EFFECT OF AC CURRENT ON WELD STRENGTH AND HEAT AFFECTED ZONE

Aim: To study the effect of AC current on weld strength and heat affected zone in Arc welding.

Equipment And Material Required:

A.C. welding machine, Bench Vice, Universal testing machine, metallurgical microscope, M.S. plates of 250x50x5mm.

Tools Required:

Hacksaw, chipping hammer, wire brush, safety goggles, hand gloves, face shield, files.

Description: The work piece is kept on a metallic table to which the ground lead of

The secondary windings of he transformer are connected. The other lead of the secondary is connected to an electrode holder into which electrode is gripped. When electrode is brought in contact with work piece, welding takes place. The maximum rated OC voltage which is the voltage between the output terminals when is being done is normally fixed at about 80volts.

The minimum welding load voltage can be calculated as

Vm = 20+0.041.

The percentage time in 10min period is duty cycle that a welding machine can be used at its rated output over loading. Normally 60% duty cycle is suggested.

Procedure:

1. Two M.S. plates given are filed at an angle 450 at the surface to be joined.

2. Beads on the plates are laid on given plates by using various currents by selecting at least 5 correct current values.

3. After welding at various currents, the beads are cross-sectioned and polished, etched with 2% natal solution.

4. The strength of the welded joints is found by suing tensile testing machine.

5. The observation are recorded and plotted for analysis.

Precautions:

1. Edge preparation should be done very carefully.

2. Before welding ensure that the surface are extremely clean.

3. While welding, always use face shields and goggles.

4. Note the current values carefully.