Mechanical Engineering - Workshop Technology - Discussion

Polarity in resistance spot welding has to do with the direction of the current flow in the welding process. With direct current (DC) the welding circuit can either be straight, or reverse polarity. When the machine is set for straight polarity, the current flows from the electrode to the weld surface and creates considerable heat in the metal.

When the machine is in reverse polarity, the current is backwards and is flowing from the metal to the electrode causing a greater concentration of heat at the electrode. In an opposed weld, there are three material interfaces: two electrode-to-part interfaces and one part-to-part interface.

Since conductive electrodes are generally placed against resistive materials, and vice-versa, it is not uncommon to have dissimilar junctions in welding (see blog Spot Welding? Remember the old adage 'opposites attract.')

To take advantage of polarity, the negative electrode should be placed on the most resistive part and the positive electrode against the most conductive part. This will increase the heat at the interface of the two materials and reduce the heat at the electrode"to-part interfaces. Reversing the polarity will cause the material interface to be colder and may cause electrode sticking.

DCSP and DCEN both are same used for maximum heat generation and high melting point temperature.

DCRP are used for minimum heat required and low melting point temperature and al mg is highly reactive metal required low heat.

Actually only for al and mg, DCRP is used in TIG because these metals have heavy oxides coating which can be readily removed by the use of DCRP.

TIG should never be used with reverse polarity. This will melt the electrode of tungsten!

TIG - Straight polarity, AC & DC can be used.

MIG - Only DC with reverse polarity.

Alumimium - TIG AC.
CU- TIG DC straight polarity.
Mg- TIG DC Reverse polarity.

Only FUH Magnesium dc reverse polarity is used not for aluminium.

@Shakti.

Direct Current Reverse Polarity.

Reverse polarity is the right answer.

I agree with the given answer.