Frequency Control - A Way To Improve Aluminum Welding
Adjustable-output frequency has been pivotal in emerging
technologies that have made Gas
Tungsten Arc Welding (GTAW) applications more adaptable
for aluminum welding - particularly after the advent
of inverter-based GTAW machines. Advanced inverter-based welding machines
give welding persons the possibility to enhance shaping of the bead
profile - frequency control. Decreasing frequency produces a broader arc cone, which widens the weld bead profile and more effectively removes impurities from the surface
of the metal. It also transfers the maximum amount of energy to the
work piece. Increasing frequency produces a tight, focused arc cone.
This helps deeper penetration and it narrows the weld bead, which is
useful when welding in corners, on root passes and fillet welds.
Conventional AC TIG
Welders have a fixed output of 50 or 60 Hz, but certain
inverters provide the operator the option to adjust the welding output
frequency. While referring to Alternating Current (AC), GTAW frequency
means the number of times that the direction of the electrical current
completes a full cycle per second, expressed in terms of hertz. Frequency
is represented by a sine wave, which depicts the current flow rising
and falling as it reverses direction. Gas tungsten arc welding (GTAW) or
tungsten inert gas (TIG) welding is widely deemed as
the most difficult welding process to master. AC GTAW inverters-through
new arc controls and waveform options-have made it easier for operators
to fashion arc characteristics, weld puddle behavior, weld bead profile,
penetration, and appearance.
Of course, Direct current (DC) cannot be used with nonferrous metals
like aluminum because of the oxide layer that forms on the surface of
the base material. With DC electrode negative (DCEN) GTAW, the current
flows from the tungsten electrode to the work surface, and the positively
charged argon gas ions flow from the work surface to the tungsten.
DCEN works well most ferrous metals
principally steel, but the oxide layer that forms
on nonferrous metals like aluminum
melts at a higher temperature than the base metal
making welding difficult. But Direct Current Electrode
Positive (DCEP) solves the oxide problem in a way
because the current flows from the work surface to
the tungsten, lifting the oxide off the material in
the arc zone.
The range of most inverter-based
power sources provide AC output frequencies between
20 Hz and 150 Hz. Miller inverter TIG machines provide
AC output frequencies between 20-400 Hz output frequencies.
Some manufacturers offer machines with frequencies
from 20 to 100 Hz, while others make machines outputting
20- to 400-Hz. In general, 120 to 200 Hz is a suitable
frequency for most aluminum welding.
An inverter power source takes input power, filters it to DC, and, increases its frequency up to 100,000 Hz with fast, solid-state switches. Input
power then is transformed into usable, and then transforms it into useable
welding power with an advanced level of arc control.
The ideal starting point for general welding may be 80 to 120 Hz and
increase control of the arc direction and boost travel speed. For a
fillet weld application with full penetration in the weld, increase
the frequency to 225 to 250 Hz. For build up work, start at 60 Hz and
adjust lower from there.
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