Never!! (I fluff things in the dryer.) To help me remember the word "smwddio" I think of it as "smoothing" wrinkles out of fabric.
"Dashing away with the smoothing iron..." (an English song)
Indeed, smwddio comes from the English smooth.
Why isn't it "i'r smwddio" since we're saying "THE ironing?"
smwddio = ironing, to iron, to do the ironing
Welsh words do not necessarily have an exact one-to-one correspondance with English.