Livingston & Company WELDWISE 2400, Руководство пользователя

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0429-INS-400 Rev. C
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Weld Lobes and the Weld Process
Each of the factors involved in the creation of a weld (Current, Voltage, Resistance, etc.) has a specific
range in which good welds can be made. This range is commonly known as the
weld lobe . Bad welds
are made when the weld process falls outside of the lobe, so the simple answer to making consistently
good welds is to keep the process inside the lobe. It is not so simple, however, to ensure that this
happens for each weld made. This is where resistance weld monitoring is most valuable. The following
example uses a weld nut and the relative movement of the electrodes during the weld to examine what
goes on during the weld process. Livingston terminology (
in italics ) is used to describe various
measurements.
The nut itself has a number of little metal feet or projections on the bottom of it. These projections sit
on top of the workpiece to which they'll be welded. A measurement of the nut sitting on top of the
workpiece with the electrodes clamped on it before the weld is made is called the
Initial Thickness .
When the proper electrode force is applied and weld current is fired, the projections melt into the
workpiece and create a weld. When the projections melt, the molten metal expands for a moment,
pushing the electrodes apart (this movement is called
Expansion ) before sinking down into the
workpiece (this movement is called Setdown ). The expansion-setdown process is very much like a pot
of water boiling over before it's removed from the heat: as the metal is heated, it expands and then
quickly contracts as it cools to form the weld. A subsequent measurement of the nut/workpiece after
the weld is made is called the
Final Thickness . All these different measurements of electrode
movement are measures of what's commonly called Electrode Displacement, or simply Displacement.
Measuring displacement provides a good indication of whether or not the resulting weld was formed
properly. If the nut sinks too far into the workpiece, it may be a sign of excessive heat which could
render the weld no good. It could also indicate that too much force was applied, the weld time was too
long, or a number of other things. Conversely, if the nut doesn't sink far enough, it may mean that not
enough heat was generated for the materials to weld properly, the force was insufficient, etc. Problems
with displacement can be problematic in many applications, such as welding hydraulic fittings. If the
setdown is too much/too little, chances are that the welded fitting will leak. When taken into account
that displacement is only one of many factors that, when measured, provide valuable information about
the formation of the weld and its overall quality, it becomes clear that weld monitoring is indeed a
valuable tool. Weld monitoring provides the user with an easy way to access a wealth of information
about the welding process— information that can actually help improve the process itself, as well as
alert the user to any number of potential problems.
Styles of Monitoring
There are many different types of monitoring systems on the market nowadays. These systems can be
broadly categorized into three different styles, which for educational purposes are nicknamed as
follows:
Before & After monitoring, Mass monitoring, and Dynamic monitoring.
Before & After Monitoring
As the name suggests, Before & After monitoring (hereafter referred to as BA monitoring) focuses on
only two phases of the weld process: before the weld is made, and after the weld is made. This type of
monitoring is typically used to measure displacement only. As mentioned above, measuring