Weldingis a process of joining two metal with the help of heat or pressure. The welding is used for the following Engineering.
1.Manufacturing of machine tools, Auto parts, and cycle parts
2.Fabrication of farm machinery and equipment
3.Fabrication of buildings bridges and ships
4.Construction of boiler, furnace, Railway, cars, airplanes, rockets and missiles
5. Manufacturers of televisions set, refrigerator, kitchen cabinets
Basic Principle of welding
The main purpose of welding is to joining two-piece. The homogenous mixture is formed. The next process the end to be joined are brought to the plastic stage and then apply external pressure to join them. it is pressure welding in both the above cases of the source of heat is listed below.
It is a furnace in forge welding
It is gas in gas welding
It is electrical energy in arc welding
It is a chemical reaction in thermit welding
Types of welding
Many types of welding processes have been developed depending upon the field or their application.
The welding in which the electrical Arc is produced to give heat for the purpose of joining two surfaces is called electrical arc welding. The principle of the electric arc welding power supply is given to the electrode and the work is a suitable gap is kept between the work. The electrode is a high current is passed through the circuit. The electrical energy is converted into heat energy producing a temperature of 3000 degree Celsius to 4000 degree Celsius. This heat melts the age to be welded and the molten pool is formed. On a solidification, the weld joint is obtained.
Electrical power for welding
The arc welding can be used AC current or DC current. For most purposes, DC current is preferred. In DC Welding a DC generator or solid state rectifier is used.DC machines are made up to the capacity range 600 amperes. The voltage in open circuit is kept around 45 to 95 volt and in the closed circuit, it is kept 17 to 25 volt.DC current can be given in two categories
Straight polarity and Reverse polarity
In straight polarity, welding workpiece is connected to a positive wire(+)or made anode and the electrode is connected to a negative wire (-) made a cathode electrode. Electron flow from cathode to anode thus heat is produced at the material to be welded.
In reverse polarity, the system is opposite to the straight polarity system. The work is made cathode means negative wire and the electrode is made anode means positive wire This types of welding is done specially for the thin section.
AC welding has the advantage of being cheap. The equipment used in simpler than DC Welding. The current output is increased at the electrode by the transformer. An AC welding circuit the current vary from 150 to 1000 ampere depending upon the types of work.
Welding Transformer set
It consists of a primary and secondary circuit. The input is given to the primary winding. By electromagnetic induction the current flow through the secondary coil. The output can be controlled as per requirement