WOW Episode 16: Plasma Keyhole Joining

No other arc welding process allows you to make full penetration welds on a variety of metals up to 3/8” thick without a bevel and filler material. The arc punches through the part creating the “keyhole”, molten metal fills behind the arc making narrow, deep weld through the entire section.

Keyhole is rarely used because this variation on plasma welding requires perfect square butt joints without any gap.

At ARC, we use a lot of powder feed plasma for overlay, but we have never used powdered filler materials for plasma joining.

Chip Arata once suggested that powder might make keyhole welding possible on less than perfect parts. Fast forward to 2021 as we go to the lab to investigate.

Results were encouraging. On 4mm 304 stainless can produce full penetration welds with reinforcement on both root and cap in a single pass. We can handle small joint gaps and are currently investigating the limits of the process. Powder allowed us to add a small amount of filler without the added complexity of wire alignment.

Included in this Weld of the Week is a video taken with a Xiris Automation Inc. camera from the side of the joint to show the plasma column punching through the part.