Device for plane double welding of large boards

The invention relates to a fully-automatic double-plane flat welding turnover die and a welding method. A roller is composed of an upper roller body and a lower roller body; the upper roller body can horizontally move relative to the lower roller body; a horizontal slideway is correspondingly arranged between the upper roller body and the lower roller body; a workpiece supporting die is arranged in the middle in the roller; an axially arranged truss is fixed to the inner wall of the end face of the roller; the truss is provided with a workpiece fixing device matched with the workpiece supporting die, and is further provided with a two-shaft welding robot. When workpieces are installed, the upper roller body moves outwards in the horizontal direction, the workpieces are arranged on the workpiece supporting die and are fixed with the workpiece fixing device, and the upper roller body and the lower roller body are fixed and reset; the two-shaft welding robot on the truss welds the upper surfaces of the workpieces; after welding of the upper surfaces of the workpieces is finished, the whole upper roller body and lower roller body are overall turned over by 180 degrees, and then the two-shaft welding robot welds the lower surfaces of the workpieces.