resistance weld monitors come in many configurations, answering a few
questions will help you decide the kind of monitor your application
weld parameters are critical to your process? Since resistance
welding machines tend, by nature, to exhibit constant current characteristics,
current monitoring alone may not be an adequate indicator of weld quality.
Tests show that some welders may produce nearly the same current under
tip-to-tip conditions as when the work is present between the tips.
Voltage measuring capability helps a monitor accurately determine the
displacement information play a critical role in determining weld quality?
As described in the case of an incorrectly positioned projection weld
fastener, measuring displacement may save you money by helping to reduce
back charges. Displacement information will also indicate inadequate
setdown, which results in a low-strength weld.
monitoring electrode force - either directly as with a load cell or
strain gauge or indirectly as related to airline pressure - will
you be able to spot problems before rejects occur?
Too much pressure may produce unwanted part deformation. Too little
pressure results in expulsion and the inability to form a weld nugget.
you need to measure only? For machine setup or when records
need not be kept, measurement alone may be adequate. On the other hand,
do you need to set high and low tolerances? Tolerances allow you to
define accept and reject limits. With these properly set, the monitor
instantly alerts the operator to weld problems and identifies reject
have built-in electrical interlock relays that can be wired to your
welding control to prevent further operation if a reject is detected.
You may also be able to divert rejects to a different bin when they
are ejected from an automatic welding machine.
the monitor work with your process? Most monitors work well
with alternating current (AC) spot welders. However, frequency converters,
high-frequency direct current (DC), capacitor-discharge (stored energy),
and seam welders impose unique requirements on the monitor.
one type of monitor handle all the resistance welding processes you
use in your plant? For example, seam welds usually exceed
the 99-cycle limit imposed by most monitors. You may need a monitor
designed to record welds lasting several thousands of cycles.
will you do with the monitored data?
If it is for temporary use only, during machine setup, for example,
storing the data is not very important. You should still consider whether
or not it would be helpful to print a record of the weld for future
reference. Does the monitor print waveforms, numeric data, or both?
Does it provide a time and date stamp for future reference?
does the monitor handle the data? If you routinely weld coated
materials, you may want to ignore or "blank" the first few weld cycles
during which expulsion may occur. When monitoring an impulse weld, are
cool times ignored or averaged in with heat times? Are the current (and
voltage) readings in root-mean-square (RMS) or average units?
each weld has a distinct pattern, does the monitor look for a single
average current for the entire weld, or can it recognize the weld's
signature, including slopes or pulsation?
Some monitors are not able to distinguish such weld features. Others
apply the specified tolerance to each half-cycle of the weld.
the monitor learn what a good weld looks like and then store the parameters
for future recall as a master weld?
If you plan to use the monitor with several welding heads, can the monitor
store and recall a different signature for each head? Do you have to
be a rocket scientist to use the monitor? Some monitors have almost
no setup requirements. Others display English language prompts which
give helpful instructions during setup. Still others require a skill
level beyond that of the typical user. Next>>