JP4120360B2 - Ultrasonic spot weld evaluation method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for inspecting the diameter of a melted portion (nugget) formed by spot welding with nondestructive means using ultrasonic waves.
[0002]
[Prior art]
2. Description of the Related Art In recent years, for example, in an automobile body manufacturing factory, a spot welding inspection method that can be simply implemented is desired in order to enable inspection of a spot welded portion with high efficiency on site.
[0003]
The body of an automobile is assembled by spot welding that reaches several thousand points. Since the quality of spot welding directly affects the strength and durability of the car body, it is inspected whether spot welding is performed properly. It is very important to do. Conventionally, as an inspection method for such a spot welded portion, a peel inspection is performed in which the spot welded portion is peeled off with a chisel to determine whether it is good or bad. However, since the peeling inspection is a destructive inspection, the inspection requires a great deal of labor and time, and the cost is high. In addition, there is a problem that it is difficult to accurately determine the quality of spot welding. Therefore, various devices and methods for non-destructively inspecting the quality of spot welds using ultrasonic waves have been proposed recently.
[0004]
For example, in Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4, an ultrasonic wave is applied perpendicularly to the plate surface in order to evaluate the quality of a spot welded portion that is produced by superimposing and welding two plates. A method and apparatus for detecting a reflected wave by making it incident are disclosed. Further, in Patent Document 5, a pair of local water immersion probes are arranged on the upper and lower sides of a subject so as to face each other, and the subject is moved in the horizontal direction and transmitted from a transmission-side local water immersion probe. An ultrasonic flaw detector is disclosed that scans a spot welded portion of a subject with an ultrasonic beam and determines the presence or absence of a flaw in the spot welded portion from a reception signal of a reception-side local water immersion probe.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-146828 [Patent Document 2]
JP 2002-131297 A [Patent Document 3]
Japanese Patent Laid-Open No. 11-2627 [Patent Document 4]
JP-A-6-265529 [Patent Document 5]
Japanese Patent Laid-Open No. 62-52456 [0006]
[Problems to be solved by the invention]
However, since these prior arts perform inspection by transmitting and receiving ultrasonic waves in a vertical direction with respect to a flat specimen, an inclination formed around a recess formed in a spot welded part of the specimen. On the surface, there is a problem that the ultrasonic beam cannot efficiently enter the subject and it is difficult to detect the shape of the nugget formed in the spot welded portion with high accuracy.
[0007]
That is, as shown in FIG. 7, when the upper plate 111a and the lower plate 111b are overlapped and spot welded, the spot welded portion 102 has a melt-solidified structure called “nugget” at the joint between the upper plate 111a and the lower plate 111b. 102a is formed. Further, spot welding is performed by strongly pressing the upper plate 111a and the lower plate 111b with an electrode tip (not shown), and therefore, the surface of the upper plate 111a and the lower plate 111b corresponds to the shape of the tip portion of the electrode tip. A recess 102b is formed, and a conical inclined surface 102c is formed between the bottom surface of the recess 102b and the surfaces of the upper plate 111a and the lower plate 111b. When welding is performed normally, the nugget 102a has a diameter slightly larger than or equal to the diameter of the electrode tip used for welding, and the inner diameter of the recess 102b is chamfered because the shape of the tip of the electrode tip is chamfered. In general, the diameter is slightly smaller than the diameter of the cylindrical portion of the electrode tip, and therefore is slightly smaller than the diameter of the nugget 102a. When welding is not performed normally, the nugget diameter is smaller than when welding is performed normally, and abnormalities such as insufficient strength occur. In addition, the code | symbol S in a figure has shown the toe of the nugget 102a.
[0008]
Thus, since the conical inclined surface 102c is formed in the spot welded portion 102 between the bottom surface of the recess 102b and the surfaces of the upper plate 111a and the lower plate 111b, the ultrasonic inspection apparatus according to the prior art described above. When the ultrasonic beam is transmitted and received in the direction perpendicular to the surfaces of the upper plate 111a and the lower plate 111b, which are subjects, as described above, the ultrasonic beam is reflected on the inclined surface 102c and almost inside the subject. Since it is not propagated, almost no signal is obtained from the examination site. As described above, since the size of the nugget 102a is slightly larger than or equal to the diameter of the electrode tip, the toe S of the nugget 102a and the inclined surface 102c formed on the subject almost overlap each other. When the ultrasonic beam is reflected on the inclined surface 102c, it is difficult to obtain an accurate signal from the vicinity of the nugget toe S, and it is difficult to accurately determine the nugget diameter and the presence / absence of a defect.
[0009]
The present invention has been made to solve such deficiencies of the prior art, and the problem is that it is not affected by the inclined surface formed around the recess formed in the spot welded portion. This is to enable evaluation of spot welds.
[0010]
[Means for Solving the Problems]
This invention relates to an ultrasonic evaluation method of a spot welded portion formed by superposing and welding a plurality of metal plates, and has two frequencies f ₁ toward the weld metal of the spot welded portion on the metal plate outside the spot welded portion. And f ₂ (f ₁ <f ₂ ), exciting the Lamb wave through the weld metal, receiving the Lamb waves of _two frequencies f ₁ and f ₂ after transmission, and 2 after the transmission One of detecting the frequency _{f 1} and the amplitude _{a 1} and _{a 2} of the Lamb wave of _{f 2,} by Rukoto seek their ratio _(a 2 / _{a 1),} by measuring the diameter of the nugget of the spot weld, it is obtained by solving the previous Symbol challenges.
[0013]
The present invention is also directed to an ultrasonic evaluation apparatus for a spot welded portion formed by superposing and welding a plurality of metal plates, and having two frequencies f toward the weld metal of the spot welded portion on the metal plate outside the spot welded portion. ₁ and _f 2 _(f 1 _{<f 2)} means for exciting a Lamb wave, and means for receiving the two Lamb waves of a frequency _{f 1} and _{f 2} that after passing through the weld metal, the two frequency after the transmission and means for detecting the f ₁ and amplitude _{a 1} and _{a 2} of the Lamb wave _{f 2,} seeking their ratio _(a 2 / _{a 1),} means for measuring the diameter of the nugget of a spot welded portion, a This solves the problem.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0015]
Hereinafter, the upper plate of the two metal plates is referred to as the upper plate, and the lower plate is referred to as the lower plate. In the present invention, as shown in FIG. 1, a Lamb wave probe 10 is used to excite a Lamb wave toward the welded portion 2 on the upper plate 1a. This Lamb wave has several modes depending on the product f · d of the frequency f of ultrasonic waves and the plate thickness d. Select the A ₀ mode, S ₀ mode, or A ₀ S ₀ mixed mode. Is good. When the excited Lamb wave enters the weld, the product f ・ d changes due to the change of the plate thickness d, so the propagation condition changes, but in the above mode, the product f ・ d is 5 MHz ・ mm. If it exceeds, it will not be affected by the change in product f · d, so by appropriately selecting the frequency, it will propagate in the mode as it is in the weld. For the same reason as described above, the Lamb wave transmitted through the welded portion propagates through the metal plate in the same mode and is received by the Lamb wave probe 11.
[0016]
As shown in FIG. 2, the nugget 2a generated in the welded portion is a molten and solidified structure 2b having a directionality substantially parallel to the plate thickness direction. This melt-solidified structure 2b is the weld metal referred to in the present invention. The melt-solidified structure 2b is also called a dendrite structure and is a collection of coarse crystals extending in one direction. In FIG. 2, the transmission of ultrasonic waves is poor particularly in the direction parallel to the plate surface and the direction parallel to the plate thickness. It has a property (attenuation is large). Therefore, when the Lamb wave is propagated to the weld along the direction parallel to the plate surface, the Lamb wave is attenuated according to the length parallel to the plate surface of the molten solidified structure 2b, so the amount of Lamb wave attenuation is measured. Thus, the length parallel to the plate surface of the melt-solidified structure 2b, that is, the diameter of the nugget 2a can be measured.
[0017]
Figure 3 shows the relationship between the Lamb wave attenuation and the nugget diameter in a sample where the nugget diameter was changed by spot welding using two steel plates with a thickness of 2.6mm. It is a result. An A ₀ S ₀ mixed mode Lamb wave with a frequency of 5 MHz was used. It can be seen that there is a good proportional relationship between the Lamb wave attenuation and the nugget system.
[0018]
FIG. 4 shows the amplitude of the Lamb wave transmitted through the weld using the above sample and the Lamb wave in the A ₀ S ₀ mixed mode having the frequency of 5 MHz and the Lamb wave in the A ₀ S ₀ mixed mode having the frequency of 2 MHz. This is a result of investigating the relationship between the ratio of the amplitude of the Lamb wave transmitted wave at a frequency of 5 MHz to the amplitude of the Lamb wave transmitted wave at a frequency of 2 MHz and the nugget diameter. It can be seen that there is a good correlation between the two.
[0019]
【Example】
Fig. 5 shows the nugget diameter measured from the attenuation of Lamb waves in the A ₀ S ₀ mixed mode with a frequency of 5 MHz for 30 samples made by spot welding two steel plates with a thickness of 2.6 mm. And the nugget diameter confirmed by the cutting test. A calibration curve obtained from the relationship shown in FIG. 3 was used to calculate the nugget diameter from the Lamb wave attenuation. It can be seen that the nugget diameter can be measured with an accuracy of about 0.2 mm by the method of the present invention.
[0020]
FIG. 6 is measured from the ratio between the amplitude of the Lamb wave transmitted wave in the A ₀ S ₀ mixed mode at the frequency of 5 MHz and the amplitude of the Lamb wave transmitted wave in the A ₀ S ₀ mixed mode at the frequency of 2 MHz using the sample. The relationship between the nugget diameter and the nugget diameter confirmed by the cutting test is shown. For the calculation of the nugget diameter from the amplitude ratio, a calibration curve obtained from the relationship of FIG. 4 was used. It can be seen that the nugget diameter can be measured with an accuracy of about 0.2 mm even by the method of the present invention.
[0021]
In addition, in the said description, although this invention was applied to the welding test | inspection of the steel plate, the application object of this invention is not limited to this. Further, the number of welds is not limited to two, and the evaluation of the soundness of the spot welded portion is not limited to the measurement of the nugget diameter using the relationship shown in FIGS.
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to evaluate a spot-welded part correctly and non-destructively, without being influenced by the inclined surface formed around the hollow formed in a spot-welded part.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the structure of an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the structure of a spot weld in order to explain the principle of the present invention. FIG. 4 is a diagram showing the relationship between the amplitude ratio of two Lamb waves of two frequencies and the nugget diameter. FIG. 5 is a diagram showing the relationship between the nugget diameter and the nugget diameter. Diagram showing effect (accuracy) [FIG. 6] Diagram showing effect (accuracy) of the present invention when using the relationship of FIG. 4 [FIG. 7] Cross-sectional view for explaining spot welds [Explanation of symbols] ]
1a, 111a ... Upper plate 1b, 111b ... Lower plate 2, 102 ... Spot welds 2a, 102a ... Nugget 2b ... Melt solidified structure (welded metal)
10, 11 ... Lamb wave probe

Claims (2)

In the evaluation method by ultrasonic of the spot welding part formed by superposing and welding a plurality of metal plates,
Excitation of Lamb waves of _two frequencies f ₁ and f ₂ (f ₁ <f ₂ ) toward the weld metal of the spot weld on the metal plate outside the spot weld,
Passing the Lamb wave through the weld metal;
The Lamb waves of the _two frequencies f ₁ and f ₂ after transmission are received, and the amplitudes A ₁ and A ₂ of the Lamb waves of the _two frequencies f ₁ and f ₂ after the transmission are detected , and their ratio (A ₂ / a ₁₎ by Rukoto seek evaluation method of the spot welded portion by ultrasonic waves and measuring the diameter of the nugget of the spot weld. In an ultrasonic evaluation apparatus for spot welds formed by superimposing and welding a plurality of metal plates,
Means for exciting Lamb waves of _two frequencies f ₁ and f ₂ (f ₁ <f ₂ ) toward the weld metal of the spot weld on the metal plate outside the spot weld;
Means for receiving the two Lamb waves of a frequency _{f 1} and _{f 2} that after passing through the weld metal,
Means for detecting the amplitudes A ₁ and A ₂ of the Lamb waves of the _two frequencies f ₁ and f ₂ after the transmission;
A means for determining the ratio (A ₂ / A ₁ ) and measuring the diameter of the nugget of the spot weld,
An apparatus for evaluating spot welds using ultrasonic waves.

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