US 6,188,041 B1 · Method and apparatus for real-time weld process monitoring in a pulsed laser welding

Abstract

A method and apparatus for real-time weld process monitoring are provided for a pulsed laser welding. The thermal radiation from a weld pool is measured at several spectral bands through an aperture with single-element detectors after splitting the spectral bands with dichromatic mirrors and beam splitters. The distal end of an optical fiber for laser delivery can be used as an aperture and each spectral band signal is measured with a single-element detector. Due to the chromatic aberration of an imaging optics, the field of view from a single-element detector through the aperture is varied by the wavelength of spectral band. The weld pool size contributing to the spectral band signal varies by the wavelength of the spectral band. The transmittance profile of each spectral band also depends on the focus shift of imaging optics. By processing the measured spectral band signals, the size of a weld pool, the power variation on a workpiece and the focus shift of imaging optics can be monitored simultaneously. Furthermore, the weld pool sizes at predetermined positions in time are correlated to the weld depth and the weld defect such as a weld gap for weld quality assurance.

Claims32

Dependent claims

A method for real-time monitoring a weld pool size, a weld depth and a weld gap in a pulsed laser welding, the method comprising the steps of:

transmitting a plurality of laser pulses through an aperture which limits a size of a pulsed laser beam;
focusing transmitted laser pulses with at least one lens with large chromatic aberration but minimum spherical aberration on a workpiece;
sensing a thermal radiation from a weld pool through said at least one lens, and through said aperture;
separating the thermal radiation and the laser pulses with a dichromatic mirror;
splitting the thermal radiation with a dichromatic beam splitter into two spectral bands;
filtering each spectral band of the thermal radiation with a narrow band-pass optical filter;
detecting each narrow band-pass filtered thermal radiation with a detector during the laser pulses and between the laser pulses;
sampling electrical signals as detector signals from said detectors digitally for each laser pulse;
processing said two detector signals as processed signals;
and
analyzing the processed signals for real-time monitoring of the weld pool size, the weld depth and the weld gap.

8 more elements

A method for controlling a focus position of laser spot in a pulsed laser welding, the method comprising the steps of:

transmitting a plurality of laser pulses through an aperture which limits a size of a pulsed laser beam;
focusing transmitted laser pulses with at least one lens with some chromatic aberration but minimum spherical aberration on a workpiece;
sensing a thermal radiation from a weld pool through said at least one lens, and through said aperture;
separating the thermal radiation and the laser pulses with a dichromatic mirror;
splitting the thermal radiation with a dichromatic beam splitter into a plurality of spectral bands;
filtering each spectral band of the thermal radiation with a narrow band-pass optical filter;
detecting each narrow band-pass filtered thermal radiation with a detector during the laser pulses and between the laser pulses;
sampling electrical signals as digitized detector signals from said detectors for each laser pulse;
processing a plurality of digitized detector signals;
and
analyzing processed signals for real-time control of focus position.

8 more elements

A method for real-time monitoring a laser power variation on a workpiece in a pulsed laser welding, the method comprising the steps of:

transmitting a plurality of laser pulses through an aperture which limits a size of a pulsed laser beam;
focusing transmitted laser pulses with at least one lens with minimum spherical aberration on the workpiece;
sensing a thermal radiation from a weld pool through said at least one lens, and through said aperture;
separating the thermal radiation and the laser pulses with a dichromatic mirror;
filtering the thermal radiation with a narrow band-pass optical filter;
detecting narrow band-pass filtered thermal radiation with a detector during the laser pulses and between the laser pulses;
sampling electrical signals as digital detector signals from said detector for each laser pulse;
processing said digital detector signals;
and
analyzing processed signals for real-time monitoring of a laser power variation on the workpiece.

7 more elements

Dependencies are inferred from the claim text.

Method and apparatus for real-time weld process monitoring in a pulsed laser welding

Life of this patent

Method and apparatus for real-time weld process monitoring in a pulsed laser welding

Life of this patent

Abstract

Claims32