PRESENTED BY

M.GNANASEKARAN

ARC WELDING MACHINES

ARC WELDING MACHINEIn arc welding process, the source of heat is

electricity. (High ampere-low voltage)

The required electrical energy for welding is obtained from an arc welding machine, a power source.

ARC WELDING SYSTEM

Necessity The equipment is used to:To provide AC or DC welding supply for arc weldingProvide higher voltage (OCV) for striking the arc and lower

voltage (AV) for maintaining the arc.Change the high voltage of the main supply (AC) to low

voltage and heavy current supply (AC or DC) suitable for arc welding.

Establish a relationship between arc voltage and welding current during arc welding

Weld with all gauges of electrodeWeld thin and thick plates, both ferrous and non-ferrous

metals.

TYPES OF WELDING MACHINE

Basically Power sources are,

Alternating current welding machine,

Direct current welding machine.

These may be further classified as AC machines and DC machines.

AC machines… Transformers

DC Machines… Motor generator setEngine generator setRectifier set Inverter type machine

TYPES OF WELDING MACHINE

AC WELDING TRANSFORMERAC means alternating current. It changes or reverses its

direction of flow 50 times per second, if it is 50 cycles.Eg.50 cycles means it changes its direction 50 times per second.

Its rate of change is called frequency i.e. hertz (HZ). In India the frequency of AC is 50 cycles per second.

AC WELDING TRANSFORMER

This is a type of welding machine which converts AC main supply in to AC welding supply.

AC main supply has high voltage – low ampere. AC welding supply has high ampere – low voltage. It is step down transformer, which reduce the main

supply voltage (220 or 440 volts) to welding supply open circuit voltage (OCV), between 40 to 100 volts.

A Transformer may be operated from the mains on single phase, two phases or three phases and may be air – cooled or oil cooled.

Single phase transformers supply lower currents, and are therefore used for welding thinner sections with small diameter of electrode.

AC WELDING TRANSFORMER

Generally we are using, Simple works – 220 amps (I Phase)General works – 300 amps (II Phase)Hard works – 600 amps (III Phase)

AC WELDING TRANSFORMER

AC WELDING MACHINE

ADVANTAGES

Less initial cost Less maintenance

costFreedom from arc

blowNoiseless operationsHigher work efficiency.

DIS-ADVANTAGES

Fine current setting not possibleNot suitable for non-ferrous metals It is not suitable for bare and light

coated electrodes It can only be used where electrical

mains supply is available. It has more possibility for electrical

shock because of higher open circuit voltage.

DC WELDING MACHINES

DC means direct current. It flows steadily and constantly in one direction.

DC Machines are… 1. Welding generators 2. Welding rectifiers

Welding generators may be driven by: 

- A motor connected to main supply. (Generate DC welding supply with the help of welding supply.)

- A petrol or diesel engine. (Generate welding supply where electricity main supply is not available with help of engine driven sets.)

DC WELDING MACHINES

Welding rectifierA welding rectifier set is used to

convert A/C welding supply in to DC welding supply.

(It consists of a step down transformer and a welding current rectifier cell cooling fan.)

It can be designed to provide either AC/DC welding supply by changing a switch. This machine is called AC/DC welding machine.

Inverter types weld machines

A solid-state inverter is a circuit which uses solid-state devices to convert DC into high frequency AC, usually in the range 1 KHz to 50 KHz. Since transformer size is inversely proportional to frequency, transformer size reductions of up to 75% are possible by using inverter circuits.

Inverter types weld machinesBasic Inverter circuit components and current wave forms through them

The figure above gives a schematic illustration of the inverter components and the electrical waveform passing through each of the components.

ADVANTAGES OF DC WELDING MACHINE

Polarity systemIt can be used successfully to weld ferrous

and non- ferrous metals, thin sheets, and cast iron metals.

Bare wires and light coated electrode can be easily used.

Positional welding is easy due to polarity advantage.

It can be run with the help of diesel or petrol engine where electrical mains supply is not available.

It has less possibility for electrical shock because of less open circuit

voltage.

DIS-ADVANTAGES

Higher initial cost A higher operating cost A higher maintance cost Trouble of arc blow during welding Noisy operation Occupies more space.

Care and Maintenance of Arc Welding Machines

Every machine and accessory used for any useful purpose requires some care and maintenance to increase its usage for a long time. In the case of arc welding machines and accessories the following points or of importance.

Arc welding machines: do not keep the machine in open air. In a DC welding generator do not put the starting switch on DELTA position directly; keeps the switch on START position first. Run it for a few seconds and they put the switch in DELTA position. Do not disconnect the cooling fan of a welding generator.

Maintain the cooling oil level in the transformer welding set.Periodically drain the cooling oil from the transformer and

purify, and then refill the transformer. Fix the input cables from the mains to the machine and the electrode and earth cable firmly. Replace the carbon brushes of the DC welding generator whenever necessary.

Do not clean any welding machine with water. The dust and impurities are to be removed by compressed air only. Operate all control knobs and handles gently.

Care and Maintenance of Arc Welding Machines