining tubes
• Pipe/Tubing joining (HVAC)
• Electrical equipment - joining wires
• Jewelry Making
• Joint can possess significant strength
Brazing Metal Joining Processes
Brazing
Use of low melt point filler metal to fill thin gap between mating surfaces to
be joined utilizing capillary action
• Filler metals include Al, Mg & Cu alloys (melt point
typically above 840 F)
• Flux also used
• Types of brazing classified by heating method:
– Torch, Furnace, Resistance
Applications:
• Automotive - joining tubes
• Pipe/Tubing joining (HVAC)
• Electrical equipment - joining wires
• Jewelry Making
• Joint can possess significant strength
Welding defects
• Misalignment (hi-lo) • Inclusions • Base Metal
• Undercut – Slag Discontinuities
– Wagontracks – Lamellar tearing
• Underfill
– Tungsten – Laminations and
• Concavity or Convexity Delaminations
• Excessive reinforcement • Spatter
– Laps and Seams
• Improper reinforcement • Arc Craters
• Porosity
• Overlap • Cracks
– Uniformly Scattered
– Longitudinal
• Burn-through – Cluster
– Transverse
• Incomplete or Insufficient – Linear
– Crater
Penetration – Piping
– Throat
• Incomplete Fusion • Heat-affected zone
– Toe
• Surface irregularity microstructure alteration
– Root
– Overlap • Base Plate laminations
– Underbead and
• Arc Strikes Heat-affected zone • Size or dimensions
– Hot
– Cold or delayed
