Advanced Welding Processes: Technologies and Process Control

3.1 Introduction
Many of the recent developments in arc welding have been made possible by
improvements in the design of the welding power supplies and, in particular,
the introduction of electronic control. The basic requirements of arc welding
power supplies will be examined below and the principles of both conventional
and advanced power source designs, their advantages and limitations will be
described.
3.2 Basic power source requirements
There are three basic requirements for arc welding power sources:
∑ to produce suitable output current and voltage characteristics for the process;
∑ to allow the output to be regulated to suit specific applications;
∑ to control the output level and sequence to suit the process and application
requirements.
These requirements are illustrated in Fig. 3.1.
In order to produce suitable output levels for most arc welding processes,
the normal mains power supply must be converted from high voltage–low
current to relatively high current at a safer low voltage. This function may be
performed by a conventional transformer and, if direct current is required, a
rectifier may be added to the output. The addition of a rectifier has the added
advantage that a three-phase supply may be used 1 and the loading on the
supply will be more uniform with approximately equal currents being drawn
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Welding power source technology
1 Although the ‘Scott connection’ system may be used to obtain a single-phase output
from a three-phase supply this does not give balanced loading. Multi-operator transformers
with a three-phase input and three single-phase outputs have been used, but the loading
of the three-phase input is dependent on the number of arcs in use and the output current.