Joining tool unit, tool gripper, and joining process

A joining tool unit comprising a holding-down device with a linearly movable tool, and a tool counter-element,

• wherein the holding-down device with the linearly movable tool and the tool counter-element are located opposite each other, wherein a workpiece in the arranged state at the joining tool unit rests on the tool counter-element, wherein the holding-down device in the arranged state of the workpiece at the joining tool unit is arrangeable so as to abut a surface of the workpiece, wherein the holding-down device has a light guidance system,
• wherein the light guidance system is designed to guide a light beam of light in the direction of a joining site of the workpiece when the workpiece is arranged at the joining tool unit, wherein the light guidance system is present at the holding-down device in such a way that the light beam irradiates the joining site exclusively at an angle of greater than 0° to a movement axis of the linearly movable tool, wherein the light guidance system of the holding-down device shields the light along its light beam against the outside in a light-tight manner, wherein the light guidance system is integrated in the holding-down device such that the light beam can be brought directly to the workpiece, wherein the light-tight shielding at the holding-down device by way of the light guidance system is set up due to the line of the light guidance system within the holding-down device carved out from the solid material of the holding-down device, and
• wherein the holding-down device is designed in such a way that in the arranged state of a workpiece at the joining tool unit, the holding-down device is arrangeable so as to abut the surface of the workpiece such that the holding-down device encloses the joining site so that a maximum of 20% of the radiant power of the light is emitted to the outside between the holding-down device and the surface.