Never!! (I fluff things in the dryer.) To help me remember the word "smwddio" I think of it as "smoothing" wrinkles out of fabric.
A more comfortable translation seems like it would be "going to iron". "Going to do the ironing", presented as the only option, as it was in my exercise, seems confusing.
smwddio = ironing, to iron, to do the ironing
Welsh words do not necessarily have an exact one-to-one correspondance with English.
I agree in my example "when are you going to do ironing" is a valid english translation