Bending machine for producing bent parts from flat material, comprising: a drawing-in device for drawing in flat material from a material supply with flat material, a bending device with a bending head for bending the flat material to form a bent part composed of flat material that is bent in a two-dimensional or three-dimensional manner; and a cutting device for cutting off the bent part from the fed flat material, wherein the bending head has a bending mandrel (400, 600) with a peripheral groove (420, 620) for receiving a portion of the flat material that is to be bent, and has a bending tool which is rotatable around the bending mandrel and which serves for acting on a portion of the flat material that is to be bent over, characterized in that the bending mandrel (400, 600) is designed as a split bending mandrel which has a lower mandrel part (430, 630) and an upper mandrel part (440, 640) that is movable relative to the lower mandrel part, wherein a lower delimitation surface of the peripheral groove is formed on the lower mandrel part and an upper delimitation surface of the peripheral groove is formed on the upper mandrel part, and the upper mandrel part and the lower mandrel part are displaceable relative to one another for changing the clear height of the peripheral groove between a closed configuration with a relatively small clear height and an open configuration with a larger clear height in comparison with the relatively small clear height, wherein one of the mandrel parts has a guide opening for axial guidance of a displacement movement of the other mandrel part, and the other mandrel part has a guide portion dimensioned for introduction into the guide opening and has a head portion which is widened in comparison with the guide portion, wherein a radial outer surface of the guide portion inwardly delimits the peripheral groove (420, 620) and one of the delimitation surfaces of the peripheral groove is formed on the head portion. a drawing-in device for drawing in flat material from a material supply with flat material, a bending device with a bending head for bending the flat material to form a bent part composed of flat material that is bent in a two-dimensional or three-dimensional manner; and a cutting device for cutting off the bent part from the fed flat material, wherein the bending head has a bending mandrel (400, 600) with a peripheral groove (420, 620) for receiving a portion of the flat material that is to be bent, and has a bending tool which is rotatable around the bending mandrel and which serves for acting on a portion of the flat material that is to be bent over, characterized in that the bending mandrel (400, 600) is designed as a split bending mandrel which has a lower mandrel part (430, 630) and an upper mandrel part (440, 640) that is movable relative to the lower mandrel part, wherein a lower delimitation surface of the peripheral groove is formed on the lower mandrel part and an upper delimitation surface of the peripheral groove is formed on the upper mandrel part, and the upper mandrel part and the lower mandrel part are displaceable relative to one another for changing the clear height of the peripheral groove between a closed configuration with a relatively small clear height and an open configuration with a larger clear height in comparison with the relatively small clear height, wherein one of the mandrel parts has a guide opening for axial guidance of a displacement movement of the other mandrel part, and the other mandrel part has a guide portion dimensioned for introduction into the guide opening and has a head portion which is widened in comparison with the guide portion, wherein a radial outer surface of the guide portion inwardly delimits the peripheral groove (420, 620) and one of the delimitation surfaces of the peripheral groove is formed on the head portion.