1. Electricity in Welding Unit 212/255 – Principles of Fabrication and Welding Technology

2. Electricity in Welding Electricity is used extensively in welding and fabrication Electrical polarity has a huge influence on heat distribution in a welded joint. There are two types of current available: Alternating current (ac) (mains electricity) Direct current (battery or from a transformer)

3. AC Electrical Supply Electricity supplied to homes and factories has an AC (alternating current) waveform. The frequency of the UK supply is 50 hertz Hertz is a measure of cycles per second. The polarity of the supply is switching 50 times per second.

4. DC Electricity The DC (direct current) supply has no waveform. Polarity is fixed High voltage DC for welding is achieved by converting an AC current. The current supplied by a battery is DC.

5. Electricity in Welding Terminology : Open Circuit Voltage (OCV) –The voltage needed to strike the arc Arc Voltage –The voltage needed to maintain the arc (Lower than OCV)

6. Arc Blow –Happens when using DC current –Arc is deflected either backwards or forwards. –Caused by magnetic build up in the weld metal. –More pronounced in corners of fillet welds Preventing Arc Blow –Move the current return lead –Weld in a different direction –Wrap the current return cable around the component being welded.