Describe with a neat diagram, the process of any one type of electric welding. 
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Type Of welding:-  

 i) Resistance Welding:-(Plastic / Non- Fusion / Pressure Welding ) 1) Spot welding 2) Seam welding 3) Projection Welding 4) Butt Welding 5) Flash Butt welding 


 ii) Arc welding (Fusion/Non pressure welding):- 1) Carbon Arc Welding 2) Metal Arc Welding


Explanation : 


i) Spot Welding:

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Explanation Spot welding means the joining of two metal sheets at suitable spaced interval. It consists of: Transformer used for spot welding is designed for low voltage and high current secondary. Transformer is oil cooled and portable There are two electrodes one is fixed and other is movable The electrodes are hollow and water cooled.  Electrodes are made from copper or copper alloys and tips of electrodes are made from CdCu or Cr-Cu.


Working: As shown in fig. Job to be welded is placed one over the other between two electrodes under pressure Sufficiently heavy current at low voltage is passed directly through two metals in contact to be welded. Heat is produced due to I2R losses where ‘R’ is the contact resistance. This heat is utilized to obtain welding temperature (to become a plastic state) When welding temperature is reached supply is cut down and external pressure is applied simultaneously across the job to complete weld. Magnitude of current varies from 1000A to 10000A.and the voltage between electrodes is usually less than 2V. The period of flow of current and magnitude of current depends upon thickness of sheet (job) to be welded. 


ii) Seam Welding: 

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Explanation: Seam welding is nothing but series of continuous spot welding It consists of: Transformer used for seam welding is designed for low voltage and high current secondary. Transformer is oil cooled There are two electrodes, in this type beam or roller type electrodes are used. 


Working: Job is kept in between two electrodes under pressure. This pressure is kept constant throughout. In this type intermittent current is used, it means current is ON for definite time and OFF for another time interval with the help of timer. If current is continuously passes then heat produced may cause burning of job. Heat is produced due to I2R losses where ‘R’ is the contact resistance. This heat is utilized to obtain welding temperature (to become a plastic state) When welding temperature is reached supply is cut down and external pressure is applied simultaneously across the job to complete weld. 


iii) Projection Welding: 

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Explanation: It is modified form of spot welding, before welding projections are made to job on both or one part to be welded by mechanical means. Hence it is called as a Projection Welding. It consists of: Transformer used for projection welding is designed for low voltage and high current secondary. Transformer is oil cooled There are two electrodes .In this type flat electrodes are used as shown in figure. Therefore it is possible to join several welding points (spots) simultaneously Working: Job is kept in between two electrodes under pressure. This pressure is kept constant throughout. Sufficiently heavy current at low voltage is passed directly through two metals in contact to be welded. Heat is produced due to I2R losses where ‘R’ is the contact resistance. This heat is utilized to obtain welding temperature (to become a plastic state) When welding temperature is reached supply is cut down and external pressure is applied simultaneously across the job to complete weld


iv) Upset Butt Welding: 

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Explanation: Transformer used for welding is designed for low voltage and high current secondary. Transformer is oil cooled The job is clamped as shown in fig. two parts which are to be welded are brought together Sufficiently heavy current is passed through joints by welding transformer, which creates necessary heat at joints due to I2R When welding temperature is reached supply is cut down. And external pressure is applied simultaneously across the job to complete weld 


v) Flash Butt welding: - 

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Explanation: The job is clamped as shown in fig. two parts which are to be welded are brought near to each other by keeping small air gap, When welding transformer is made ON, due to heavy currents flash (arc) is produced between joints. This arc will produce heat which will create welding temperature. When welding temperature is reached, supply is cut down and at the same time mechanical pressure is applied for final weld. 


2) Electric Arc Welding:- 

i) Metal Arc Welding: 

Principle of arc welding: The process in which two metal parts to be welded are brought to a molten state and then allowed to solidify is called as arc welding. Melting of metal is obtained due to heat developed by an arc struck between an electrode (Filler material) and metal to be welded (job)  

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Type of supply used: Both AC/DC Supplies can be used but generally A.C. Supply is used because it has more advantages. Supply Equipment used: Welding Transformer designed for low voltage high current secondary. Arc Stability: Series Reactor is used for arc stability. Temperature obtain: Less as A.C. supply is used. Possibility of arc blow is less. Capital Cost: Less since welding transformer is used as a supply equipment. Running cost: Less Maintenance cost :Less Stand by losses: Less Efficiency: More Voltage required: 72 to 100 volt A.C Types :Shielded & unshielded welding Application: For welding Ferrous Metals, Can be used for vertical & overhead welding. 


ii) Carbon Arc Welding: It is explain on following points


Principle of arc welding: The process in which two metal parts to be welded are brought to a molten state and then allowed to solidify is called as arc welding. Melting of metal is obtained due to heat developed by an arc struck between carbon electrode and metal to be welded (Job) and the additional metal is deposited in the weld from a filler rod. 

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Type of supply used: Only DC supply is used. 

Type of Electrode: Carbon Electrode are used. 

Supply Equipment used: D.C Differential component Generator or Rectifier 

Arc Stability: D.C Differential component. Generator has dropping characteristics. 

Temperature obtain: 

Possibility of arc blow is more. More More 

Capital Cost: More 

Running cost: More 

Maintenance cost: More 

Stand by losses: More 

Efficiency: Less 

Voltage required: 50 to 60 volt D.C 

Types: Flux is used and flux is not used 

Application: For welding non ferrous metals 

Limitation: Not suitable for overhead welding  

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Methods of electric welding : 

1. Resistance welding 

i Butt welding 

ii Spot welding 

iii Seam welding 

iv Projection welding 


2. Arc Welding 

i Carbon arc welding 

ii Metal arc welding 


Working Principle :- Resistance welding: Heavy current is passed through the work piece and heat is developed by the contact resistance of job is utilized in welding them together. 


Arc welding: Arc is an electric discharge between one electrode and another which may be a work piece. The arc current while flowing through air in the form of electrons bombards the atoms in air and produces ions. Such state of matter is almost plasma state and the temperature in the vicinity is around 3000 to 4000 0C, which is generally 2 to 3 times the melting point of general metals such as copper, iron etc. The electric arc effectively concentrate heat on the surfaces it is desired to join.

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