Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/03—Observing, e.g. monitoring, the workpiece
  • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/55—Specular reflectivity
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
  • B23K26/082—Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/20—Metals
  • G01N33/205—Metals in liquid state, e.g. molten metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/03—Observing, e.g. monitoring, the workpiece
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/20—Bonding
  • B23K26/21—Bonding by welding
  • B23K26/22—Spot welding

Definitions

• the present invention relates to a welded portion inspection apparatus and an inspection method thereof, and relates to an inspection apparatus that inspects a welding state of a welded portion formed at the time when a plurality of workpieces is welded by a laser beam, for example, and an inspection method thereof.
• JP 2008-87056 A describes a technique to perform a quality evaluation of laser beam welding by use of reflection light of a laser beam.
• a YAG laser is radiated from a laser torch, for example, and laser reflection light is received by first light receiving output means from a forward-diagonally upward side of a welding proceeding direction. Further, welding light including vapor light (plume) and the laser reflection light is received by second light receiving output means in a direction coaxial to a radiation direction of the laser beam. The laser reflection light and the welding light that are received simultaneously in two predetermined directions are converted into electrical signals according to their respective intensities. This system determines a welding quality based on the signal intensities of the electrical signals or changes thereof.
• the laser reflection light and the welding light are received simultaneously in two predetermined directions different from each other and their respective light receiving signal intensities are compared with a threshold set appropriately.
• weld shrinkage underfill
• unjoined weld in which upper and lower steel sheets are not joined due to an excessively large gap between the steel sheets
• depressed weld in which a bead is depressed similarly due to an excessively large gap between steel sheets
• molten weld in which a bead disappears accidentally due to fluctuation of a thermal balance
• vapor light caused due to melting and evaporation of the workpieces and thermal radiation light emitted from a molten pool of the workpieces change according to a workpiece temperature
• the electrical signals obtained from the received laser reflection light and the welding light and the threshold to determine the quality of the laser beam welding change according to the workpiece temperature. Because of this, in a case where the workpiece temperature largely fluctuates in the laser beam welding, the determination accuracy of the poor welding of the workpieces may further decreases.
• the present invention provides a welded portion inspection apparatus that is able to minutely inspect a welding state of a welded portion of workpieces in remote welding in which welding is performed such that the workpieces are spaced from a laser torch, and an inspection method thereof.
• a first aspect of the invention relates to a welded portion inspection apparatus that inspects a welding state of a welded portion formed at the time when a plurality of workpieces is welded.
• the welded portion inspection apparatus includes: a radiation portion that radiates a welding laser beam along a welding locus set in the workpieces so as to Weld the workpieces, or radiates an inspection laser beam along a scanning locus set in a molten pool of the workpieces that are molten by the welding laser beam; a light-receiving portion that receives a returned light beam including at least one of reflection light of the welding laser beam or the inspection laser beam radiated by the radiation portion, the reflection light being reflected from the molten pool of the workpieces, vapor light caused due to melting and evaporation of the workpieces, and thermal radiation light emitted from the molten pool of the workpieces; and an inspection portion that inspects a welding state of the welded portion of the workpieces based on an intensity
• the welding state of the welded portion of the workpieces is inspected based on the intensity change of the returned light beam received by the light-receiving portion at the time when the welding laser beam is radiated along the welding locus or at the time when the inspection laser beam is radiated along the scanning locus.
• the radiation portion may radiate the welding laser beam several times along the same welding locus or may radiate the inspection laser beam several times along the same scanning locus.
• the inspection portion may inspect the welding state of the welded portion of the workpieces based on a periodicity of the intensity change of the returned light beam at the time when the welding laser beam is radiated along the same welding locus or at the time when the inspection laser beam is radiated along the same scanning locus.
• the welding state of the welded portion of the workpieces is inspected based on the periodicity of the intensity change of the returned light beam at the time when the welding laser beam is radiated several times along the same welding locus or at the time when the inspection laser beam is radiated several times along the same scanning locus. Accordingly, even if an electrical signal obtained from a returned light beam at the time when the welding laser beam is radiated once along the welding locus or at the time when the inspection laser beam is radiated once along the scanning locus is weak or even if the electrical signal obtained from the returned light beam includes noise, it is possible to restrain a decrease of inspection accuracy due to the noise included in the returned light beam or the like. As a result, it is possible to increase the inspection accuracy of the welding state of the welded portion.
• a scanning period of the welding laser beam at the time when the welding laser beam is radiated along the same welding locus, or a scanning period of the inspection laser beam at the time when the inspection laser beam is radiated along the same scanning locus may be the same as an unique period of the intensity change of the returned light beam which is obtained when the welding state of the welded portion is normal.
• a liquid level of the molten pool formed in the workpieces by radiation of the welding laser beam vibrates at the same frequency as a unique frequency of the molten pool. Therefore, even if the welding state of the welded portion is normal, the intensity of the returned light beam received by the light-receiving portion changes periodically.
• the scanning period of the welding laser beam or the inspection laser beam is the same as that unique period of the intensity change of the returned light beam which is obtained when the welding state of the welded portion is normal.
• the scanning period of the welding laser beam or the inspection laser beam is a time during which the welding laser beam or the inspection laser beam scans a welding locus or a scanning locus having a predetermined length once, in a case where the welding laser beam is radiated several times along the same welding locus or the inspection laser beam is radiated several times along the same scanning locus. That is, the scanning period is a time obtained by dividing the length of the welding locus irradiated with the welding laser beam by a scanning speed of the welding laser beam, or a time obtained by dividing the length of the scanning locus irradiated with the inspection laser beam by a scanning speed of the inspection laser beam.
• the inspection portion may inspect the welding state of the welded portion of the workpieces by performing Fourier transform or differentiation on an intensity of the returned light beam.
• a second aspect of the invention relates to a welded portion inspection method that inspects a welding state of a welded portion formed at the time when a plurality of workpieces is welded.
• the welded portion inspection method includes radiating a welding laser beam along a welding locus set in the workpieces so as to weld the workpieces, or radiating an inspection laser beam along a scanning locus set in a molten pool of the workpieces that are molten by the welding laser beam; receiving a returned light beam including at least one of reflection light of the welding laser beam or the inspection laser beam which is reflected from the molten pool of the workpieces, vapor light caused due to melting and evaporation of the workpieces, and thermal radiation light emitted from the molten pool of the workpieces; and inspecting a welding state of the welded portion of the workpieces based on an intensity change of the returned light beam received at the time when the welding laser beam is radiated along the welding locus or at the time when the
• the welding state of the welded portion of the workpieces is inspected based on the intensity change of the returned light beam received at the time when the welding laser beam is radiated along the welding locus or at the time when the inspection laser beam is radiated along the scanning locus. Accordingly, in a case of remote welding in which welding is performed such that a laser radiation portion is spaced from the workpieces, for example, even if an electrical signal obtained from a received returned light beam is weak or even if an intensity of a received returned light beam changes according to a change of a workpiece temperature, it is possible to minutely inspect a welding state of a welded portion formed in the workpieces.
• the first and second aspects of the invention have such a simple configuration that in a case where a plurality of workpieces is welded, a welding state of a welded portion of the workpieces is inspected based on an intensity change of a returned light beam received at the time when a welding laser beam is radiated along a welding locus or at the time when an inspection laser beam is radiated along a scanning locus. Accordingly, even if an electrical signal obtained from the returned light beam is weak or even if an intensity of the returned light beam changes according to a change of a workpiece temperature, it is possible to minutely inspect the welding state of the welded portion of the workpieces. BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is an overall configuration diagram schematically illustrating an overall configuration of Embodiment 1 of a welded portion inspection apparatus of the present invention
• FIG. 2 is a top view to describe a form of radiation of a welding laser beam from a welding radiation portion of the inspection apparatus as illustrated in FIG. 1 ;
• FIG. 3 is a top view to describe a form of radiation of. an inspection laser beam from an inspection radiation portion of the inspection apparatus as illustrated in FIG. 1 ;
• FIG. 4 is a view illustrating an example of an intensity of a returned light beam in time series
• FIG. 5A is a top view to describe a relationship between a molten pool and a focal point of the inspection laser beam in a case where a welding state of a welded portion is normal;
• FIG. 5B is a view taken along an arrow VB-VB in FIG. 5A;
• FIG 6A a top view to describe a relationship between the molten pool and the focal point of the inspection laser beam in a case where the welding state of the welded portion is poor;
• FIG. 6B is a view taken along an arrow VIB-VIB in FIG. 6A;
• FIG. 7 is a view illustrating an example of a relationship between frequency and amplitude of the returned light beam
• FIG. 8 is an overall configuration diagram schematically illustrating an overall configuration of Embodiment 2 of the welded portion inspection apparatus of the present invention.
• FIG. 9A is a top view enlarging and illustrating a welded portion of an inspection sample according to Example 1 ;
• FIG. 9B is a view taken along an arrow ⁇ - ⁇ in FIG 9A;
• FIG 9C is a view illustrating an intensity of a returned light beam in the inspection sample according to Example 1 in time series;
• FIG. 10A is a top view enlarging and illustrating a welded portion of an inspection sample according to Example 2;
• FIG. 10B is a view taken along an arrow XB-XB of FIG. 10A;
• FIG. IOC is a view illustrating an intensity of a returned light beam in the inspection sample according to Example 2 in time series;
• FIG. 11 A is a top view enlarging and illustrating a welded portion of an inspection sample according to Example 3;
• FIG 1 IB is a view taken along an arrow XIB-XIB of FIG. 11 A;
• FIG. 11 C is a view illustrating an intensity of a returned light beam in the inspection sample according to Example 3 in time series;
• FIG. 12 is a view illustrating a relationship between frequency and amplitude in the returned light beams of the inspection samples according to Examples 1 to 3;
• FIG 13 is a view illustrating other examples of the relationship between frequency and amplitude in the returned light beams of the inspection samples according to Examples 1 to 3.
• Embodiment 1 of the welded portion inspection apparatus of the present invention with reference to FIGS. 1 to 3.
• FIG. 1 is an overall configuration diagram schematically illustrating an overall configuration of Embodiment 1 of the welded portion inspection apparatus of the present invention.
• FIG. 2 is a top view to describe a form of radiation of a welding laser beam from a welding radiation portion of the inspection apparatus as illustrated in FIG. 1
• FIG. 3 is a top view to describe a form of radiation of an inspection laser beam from an inspection radiation portion of the inspection apparatus.
• An inspection apparatus 100 illustrated in FIG. 1 is mainly constituted by a welding radiation portion 1 , an inspection radiation portion 5, a light-receiving portion 2, a conversion portion 3, an amplifier 4, an inspection portion 6, and a CRT (Cathode Ray Tube) 7.
• the welding radiation portion 1 radiates a welding laser beam (e.g., a YAG laser having a predetermined laser wavelength) LI to the two workpieces Wl, W2. More specifically, as illustrated in FIG. 2, the welding radiation portion 1 rotates a focal point Fl of the welding laser beam LI several times along a generally round-shaped welding locus Cl l having a radius Rl l set in the workpiece Wl , so as to radiate the welding laser beam LI several times on the welding locus CI 1.
• a welding laser beam e.g., a YAG laser having a predetermined laser wavelength
• the welding radiation portion 1 moves the focal point Fl of the welding laser beam LI inside the welding locus Cl l , and rotates the focal point Fl of the welding laser beam LI several times along a generally round-shaped welding locus CI 2 which has a radius R12 that is smaller than the radius Rl l and which is coaxial to the welding locus CI 1, so as to radiate the welding laser beam LI several times on the welding locus CI 2.
• a generally round-shaped welded portion is formed in the workpieces Wl, W2, thereby joining the workpieces Wl, W2 by welding (also referred to as Laser Screw Welding).
• a center CO of the welding locus Cll or the welding locus CI 2 is a welding center of the welded portion formed in the workpieces Wl, W2.
• a molten pool Yl where the workpieces Wl, W2 are molten is formed on right and left sides of the welding laser beam LI and behind the welding laser beam LI in a traveling direction of the welding laser beam LI .
• the welding laser beam LI is radiated along the generally round-shaped welding loci CI, C2 as described above, a generally round-shaped molten pool Yl is formed in the workpieces Wl, W2.
• the inspection radiation portion 5 radiates an inspection laser beam L5 to the molten pool Yl in a molten state via an optical system 8 and the light-receiving portion 2. More specifically, as illustrated in FIG. 3, the inspection radiation portion 5 rotates a focal point F5 of the inspection laser beam L5 several times at a generally constant speed along a generally round-shaped scanning locus C51 having a radius R51 set inside an outer edge of the molten pool Yl , so as to radiate the inspection laser beam L5 several times on the scanning locus C51.
• the inspection radiation portion 5 moves the focal point F5 of the inspection laser beam L5 inside the scanning locus C51 , and rotates the focal point F5 of the inspection laser beam L5 several times along a generally round-shaped scanning locus C52 which has a radius R52 that is smaller than the radius R51 and which is coaxial to the scanning locus C51 , so as to radiate the inspection laser beam L5 several times on the scanning locus C52.
• the inspection radiation portion 5 radiates the inspection laser beam L5 to a whole of the generally round-shaped molten pool Yl formed in the workpieces Wl , W2.
• a center of the scanning loci C51 , C52 is set to the aforementioned center CO of the welding loci CI 1, CI 2, for example.
• the light-receiving portion 2 receives a returned light beam L2 including reflection light of the inspection laser light L5 which is reflected from the molten pool Yl of the workpieces Wl, W2, vapor light (plasma light) caused due to melting and evaporation of the workpieces Wl, W2, thermal radiation light (infrared light) emitted from the molten pool Yl of the workpieces Wl, W2, and the like.
• a returned light beam L2 including reflection light of the inspection laser light L5 which is reflected from the molten pool Yl of the workpieces Wl, W2, vapor light (plasma light) caused due to melting and evaporation of the workpieces Wl, W2, thermal radiation light (infrared light) emitted from the molten pool Yl of the workpieces Wl, W2, and the like.
• the conversion portion 3 converts, into an electrical signal, the returned light beam L2 received by the light-receiving portion 2 and condensed via the optical system 8 and a condenser lens 9, and outputs the electrical signal to the amplifier 4.
• the amplifier 4 amplifies a signal intensity of the electrical signal output from the conversion portion 3, and transmits it to the inspection portion 6.
• the inspection portion 6 performs signal processing on the electrical signal transmitted from the amplifier 4, and inspects a welding state of the welded portion formed in the workpieces Wl, W2. More specifically, when the inspection laser beam L5 is radiated to the molten pool Yl from the inspection radiation portion 5 several times along the scanning loci C51 , C52, the inspection portion 6 detects an intensity change of the returned light beam L2 received by the light-receiving portion 2. Then, the inspection portion 6 inspects the welding state of the welded portion formed in the workpieces Wl, W2 based on a periodicity of the intensity change. Further, the inspection portion 6 transmits, to the CRT 7, a signal processing result on the electrical signal transmitted from the amplifier 4. The CRT 7 displays the signal processing result transmitted from the inspection portion 6.
• Embodiment 1 of a welded portion inspection method of the present invention by use of the welded portion inspection apparatus 100 illustrated in FIG. 1, with reference to FIGS. 4 to 7.
• FIG. 4 is a view illustrating, in time series, an example of that intensity of the returned light beam which is transmitted to the inspection portion 6 of the inspection apparatus 100 illustrated in FIG 1.
• FIG. 5 A is a top view to describe a relationship between the molten pool and the focal point of the inspection laser beam in a case where the welding state of the welded portion is normal
• FIG. 5B is a view taken along an arrow VB-VB of FIG. 5A.
• FIG. 6A is a top view to describe a relationship between the molten pool and the focal point of the inspection laser beam in a case where the welding state of the welded portion is poor
• FIG. 6B is a view taken along an arrow VIB-VIB of FIG. 6A.
• FIG. 7 is a view illustrating an example of a relationship between frequency and amplitude of the returned light beam on which the signal processing is performed by the inspection portion 6.
• the intensity of the returned light beam L2 received by the light-receiving portion 2 and transmitted to the inspection portion 6 via the conversion portion 3 and the amplifier 4 changes in part of one scanning period (e.g., a period during which the inspection laser beam L5 goes around a scanning period C5 once) of the inspection laser beam L5, and periodically changes every scanning period of the inspection laser beam L5.
• a liquid level of the molten pool Yl formed in the orkpieces Wl , W2 by radiation of the welding laser beam LI vibrates periodically, and it is found by the inventor(s) of the present invention that even in a case where the welding state of the welded portion is normal, the intensity of the returned light beam L2 changes periodically. That is, it is considered that one of the frequencies at which the amplitude peaks are detected in FIG. 7 is a unique frequency to the intensity change of the returned light beam L2 which unique frequency is obtained when the welding state of the welded portion is normal.
• a scanning speed of the inspection laser beam L5 is adjusted, for example, so that the scanning period (e.g., a period during which the inspection laser beam L5 goes around the scanning locus C51 or the scanning locus C52 once) of the inspection laser beam L5 accords with a unique period of the intensity change of the returned light beam L2.
• the scanning period e.g., a period during which the inspection laser beam L5 goes around the scanning locus C51 or the scanning locus C52 once
• intensity change of the returned light beam L2 transmitted to the inspection portion 6 which is obtained when the welding state of the welded portion is normal to be in a form of a generally sine curve (a dotted line in FIG. 4).
• the inspection laser beam L5 is radiated along the scanning loci C51, C52 set in the molten pool Yl formed by radiation of the welding laser beam LI . Then, the welding state of the welded portion is inspected based on the intensity change of the returned light beam L2 received by the light-receiving portion 2 at the time when the inspection laser beam L5 is radiated along the scanning loci C51, C52.
• FIG. 8 is an overall configuration diagram schematically illustrating an overall configuration of Embodiment 2 of the welded portion inspection apparatus of the present invention.
• An inspection apparatus 100A of Embodiment 2 as illustrated in FIG. 8 is different from the inspection apparatus 100 of Embodiment 1 as illustrated in FIG. 1 in that a welding state of a welded portion is inspected by use of reflection light of a welding laser beam radiated from a welding radiation portion.
• the other configuration is generally the same as the inspection apparatus 100 of Embodiment 1. Accordingly, constituents similar to those in Embodiment 1 have the same reference signs as those in Embodiment 1 and detailed descriptions thereof are omitted.
• the inspection apparatus 100A illustrated in the figure is mainly constituted by a welding radiation portion 1A, a light-receiving portion 2A, a conversion portion 3A, an amplifier 4A, an inspection portion 6A, and a CRT 7A.
• the welding radiation portion 1A radiates a welding laser beam LI A to the two workpieces Wl, W2 via an optical system 8 A and the light-receiving portion 2 A.
• a molten pool Yl where the workpieces Wl, W2 are molten is formed on right and left sides of the welding laser beam LI A and behind the welding laser beam LI A in a traveling direction of the welding laser beam LI A.
• the light-receiving portion 2A receives a returned light beam L2A including reflection light of the welding laser light LI A radiated from the welding radiation portion 1A, the reflection light being reflected from the molten pool Yl of the workpieces Wl , W2, vapor light (plasma light) caused due to melting and evaporation of the workpieces Wl , W2, thermal radiation light (infrared light) emitted from the molten pool Yl of the workpieces Wl, W2, and the like.
• a returned light beam L2A including reflection light of the welding laser light LI A radiated from the welding radiation portion 1A, the reflection light being reflected from the molten pool Yl of the workpieces Wl , W2, vapor light (plasma light) caused due to melting and evaporation of the workpieces Wl , W2, thermal radiation light (infrared light) emitted from the molten pool Yl of the workpieces Wl, W2, and the like.
• the conversion portion 3A converts, into an electrical signal, the returned light beam L2A received by the light-receiving portion 2A and condensed via the optical system 8A and a condenser lens 9A, and outputs the electrical signal to the amplifier 4A.
• the amplifier 4A amplifies a signal intensity of the electrical signal output from the conversion portion 3 A, and transmits it to the inspection portion 6A.
• the inspection portion 6A performs signal processing on the electrical signal transmitted from the amplifier 4A, and inspects a welding state of the welded portion formed in the workpieces Wl , W2. More specifically, the inspection portion 6A detects an intensity change of the returned light beam L2A received by the light-receiving portion 2A at the time when the welding laser beam LI A is radiated from the welding radiation portion 1A along a welding locus. Then, the inspection portion 6A inspects the welding state of the welded portion formed in the workpieces Wl , W2 based on a periodicity of the intensity change. Further, the inspection portion 6A transmits, to the CRT 7A, a signal processing result on the electrical signal transmitted from the amplifier 4A. The CRT 7A displays the signal processing result transmitted from the inspection portion 6A.
• the welding laser beam LI A is radiated along the welding locus at that unique period of the intensity change of the returned light beam L2A which is obtained when the welding state of the welded portion of the workpieces Wl , W2 is normal. Accordingly, it is possible to specify that unique frequency of the intensity change of the returned light beam L2A which is obtained when the welding state of the welded portion is normal, from specific frequencies at which amplitude peaks are detected by performing Fourier transform on the intensity of the returned light beam L2A, thereby making it possible to extract only a frequency caused due to a poor welding state of the welded portion, for example.
• Embodiment 1 described above deals with an embodiment in which the center of the scanning locus of the inspection laser beam is set to the center of the welding locus of the welding laser beam. However, it is possible to set the center of the scanning locus of the inspection laser beam to an appropriate position in the molten pool formed by radiation of the welding laser beam.
• the embodiments described above deal with an embodiment in which the welding locus of the welding laser beam and the scanning locus of the inspection laser beam have a generally round shape.
• the welding locus of the welding laser beam and the scanning locus of the inspection laser beam may have a closed loop shape such as an elliptical shape or a polygonal shape, a curved or linear shape having a predetermined length, or the like.
• the welding locus of the welding laser beam and the scanning locus of the inspection laser beam be set to pass through that part.
• the above embodiments deal with an embodiment in which the welding laser beam and the inspection laser beam are radiated to workpieces fixed to a predetermined position.
• focal positions of the welding laser beam and the inspection laser beam may be fixed and laser beam welding may be performed on the workpieces while the workpieces are being moved appropriately
• laser beam welding may be performed on the workpieces such that the workpieces and the focal positions of the welding laser beam and the inspection laser beam are moved relative to each other.
• the inventor(s) of the present invention manufactured three types of inspection samples (Examples 1 to 3) having different welding states, and performed intensity measurement of a returned light beam from each of the inspection samples so as to evaluate a relationship between an intensity change of the returned light beam and a welding state of a welded portion thereof.
• the following generally describes a manufacturing method of an inspection sample and a measurement method of an intensity of a returned light beam from an inspection sample.
• Two workpieces each made from SCGA440 having a thickness of 0.7 mm were put on top of one another, and a welding laser beam (with an output of 1000 W and at a scanning speed of 80 m/min) was radiated several times to the workpieces along a generally round-shaped welding locus so as to form a generally round-shaped welded portion having a radius of about 2.2 mm.
• an inspection laser beam (with an output of 1000 W and at a scanning speed of 80 m/min) was radiated to go around six times along a generally round-shaped scanning locus having a radius of about 1.5 mm so as to pass through a molten pool formed in the workpieces by radiation of the welding laser beam. Then, a focal point of the inspection laser beam was moved only by about 0.5 mm, and the inspection laser beam was radiated to go around ten times along a generally round-shaped scanning locus having a radius of about 1.0 mm.
• a returned light beam including reflection light of the welding laser beam which was reflected from the molten pool of the workpieces, vapor light caused due to melting and evaporation of the workpieces, thermal radiation light emitted from the molten pool of the workpieces, and the like was received, and a returned light beam including reflection light of the inspection laser light which was reflected from the molten pool of the workpieces, vapor light, thermal radiation light, and the like was received.
• the returned light beam thus received was converted into an electrical signal, and a signal intensity thereof was measured. Note that, in the returned light beam, particularly a signal intensity of the vapor light (plasma light) caused due to melting and evaporation of the workpieces was measured in this experiment.
• FIG. 9A is a top view enlarging and illustrating a welded portion of the inspection sample according to Example 1
• FIG. 9B is a view taken along an arrow IXB-IXB in FIG. 9A
• FIG. 9C is a view illustrating an intensity of a returned light beam in the inspection sample according to Example 1 in time series.
• FIG. 10A is a top view enlarging and illustrating a welded portion of the inspection sample according to Example 2
• FIG. IOC is a view illustrating an intensity of a returned light beam in the inspection sample according to Example 2 in time series.
• FIG. 11A is a top view enlarging and illustrating a welded portion of the inspection sample according to Example 3
• FIG. 1 IB is a view taken along an arrow XIB-XIB in FIG. 11 A
• FIG. 11C is a view illustrating an intensity of a returned light beam of the inspection sample according to Example 3 in time series.
• FIG. 12 is a view illustrating a relationship between frequency and amplitude at the time when fast Fourier transform was performed on an intensity of the returned light beam measured in the zone R2 (about 0.41 to about 0.46 sec) in which the inspection laser beam was radiated to the inspection sample according to each of Examples 1 to 3.
• the frequency (about 141 Hz) at which the amplitude peaks were found in the inspection samples of Examples 2 and 3 generally corresponds to a scanning frequency (1/(1.5 mm x 2 x 3.14/(80000 mm 60 sec)) Hz) of an inspection laser beam of a scanning speed of 80 m/min at the time when the inspection laser beam was radiated along the scanning locus having a radius of about 1.5 mm.
• the inventor(s) of the present invention calculated an unique frequency of the molten pool based on a surface tension and a density of the workpieces in a molten state, a magnitude and a thickness of the molten pool formed in the workpieces, etc.
• the scanning speed of the inspection laser beam was adjusted so that the scanning period of the inspection laser beam accorded with an unique period of the intensity changes of the returned light beams which is calculated from the unique frequency of the molten pool, and the inspection laser beam was radiated to the workpieces.
• FIG. 13 is a view illustrating a relationship between frequency and amplitude at the time when the inspection laser beam was radiated to the molten pool in Example 1 (the welding state is normal) at the unique period of the intensity change of the returned light beam and fast Fourier transform was performed on the intensity of the returned light beam (particularly, thermal radiation light emitted from the molten pool of the workpieces) measured in the zone R2.
• the zone R2 As illustrated in FIG. 13, even in a case where the welding state of the welded portion was normal, when fast Fourier transform was performed on the intensity of the returned light beam measured in the zone R2, a large amplitude peak was found at a specific frequency (about 195 Hz).

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• 2013
  • 2013-03-29 JP JP2013073202A patent/JP5947740B2/ja not_active Expired - Fee Related
• 2014
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• 2015
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