Patent ID: 8163118

Claim:
A method for joining together thermoformable sheets, comprising: providing a first thermoformable sheet overlapped with a second thermoformable sheet; moving a heating element through the first sheet and the second sheet to form a trailing terminal edge on the first thermoformable sheet and a leading terminal edge on the second thermoformable sheet; aligning in proximate, spaced-apart relation the trailing terminal edge and the leading terminal edge; holding the heating element between and spaced from the trailing terminal edge and the leading terminal edge; while holding, heating the trailing terminal edge and the leading terminal edge with the heating element sufficiently to impart melt-back of each edge away from the heating element; while heating, moving the leading terminal edge and the trailing terminal edge each towards the heating element at a rate that maintains separation of the leading terminal edge and the trailing terminal edge with the heating element while maintaining proximity with the heating element sufficient to melt back each edge; removing the heating element from between the trailing terminal edge and the leading terminal edge; and after removing, fusing together the leading terminal edge and the trailing terminal edge by moving together the leading terminal edge and the trailing terminal edge until respective melted portions on each edge engage.