Welding Application - Cold Metal Transfer
"Cold" is a relative term in perspective to welding. Cold Metal Transfer welding is commonly referred to as CMT. The workpieces to be joined as well as the weld zones remain considerably "colder" in the cold metal transfer process (CMT) than they would with conventional gas metal arc welding.
The cold metal transfer process is based on short circuiting transfer, or more accurately, on a deliberate, systematic discontinuing of the arc. Results are a sort of alternating "hot-cold-hot-cold" sequence. The "hot-cold" method significantly reduces the arc pressure. During a normal short circuiting transfer arc, the electrode is distorted while being dipped into the weld pool, and melts rapidly at high transfer arc current. A wide process window and the resulting high stability define the cold metal transfer process. Automation and robot-assisted applications is what the process is designed for.
The major advancement is that the motions of the wire have been integrated into the welding process and into the overall management of the procedure. Every time short circuiting occurs, the digital process control interrupts the power supply and controls the retraction of the wire. The forward and back motion takes place at a rate of up to 70 times per second. The wire retraction motion aides droplet detachment during the short circuit.
The fact that electrical energy is converted into heat is both a defining feature and sometimes critical side effect of arc welding. Ensuring minimal current metal transfer will greatly reduce the amount of heat generated in the cold metal transfer process. The restricted discontinuations of the short circuit leads to a low short-circuit current. The arc only inputs heat into the materials to be joined for a very short time during the arcing period because of the interruption in the power supply.
The reduced thermal input offers advantages such as low distortion and higher precision. Benefits include higher-quality welded joints, freedom from spatter, ability to weld light-gauge sheet as thin as 0.3 mm, as well as the ability to join both steel to aluminum and galvanized sheets.
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