Laser welding quality inspection method and laser welding quality inspection apparatus

1. A laser welding quality inspection method of a welded portion between a joining object and a joined object, when the joining object and the joined object are welded by being irradiated with a laser beam, the method comprising:

acquiring first data indicating a signal intensity of thermal radiation light radiated from the welded portion during the welding;

acquiring second data indicating a signal intensity of plasma light radiated from the welded portion during the welding; and

determining whether or not the welded portion includes an abnormality based on a difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light which are acquired,

wherein the determining whether or not the welded portion includes an abnormality based on a comparison between the signal intensity of the thermal radiation light and the signal intensity of the plasma light which are acquired includes:

calculating a difference signal indicating the difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light,

determining that the welded portion includes an abnormality when the calculated difference signal includes a peak having a signal intensity larger than a preset determination reference value, and

acquiring an irradiation output waveform indicating an intensity of irradiation light of the laser beam by measuring the irradiation light of the laser beam during the welding,

wherein the calculating a difference signal indicating a difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light includes:

setting, as a determination period, a period during which the intensity of the irradiation light of the laser beam is constantly maintained, based on the irradiation output waveform,

extracting the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period respectively from the signal intensity of the thermal radiation light and the signal intensity of the plasma light which are acquired, and

calculating a difference between the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period, as the difference signal.

2. The laser welding quality inspection method of claim 1 ,

wherein the calculating a difference signal indicating a difference between the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period includes:

calculating a normalization signal of the thermal radiation light and a normalization signal of the plasma light by respectively normalizing the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period, and

calculating a difference signal indicating a difference between the normalization signal of the thermal radiation light and the normalization signal of the plasma light.

3. The laser welding quality inspection method of claim 2 ,

wherein in the calculating a normalization signal of the thermal radiation light and a normalization signal of the plasma light, the following expressions are satisfied

Hm ( t )=( H ( t )− m av )/ m av   [Equation 1]:

Sn ( t )=( S ( t )− n av )/ n av   [Equation 2]:

where m av is an average value of the signal intensity of the thermal radiation light within the determination period,

n av is an average value of the signal intensity of the plasma light within the determination period,

H(t) is a time function of the signal intensity of the thermal radiation light before being normalized within the determination period,

S(t) is a time function of the signal intensity of the plasma light before being normalized within the determination period,

Hm(t) is a time function of the normalization signal of the thermal radiation light within the determination period, and

Sn(t) is a time function of the normalization signal of the plasma light within the determination period.

4. The laser welding quality inspection method of claim 2 ,

wherein in the calculating a normalization signal of the thermal radiation light and a normalization signal of the plasma light, the following expressions are satisfied

Hm ( t )=( H ( t )− m av ( t ))/ m av ( t )  [Equation 3]:

Sn ( t )=( S ( t )− n av ( t ))/ n av ( t )  [Equation 4]:

where m av (t) is an average value of a time function of the signal intensity of the thermal radiation light of a plurality of times of welding determined to have no abnormality in the welded portion within the determination period,

n av (t) is an average value of a time function of the signal intensity of the plasma light of the plurality of times of welding within the determination period,

H(t) is a time function of the signal intensity of the thermal radiation light before being normalized within the determination period,

S(t) is a time function of the signal intensity of the plasma light before being normalized within the determination period,

Hm(t) is a time function of the normalization signal of the thermal radiation light within the determination period, and

Sn(t) is a time function of the normalization signal of the plasma light within the determination period.

5. A laser welding quality inspection method of a welded portion between a joining object and a joined object, when the joining object and the joined object are welded by being irradiated with a laser beam, the method comprising:

acquiring first data indicating a signal intensity of thermal radiation light radiated from the welded portion during the welding;

acquiring second data indicating a signal intensity of plasma light radiated from the welded portion during the welding; and

determining whether or not the welded portion includes an abnormality based on a difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light which are acquired,

wherein the signal intensity of the thermal radiation light includes a first thermal radiation light intensity indicating an intensity of the thermal radiation light at a first time point during the welding, and a second thermal radiation light intensity indicating an intensity of the thermal radiation light at a second time point different from the first time point during the welding,

wherein the signal intensity of the plasma light includes a first plasma light intensity indicating an intensity of the plasma light at the first time point and a second plasma light intensity indicating an intensity of the plasma light at the second time point, and

wherein the comparison between the signal intensity of the thermal radiation light and the signal intensity of the plasma light includes calculating a first difference value indicating a difference between the first thermal radiation light intensity and the first plasma light intensity, and a second difference value indicating a difference between the second thermal radiation light intensity and the second plasma light intensity, and generating a difference signal including the first difference value and the second difference value.

6. The laser welding quality inspection method of claim 5 ,

wherein the determining whether or not the welded portion includes an abnormality based on a comparison between the signal intensity of the thermal radiation light and the signal intensity of the plasma light which are acquired includes

calculating a difference signal indicating the difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light, and

determining that the welded portion includes an abnormality when the calculated difference signal includes a peak having a signal intensity larger than a preset determination reference value.

7. The laser welding quality inspection method of claim 6 , further comprising:

acquiring an irradiation output waveform indicating an intensity of irradiation light of the laser beam by measuring the irradiation light of the laser beam during the welding,

wherein the calculating a difference signal indicating a difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light further includes

setting, as a determination period, a period during which the intensity of the irradiation light of the laser beam is constantly maintained, based on the irradiation output waveform, and

extracting the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period respectively from the signal intensity of the thermal radiation light and the signal intensity of the plasma light which are acquired, and

wherein the calculating a difference signal indicating a difference between the signal intensity of the thermal radiation light and the signal intensity of the plasma light includes calculating a difference between an intensity of the thermal radiation light within the determination period and an intensity of the plasma light within the determination period.

8. The laser welding quality inspection method of claim 7 ,

wherein the calculating a difference signal indicating a difference between the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period includes:

calculating a normalization signal of the thermal radiation light and a normalization signal of the plasma light by respectively normalizing the signal intensity of the thermal radiation light within the determination period and the signal intensity of the plasma light within the determination period, and

calculating a difference signal indicating a difference between the normalization signal of the thermal radiation light and the normalization signal of the plasma light.

9. The laser welding quality inspection method of claim 8 ,

wherein in the calculating a normalization signal of the thermal radiation light and a normalization signal of the plasma light, the following expressions are satisfied

Hm ( t )=( H ( t )− m av )/ m av   [Equation 1]:

Sn ( t )=( S ( t )− n av )/ n av   [Equation 2]:

where m av is an average value of the signal intensity of the thermal radiation light within the determination period,

n av is an average value of the signal intensity of the plasma light within the determination period,

H(t) is a time function of the signal intensity of the thermal radiation light before being normalized within the determination period,

S(t) is a time function of the signal intensity of the plasma light before being normalized within the determination period,

Hm(t) is a time function of the normalization signal of the thermal radiation light within the determination period, and

Sn(t) is a time function of the normalization signal of the plasma light within the determination period.

10. The laser welding quality inspection method of claim 8 ,

wherein in the calculating a normalization signal of the thermal radiation light and a normalization signal of the plasma light, the following expressions are satisfied

Hm ( t )=( H ( t )− m av ( t ))/ m av ( t )  [Equation 3]:

Sn ( t )=( S ( t )− n av ( t ))/ n av ( t )  [Equation 4]:

where m av (t) is an average value of a time function of the signal intensity of the thermal radiation light of a plurality of times of welding determined to have no abnormality in the welded portion within the determination period,

n av (t) is an average value of a time function of the signal intensity of the plasma light of the plurality of times of welding within the determination period,

H(t) is a time function of the signal intensity of the thermal radiation light before being normalized within the determination period,

S(t) is a time function of the signal intensity of the plasma light before being normalized within the determination period,

Hm(t) is a time function of the normalization signal of the thermal radiation light within the determination period, and

Sn(t) is a time function of the normalization signal of the plasma light within the determination period.