A welding machine having a frame that includes end supports spanned by a top beam with a truncated V-shaped cross-section. A vacuum track assembly disposed vertically beneath the top beam retains fabrics to be welded on a perforated surface using suction. A welding head travels along the top beam and applies heat and pressure to the surface to weld the fabrics together. The top beam and vacuum track assembly are extendable by including additional unit segments from which the beam and assembly are constructed.