2. WELDING
• Welding is a materials joining process which
produces coalescence of materials by heating them to
suitable temperatures with or without the application
of pressure or by the application of pressure alone,
and with or without the use of filler material.
• Welding is used for making permanent joints.
• It is used in the manufacture of automobile bodies,
aircraft frames, railway wagons, machine frames,
structural works, tanks, boilers, general repair work
and ship building.
3. TYPES
• 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
4.
5.
6. Gas Welding
• Utilizes oxygen and a fuel gas to heat metal until it is in a molten
state and fuse multiple pieces of metal together. Can be used with or
without a filler rod.
• Flame formed by burning a mix of acetylene (C2H2) and oxygen
• Fusion of metal is achieved by passing the inner cone of the flame
over the metal
• Oxyacetylene can also be used for cutting metals.
• The flux may be used to deoxidize and cleanse the weld metal.
• The flux melts, solidifies and forms a slag skin on the resultant weld
metal.
8. GASWELDING EQUIPMENTS
1. Gas Cylinders
Pressure
Oxygen – 125 kg/cm2
Acetylene – 16 kg/cm2
2. Regulators
Working pressure of oxygen 1 kg/cm2
Working pressure of acetylene 0.15 kg/cm2
Working pressure varies depending upon the thickness of the
work pieces welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
11. TYPESOFFLAMES
• Oxygen is turned on, flame immediately changes into a long white
inner area (Feather) surrounded by a transparent blue envelope is
called Carburizing flame (30000c)
• Addition of little more oxygen give a bright whitish cone surrounded
by the transparent blue envelope is called Neutral flame (It has a
balance of fuel gas and oxygen) (32000c)
• Used for welding steels, aluminium, copper and cast iron
• If more oxygen is added, the cone becomes darker and more
pointed, while the envelope becomes shorter and more fierce is
called Oxidizing flame
• Has the highest temperature about 34000c
• Used for welding brass and brazing operation
12.
13. 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
• Lower temperatures than welding
– gap at joint important (0.001 – 0.010”)
• Metallurgical bond formed between filler & base metals
14. Solder = Filler metal
Soldering
Applications:
• Printed Circuit Board (PCB) manufacture
• Pipe joining (copper pipe)
• Jewelry manufacture
• 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)
15. Use of low melt point filler metal to fill thin gap between mating
surfaces to be joined utilizing capillary action
Brazing
Applications:
• Pipe/Tubing joining
• 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
