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Improving welding processes with the
With the Fluke 345 set to read Single-phase watts, the heat input applied to a given length of weld can be determined.
As technology continues to improve welding pro- cesses it becomes important to update evaluation and troubleshooting methods in order to ensure
weld quality and productivity. Knowing power supply issues, understanding advanced waveform manipulation and the commonly used Pulsed Gas Metal Arc Welding (GMAW-P) technology, often referred to as “pulsed MIG,” is important to determining what is happening at the end of the welding gun.
In pulsed MIG welding, a high-speed inverter in the welding machine pulses the output current between the wire electrode in the welding gun and the
weld material. The current pulse is usually a square wave, pulsing from a maximum flat peak value to a minimum or background value up to 5,000 pulses per second in some machines. During each pulse the weld bead is squeezed off from the wire feed through the arc and into the weldment. If the pulsed current drops too low, the arc will not be maintained and the weld puddle may cool creating problems. Improperly applying cur- rent and voltage can result in welding spatter and create metallurgical issues at the weld. In short, improper waveforms at the weld gun can reduce production.
While some welding machines can now monitor the output waveform through their controls, external trou- bleshooting with handheld test tools is still often necessary to ensure weld quality. A tool such as the Fluke 345 Power Quality Clamp Meter measures ac or dc
voltage and current, power in watts, displays waveforms, and utilizes sample rates at just over 15 kHz.
Weld quality is so important, that where safety is con- cerned, the International Boiler and Pressure Vessel Code, the code that establishes rules for pressure integ- rity of boilers and pressure vessels revised ASME IX,
“Welding and Brazing Qualifications,” in 2010 to allow the use of either of two methods to measure the energy being delivered per unit length of weld.
• When voltage or current are held at constant values on the welding machine output, a conventional for- mula of volts times amps divided by the length of weld can be used to monitor the heat input per unit length of weld. Such measurements are required as part of the welding qualification process by this code section.
• With pulsing outputs, a more technologically advanced equation using test tools for power and energy measurement can be used. (see sidebar)
Joel Pepin is the Quality Systems Engineer at the PCL Industrial Fabrication Facility located in Nisku Alberta, Canada. He is a licensed professional engineer and rec- ognized expert on the effects of advanced waveform variables on the welding of pipeline steels.
Pepin says with a portable tool such as the Fluke 345 Power Quality Clamp Meter you can squeeze the trigger and clamp around a conductor to read ac or dc amps or view the current waveform. Attaching the voltage leads allows for reading of voltage values in addition to the current values, and the display of voltage and current waveforms together on the same screen. The meter also has a Watts function.
Because of its ability to capture and download data, the 345 can be used to record and analyze baseline information when evaluating a new process. Spikes and average maximum values can be observed.
“We get a better idea of the envelope we are working within,” Pepin said. Observing waveforms is critical.
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