Derived from the process of sheet welding (i.e. sticking two sheets together), refers to bed-based masturbatory activities, with the assumed consequence that the 'sheets' (substituted for 'blankets' for increased differentiation from the innocent metal-work activity), will be welded (i.e. stuck together with semen) together.
Ash: "Euurrggh Doug, is that your hand moving up and down under your covers?"

Doug: "No!"

Ash: "Don't lie, you're blanket welding again, aren't you?"

Doug: "Is it okay if I was thinking of you while I was doing it?"

Ash: "You're sooo not waking up tomorrow".
by Nuciphaal January 13, 2005

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