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Chapter: Mechanical : Manufacturing Technology : Metal Joining Process

Welding and Types of welding

Types of welding 1)GAS Welding 2)ARC Welding

Welding

 

Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the pplication 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.

 

Types of welding

 

GAS Welding

 

ARC Welding

 

 

GAS 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 33000c.

 

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.

 

1GAS WELDING EQUIPMENT

 

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 depends upon the thickness of the work pieces welded.

3. Pressure Gauges

4. Hoses

5. Welding torch

 

6. Check valve

7. Non return valve



 


2FLAMES PRODUCED DURING GAS WELDING

 

Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations:

 

(a) neutral flame;  (b) oxidizing flame; (c) carburizing, or reducing flame.

 


Addition of 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


 

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.

 


 

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)

 

Advantages of Gas welding.

 

1.Simple Equipment 2.Portable 3.Inexpensive

4.Easy for maintenance and repair

 

Disadvantages Of Gas welding

 

1.Limited power Density 2.Very low welding speed.

 

3.High total heat input per unit length 4.Large Heat affected Zone

5.Severe Distortion

6.Not recommended for welding reactive metals such as titanium and Zirconium.

 

Difference between Gas Welding and Arc Welding

 


 

GAS WELDING

 

1. Heat is produced by the Gas Flame

2. The Flame temperature is about 3200oC

3. Separate Filler rod introduced

4. Suggested  for thin materials

5. Gas welded parts do not have much strength

6. Filler metal may not be the same parent metal

7. Brazing and soldering are  done using gas

 

 

ARC WELDING

 

1. Heat is produced by Electric Arc

2. The temperature of Arc is about 4000oC

3. Arc Producing as well as filler rod material is the  electrode.

4. Suggested for medium and thick materials

5. Arc welded parts have very high strength

6. Filler metal must be same or an alloy of the parent  metal

7. Brazing and soldering can’t be carried out by electric arc.

 

 

 

ARC WELDING

 

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

 

 

1.Arc welding 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

 

     Goggles

 

 

2.Electrode

 

Electrode is a thin rod made up of same as that of parent material. Flux is coated over the electrode to avoid oxidation. It is mostly connected to the negative polarity.

 

Two Basic Types of AW Electrodes

Consumable  consumed during welding process Source of filler metal in arc welding

 

Nonconsumable  not consumed during welding process

 

Filler metal must be added separately

 

Consumable Electrodes

Forms of consumable electrodes

 

        Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch or less in diameter and must be changed frequently

 

        Weld  wire  can  be  continuously  fed  from  spools  with  long

lengths  of  wire, avoiding frequent interruptions

 

In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal.

 

Nonconsumable Electrodes

Made of tungsten which resists melting

 

Gradually depleted during welding (vaporization is principal mechanism) Any filler metal must be supplied by a separate wire fed into weld pool

 

3.Flux

 

A substance that prevents formation of oxides and other contaminants in welding, or dissolves them and facilitates removal

 

Provides protective atmosphere for welding Stabilizes arc

 

Reduces spattering

 

 

4.STEPS FOLOWED IN ARC WELDING :

 

      Prepare the edges to be joined and maintain the proper position

 

      Open the acetylene valve and ignite the gas at tip of the torch

 

      Hold the torch at about 45deg to the work piece plane

 

      Inner flame near the work piece and filler rod at about 30  40 deg

 

        Touch filler rod at the joint and control the movement according to

the flow  of the material

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

 

Disadvantages

•  Manually applied, therefore high labor cost.

 

      Need high energy causing danger

 

      Not convenient for disassembly.

 

      Defects are hard to detect at joints.

 

 

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