Welding Techniques and Lathe [www.mastercnc.org]

Welding arc phenomena there are actually 2 kinds hopefully the following review helpful for you.

1. Characteristics of a welding arc.
2. Functions of the arc.

Pinch effect:The arc column is,in a sense a collection of parallel electric conductors.Each conductor attracts other by magnetic force and the section of the arc column shrinks.This is called magnetic also shrink due to cooling of the surrounding gas(es).
This is called thermal pinch effect .Also,as current density rices plasma temperature of the column increases.

This pinch effect act on the molten metal of electrode and causes the necking gas as shown in Fig.1.8.it is an important phenomena understanding the detachment of the droplet.
Magnetic arc blow (DC arc welding);the arc is affected not only by its own magnetic field,but also by surrounding magnetic fields.When a magnetic field caused by a welding current or a magnetized base metal is asymmetric to the arc column,the arc deflects.This is called magnetic arc blow.Magnetic arc blow most often occurs at the start and end of the weld line in DC welding.
This phenomenon can occur even when the base metal in non magnetic,but occurs more often when the base metal is magnetic.
Demagnetizing of the base plate,use of a double grounding cable to the base plate and consideration to the location of ground connection help to prevent magnetic arc blow.This phenomenon hardly occur with AC welding.
Many articles can I write, may be useful for you, if anyone would please complete this article, and if you want to criticize because it also please your rights.