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Monday, August 5, 2013

PPT On Electric Welding


Electric Welding Presentation Transcript:
1.Power Distribution & Utilization

2.Contents To Be Covered:
Gas Welding
Resistance Welding
Electric Arc Welding
Ultrasonic Welding
Electron Beam Welding
Laser Beam Welding
Power Supply For Resistance Welding
Power Supply For Arc Welding
Comparison Between Resistance And Arc Welding

Welding is a materials-joining process.
Produces coalescence of materials by heating them to the welding temperature.
Almost, all metals can be joined by welding.

It is the most efficient way to join metals.
Widely employed for manufacturing or repairing.
The expense of using bolts and rivets can be reduced.
Used extensively in automobile industry, aircraft machine frames, structural work, tanks, machine repair work, ship building etc.

5.Advantages & Disadvantages:
It is the lowest-cost joining method.
Affords lighter weight.
Joins all commercial materials.
Can be used anywhere.
Provides design flexibility.
Often needs internal inspection.
Some welding depends on human factor.

6.Personnel Protection & Safety Rules:
Combustible materials must not be allowed to collect in or near the welding work place.
Good house keeping practices should always be employed.
Adequate safety devices should be provide.
Only approved equipment should be used.
Proper maintenance of equipment should be done.

7.Classification Of Welding Processes:
It can be classified into:
Gas Welding
Resistance Welding
Arc Welding
Thermit Welding
Solid State Welding
Newer Welding

8.Gas Welding:
Oxygen-Acetylene Welding:
Oxygen tank (green)
Acetylene tank (red, or black with a red top)
Oxygen pressure valves have a right-hand internal thread
Acetylene pressure valve has an external left-hand thread.
An oxygen-acetylene flame is very hot, approaching 3500°F.

9.Fusion weld is to place the two pieces against each other and melt their surfaces together.
Reducing flame is used to melt low-melting-point metals and alloys because it does not oxidize or corrode the metals.
Neutral flame is the hottest one possible and is the proper adjustment for welding.
Oxidizing flame that can cause corrosion in the metal. It is only used for cutting flames or burning pieces of metal from a piece of stock.

10.Types Of Gas Welding:
Oxygen-Hydrogen Welding
The oxygen-hydrogen torch can reach temperatures much higher than the oxy-acetylene torch.
More expensive than oxy-acetylene welding and involves the flammability risk with hydrogen.
Plasma Welding
Hydrogen plasma burns even hotter than hydrogen gas, permitting the welding of extremely high-melting-point metals.
Very clean procedure that results in very little slag or foreign matter in the weld.

11.Resistance Welding:
It is the process in which a sufficiently strong electric current is sent through the two metal pieces in contact to be welded which melts the metals by the resistance they offer to the flow of electric current.
It includes:
Butt Welding
Spot Welding
Projection Welding
Seam Welding
Percussion Welding

12.Butt Welding:
The butt weld consists of two pieces of metal together either on face or on edge.
It is of two types.
Upset Butt Welding
Flash Butt Welding

13.Upset Butt Welding
It is resistance welding process that produces coalescence over the entire area of surfaces.
It can be used only if the parts to be welded are equal in cross-sectional area.
The faces of the metal pieces to be joined are prepared for even contact.
When sufficient heat is developed, a pressure is applied to complete the weld and the pressure is removed after cooling.
Voltage required for welding is 2-8 volts and current required varies from 50A to several thousand Amperes. 

14.Flash Butt Welding:
It may be defined as a resistance welding process that produces coalescence at the surfaces of a butt joint by flashing action.
No special preparation of the faces to be welded is necessary.
Voltage to the metal parts to be joined is applied before putting them together which gives rise to a small arc hence the name Flash Butt welding.
It causes whole of the surfaces to be heated to welding or forging temperature.
When the forging temperature is reached pressure is applied and power supply is cut off.

15.Spot Welding:
Spot welding is usually employed for joining or fabricating sheet metal structure.
This type of joint only provides mechanical strength and is not air or water tight.
The plates to be welded are placed overlapping each other between two electrodes.
Sufficient mechanical pressure is applied through the electrodes.
The welding current flows through electrodes tips producing a spot weld.
The welding current and period of current flow depend on the thickness of the plates.

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