1. A joining tool unit comprising a hold-down device with a movable tool and a tool counter element, wherein the hold-down device together with the movable tool and the tool counter element are provided opposite each other, wherein a workpiece can be positioned between the hold-down device and the tool counter element in an arranged state, wherein the movable tool and the tool counter element cooperate to form a joint connection by the moveable tool pushing against the workpiece and the tool counter element to deform the workpiece to form the joint connection, wherein a light guiding system is formed on the hold-down device, wherein the light guiding system is designed to conduct a light beam of a light in a direction of a joint location of the workpiece when the workpiece is arranged on the joining tool unit, wherein a flow channel for a fluid is defined along a section of the light beam of the light to a workpiece-side end of the hold-down device, wherein the flow channel has an inlet and a first outlet, wherein the first outlet for the fluid is formed on a workpiece-side end of the hold-down device, said outlet being in contact with the workpiece during a joining process, and wherein a second outlet at an end of an indentation of the flow channel and connected to a suction line in the hold-down device is provided, and wherein the movable tool is provided to be movable along a movement axis of the joining tool unit.