A historical look back at welding technology, Reprinted from 2004 Aftek press release.
HISTORY of the AFTek MULTI-PROCESS WELDING SYSTEM
AFTEK – “the Best Welders you never heard of…”
The heart of the AFTEK SYSTEM is one of the oldest welding technologies still in use today -the resistor controlled arc. BUT, its BRAIN is as modern as the latest machines around! AFTek uses EDGE-WOUND resistors made with an alloy specially selected to CONTROL CURRENT (NOT Ni-Chrome, which is intended to produce HEAT -which it does, admirably) to control the welding output. Historically, the most common application of resistor controls has been in Multiple Operator Welding Systems, widely used in shipyards and heavy construction. Nearly all the Nuclear Electric Power Plants were built using Multiple Operator Systems. Today, only one US manufacturer of Multiple Operator remains. AFTek. Crafted with PRIDE in the USA !
Most "conventional" arc welders use a transformer-like device called a reactor to control the "heat" of the welding arc. If you look at the V/A curve for a conventional constant current (or constant voltage) welding power supply, you will see a bulge in the volt/ampere curve. This is inherent in the design. The V/A curve of a resistor control is a straight line.
A RESISTOR controlled arc is more CONSTANT POWER - if you shorten the arc, thus lowering the arc voltage, the current will INCREASE, and maintain virtually the same POWER, or heat. If you lengthen the arc, you RAISE the voltage and the power remains virtually constant. In any welding process, increasing the amperage increases penetration. Increasing the voltage widens and flattens the head (and reduces penetration). With a resistor controlled arc, if you are welding along the seam and it closes up on you, shortening the arc length will increase penetration. If the weld opens wider, lengthening the arc will lessen the penetration and widen the weld. It's like having a remote control right in your electrode holder.
From the thirties until 1990, nearly all Multiple Operator Systems were the same general layout – a big bulk power supply, with “grids” connected by means of cable to form a system of distributed power. Originally designed for use in shipyards, this system minimized the use of high voltage primary power, distributing 75-80 volts of secondary voltage instead.
Somewhere along the line, “packs” became popular, with 2, 4, 8, even 16 arcs in a steel rack, connected to a separate power supply. Big Four pioneered the concept of connecting Multiple Operator systems in a complete loop configuration. This LOOP concept greatly improved the voltage stability of Multiple Operator systems, because with all the power connected to a single circuit, voltage drops were reduced or eliminated due to the nature of a DC circuit.
In 1990, the loop was placed in an integrated package, and the Power 88 was born. The Power88, Power 44, and Power 22 are a family of modular welding packages, using an internal power supply of sufficient size to power all the arcs without any interference. The base power ranges from 500 to 2000 amps, depending on the type of welding, and the duty cycle or arc on time.
Loop systems are still being used, and are the most economical way to place power in a new facility, or one that is being upgraded. One recent loop needed twenty MIG arcs. This was accomplished using 4 500-ampere power supplies, connected to a single 500 MCM cable which circled the 200’X50’ building. Twenty DPM245MV Control Modules were connected wherever needed on the closed loop of cable. Four primary connections instead of twenty saved almost as much as the cost of the equipment!
About twenty years ago, after Three Mile Island killed the Nuclear Power Industry, Big 4 Manufacturing Company of Saint Louis, Missouri was trying to expand into the general fabricating, refinery and petro-chemical market, The soft arc that everybody liked, while GREAT for most welding, didn't do very well on pipe root passes with 5P, the most common method then in use for oil related pipe.
So Big 4 devised a circuit to make their resistor grid think it was a Lincoln generator. They called it Arc Ram, and it worked beautifully with 5P and similar electrodes Building upon that, a MIG system was developed, which they called Demand Pulse.
Short Arc, or "Short-circuiting Metal Transfer", was introduced by Linde in the late fifties for welding sheet metal. During the sixties, short-arc became widely used, often for applications for which it was not intended. When the wire would contact the molten weld pool, many times the weld did not fuse to the base metal. This was called a "cold lap". That is the main reason many shops refuse to accept ANY GMAW or “wire” welding on pressure welds. Mis-used, Short Arc welding has given ALL GMAW welding on pressure welds a bad name.
"Short Circuit Transfer…
encompasses the lowest range of welding currents and electrode diameters associated with Gas Metal Arc Welding. This type of transfer produces a small, fast freezing weld pool that is generally suited for joining thin sections, for out -of-position welding, and for bridging large root openings. Metal is transferred from the electrode to the workpiece only during a period when the wire is in contact with the workpiece (short-circuited). No metal is transferred across the arc gap...As the wire touches the work the current increases...the molten tip is pinched off by the magnetic flux created by the high current, and the arc is re- initiated...The wire contacts the workpiece in the range of 20-200 times per second."
While not mentioned in the above, research shows that the arc is out approximately 60 percent of the time. This is the main reason cold laps occur.
Now, Demand Pulse, on the other hand...
The arc is rarely extinguished. Metal transfers through the arc, a much shorter arc than Pulse Spray...The transfer occurs above the molten pool, so spatter doesn't explode from the puddle...It is a "constant current" process. The operator selects a base current, similar to some GMAW Pulse Spray applications, adjusts the wire feed speed to give the correct voltage, and begins to weld. Lower voltage will cause the puddle to freeze faster, higher voltage will cause the puddle to he more fluid.
In short arc, a current PULSE is triggered by the short-circuit condition caused by the wire driving into the work piece. Demand Pulse FORCES the transfer to occur BEFORE short-circuit, at a voltage selected by the operator, above the weld pool. This has two important effects: the arc does NOT extinguish and the spatter level is greatly reduced because the molten tip of the wire does NOT contact the weld pool. Because the arc is not extinguished, cold laps are virtually eliminated.
Many reference books describe short arc as a "random Pulse" method of welding, random in the sense that the pulse is triggered as a function of wire feed speed - the faster the wire feed speed the faster the short circuits (Pulses). Demand Pulse is exactly the same, except it DOES NOT SHORT!
Weld outside corners on 18-gauge aluminum and stainless steel. Or weld 20-gauge mild steel with .035 wire, or weld beautiful root passes on 4 to 10 inch pipe at 90 amperes with excellent fusion. This bonding has to be due to the arc RARELY being extinguished as it is when Short Arc welding.
And do not overlook HEAVY aluminum. Remember, Demand Pulse is a Constant Current MIG process. Most primary aluminum manufacturers recommend constant current for MIG welding aluminum, claiming less porosity and better fusion than when welding with Constant Voltage.
AFTek currently manufactures single operator machines from 400 amps to 1250 amps, with and without Demand Pulse. A twin unit is available, with 250 amperes per side, or 500 amps combined, with and without Demand Pulse – the Power 22. A four pack and eight pack – the Power 44 and Power 88 are available, with a wide range of options, including up to 2000 amps of power, and with or without Demand Pulse.
ALL single operator machines are available with the DPM-III control, recently introduced with expanded capabilities when using .045 and larger wires.
And, a full line of Resistor Controls and Multiple Operator Power Supplies. AFTek Resistor Controls work on ANY Multiple Operator System.