Method and apparatus for monitoring laser weld quality via plasma size measurements

A method of monitoring weld quality of a laser welding process in which a laser beam impinges onto a surface of a workpiece and a plasma is produced above the surface of the workpiece, the method comprising the steps of:

• a) providing a predetermined value of at least one physical dimension of the plasma above the surface of the workpiece, the predetermined value being determined under laser welding process conditions that produce acceptable quality welds;
• b) monitoring the spatial distribution of the intensity of light emitted from the plasma during the welding process, the light being monitored along an optical axis substantially parallel to the surface of the workpiece and at a height less than 0.5 mm above the surface of the workpiece as a function of time;
• c) assigning a value of the physical dimension of the plasma based on the intensity of light monitored in step (b) as a function of time during the laser welding process;
• and
• d) comparing the value of the physical dimension of the plasma assigned in step (c) to the predetermined value, wherein the weld formed during the laser welded process is evaluated as acceptable quality for values of the physical dimension of the plasma assigned in step (c) within a predetermined range of the predetermined value of the physical dimension.

A method of monitoring a laser welding process in which a laser beam impinges onto a surface of a workpiece to form a weld and a plasma is produced surrounding the surface of the workpiece, the method comprising the steps of:

• a) monitoring the intensity of light emitted from the plasma along an optical axis substantially parallel to the surface of the workpiece and at a height less than 0.5 mm above the surface as a function of time during the laser process;
• b) assigning a numerical value representative of at least one physical dimension of the plasma to the monitored intensity of light, the numerical value being assigned as a function of time during the laser process;
• and
• c) evaluating the numerical value for dips representing changes in the numerical value of a predetermined magnitude and ration as a function of time during the laser welding process, wherein the dips representing welds of unacceptable quality.

An apparatus for monitoring a laser welding process in which a laser beam impinges onto a surface of a workpiece to form a weld and a plasma is produced surrounding the surface, the apparatus comprising:

• a) means for monitoring the intensity of light emitted from the plasma along an optical axis substantially parallel to the surface of the workpiece and at a height less than 0.5 mm above the surface as a function of time during the laser welding process;
• b) means for determining from the monitored intensity of light a numerical value representative of at least one physical dimension of the plasma, the numerical value being determined as a function of time during the laser welding process;
• and
• c) means for calculating a time-averaged value of the numerical value for at least a portion of the laser welding process.

An apparatus for monitoring a laser welding process in which a laser beam is directed onto a surface of a workpiece to form a weld and a plasma is produced above the surface, the apparatus comprising:

• a) means for monitoring the intensity of light emitted from the plasma along an optical axis substantially parallel to the surface of the workpiece and at a height less than 0.5 mm above the surface as a function of time during the laser welding process;
• b) means for determining a numerical value representative of at least one of the plasma width and the plasma height from the monitored intensity of light as a function of time during the laser welding process;
• and
• c) display means for displaying the numerical value as a function of time during the laser welding process.