Method for monitoring an attachment area during the laser welding of bent bar-type conductors containing copper

A method for monitoring an attachment area during laser welding of bent bar-type conductors containing copper, the method comprising:

• arranging a first bar-type conductor relative to a second bar-type conductor in partially overlapping fashion;
• welding the first and second bar-type conductors to one another using a processing laser beam, the welding including forming a weld bead interconnecting the first and second bar-type conductors to one another;
• after the welding, measuring on at least one portion of the weld bead at least one measurement variable that changes with a temperature of the weld bead as a function of time during a cooling down of the weld bead;
• determining a parameter depending on a heat capacity of the weld bead from the at least one measured measurement variable;
• determining the attachment area qualitatively or quantitatively from the parameter;
• and
• welding a multiplicity of pairs of bar-type conductors in succession, with one or more welding parameters being optimized and/or updated in a control loop when the pairs of bar-type conductors are welded such that the parameter or an-the attachment area quantitatively determined from the parameter is set to a specified target value for the pairs of welded bar-type conductors.

An apparatus for laser welding bent bar-type conductors containing copper, the apparatus comprising:

• a holding device configured to arrange two bar-type conductors in overlapping fashion, the holding device comprising a stator mount with a multiplicity of bar-type conductors to be welded;
• a laser processing head configured to provide a processing laser beam configured to weld the two bar-type conductors to one another such that a weld bead interconnecting the two bar-type connectors is formed;
• a sensor device configured to measure at least one measurement variable that changes with a temperature of the weld bead on a portion of the weld bead following an end of exposure to the processing laser beam and while the weld bead cools down, wherein the sensor device comprises a camera or a photodiode, and wherein the at least one measurement variable comprises an intensity of a thermionic emission from the portion of the weld bead determined by a mean grayscale value from a partial region of an image recorded by the camera or a grayscale value recorded by the photodiode;
• an electronic evaluation device configured to:
• determine a parameter depending on a heat capacity of the weld bead from the at least one measurement variable, and
• qualitatively or quantitatively determine an attachment area set up by the weld bead from the parameter.