Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
The welding waveform in memory may be displayed on a monitor and
analysed. Some instruments also allow calculations to be performed on the
waveform and discrete values of pulse parameters may be displayed. The
number of data which may be captured is, however, restricted by the memory
available and, at high sample rates, the random access memory will be filled
very quickly. If detailed information concerning the waveform is not required
the incoming signal may be processed in real time and a more compact data
file maintained. Two common techniques which have been used in welding
applications are event monitoring and derived data storage.
In event-monitoring techniques, only the data relating to those transient
features of the waveform which satisfy certain criteria are recorded. A common
application is the recording of pulse or short circuit current peaks in GMAW.
A threshold current is preset and only excursions of the current which exceed
this threshold are recorded. Each time the current rises above the threshold,
the time, amplitude and duration of the event are stored. Since only events
of interest are captured and the data concerning these phenomena are
compressed, a large amount of relevant information may be obtained over an
extended sampling period. The application of this type of system for stability
analysis is described in Section 3.1.2.
The information may also be compressed by performing calculations on
the raw data during the measuring process and storing only the results.
Derived data such as mean current and voltage may be obtained for example
for every thousand readings, the raw data may then be discarded and the
averages stored in RAM. Alternatively, secondary process parameters such
as heat input, or dynamic resistance may be calculated on-line in this way.
A purpose-designed welding data logger monitor has been designed to
master arc voltage, current and wire feed speed and has facilities for waveform
capture and analysis and the capability of monitoring mean values for each
weld run. In the case of waveform capture, variable sample rates and pretriggering
facilities are available. The output may be directed to:
∑ an external oscilloscope for general analysis and measurement of the
waveform;
∑ an internal display which gives a digital read-out of the values of current
or voltage identified by a movable cursor on the oscilloscope screen;
∑ an internal printer which prints the calculated values of peak and background
current and voltage, peak and background time and mean current and
voltage;
∑ a removable battery-backed RAM cartridge or ‘thumbdrive’, which may
be used to store data and transfer it to a personal computer for more
detailed display and analysis. Using this facility, the measured data may
be presented as a welding procedure, a weld costing or a comparison of
the measured values with a preset procedure.