JPS6252678B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a welding defect detection method for detecting whether the welding condition is good or bad in overlap laser welding.

[Technical background of the invention and its problems]

Generally, the welding process involves melting the respective welds of the workpieces to be welded, mixing the molten parts with each other, solidifying, and joining together. There are various methods for this depending on the purpose, but arc welding, resistance welding, etc. are usually used. Furthermore, in recent years, welding processing using laser beams has become popular, taking advantage of the characteristics of laser light. It is particularly useful for spot welding minute parts and welding the inside of workpieces with complex shapes. In particular, welding inside the workpiece takes full advantage of the fact that the laser is light, and welding is carried out by passing the laser beam through the gap in the workpiece.
It is now possible to make the glass part transparent and weld the inside. Furthermore, welding of large workpieces is also performed using high-power lasers.

In laser welding, when welding two workpieces one on top of the other, it is preferable to weld them in close contact with each other without any gaps between them. Particularly in spot welding, the gap between overlapping parts of workpieces is a factor that determines the quality of the welding result. The welding state by laser welding is as shown in FIGS. 1 and 2. That is, in FIG. 1, an upper member 1 and a lower member 2 are stacked together as workpieces, and a laser beam 3 is irradiated from above the upper member 1. At this time, the upper member 1 is melted by the laser beam 3, and then the lower member 2 is melted. At this time, the energy transmitted to the lower member 2 is the heat E1 directly transmitted to the lower member 2 from the laser beam 3 that has passed through the upper member 1, and the energy transmitted when the melted part 4 of the upper member 1 contacts the lower member 2. There is a heat E2. The lower member 2 is melted by the heat E1, E2, and the respective melted parts 4,
5 are mixed, a molten solidified portion 6 is formed as shown in FIG. 2, and the upper and lower members 1 and 2 are joined together. At this time, it is the heat E2 transmitted from the fusion zone 4 that has a greater effect on welding. If welding is performed with a gap existing between the upper and lower members 1 and 2, the molten part 4 of the upper member 1 will be difficult to contact the lower member 2 after irradiation with the laser beam 3, and the heat E2 will not be sufficiently transferred. It will no longer be carried out.

3, 4 and 5 show welding conditions when a gap exists between the upper and lower members 1 and 2. Due to the gap 10 in FIG. 3, the melt-solidified portion 6 does not sufficiently join the upper member 1 and the lower member 2, resulting in insufficient welding strength. Furthermore, as shown in FIG. 4, the melted and solidified portion 6 may be biased, further weakening the bonding strength. If the gap becomes even larger, as shown in FIG. 5, the molten portions of the upper and lower members 1 and 2 may not be able to come into contact with each other and solidify, resulting in failure to achieve a tight bond.

In this way, the upper and lower members do not come into close contact with each other and a gap exists between the two members, resulting in poor welding. Furthermore, the degree of failure varies depending on the degree of gap. However, conventionally, there was no means to detect defects during welding, and the only method was to visually inspect the welded part after welding. This method requires a lot of labor and time, causing a decrease in productivity and an increase in costs.

Another possible method is to capture and detect the gap as an image before welding to prevent defective welding. However, in this method, it is necessary to separately prepare an optical system for obtaining an image of the gap and install it near the welding processing equipment, which increases spatial constraints.
Furthermore, when the shape of the workpiece is complex, it is very difficult to perform image processing on the welded part and quantitatively judge the results.

[Purpose of the invention]

The purpose of the present invention is to provide superimposed laser welding.
To provide a welding defect detection method capable of determining a welding defect in a stacked welded product in which there is a gap since not all overlapped parts to be welded are in a close contact state.

[Summary of the invention]

In overlap laser welding, the present invention detects the reflected light of the laser beam at the time when the laser beam irradiated to the welding part passes through one member, and compares the intensity of the peak value of this reflected light with a predetermined value. This is a method for detecting welding defects in overlapping laser welding, which uses this comparison to determine whether the welding condition is good or bad.

[Embodiments of the invention]

The present inventor discovered that when a welded part is irradiated with a laser beam while there is a gap between the parts to be joined by overlapping laser welding, a peculiar peak occurs in the intensity of the reflected light between before and after the laser beam penetrates the upper part. Found that the value occurs. FIG. 6 shows changes in the intensity of laser beam irradiation and changes in the reflected light from the welded part with respect to changes in processing conditions. Note that the reflected light is obtained by detecting only the component coaxial with the incident optical path of the laser light. The vertical axis is the irradiation intensity and reflected light intensity of the laser beam, and the horizontal axis is time. Irradiation of laser light to the welded portion of the members to be joined is started at time A. After this, the laser beam irradiation intensity reaches the peak value B, and gradually decreases until the welding process end point C. The reflected light intensity between A and C has various characteristics depending on the processing state of the welded part. That is, immediately after the laser irradiation start point A, the intensity of the reflected light increases rapidly, similar to the laser beam irradiation intensity,
A peak value D exists. This is the point at which a melted part 4 begins to be formed on the surface of the upper member 1 by irradiation with the laser beam 3, as shown in FIG. After this peak value D, the reflected light intensity decreases rapidly and there is a valley E, but the state of the welded part at this point is that the beam hole 15 caused by the laser beam 3 in the upper member 1 is It is in the stage of formation and growth. After this, the laser beam 3 further grows the beam hole 15 and passes through the upper member 1, as shown in FIG. At this time, if a gap 10 exists between the upper member 1 and the lower member 2, a peak value F appears in the reflected light. In addition, in the region G where the reflected light after the peak value F is weak and the distribution is gentle, the processing state is as shown in FIG.
The beam hole 15 and the melted part 4 of the lower member 2 are enlarged.
The beam hole grows and the respective melted parts mix. Furthermore, in region H where large and small peaks exist continuously, the processing state is such that the molten part in the weld closes the beam hole and solidifies, forming the molten solidified part 6, as shown in FIG. .

In this way, the reflected light from the member being welded exhibits various characteristics depending on the processing state. In particular, when a gap exists between the upper and lower members, the reflected light intensity increases rapidly and a unique peak value F appears. Here, the inventor investigated the relationship between the gap between the upper member and the lower member and the peak value F. An apparatus for investigating this relationship is shown in FIG. A laser beam 3 oscillated from a laser oscillator 21 is reflected by a dichroic mirror 22 provided in front of the laser oscillator 21, and condensed by a condensing lens 23 provided below the dichroic mirror 22. Member 1 is reached. Additionally, a visible light blocking filter 2 is provided above the dichroic mirror 22.
A reflected light detector 25 equipped with a laser beam 3 is installed coaxially with the incident optical path of the laser beam 3. This reflected light detector 25 converts the intensity of reflected light into a voltage value. The reflected light detector 25 also detects a reflected light component 26 coaxial with the incident optical path of the laser beam 3 out of the reflected light from the laser beam 3 via the dichroic mirror 24 .

Gap 20 measured by such a device
The relationship between the intensity of the peak value F and the intensity of the peak value F due to the reflected light component 26 is shown in FIG. The material of the members to be welded is stainless steel, the upper member 1 has a thickness of 0.13 mm, and the lower member 1 has a thickness of 1 mm. The irradiation energy of the laser beam 3 is 7J, and the focal length of the condenser lens 23 is
Welding was performed at a position where the laser beam 3 was narrowed down to the minimum, that is, at a focal position of the condenser lens 23 at a diameter of 90 mm. This experiment revealed that the peak value F of the reflected light intensity increases as the gap increases, and becomes constant when the gap becomes sufficiently large. In the results shown in FIG. 11, the peak value F changes drastically when the gap is within 0.1 mm. From this, it can be seen that as the peak value F increases, welding defects occur. Therefore, the allowable limit of the peak value F is determined in advance as a predetermined value, and the peak value F of the reflected light at the time when the laser beam 3 passes through the upper member 1 during the welding process is measured and compared with the predetermined value. At this time, if the peak value F is larger than a predetermined value, it can be determined that the gap is excessive and the welding is defective.

The device for measuring the peak value F of reflected light is
For example, the one shown in FIG. 10 may be used. Further, as a device for comparing the measured value and a predetermined value, and a device for processing after the comparison, a well-known technique such as an ordinary computer may be used.

As described above, it has become possible to determine whether the welding condition is good or bad by detecting the reflected light from the welded part during the overlapping laser welding process. Therefore, it is no longer necessary to visually inspect the welding state after the welding process, and as a result, it is possible to improve productivity, reduce production costs, and ensure the reliability of the welded part. Furthermore, as shown in FIG. 10, a reflected light detector 25 for detecting reflected light is installed coaxially with the incident optical path of the laser beam 3. Detecting only the component 26 means that the condensing lens 23, upper and
There is no need to install equipment for detecting reflected light, such as a reflection detector 25, around the lower members 1 and 2. Therefore, a conventional optical system can be used without placing any spatial restrictions on the optical system such as the condenser lens 23. Furthermore, regardless of the shape of the member to be welded, the reflected light can be measured without changing the position of the reflected light detector 25.
It becomes extremely versatile.

〔Effect of the invention〕

As explained above, in the method for detecting welding defects in lap laser welding of the present invention, it is possible to determine whether the welding condition is good or bad during the welding process, and inspection after the welding process is no longer necessary. This has made it possible to improve productivity and ensure reliability of welded parts.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view to explain the welding situation in lap laser welding, Figures 2 to 5 are cross-sectional views showing the welded state, and Figure 6 is the laser beam in the processing process of lap laser welding. Figures showing the irradiation intensity and reflected light intensity, Figures 7 to 9 are cross-sectional views showing the processing status of parts processed by laser welding, Figure 10 is a schematic diagram showing the laser welding processing device, and Figure 11 is FIG. 3 is a diagram showing the relationship between the gap between members and the peak value of a reflected light component. DESCRIPTION OF SYMBOLS 1... Upper member, 2... Lower member, 3... Laser light, 25... Reflected light detection device, 26... Reflected light component.

Claims (1)

[Claims] 1. Detection of welding defects in a superimposed laser that overlaps the respective welded portions of members to be joined by welding, irradiates the welded portions with laser light, and determines whether the welding condition is good or bad when welding. In the method,
The peak value of the reflected light component having the laser beam component at the time when the laser beam irradiated to the welding part penetrates one member is detected, this peak value is compared with a predetermined value, and the welding state can be determined by this comparison. A welding defect detection method in overlapping laser welding to determine whether it is good or bad. 2. The method for detecting welding defects in overlapping laser welding according to claim 1, wherein of the reflected light, only the reflected light component coaxial with the incident optical path of the laser beam is detected.