Device for the Laser Transmission Welding of an Annular Weld Seam

A device for the laser transmission welding of an annular weld seam between a first component part and a second component part, the device comprising:

• a welding unit with a tube, the tube having a tube axis and an inner circumferential surface of the tube being reflective of laser radiation emitted by a laser radiation unit;
• a beam input-side tube end, and a beam output-side tube end;
• the laser radiation unit arranged at the beam input-side tube end with a radiating direction in direction of the tube axis;
• a mandrel coaxially arranged in the tube and connected to the tube via a holding unit, the mandrel having a first mandrel part facing the beam input-side tube end, the first mandrel part having a first base area shaped as a right cone, a right conical frustum, a right pyramid or a right pyramidal frustum with a central angle (α) of less than 90° opening toward the beam output-side tube end, the mandrel further having a second mandrel part facing the beam output-side tube end, the second mandrel part having a second base area shaped as a right cylinder or a right prism, wherein the first base area and the second base area are adapted to one another, and wherein circumferential surfaces of the mandrel which face the tube are reflective of the laser radiation such that the laser radiation is annularly shaped and is deflected toward the beam output-side tube end through multiple reflections between the tube and the mandrel.