soldering iron, trowel, curling iron, flat iron
鏝 centers on heated metal tools used to shape, join, or smooth materials: a soldering iron, a trowel, a curling iron, or a flat iron. The common thread is a metal implement that applies heat or pressure to work a surface.
鏝 combines 金 (metal) with 曼, which likely contributes the sound and may relate to spreading or extending, fitting the idea of a metal tool used to spread or smooth.
The left side is metal 金, and the right side 曼 looks like a tool with a long handle and a flat working end. Picture a metal trowel spreading mortar, or a soldering iron melting metal—both are metal tools that work surfaces.
For マン, imagine a man using a heavy metal trowel to smooth a wall: man -> マン, and the metal tool is 鏝.