JPS5933078B2 - Laser welding method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser welding method and apparatus for non-destructively measuring the depth of welding.

When spot welding thin plates or the like using a laser beam, knowing the size of the fusion zone, especially its depth, is important in order to ensure the strength of the weld.

However, the conventional measuring method involves a destructive inspection in which the molten part is cut and the cross section is examined, which is extremely inappropriate for practical use. In the present invention, when two or more stacked welding members are welded by irradiating a laser beam, a change in the surface microstructure is caused on the side opposite to the laser beam irradiation side, which is thought to be due to welding thermal strain. is approximately proportional to the depth of melting,
In particular, by taking advantage of the fact that the conditions at which changes begin to occur are often the optimum conditions for welding, changes in the surface microstructure can be optically measured to enable non-destructive and optimal laser welding. It is something.

The present invention will be explained in detail below.

As described above, when two or more welded members such as thin plates stacked one on top of the other are irradiated with a laser beam and welded, a change in the microstructure occurs on the side opposite to the side irradiated with the laser beam, that is, on the back side.

Normally, this change in the microstructure of the surface is of the same magnitude or smaller than the ridges b on the surface, and therefore cannot be easily detected by normal methods. However, when the back surface is irradiated with a coherent laser beam, a granular light intensity distribution called speckle, which is determined depending on the surface microstructure, is generated in the reflected light.
Therefore, by measuring the spatial difference in the intensity distribution of speckles generated on the back surface before and after welding, changes in the surface microstructure can be known, and from this, the optimal laser welding conditions can be determined. Figure 1 is a diagram of one embodiment.
Wl and W2 are thin plate-like welding members installed with parts overlapped with each other; 1 is a condensing lens of a laser irradiation device installed on the surface of the welding member W, and the light is emitted from a laser oscillator (not shown). The laser beam L1 is focused by this condensing lens 1,
The light is irradiated onto one surface of the welding member, that is, the surface W1.

These laser oscillators and condensing lenses are welded parts Wl, W,
This is a first laser irradiation device for welding. 2 is a melted part produced by irradiation with the laser beam L1, and 3 is a thermally strained part produced around it.

The depth of the molten part, that is, the weld, reaches to the welded member W2 located on the opposite side of the laser beam irradiation side, and both welded parts Wl
, W, are welded with sufficient strength, and in this case, the thermally strained portion reaches the back surface of the welded member W, which is located on the opposite side. 5 is a condenser lens of a second laser irradiation device separate from the first laser irradiation device installed beside the welding member W2, and the laser beam L2 emitted from the laser oscillator of the second laser irradiation device (not shown) is The condensing lens 5 condenses the laser beam L, and irradiates the opposite side of the irradiation part of the laser beam L, that is, the thermally strained part on the back surface of the welding member W2.

L3 is the reflected light caused by the irradiation of this laser beam L2, 6
is a television camera installed within the area of this reflected light L3,
A detector with two-dimensional expansion such as a solid optical element, 7 a memory circuit connected to this detector, 8 a calculation circuit connected to this memory circuit, and these 6 to 8 measure the depth of welding. This is a measurement circuit. Reference numeral 9 denotes a laser oscillation automatic adjustment device for the first laser irradiation device connected to the arithmetic circuit.

Next, the welding method using this device will be described.

First, welding members Wl and W are placed one on top of the other and installed at a welding position between the first and second laser irradiation devices. Therefore, the welding member W is irradiated with laser light L2 from the second laser irradiation device.
The intensity distribution of the speckle before welding reflected from the surface of 2 is stored in the detection L storage circuit 7 by the detector 6. Next, the first laser irradiation device irradiates the welding member W1 with a laser beam L1 to weld the welding members W1 and W2, and then the second laser irradiation device irradiates the laser beam L, and the welding after welding is performed. The detector 6 detects the intensity distribution of the surface reflected from the surface of the member W2. Then, via the memory circuit, the arithmetic circuit 8 calculates the difference in the intensity distribution of speckles before and after welding, calculates the amount of change in the surface microstructure of the welding member W2 from the difference, and calculates the welding depth from the result. do. Then, this welding depth amount is output to the laser oscillation automatic adjustment device 9 of the first laser irradiation device, and the laser oscillation conditions for welding are adjusted to be optimal. In this way, stable and optimal laser welding can be performed at all times.

In FIGS. 2 and 3, the incident direction of the measurement laser beam L2 and the speckle detection direction are changed from those shown in FIG. 1.

Therefore, the same parts as in FIG. 1 are given the same numbers, and different parts will be described in detail. FIG. 2 shows that a semi-transparent mirror 11 is provided between the welding member W2 and the condensing lens 5, and the reflected light of the laser beam L2 is incident almost perpendicularly onto the surface of the welding member W2 through the condensing lens 5. , the vertically reflected light having the largest intensity distribution is guided to the detector 6 by the semi-transparent mirror 11. In addition, in FIG. 3, the laser beam L2 is irradiated obliquely onto the surface of the welding member W2 (θ
(tilt), and at this time, specularly reflected light having the largest intensity distribution is made to enter the detector 6.

When the device is configured and arranged as in these examples, the detector 6
The S/N ratio can be significantly improved, and even better welding can be performed than in the embodiments described above. In each of the above embodiments, the spatial distribution of speckles was detected by the detector 6, and the distribution before and after welding was memorized and calculated, but in FIG. 4, the spatial distribution of speckles was optically recorded and the calculations were performed optically. This is how it was done.

The same parts as in the above embodiment are given the same numbers, and the parts that are different will be described in detail. Reference numeral 13 holds a photosensitive member such as a photographic plate or film facing a semi-transparent mirror 11 provided inside the laser beam L. The photosensitive member holder 14 is a condenser lens located adjacent to the back of the photosensitive member holder, and 6a is a
This is a detector that detects the amount of light condensed by this condensing lens 15. Generally, the light transmittance of a photosensitive member that has been exposed to light decreases in proportion to the amount of exposure.

In this embodiment, by utilizing such properties of the photosensitive member, first, the photosensitive member is held in the photosensitive member holder 13, and the welding member W is irradiated with the laser beam L, to perform the welding process before welding. 8 This photosensitive member is developed and further inverted to record the speckle intensity distribution depending on the surface microstructure of the member W. The stronger the intensity distribution of the speckle is, the lower the light transmittance becomes. The member is held in the photosensitive member holder 13 in step D1. Therefore, when the welding parts W, are irradiated with the welding laser beam to weld the welding parts Wl, W, and then the laser beam L2 is irradiated again, the above speckle intensity distribution is The intensity distribution of speckles on the recording photosensitive member changes,
Light proportional to the amount of change in the surface microstructure passes through the speckle intensity distribution recording photosensitive member, is focused by the condenser lens 14, and is guided to the detector 6a. The output of this detector 6a is calculated to determine the welding depth by an arithmetic circuit 8, and the output is further led to a laser oscillation automatic adjustment device 9 of the first laser irradiation device to adjust the laser oscillation conditions. If you configure the device in this way,
As with each of the embodiments described above, the present invention is not only effective in performing stable and optimal laser welding, but also has the advantage that it does not require particularly high spatial resolution as a detector.

In the above embodiments, the force ζ welding members described above are applied to the case where two thin plate-like welding members are overlapped and welded, but the same applies to the case where two or more welding members are overlapped. As described above, the present invention overlaps two or more welding members and performs welding by irradiating a welding laser beam from the surface of one of the welding members. The change in speckle that depends on the change in surface microstructure before and after welding is measured optically, and from the amount of change,
This allows stable and optimal welding to be performed.

[Brief explanation of drawings]

FIG. 1 shows one embodiment of the present invention, and FIGS. 2 to 4 show other embodiments. 1: Condensing lens, 2: Melting part, 3: Thermal distortion part, 5: Condensing lens, 6: Detector, 7: Memory circuit, 8: Arithmetic circuit, 9:
Laser oscillation automatic adjustment device, 13: Photosensitive member holder.

Claims (1)

[Scope of Claims] 1. Two or more welding members are placed one on top of the other, and one side of the welding members is irradiated with a laser beam to weld the two or more welding members, and the two or more welding members are welded in a direction opposite to the laser beam irradiation. The depth of the weld is determined by irradiating the welded member on the side with a laser beam and optically measuring changes in the surface microstructure of the welded member that occur on the surface of the welded member on the opposite side due to the welding. A laser welding method characterized by measuring. 2. A first laser irradiation device that irradiates one surface of the welding member with laser light for welding two or more welding members, and a first laser irradiation device that irradiates one surface of the welding member with a laser beam for welding two or more welding members, and a first laser irradiation device that irradiates the welding member on the opposite side of the welding member by welding. a second laser irradiation device that irradiates a laser beam for measuring changes in the surface microstructure of the welded component that occur on the surface of the welded component; and the weld that occurs due to the irradiation of the laser beam from the second laser irradiation device. Laser welding, characterized by comprising a measuring device that measures the intensity distribution of speckles before and after welding, which depends on the surface microstructure of the member, and measures the welding depth of the welded member based on these intensity distributions. Device. 3. The laser welding device according to claim 2, wherein the first laser irradiation device has an automatic adjustment device that adjusts the laser irradiation conditions based on a command from a measuring device that measures the depth of welding. 4. A measuring device for measuring the depth of welding is located in the reflected light region generated by laser beam irradiation from the second laser irradiation device and measures the speckle intensity distribution depending on the surface microstructure of the welding member. Claims 2 and 3 include a detector and an arithmetic circuit that compares speckles measured by the detector before and after welding and calculates the depth of welding from this comparison. Laser welding equipment as described in section. 5. A measuring device for measuring the depth of welding is located in the reflected light region generated by laser beam irradiation from the second laser irradiation device and measures speckle intensity distribution depending on the surface microstructure of the welding member. A photosensitive member holder that holds a photosensitive member that is converted into a transmittance of A detector for holding the speckle intensity distribution recording photosensitive member obtained by the above photosensitive member holder and detecting the amount of light based on changes in the surface microstructure of the welded member after welding through the speckle intensity distribution recording photosensitive member. and an arithmetic circuit that calculates the change in the surface microstructure and calculates the welding depth based on the output from the detector, according to claims 2 and 3. Laser welding equipment.