What CMT is
Cold Metal Transfer — CMT — is Fronius’s trade name for a controlled dip-transfer MIG/MAG process. Fronius describes it as a low-heat-input process in which reversing wire movement changes how the droplet detaches[S2]. “Cold” is relative, not literal: this is still an arc process.
That one sentence carries this sheet’s two rules. First, CMT is best understood as a refinement of an ordinary, well-documented transfer mode — so the useful place to start is dip transfer itself. Second, because the refinement lives inside a specific manufacturer’s power source and wire-drive control, almost every specific claim about CMT — parameters, capabilities, joint ranges — belongs to that manufacturer’s documentation, not to a general web page.
Dip transfer, recapped
In conventional dip (short-circuiting) transfer, the welding set holds a low voltage and the molten tip of the continuously fed wire transfers by dipping into the weld pool — a rapid cycle of short circuits[S1]. Each short circuit brings a surge of current; the machine’s inductance setting controls that surge, and getting voltage and inductance right against the wire feed speed is what keeps spatter to a minimum[S1]. Dip is the low-current end of MIG/MAG — the mode for thin sheet and positional work — and its besetting sins are spatter and, because the arc is comparatively cold, the risk of lack-of-fusion defects when conditions drift[S1].
Notice where the trouble lives: in the short circuit. How the wire enters it, how much current flows during it, and how the molten bridge breaks — those three events decide the spatter, the heat and the stability of the whole mode.
What “cold” actually means
CMT controls exactly those events. Instead of leaving droplet detachment to current surge and arc forces alone, the process control reverses the wire feed for an instant at each short circuit: the wire physically retracts, helping the molten bridge detach mechanically while the electronics keep current low[S2].
The consequences follow from the mechanism, and they are the reasons fabricators reach for it: less current flowing during the short circuit means less spatter to clean; less energy per transfer means lower heat input into the parent metal, which thin material and distortion-sensitive work both reward.
FIG. 1 · CMT wire-movement cycle
Scroll sideways to follow all three stages.
Where it earns its keep
Fronius presents controlled dip transfer for applications including thin sheet, root runs, mixed-material joining and mechanised work[S2]:
- thin sheet, where ordinary dip transfer risks burn-through and distortion simply from heat input;
- root runs, where a stable, low-energy transfer helps control a root pass;
- mixed and coated-material joining, including brazing-style joints on galvanised sheet, where limiting the melting of the parent surface is the whole point;
- mechanised and robotic work, where the process’s tightly controlled cycle and low spatter suit automation — with the operator-qualification questions that mechanised welding brings (see the procedures sheet).
The manufacturer boundary
Three boundaries apply:
- The process is proprietary. CMT is a Fronius process name. The waveforms, wire-motion control and synergic lines live inside the manufacturer’s equipment, so capability claims travel with the documentation for the actual Fronius system in use[S2].
- The paperwork still applies. A qualified welding procedure treats this process and its essential variables exactly as it would any other MIG/MAG work: change what matters and the qualification falls. The route from pWPS to qualified procedure is walked on the WPS/PQR/WQT sheet.
- This page holds no CMT parameter data. No parameter tables, no deposition figures, no heat-input numbers. The planning tools here work only on figures you enter from your own equipment and materials — the wire runtime estimator being the obvious companion for any wire-fed process.