Why We Use Cold Metal Transfer (CMT) Welding

When it comes to custom sheet metal parts and enclosures, welding can solve a whole host of design challenges. That’s why we offer various welding processes as part of our custom manufacturing, including spot welding, seam welding, fillet welds, plug welds, and tack welds. But without deploying the right welding methods, the process of welding light-gauge sheet metal can be problematic and prone to rejection. This blog post will discuss why we use Cold Metal Transfer (CMT) welding over conventional MIG welding (metal inert gas) or TIG welding (tungsten insert gas).

Issues with other welding methods

In the welding process, heat from the welding torch heats up the workpiece and a feed wire in the torch, melting them and fusing them together. When the heat is too high, the filler can melt before reaching the workpiece and cause drops of metal to splatter onto the part. Other times, the weld can quickly heat the workpiece and cause distortion or in the worst cases, holes can be burnt into your part.

The most commonly used types of welding are MIG and TIG welding. These both have a much higher heat output compared to Cold Metal Transfer (CMT) welding.

In our experience, TIG and MIG welding is not ideal for joining light-gauge sheet metal. Due to the excessive amounts of heat, there is warping and meltback, particularly on stainless steel and aluminum. Before the introduction of CMT welding, welding light-gauge sheet metal tended to be more of an art-form than an engineered production process.

How Does CMT Work?

CMT welding has an exceptionally stable arc. The pulsed arc is made up of a base current phase with a low power and a pulsing current phase with high power without short circuits. This leads to almost no spatter being produced. (Spatter are droplets of molten material that are generated at or near the welding arc.).

In the pulsing current phase, the welding droplets are detached in a targeted manner via a precisely dosed current pulse. Because of this process, the arc only introduces heat for a very brief period during the arc-burning phase.

The arc length is detected and adjusted mechanically. The arc remains stable, no matter what the surface of the workpiece is like or how fast the user welds. This means CMT can be used everywhere and in every position.

The CMT process physically resembles MIG welding. However, the big difference is in the wire feed. Rather than continuously moving forward into the weld pool, with CMT, the wire is retracted the instant current flows. The weld wire and a shielding gas are fed through a welding torch, the electricity arcs between the weld wire and the welding surface – this causes the tip of the weld wire to liquefy and to be applied to the welding surface. CMT uses automatic activation and deactivation of the heating arc to systematically heat and cool the weld wire while bringing the wire into and out of contact with the weld pool many times per second. Because it uses a pulsing action instead of a continuous stream of power, CMT welding generates only one-tenth of the heat that MIG welding does. This reduction in heat is CMT’s greatest benefit and is why it’s called “Cold” metal transfer.

Quick fun fact: The developer of CMT welding actually describes it as, “hot, cold, hot, cold, hot cold.”

Got a Design in Mind? Talk to Us

Protocase can incorporate welding into your design to solve challenges that would otherwise be impossible. If you are curious about the welding options Protocase offers, check out our website, or our Proto Tech Tip videos on welding.

If you have any questions about incorporating welding into your design, reach out to get started. Protocase can make your custom enclosures and parts, in up to 2-3 days, with no minimum orders. Submit your professional quality one-off prototypes or low-quantity designs and get your projects started today.