Joining or Fabrication Methods
Joining or Fabrication Methods
Joining or Fabrication Methods
Fabrication
Form Type
Paste Hot melt
Liquid Reactive hot melt
Film Thermosetting
Pellets Pressure sensitive
Tape Contact
Epoxy consists of two different chemicals.
"Resin" and the "Hardener".
Resin consists of short chain polymers with an epoxide group at either end.
When Hardener is mixed with Resin, short chain polymers get cross-linked, and is
thus stiff and strong.
ROUND HEAD
BINDING HEAD
HEXAGON HEAD
Weld
It is a localised coalescence of metals or non-metals
produced either by heating the materials to a suitable
temperature with or without application of pressure or
by the application of pressure alone and with or
without the use of filler materials
Weldment
It is an assembly of component parts joined by
welding.
Tee Joint
Arc welding
Oxy-Fuel Gas Welding (OFW)
Oxy-Acetylene Welding
Edge Preparations for Butt Joints
Single or Double U-, V-, J-, and Bevel Edges
Various Weld Procedures
A weld bead made without much weaving
motion is often referred to as a stringer bead.
On the other hand, a weld bead made with side-to-
side oscillation is called a weave bead.
Types of Welding Positions
Types of Fusion Welds
Butt weld
Fillet weld
Shielded Metal Arc Welding (SMAW)
Most widely used because of its simplicity, versatility, its
less complex, more portable and less costly equipments
Consumable electrode
Shielding gas
Electrode coating
Slag layer
Electrode
Consumable (SMAW)
Non-consumable (GTAW)
Classification of electrodes
Tensile strength of deposited weld metal
Welding positions to be used in
Type of current and polarity to be used
Type of coating
Arc welding electrodes are identified using the A.W.S.
1/8" E7011
1/8" E7011
The electrode is 1/8" in diameter
Electrode coating provides flux to the molten metal pool which combines
with the oxides and other impurities present in the puddle to form the
SLAG. Slag being lighter, floats on the top of the puddle and protects it
against the surrounding air during the weld bead solidification. Slag
covering also helps the metal to cool slowly preventing the formation of
a brittle weld.
Coatings are normally insulators of electricity and thus, permit the electrode
to be used in narrow grooves, and other difficult locations without causing
any short circuiting problems.
Gas-Tungsten Arc Welding (GTAW)
Formerly known as TIG
Oxy-Acetylene Welding
Oxy-fuel gas welding
Welding process using fuel gas with Oxygen for heating
Oxy-Acetylene welding
C2H2 + O2 2CO +H2 + Heat
4CO + H2 + 3O2 4CO2 + H2O + Heat
Types of flame
Neutral Flame
Complete Combustion of Acetylene Present
Most Desirable Flame
Carburizing (Reducing) Flame:
Less Oxygen
Part of Combustible Matter Left
Presence of Additional Third Phase in Between the Outer Blue Flame and
Inner White Cone (Intermediate Flame Feather) Reddish in Color.
Metal Appears to Boil (Due to Presence of Unburnt Carbon).
Excess Carbon Causes the Steel to Become Extremely Hard and Brittle.
Useful for Material which are Readily Oxidized (by Providing Reducing
Atmosphere)
Welding High Carbon Steels, Cast Irons and Hard Surfacing with High
Speed Steel & Cemented Carbides.
Oxidizing Flame:
Oxygen in Excess
Smaller Inner White Cone (Higher Tip Temperatures ~3300 0C).
Excess Oxygen Oxidizes the Weld Metal
Weld Metal Foams and Sparks (because of Burning of Metal)
Loud Noise
Useful for Welding some Non-ferrous Alloys (Cu and Zn Based Alloys),
Cast iron, Manganese Steel
Presence of Excess Oxygen in the Oxidizing Flame Causes an Oxide
Film to Form Quickly which Provides a Protective Cover Over the Base
Material Pool.
Neutral flame
Oxidizing flame
Carburizing flame
Cylinder pressure: Oxygen ~ 13.8 MPa to 18.2 Mpa
Acetylene ~
Acetylene is Normally Made Available in the Two forms:
Acetylene Storage cylinder,
Acetylene Generator [CaC2 + 2H2O = C2H2 + Ca(OH)2]
Free Acetylene is Highly Explosive, if Stored at a Pressure > 200 kPa
then it Becomes Very Unstable and Likely to Explode.
In Forehand Welding, the Torch is Moved in the Direction of the Tip. This Tends to
Preheat the Parent Material Before the White Cone of the Tip Melts it.
In Backhand Welding, the Torch Points Backwards. The Outer Blue Flames are
Directed on the Already Welded Joint. This Allows the Joint to be Continuously
Annealed Relieving the Welding Stresses.
Backhand Welding also Allows a Better Penetration as well as Form a Bigger Weld
Bead. Backhand Welding is Generally Used for Thicker Materials.
Preheating of the welding rod should be maintained by keeping it at a
proper distance from the flame.
Too far distance makes the rod cooler and would chill the puddle
when dipped.
Too little distance makes the tip melt with the result that the molten
material would be blown away by the flame causing uneven bead
and poor penetration.
Forehand welding is the most commonly used technique for MIG welding. What the
forehand method does is produce a shallow but wide penetrating weld that is flat in
appearance. This is the type of weld and penetration is used for most weld joints
where overheating is not an issue.
Backhand welding is the least used welding technique when it comes to MIG. This
technique produces the deep and narrow type of penetration that is best suited for
thinner metals. The advantage of backhand welding is that the arc is focused onto
the filler metal and that means extra material to prevent burn through. When welding
thinner metals you always run the risk of burning a hole through the weld joint. With
the backhand method the extra filler metal at the arc helps prevent this and at the
same time can keep warp age to a minimum.
Resistance spot welding
SPOT WELDING is one of a group of resistance welding
processes that involve the joining of two or more metal parts
together in a localised area by the application of heat and
pressure. The heat is generated within the material being joined
by the resistance to the passage of a high current through the
metal parts, which are held under a pre-set pressure.