Welding (New)

(1)

ENGINEERING

PRACTICES

Welding

10/7/20

(2)

Introduction

2

 Welding is a materials joining process which produces

fusion 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,

(3)

Classifications

 Arc welding

• Carbon arc

• Shielded Metal arc or

Stick Electrode

• Gas Metal Arc or Metal

inert gas

• Tungsten inert gas

• Plasma arc

• Submerged arc

• Electro-slag

 Gas Welding

• Oxy-acetylene

• Air-acetylene

• Oxy-hydrogen

 Resistance Welding

•

Butt

•

Spot

•

Seam

•

Projection

•

Percussion

 Thermite Welding  Solid State Welding

•

Friction

•

Ultrasonic

•

Diffusion

•

Explosive

(4)

Classifications

4



Modern Welding

• _{Electron-beam}

• Laser



Related Processes

• _{Oxy-acetylene cutting}

(5)

WELDING

Arc Welding

10/7/20

(6)

Arc Welding

6

 The process of fusing two or more pieces of metal together by

using the heat produced from an electric arc is called arc welding.

(7)

Basics Of Arc Welding

10/7/20 7

 The arc is struck between the

electrode and the metal. It then heats the metal to a melting point. The electrode is then removed, breaking the arc between the electrode and the metal. This allows the molten metal to “freeze” or solidify.

 The arc is like a flame of intense

(8)

Arc Welding

8

 Equipments:

• A welding generator (D.C.) or Transformer

(A.C.)

• Two cables- one for work and one for

electrode

• Electrode holder

• Electrode

• Protective shield

• Gloves

• Wire brush

• Chipping hammer

(9)

Arc Welding Equipments

(10)

Arc Welding

10

Uses an electric arc to fuse metals.

Arc welding is the most

common method of welding metals.

(11)

Arc Welding

10/7/20 11

 Advantages

• Most efficient way to join metals • Lowest-cost joining method

• Affords lighter weight through better utilization

of materials

• Joins all commercial metals • Provides design flexibility

 Limitations

• Manually applied, therefore high labor cost • Need high energy causing danger

(12)

Types Of Arc Welding

(13)

ARC WELDING

Shielded Metal Arc

Welding

10/7/20

(14)

Shield Metal Arc Welding

14



Manual arc welding

•

Heat for welding generated by electric arc

established between flux-covered

consumable metal rod (electrode) and work

piece.

 Called stick electrode welding

 Combustion and decomposition of electrode creates

gaseous shield.

•

Protects electrode tip, weld puddle, arc, and

highly heated work from atmospheric

contamination.

 _{Additional shielding provided by covering of molten slag}

(15)

Background

10/7/20 15

 Pioneered when a man was welding with a bare metal rod on

iron, the sparks from the welding caught a stack of

newspapers on fire near him and while welding, he noticed that his welds started looking a lot better. The reason for this

(16)

SMAW Terms

(17)

SMAW Principle

10/7/20 17

 Sets up electric circuit

•

Includes welding machine, work, electric

cables, electrode holder and electrodes,

and a work clamp.

 Heat of electric arc brings work to be welded

and consumable electrode to molten state. •

Heat intense: as high as 9,000ºF at

(18)

SMAW Process

18

 An arc welding machine supplies electric current to an

electrode wire.

 The electric current travels through the air gap between

the end of the electrode wire and the base metal.

 As the electric current flows through this air gap, an

electric arc is formed.

 Heat of arc melts electrode and surface of base metal.

 Tiny globules of molten metal form on tip of electrode

and transferred by arc into molten pool on work surface.

(19)

SMAW Process

10/7/20 19

 A shielding gas is required to protect the

base metal, arc, electrode, and weld from the atmosphere during the welding

process.

 As the flux covering on the electrode wire

melts, a shielding gas is created

 When the flux cools, it solidifies and

forms a protective slag over the weld bead.

 As the electrode wire melts, it becomes

(20)

SMAW Advantages

20

 Equipment less complex, more portable and

less costly.

 Can be done indoors or outdoors, in any

location and any position.

 Electrodes available to match properties and

strength of most base metals.

(21)

Advantages and Disadvantages

10/7/20 21

Advantages

 Equipment is inexpensive.

 Equipment is portable.

 Applications are simple and adaptable to job

requirements.

 Can be used with several types of filler metals.

Disadvantages

 Requires slag removal.

(22)

ARC WELDING

Gas Metal Arc Welding

(23)

Gas Metal Arc Welding

10/7/20 23

 GMAW is defined as arc welding using a continuously

fed consumable electrode and a shielding gas (This gas has to be an inert gas).

 GMAW is also known as MIG (Metal Inert Gas).

 Produces high-quality welds.

(24)

GMAW

24

 Originally developed for welding aluminum and other

(25)

GMAW

10/7/20 25

 Gas metal arc welding (GMAW), is a

(26)

(27)

Advantages

10/7/20 27

 Due to continuously fed electrode, MIG welding

process is much faster.

 It can produce joints with deep penetration.

 Thick and thin, both types of work pieces can be

welded effectively.

 Large metal deposition rates are achieved by MIG

welding process.

 The process can be easily mechanized.

 Higher arc travel speeds associated with MIG

(28)

Disadvantages

28

 The process is slightly more complex as compared to

SMAW because a number of variables (like torch angle, welding parameters, type and size of electrode, etc.) are required to be controlled effectively to achieve good results.

 Welding equipment is more complex, more costly and less

portable.

 Since air drafts may disperse the shielding gas, MIG

welding may not work well in outdoor welding applications.

 Weld metal cooling rates are higher than the processes

(29)

Process Capability

(30)

WELDING

Oxy-fuel Welding

(31)

Oxy-fuel Welding

10/7/20 31

 Oxy-fuel welding (commonly called oxyacetylene

welding, oxy welding, or gas welding in the U.S.) is a process that uses fuel gases and oxygen to weld metals.

 We’ll discuss oxy-acetylene welding only.

 Acetylene when combined with oxygen burns

(32)

Oxy-fuel Welding Equipment

32

1. Gas Cylinders

Pressurized oxygen in one cylinder and

acetylene in the other cylinder.

2. Regulators

Working pressure of oxygen 10psi

Working pressure of acetylene 5psi

3. Pressure Gauges 4. Hoses

5. Welding torch 6. Check valve

(33)

Oxy-fuel Welding

Equipment

(34)

Types Of Flames

34

 Oxygen is turned on, flame immediately changes

into a long white inner area (Feather) surrounded by a transparent blue envelope. This is called

(35)

Types Of Flames

10/7/20 35

 Addition of little more oxygen gives a bright

whitish cone surrounded by the transparent blue envelope. This is called Neutral flame (It has a

(36)

Types Of Flames

36

 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.

(37)

Advantages

10/7/20 37

 It's easy to learn.

 The equipment is cheaper than most other types of

welding rigs (e.g. TIG welding).

 The equipment is more portable than most other types

of welding rigs (e.g. TIG welding).

 OA equipment can also be used to "flame-cut" large

(38)

Disadvantages

38

 OA weld lines are much rougher in appearance

than other kinds of welds, and require more finishing if neatness is required.

 OA welds have large heat affected zones (areas

(39)

WELDING

Types Of Welding

Joints

10/7/20

(40)

Types Of Weld

Joints

40

Butt Joint

(41)

Types Of Weld

Joints

10/7/20 41

Corner Joint

(42)

Types Of Weld

Joints

42

T-Joint

(43)

Types Of Weld

Joints

10/7/20 43

Lap Joint

(44)

Types Of Weld

Joints

44

Edge Joint