Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
50–300 A with a 1.2 mm diameter carbon steel wire) and stable projected
drop spray type transfer is maintained throughout the control range. Many
commercial systems now dispense with the direct wire feed speed feedback,
relying instead on the inherent accuracy and stability of electronic power
and wire feed speed regulation.
Developments of synergic control
The synergic control technique has been further enhanced by:
∑ improved control strategies;
∑ arc length control;
∑ parameter selection by the user;
∑ synergic control of dip and DC spray transfer.
Improved control strategies. Although these systems should only require
a single adjustment, it is quite common to incorporate a trim control to
accommodate minor deviations in arc behaviour. This fine control usually
adjusts the relationship between the wire feed speed and the pulse parameters,
changes the burn-off behaviour and lengthens or shortens the arc. It may be
required to allow the operator to select arc conditions appropriate to a specific
application or to correct any shortcomings in the control algorithm.
Three basic control strategies are adopted. In the original synergic control
systems, electronic circuits of the type shown in Fig. 7.29 were used and the
effect of increasing wire feed speed was to increase pulse frequency, increase
background current and increase pulse height. The pulse duration remained
fixed. This is illustrated in Fig. 7.30. The system gives satisfactory performance
over a reasonably wide current range, but the pulse current will eventually
Tachogenerator
Pulse
frequency
control
Pulse
duration
control
Pulse
amplitude
preset
Background
amplitude
control
Current
regulator
7.29 Early control arrangement for synergic control.
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