An apparatus for forming a bag assembly includes opposing die members. Each opposing die member defines a single die and has a perimeter-welding portion for forming a perimeter-weld of the bag assembly and a tube-welding portion for forming a tube-weld of the bag assembly. During operation, the perimeter-welding and tube-welding portions weld the bag assembly simultaneously, then the perimeter-welding portion of one of the opposing die members is moved relative to the tube welding portion of the die member to increase the distance between the perimeter-welding portions of the opposing die members. When the perimeter-welding portions are moved apart, welding by the perimeter-welding portions is generally suspended while welding by the tube-welding portions may continue.