3. WELDINGWELDING
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, furniture, boilers, general repair
work and ship building.
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4. TYPESTYPES
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
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5. Classification Of Welding Processes:Classification Of Welding Processes:
(i) Arc Welding
Carbon arc
Metal arc
Metal inert gas
Tungsten inert gas
Plasma arc
Submerged arc
Electro-slag
(ii) Gas Welding
Oxy-acetylene
Air-acetylene
Oxy-hydrogen
(iii) Resistance Welding
Butt
Spot
Seam
Projection
Percussion
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(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
6. Arc WeldingArc Welding
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Uses an electric arc to coalesce metals
Arc welding is the most common method of welding metals
Electricity travels from electrode to base metal to ground
7. Arc Welding Equipment :Arc Welding Equipment :
1) A welding generator (D.C.) or Transformer (A.C.)
2) Two cables- one for work and one for electrode
3) Electrode holder
4) Electrode
5) Protective shield
6) Gloves
7) Wire brush
8) Chipping hammer
9) Goggles
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11. Arc WeldingArc Welding
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Advantages Disadvantages
Most efficient way to join
metals
Manually applied, therefore
high labor cost.
Lowest-cost joining method Need high energy causing
danger
Affords lighter weight
through better utilization of
materials
Not convenient for
disassembly
Joins all commercial metals Defects are hard to detect at
joints.
Provides design flexibility
12. GAS WELDINGGAS WELDING
Sound weld is obtained by selecting proper size of flame,
filler material and method of moving torch
The temperature generated during the process is 33000
c
When the metal is fused, oxygen from the atmosphere and
the torch combines with molten metal and forms oxides,
results defective weld
Fluxes are added to the welded metal to remove oxides
Common fluxes used are made of sodium, potassium.
Lithium and borax.
Flux can be applied as paste, powder,liquid.solid coating or
gas.
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13. GAS WELDING EQUIPMENTGAS WELDING EQUIPMENT
1. Gas Cylinders
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 depends upon the thickness
of the work pieces welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
6. Check valve
7. Non return valve
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15. TYPES OF FLAMESTYPES OF FLAMES
Oxygen is turned on, flame immediately changes into a
long white inner area (Feather) surrounded by a
transparent blue envelope is called Carburizing flame
(30000
c)
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)
(32000
c)
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 34000
c
Used for welding brass and brazing operation
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16. Three basic types of oxyacetylene flames used in oxyfuel-gasThree basic types of oxyacetylene flames used in oxyfuel-gas
welding and cutting operations: (a) neutral flame; (b)welding and cutting operations: (a) neutral flame; (b)
oxidizing flame; (c) carburizing, or reducing flame.oxidizing flame; (c) carburizing, or reducing flame.
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17. GAS CUTTINGGAS CUTTING
Ferrous metal is heated in to red hot condition and a jet
of pure oxygen is projected onto the surface, which
rapidly oxidizes
Oxides having lower melting point than the metal, melt
and are blown away by the force of the jet, to make a
cut
Fast and efficient method of cutting steel to a high
degree of accuracy
Torch is different from welding
Cutting torch has preheat orifice and one central orifice
for oxygen jet
PIERCING and GOUGING are two important operations
Piercing, used to cut a hole at the centre of the plate or
away from the edge of the plate
Gouging, to cut a groove into the steel surface
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20. TIG WeldingTIG Welding
Development Of Tig Welding:
After the discovery of the electric arc in 1800 by Humphry Davy, arc
welding developed slowly.
C. L. Coffin had the idea of welding in an inert gas atmosphere in
1890, but even in the early 1900s, welding non-ferrous materials like
aluminum and magnesium remained difficult, because these metals
reacted rapidly with the air, resulting in porous and dross-filled welds.
To solve the problem, bottled inert gases were used in the beginning
of the 1930s.
21. In TIG welding an arc is formed between
a non-consumable tungsten electrode
and the metal being welded.
Gas is fed through the torch to shield
the electrode and molten weld pool. If
filler wire is used, it is added to the weld
pool separately.
In TIG Tungsten is used as electrode
22. Contineous WeldingContineous Welding
•A weld that is continuous along the entire
length of the joint.
•Smooth Surface
•Fine Surface
•Use for light metal
•In this the roller are used to smoth the surface
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23. Spot Welding
Lesson Objectives
When you finish this lesson you will understand:
• Basics of Resistance Welding Processes
• Heat Generation & Control
• Spot Welding Process and Applications
Learning Activities
1. View Slides;
2. Read Notes,
3. Listen to lecture
4. View Demo
5. Do on-line workbook
Keywords: Resistance Spot Welding, Heat Generation, Equipment Control,
Contact Resistance, Upslope, Downslope, Hold Time, Temper, Squeeze Time,
Electrode
24. Definition of ResistanceDefinition of Resistance
WeldingWelding
Resistance welding is a fusion welding
process in which coalescence of metals is
produced at the faying surfaces by the heat
generated at the joint by the resistance of
the work to the flow of electricity.
Force is applied before, during, and after the
application of current to prevent arcing at
the work piece.
Melting occurs at the faying surfaces during
welding.
25. Principal Types of ResistancePrincipal Types of Resistance WeldsWelds
Electrodes
or Welding
Tips
Electrodes
or Welding
Wheels
Electrodes
or Dies
Projection
Welds
Electrodes or Dies
Spot Weld Seam Weld Projection Weld
Upset Weld Flash Weld
After Welding After Welding
[Reference: Resistance Welding Manual, RWMA, p.1-3]
26. Typical Equipment of Resistance SpotTypical Equipment of Resistance Spot
WeldingWelding
(a) (b)
[Reference: Welding Process Slides, The Welding Institute]
27. Advantages of Resistance SpotAdvantages of Resistance Spot
WeldingWelding
Adaptability for Automation in High-Rate Production of
Sheet Metal Assemblies
High Speed
Economical
Dimensional Accuracy
28. Limitations of Resistance SpotLimitations of Resistance Spot
WeldingWelding
Difficulty for maintenance or repair
Adds weight and material cost to the product, compared with
a butt joint
Generally have higher cost than most arc welding equipment
Produces unfavorable line power demands
Low tensile and fatigue strength
The full strength of the sheet cannot prevail across a spot
welded joint
Eccentric loading condition
30. MIG – Metal Inert Gas WeldingMIG – Metal Inert Gas Welding
May be called GMAW (Gas Metal Arc
Welding)
Avoid cutting in drafty or windy conditions
Molten pool is shielded by the inert gas
envelope
Joints are stronger, more ductile, and
more corrosion resistant
Flux center wire has slag; Solid wire has
no slag, thus eliminating slag inclusion
Welded metal does not readily distort
32. MIG Machine OperationMIG Machine Operation
Wire is fed at a pre-set rate
Gas flows at about 35 cubic feet per hour
and is directed around the welding wire
for shielding
33. Advantages
Welding can be done in
all positions
High rates of metal
deposition
Excellent filling ability
for poor-fit joints
High weld Quality
No electrode stub loss
Less distortion due to
narrow, deep weld
profile
Easier process to learn
and use
Disadvantages
Welding power source
expensive
Shielding gas expensive
Higher electrode wire
cost
Most machines require
three-phase input power
Not as versatile as
SMAW for maintenance
Welding cast iron
Cutting
Carbon arc torch
applications
Spot, seam, and projection welding operations involve a coordinated application of electric current and mechanical pressure of the proper magnitudes and durations. The welding current must pass from the electrodes through the work. Its continuity is assured by forces applied to the electrodes, or by projections which are shaped to provide the necessary current density and pressure. The sequence of operation must first develop sufficient heat to raise a confined volume of metal to the molten state. This metal is then allowed to cool while under pressure until it has adequate strength to hold the parts together. The current density and pressure must be such that a nugget is formed, but not so high that molten metal is expelled from the weld zone. The duration of weld current must be sufficiently short to prevent excessive heating of the electrode faces. Such heating may bond the electrodes to the work and greatly reduce their life.
The heat required for these resistance welding processes is produced by the resistance of the workpiece to an electric current passing through the material. Due to the short electric current path in the work and limited weld time, relatively high welding currents are required to develop the necessary welding heat.
The machine shown in Figure (a) in this slide is typical of many resistance spot welding machines with a foot-operated control (D) which initiates both the pressure and current cycles. The type illustrated is a swinging arm machine, the top arm being pivoted. In other machines, the upper electrode assembly may be carried on a slide.
The workpieces shown in Figure (b) are placed between the electrodes which can be interchanged for different applications. The type illustrated is a typical method of joining stiffeners to thin sheet (0.5 mm) as shown here using 18 mm diameter electrodes with a tip diameter of 3.5 mm.
Disassembly for maintenance or repair is very difficult.
A lap joint adds weight and material cost to the product when compared to a butt joint.
The equipment costs are generally higher than the costs of most arc welding equipment.
The short time, high-current power requirement produces unfavorable line power demands, particularly with single phase machines.
Spot welds have low tensile and fatigue strength due to the notch around the periphery of the nugget between the sheets.
The full strength of the sheet cannot prevail across a spot welded joint, because fusion is intermittent and loading is eccentric due to the overlap.