Method for detecting and identifying defects in a laser beam weld seam

• US 20040032597A1
• Filed: 12/30/2002
• Published: 02/19/2004
• Est. Priority Date: 07/06/2000
• Status: Active Grant

• Current Assignee: Aerospatiale Matra Ccr
• Original Assignee: Aerospatiale Matra Ccr
• Inventors: Esmiller, Bruno
• Granted Patent: US 6,937,329 B2
• Time in Patent Office: Days
• US Class Current: 356/636
• CPC Class Codes: B23K 1/0056 soldering by means of beams, e.g. lasers, E.B.
• CPC Class Codes: B23K 26/032 using optical means
• CPC Class Codes: B23K 26/242 Fillet welding, i.e. involving a weld of substantially triangular cross section joining two parts
• CPC Class Codes: B23K 31/125 Weld quality monitoring

Abstract

A method for detection and identification of defects in a weld seam created using a laser beam.

According to this method, at least two measurement signals are acquired in real time delivered by optical sensors (C1 to C6) detecting variations in luminous intensity of the plasma formed by the laser beam (14). These signals are then combined by applying a mathematical operation. The combined signal obtained is then compared to a predetermined threshold. Depending on the result of this comparison, a determination is made of the presence or absence of a defect corresponding to the operator used.

Claims

1. A method for detecting and identification of defects at the time of realizing a welding seam (6) by means of a laser beam (14) forming a plasma in a welding region, according to which at least tow measurement signals are acquired in real time, said signals being supplied by distinct optical sensors (C1 to C6) that detect the variations in luminous intensity of the plasma, characterized in that the measurement signals are combined by applying to them at least one mathematical operator suitable for detecting a corresponding defect, in order to obtain at least one combined signal;

each combined signal is compared to a predefined threshold and the presence or absence of a defect is diagnosed that corresponds to each mathematical operator according to the result of the comparison.

2. A method according to claim 1 in which the mathematical operator is chosen from the group comprising addition, subtraction, multiplication, division and a combination thereof.

3. A method according to claim 2 applied to welding of a stiffener (12) onto a metal plate (1) using two laser beams (14) arranged on either side of the stiffener, wherein two groups of at least one optical sensor (C1, C2, C3, C4, C5, C6) are used and disposed on either side of the stiffener;

said optical sensors of the two groups being identical, the measurement signals supplied by one sensor of each group are added and the presence of an insufficient interpenetration of the welding seams owing to insufficient laser beam power is detected when the result is lower than a predefined first threshold.

4. A method according to any one of claims 2 and 3, applied to welding of a stiffener (12) onto a metal plate (10) using two laser beams arranged on either side of the stiffener, wherein two groups of at least two optical sensors (C1, C2, C3;

C4, C5, C6) are used and detecting variations in luminous intensity of the plasma in different optical bands;

said optical sensors of the two groups being identical, the measurement signals supplied on the one hand by a first pair of identical sensors are added and on the other hand the measurement signals supplied by a second pair of identical sensors are added;

the one sum is multiplied by the other sums so obtained and an inadequate interpenetration of the welding seams is detected, which due to a defect other than insufficient laser beam power, when the result is greater than a predefined second threshold.

5. A method according to any one of claims 2 to 4, applied to soldering of a stiffener (12) onto a metal plate (10) using two laser beams (14) arranged on either side of the stiffener, the stiffener and the metal plate being positioned in advance relative to each other by welding points, wherein two groups of at lest one optical sensor (C1, C2, C3;

C4, C5, C6) are used and disposed on either side of the stiffener, the one of the two groups of optical sensors of being identical, the measurement signals supplied by two identical sensors being divided by each other and the presence of previously positioned welding points being detected as deficient, when the result is greater than the third predefined threshold.

6. A method according to any one of claims 2 to 5, applied to welding of a stiffener (12) onto a metal plate (10) using two laser beams (14) placed on either side of the stiffener, wherein two groups of at least two sensors (C1, C2, C3;

C4, C5, C6) are used that detect variations in the luminous intensity of the plasma in different optical bands, dispose on either side of the stiffener;

the optical sensors of the two groups being identical, on the one hand the measurement signals supplied by a first pair of identical sensors and on the other hand the measurement signals supplied by the second pair of identical sensors are added;

the one of the sums is divided by the other of the two sums, and an insufficient welding seam width is detected, when the result of the division is less than a fourth predefined threshold.

7. A method according to any one of claims 1 and 2, applied to edge-to-edge welding of two metal plates using a single laser beam, wherein at least two optical sensors are used that detect variations in the luminous intensity of the plasma in different optical bands, the one measurement signal is divided by the other measurement signal of the measurement signals supplied by two of the sensors and an insufficient thickness of the welding seam is detected, when the result obtained is less than a first threshold and an absence of welding, when the result is greater than a second threshold, greater than the first.

8. A method according to any one of the above claims, wherein the measurement signals are acquired by means of a group of three sensors (C1, C2, C3;

C4, C5, C6), the sensors of each group detecting the variations in luminous emission of the plasma in a principally ultraviolet frequency band, a principally visible frequency band, and a principally infrared frequency band, respectively.

9. A method according to any one of the above claims, wherein optical sensors are used (C1, C2, C3;

C4, C5, C6) are used each comprising a fiberoptic (16-1 to 16-6), of whose first end is arranged in proximity to the welding region, an optical filter (18-1 to 18-6) is disposed in the extension of the second end of the fiberoptic and a photodiode (20-1 to 20-6) is disposed facing the second end o the fiberoptic, on the other side of the filter.

10. A method according to claim 9, wherein the first end of the fiberoptic is disposed approximately 10 cm form the welding region.

11. A method according to any one of the above claims, wherein a supplementary measurement signal is obtained by means of another optical sensor (C7), detecting variations in thermal energy of the welding seam in back of the welding region.

12. A method according to claim 11, wherein the other optical sensor (C7) comprises another fiberoptic (16-7), whose first end is disposed behind the welding region and oriented—

-towards the welding seam and a photodiode (20-7) sensible to thermal radiation is arranged in the extension of the second end of the other fiberoptic.

13. A method according to claim 12, wherein the first end of the other fiberoptic (16-7) is disposed at a distance of between approximately 10 cm and 20 cm from the welding region.

14. A method according to any one of claims 12 and 13, wherein an optical focussing means (22-7) is arranged at the first end of the other fiberoptic (167).

15. A method according to any one of the above claims, wherein the measurement signals are combined and are compared to said predefined thresholds after said signals have been acquired in real-time for the welding seam being considered.

16. A method according to claim 15, wherein the mean, the standardized mean, then the standard deviation of each measurement signal is calculated and a qualitative welding irregularity is diagnosed, when the standard deviation exceeds a predefined value.

17. A method according to claim 16, wherein the mean of each measurement signal is compared to the previous means of said signal recorded for a given number of welding seams inspected previously and a deterioration in the measurement apparatus is diagnosed, when the mean of the signal has shifted by at least about 30% relative to the previous means.