The invention is a welding tool for welding and cutting a tear seal edge into multiple plies of plastic film. The welding tool includes a base and a knife edge on the base. A cross section of the knife edge has three surfaces for engaging the multiple plies of plastic film. The three surfaces at the cross section are a planar cutting surface (41), a planar welding surface (42), and a planar separating surface (43). The planar cutting surface (41) presses into the multiple ply plastic film (25) in a coplanar engagement with the multiple ply plastic film (24). The planar welding surface is located on a first side of the planar cutting surface. The planar welding surface fuses the multiple plies of plastic film to substantially eliminate any flash of a weld formed by the fusion of the multiple plies of plastic film. The planar separating surface is on a second side of the planar cutting surface opposite to the planar welding surface. The planar separating surface pushes the multiple ply plastic film away from the weld of the multiple ply plastic film at the tear seal edge. A method for forming plastic bags and other articles is also disclosed. IMAGE
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