Method and device for measuring the depth of the vapor capillary during a machining process with a high-energy beam

Apparatus for measuring a depth of a vapor capillary during a high energy beam machining process, wherein the apparatus comprises:

• an optical coherence tomograph configured to perform the following steps:
• a) directing an optical measuring beam to the bottom of the vapor capillary formed in an area of interaction between a workpiece and a high energy beam;
• b) detecting reflections of the measuring beam in the optical coherence tomograph;
• c) generating raw measurement data from the reflections detected in the optical coherence tomograph;
• and
• d) repeating steps a) to c) at several times ti, where i=1, 2, 3, . . . , during the machining process, wherein a set of raw measurement data for a first distance (a1) to the bottom of the vapor capillary is obtained for each time ti, and
• an evaluation device, which is configured to carry out the following steps:
• e) calculating a set of undisturbed measurement data for a time tn by commonly processing in a mathematical operation a first set of raw measurement data generated at the time tn and a second set of raw measurement data generated at an earlier time tm, where m<n;
• f) calculating a final value for the first distance (a1) at time tn from the set of undisturbed measurement data calculated in step e);
• and
• g) calculating the depth of the vapor capillary wherein a measured second distance (a2) to a portion of the surface of the workpiece that is not exposed to the high energy beam is subtracted from the final value for the first distance (a1) calculated in step f).

Apparatus for measuring a depth of a vapor capillary during a high energy beam machining process, wherein the apparatus comprises:

• a spectral domain optical coherence tomograph configured to perform the following steps:
• a) directing an optical measuring beam to the bottom of the vapor capillary formed in an area of interaction between a workpiece and the high energy beam;
• b) detecting reflections of the measuring beam in the spectral domain optical coherence tomograph;
• c) generating raw measurement data from the reflections detected in the spectral domain optical coherence tomograph;
• and
• d) repeating steps a) to c) at several times ti, where i=1, 2, 3, . . . , during the machining process, wherein a set of raw measurement data for a first distance (a1) to the bottom of the vapor capillary is obtained for each time ti, wherein each set of raw measurement data represents an interference spectrum, which is generated by the spectral domain optical coherence tomograph, and
• an evaluation device, which is configured to carry out the following steps:
• e) calculating a set of undisturbed measurement data for a time tn by commonly processing in a mathematical operation a first set of raw measurement data generated at the time tn and a second set of raw measurement data generated at an earlier time tm, where m<n, wherein in the mathematical operation the interference spectrum generated at the time tn is divided by an averaged spectrum representing an average of a plurality of interference spectra which were generated at earlier times tj, where j≤m;
• f) calculating a final value for the first distance (a1) at time tn from the set of undisturbed measurement data calculated in step e);
• and
• g) calculating the depth of the vapor capillary wherein a measured second distance (a2) to a portion of the surface of the workpiece that is not exposed to the high energy beam is subtracted from the final value for the first distance (a1) calculated in step f).