A device for mechanically closing a bag neck of a gathered bag with a bending-flexible polymeric and/or metal-free closure band strip, comprising - a punch unit with a displaceable punch and - a die formed from at least two die jaws (3.1, 3.2) in a divided manner, which can be brought together, with mutually facing die guide surfaces (25.1, 25.2) for guiding the closure band strip, - wherein the die jaws (3.1, 3.2), in a use position, are placed against one another in such a way that a substantially U-shaped and/or pocket-shaped die recess that is open laterally and towards the punch is formed between the die guide surfaces (25.1, 25,2), - wherein the punch presses the closure band strip, with the strip ends (33.1, 33.2) of the bent strip legs (32.1, 32.2) first, into the die recess for closing, - wherein the die guide surfaces (25.1, 25.2) of the die jaws (3.1, 3.2) are formed to close the closure band strip in the die recess with mutually facing and/or overlapping strip ends (33.1, 33.2), characterized in that the punch unit is formed to pre-shape the closure band strip in a U-shape with two bent strip legs (32.1, 32.2), - wherein the die jaws (3.1, 3.2) each have at least one side cheek with a guide cam, wherein in the use position of the die jaws (3.1, 3.2), the side cheeks laterally encompass the die recess in any case in sections, wherein the guide cams have cam guide surfaces facing the die guide surfaces (25.1, 25.2), and wherein the guide cams engage in the die recess in such a way that the strip legs (32.1, 32.2) of the closure band strip are guided in the die between the mutually facing die guide surfaces (25.1, 25.2) and cam guide surfaces during reshaping, and - wherein the punch unit has a punch die with a punch recess in which the punch is guided, wherein the punch unit is formed for preshaping the closure band strip, and wherein the punch die is displaceable relative to the punch, and wherein the punch die of the punch unit is arranged such that the closure band strip can be severed from a closure band material by a first cutting edge (22.1) provided on the punch die being displaceable relative to a rigidly held second cutting edge (22.2). - a punch unit with a displaceable punch and - a die formed from at least two die jaws (3.1, 3.2) in a divided manner, which can be brought together, with mutually facing die guide surfaces (25.1, 25.2) for guiding the closure band strip, - wherein the die jaws (3.1, 3.2), in a use position, are placed against one another in such a way that a substantially U-shaped and/or pocket-shaped die recess that is open laterally and towards the punch is formed between the die guide surfaces (25.1, 25,2), - wherein the punch presses the closure band strip, with the strip ends (33.1, 33.2) of the bent strip legs (32.1, 32.2) first, into the die recess for closing, - wherein the die guide surfaces (25.1, 25.2) of the die jaws (3.1, 3.2) are formed to close the closure band strip in the die recess with mutually facing and/or overlapping strip ends (33.1, 33.2), characterized in that the punch unit is formed to pre-shape the closure band strip in a U-shape with two bent strip legs (32.1, 32.2), - wherein the die jaws (3.1, 3.2) each have at least one side cheek with a guide cam, wherein in the use position of the die jaws (3.1, 3.2), the side cheeks laterally encompass the die recess in any case in sections, wherein the guide cams have cam guide surfaces facing the die guide surfaces (25.1, 25.2), and wherein the guide cams engage in the die recess in such a way that the strip legs (32.1, 32.2) of the closure band strip are guided in the die between the mutually facing die guide surfaces (25.1, 25.2) and cam guide surfaces during reshaping, and - wherein the punch unit has a punch die with a punch recess in which the punch is guided, wherein the punch unit is formed for preshaping the closure band strip, and wherein the punch die is displaceable relative to the punch, and wherein the punch die of the punch unit is arranged such that the closure band strip can be severed from a closure band material by a first cutting edge (22.1) provided on the punch die being displaceable relative to a rigidly held second cutting edge (22.2).