This document discusses various welding and metal joining processes. It describes gas welding (oxy-acetylene welding) where a flame is used to heat and join metal parts. Resistance welding uses electric current to heat and join metals under pressure. Solid state welding techniques like friction and ultrasonic welding join materials without melting them. The document also covers soldering and brazing which use filler metals to join parts through capillary action without melting the base metals.

1. Dr. Shailesh Kumar Dewangan
Assistant Professor
Department of Production Engineering,
BIT Mesra Ranchi
Welding Process
Gas and Other Welding

2. Welding
• Welding is a process of joining with similar or
dissimilar metal with the application of heat
and with and without application of pressure.
• Filler rod may or may not be used.

3. • Plastic Welding or Pressure Welding
The piece of metal to be joined are heated to a
plastic state and forced together by external
pressure
(Ex) Resistance welding
• Fusion Welding or Non-Pressure Welding
The material at the joint is heated to a molten state and allowed
to solidify
(Ex) Gas welding, Arc welding
TYPES

4. Classification of welding processes:
(i). Arc welding
• Shielded Metal arc
• Metal inert gas
• Tungsten inert gas
• Plasma arc
• Submerged arc
• Atomic Hydrogen
• Electro-slag
(ii). Gas Welding
• Oxy-acetylene
• Air-acetylene
• Oxy-hydrogen
(iii). Resistance Welding
• Butt
• Spot
• Seam
• Projection
• Percussion
(iv)Thermit Welding
(v)Solid State Welding
Friction
Ultrasonic
Diffusion
Explosive
(vi)Newer Welding
Electron-beam
Laser
(vii)Related Process
Oxy-acetylene cutting
Arc cutting
Hard facing
Brazing
Soldering

5. Gas Welding (Oxy-acetylene)
Separate cylinders and
a hose pipe from each
cylinder transports the
gases to a torch.
Gas and fuel mix in
the torch
burns @ 3100°C.
A number of welding processes use a flame
produced by burning a mixture of fuel gas and
oxygen. The gas usually used is Acetylene but other
gases are also used.

6. During the welding heat from the flame is
concentrated on the joint edges until the metal
melts and starts to flow. When the molten metal
from both sides melts it starts to fuse, when the
metal cools down the two parts become
Permanently joined
Additional Filler
Metal is fed in by
hand into the weld
pool, at regular
intervals where it
becomes molten
and joins with the
parent metal.

7. The Oxy-acetylene welding Flame
Types of Oxy-Acetylene Flame

8. • Neutral flame - Acetylene (C2H2) and O2 are mixed in equal
amounts and burn at the tip of the welding torch. The inner cone
gives 2/3 of heat whereas the outer envelope provides 1/3 of the
energy.
• Reducing flame - The excess amount of acetylene is used, giving
a reducing flame. The combustion of acetylene is incomplete
(greenish) between the inner cone and the outer envelope. Good for
welding aluminum alloys, high carbon steels.
• Oxidizing flame - The excess amount of Oxygen is used, giving
an oxidizing flame. Good for welding brass.
Types of Oxy-Acetylene Flame

9. Gases used
Oxygen extracted from air and compressed into
cylinders at high pressure. Cylinder is black. These
cylinder have no welding joint these are complete tube
like cylinders.
Acetylene (C2H2) is a fuel gas. Cannot be compressed
directly as explodes at high pressures. Cylinder colour
coded maroon. We made these cylinders by welding
three parts.
Types of Oxy-Acetylene Flame

10. Gas Pressure Regulators
One gauge indicates the pressure of the cylinder and the
other indicates the pressure in the supply pipe to the torch.

11. Welding torch
Oxygen and acetylene are delivered to the torch by separate
hoses. Each gas is controlled by a valve on the torch. The
two gases mix in the torch and after they are ignited burn at
the nozzle.

13. Resistance welding
Resistance welding uses the application of electric current and
mechanical pressure to create a weld between two pieces of
metal. Weld electrodes conduct the electric current to the two
pieces of metal as they are forged together.
The welding cycle must first develop sufficient heat to raise a
small volume of metal to the molten state. This metal then
cools while under pressure until it has adequate strength to hold
the parts together.
1. Spot Welding
2. Seam Welding
3. Projection Welding

14. Spot welding
Ideal for joining light sheet metal. The
electrodes are made from copper.
Pressure is applied to the electrodes and
an electric current is passed through the
circuit. The high resistance between the
joint faces causes rapid heating and
fusing of a small globule of metal from
both faces.

15. Seam welding
The rollers allow the workpiece to
move through the welder
continously. A stream of electrical
pulses pass through the rollers and
welds the joint

16. Projection welding is a resistance weld where the design or shape of the part is
used to make discreet individual point contacts to concentrate the current during
the welding process. In most applications multiple small projections are formed on
one surface of the parts to be welded.

17. Solid State Welding Processes
Friction Welding

18. Solid State Welding Processes
Ultrasonic welding is an
industrial process whereby high
frequency ultrasonic acoustic
vibrations are locally applied to
workpieces being held together
under pressure to create a solid-
state weld. It is commonly used
for plastics and metals, and
especially for joining dissimilar
materials.

19. Welding Processes
Laser Welding
Typical laser welding applications :
•Catheters & Other Medical Devices
•Small Parts and Components
•Fine Wires
•Jewelry
•Small Sensors
•Thin Sheet Materials Down To 0.001" Thick
• Laser beam produced by a CO2 or YAG Laser
• High penetration, high-speed process
• Concentrated heat = low distortion
• Laser can be shaped/focused & pulsed on/off
• Typically automated & high speed (up to 250 fpm)
• Workpieces up to 1” thick

20. Soldering & Brazing Metal Joining Processes
Soldering & Brazing
• Filler metal distributed by capillary action
• Only filler metal is melted, not base metal
• Strength of joint typically
– Can join dissimilar metals
– Less heat - can join thinner sections (relative to welding)
– stronger than filler metal itself
– weaker than base metal
– Excessive heat during service can weaken joint
• Pros & Cons
• Lower temperatures than welding
– gap at joint important (0.001 – 0.010”)
• Metallurgical bond formed between filler & base metals

21. Soldering
Solder = Filler metal
Metal Joining Processes
Soldering
Applications:
• Printed Circuit Board (PCB) manufacture
• Pipe joining (copper pipe)
• Jewelry manufacture
Easy to solder: copper, silver, gold
Difficult to solder: aluminum, stainless steels
(can pre-plate difficult to solder metals to aid process)
• Alloys of Tin (silver, bismuth, lead)
• Melt point typically below 840 F
Flux used to clean joint & prevent oxidation
• Typically non-load bearing
Tinning = pre-coating with thin layer of solder
• separate or in core of wire (rosin-core)

22. PCB Soldering
• Soldering Iron & Solder Wire
Metal Joining Processes
Manual PCB Soldering
• Heating lead & placing solder
• Trim excess lead
• Heat for 2-3 sec. & place wire
opposite iron
PTH - Pin-Through-Hole connectors

23. Brazing
Use of low melt point filler metal to fill thin gap between
mating surfaces to be joined utilizing capillary action
Metal Joining Processes
Brazing
Applications:
• Pipe/Tubing joining (HVAC)
• Filler metals include Al, Mg & Cu alloys (melt point
typically above 840 F)
• Automotive - joining tubes
• Electrical equipment - joining wires
• Jewelry Making
• Flux also used
• Types of brazing classified by heating method:
– Torch, Furnace, Resistance
• Joint can possess significant strength

24. Brazing
Use of low melt point filler metal to fill thin gap between
mating surfaces to be joined utilizing capillary action
Metal Joining Processes
Brazing
Applications:
• Pipe/Tubing joining (HVAC)
• Filler metals include Al, Mg & Cu alloys (melt point
typically above 840 F)
• Automotive - joining tubes
• Electrical equipment - joining wires
• Jewelry Making
• Flux also used
• Types of brazing classified by heating method:
– Torch, Furnace, Resistance
• Joint can possess significant strength