Welding arc

Topic overview

The welding arc is a low-voltage, high-current electrical discharge in an ionised gas. For the welding engineer, it matters not as an isolated physical phenomenon but as the link between the power source , electrode , shielding medium , metal transfer , shape of the weld pool a joint quality .

The same set current can produce a completely different result if arc length, polarity, source dynamics, electrode extension, shielding gas or the magnetic field around the weld changes. The arc must therefore be assessed as a system: power source – torch – electrode – gas/flux – base material – joint geometry – movement .

The model is indicative. It demonstrates trends: arc length increases voltage, gas changes conductivity and heat concentration, and polarity changes the energy loading of the electrode and workpiece.

For engineering purposes, total arc voltage can be divided into cathode drop, anode drop and plasma-column voltage.

What the module covers

• The arc is not merely a ‘spark’. It is a controlled plasma energy converter.
• Interactive engineering model
• 1. Arc regions and voltage drop
• 2. Cathode, anode and polarity
• 3. The arc as part of a control circuit
• Physical mechanisms that the welding engineer must relate to the weld result
• Static characteristics of the arc and power source
• Dynamics: short circuit, reignition and pulse