Welding is a fabrication process which is used for joining materials, generally metals and thermoplastics. This is achieved by raising the temperature of the materials and melting them. Then filler materials may or may not be added to the pool of molten metal. This cools down to form a strong joint. The joining of materials is at times done by using pressure in conjunction to the heat, though it is possible to weld in the absence of pressure as well.
Welding machines are classified into constant current (CC) and constant voltage (CV). They differ in their manner of working. In the constant current welding machines the voltage is varied to give a constant current. Whereas, in constant voltage welding machines, the current is altered to return a steady voltage output. Flux cored arc welding and gas metal arc welding use constant voltage sources but Shielded metal arc welding process mainly employs the constant current sources.
Most welding machines usually have the following design:
1.Generator and alternator:
To convert mechanical energy into electrical energy many welding machines use a generator or an alternator. An internal combustion engine is generally used to drive the generator in most modern machines, but some older varieties may use an electric motor too. They help to attain the same effect like that of a step-down generator by first converting the power into mechanical energy and then into electrical energy. The output of these machines can be direct current as well, thus they can be used to get DC from AC without the use of any rectifiers.
These type of welding machines change high voltage and low current electricity to low voltage and high current electricity, for improved utility. This is usually between the range of 55 to 590 amperes and 17 to 45 volts. In these machines the welder can select the output current by either stirring a magnetic shunt in and out of the transformer core or by selecting from a set of taps on the transformer. These are characteristically the least expensive of machines.
With the introduction of high-power semiconductors such as the IGBT, we can now build a switching power supply which can handle the high loads of arc welding. These supplies typically convert power to high voltage and accumulate this energy in a capacitor bank. A microprocessor controller is then used to exchange this energy into a second transformer, which then helps to produce the preferred welding current. The switching frequency is typically high, of the order of 10,000 Hz or higher. The high frequency inverter-based welding machines are found to be more efficient and have enhanced control than non- inverter welding machines.
The IGBT’s is an inverter based machine which works using a microcontroller.Using these, the electrical features of the welding power can be changed by software.Normally the software controlling the working will execute features such as changing the welding current, varying ratios and current densities during a welding cycle, alter frequencies, and performing automatic spot-welding. But in the case of a transformer-based machine this proposition becomes expensive, since, in the case of software controlled inverter machine only program space is required.