Improving Resistance Weld Quality with Monitoring
Monitoring to
Work for You
More than Measuring Current
Questions to Consider
What Monitors Cannot Do

Example : Consider the need to produce an assembly consisting of two pieces of 16-gauge steel. Published guidelines say that a welding current of 15-12 kilo-amperes, a weld time of 10 to 14 cycles, and an electrode force of 800 pounds will produce a good weld.

You can easily set the weld time, since almost all modern weld controls accurately control cycles. You can calculate the airline pressure required to produce the correct electrode force. Still, you need some kind of instrument to measure weld current. For this, you need at least a simple weld monitor.

Now, you need to determine what combinations of current and cycles produce good welds. By making a number of parts using various weld heats and cycles and then performing nugget pull tests, you can determine the correct heat setting for the chosen weld time without ever knowing current.

However, destructive testing takes time and may be difficult. In addition, parts with several welds may exhibit current shunting from earlier welds. Distance of the weld to the sheet edge can also have a major effect on weld quality. These are examples where advanced weld monitoring techniques - not just measurement - can help.

If your weld monitor is able to measure dynamic resistance, you can look for formation of the weld nugget by observing how weld resistance decreases toward the end of the weld. You may learn that some welds require more current or that you can shorten weld time for others. Thus, monitoring can help you better control your process and gain higher production rates through increased knowledge of weld dynamics. Next >>

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