Abstract: Two rectangular rigid foam boards are supported horizontally above and below an elongated horizontal heating blade which extends laterally across the width of the boards. The heating blade is supported for vertical floating movement for uniformally heating and softening the opposing side surfaces of the boards while the boards are fed between horizontal driven pressure rolls. The rolls cooperate with the blade to heat-fuse or weld the boards together and form a laminated foam core assembly. The foam core assembly is planed to a precision thickness and then bonded by adhesive to facing sheets of preselected materials. The temperature of the blade is sensed and controlled according to the speed of the pressure rolls and the pressure applied by the rolls during the heat-fusing operation.