An apparatus for forming a bag assembly includes opposing die members. Each die member 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. During operation, first the perimeter-welding and tube-welding portions weld the bag assembly simultaneously, then the perimeter-welding portions are moved to increase the distance between them. 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.