JPH04265854A - Inspecting apparatus of spot welding - Google Patents

Abstract

PURPOSE:To positively discern whether a reflecting wave is generated at a nugget part or a corona bonding part, and to directly display the result whether or not the spot-welding part is proper. CONSTITUTION:The degree of attenuation of the reflecting waves of the ultrasonic waves is obtained by an operating means 15. It is discerned from the degree of attenuation whether the reflecting waves are generated at a nugget part 1 or at a corona bonding part 2. The discerning result whether the spot welding is good or bad is indicated at a display part 14.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting a weld in spot welding, and more particularly to an apparatus for non-destructively determining whether a spot weld has passed or failed using ultrasonic waves.

0002

[Prior Art] In spot welding, which is a type of lap resistance welding, when welding is performed normally, a part of the upper plate and a part of the lower plate are connected at the overlap welded part between the upper plate and the lower plate. are melted and solidified into one piece, and a melted-resolidified portion with a cross-section of Go stone called a nugget is formed at that portion. The diameter of the nugget has a strong correlation with the welding strength, and the lower limit of the nugget diameter has traditionally been controlled as a control item for spot welding. That is, the nugget diameter is detected, and if the diameter is smaller than a predetermined lower limit value, the welding strength is determined to be insufficient and the welding is determined to be defective, and if the nugget diameter is greater than or equal to the lower limit value, the welding is determined to be acceptable.

[0003] In order to carry out such management, a technique for non-destructively detecting the nugget diameter is required, and one known example is a technique for detecting the nugget diameter using ultrasonic waves reflected from the ultrasonic wave. As a typical example of the prior art, Japanese Patent Publication No. 14187/1987 is known. This device has a waveguide for guiding reflected waves from the object to be inspected to the probe, and displays the reflected waves from the object to be inspected as an image of multiple reflected waves on a display means such as an oscilloscope. The pass/fail of welding is determined from images of reflected waves.

An example of a conventional spot weld inspection technique will be described below. As shown in FIG. 7, the spot weld part of the inspected object 3 consists of a nugget part 1 where the metals of the upper plate 31 and the lower plate 32 are fused together, and a corona bond part 2 which is a heat affected zone where the two are crimped together. It is formed by. In the above-mentioned Japanese Patent Publication No. 59-14187, as shown in FIG. 8, a waveguide 6 is attached to the tip of an ultrasound probe 7 via an ultrasound transmission medium (not shown). When in use, the waveguide 6 is pressed against the object 3 to be inspected via the ultrasonic couplant, and in this state ultrasonic waves are output from the waveguide 6 toward the spot weld. The outputted ultrasonic waves are reflected at the welded portion, and reflected waves (echoes) from the upper plate 31 and lower plate 32 in FIG. 7 are input to the ultrasonic probe 7. The reflected waves input to the ultrasonic probe 7 are displayed as images of multiple reflected waves as shown in FIGS. 11 and 12 by a display means 8 such as an oscilloscope.

As described above, Japanese Patent Publication No. 14187/1987 is a technique for making the image of multiple reflected waves clearer, and in order to achieve this, improvements are made to the waveguide. This waveguide, as shown in Figure 10,
The outer wall of the waveguide 6 is formed into a conical shape with a cone angle β that decreases toward the tip, and the inner hole that accommodates the ultrasonic absorber 4 has a cone angle α that widens toward the tip. It is shaped like a cone. Here, if the outer wall conical angle β formed by the inner wall surface of the inner hole is within the following range, it becomes possible to receive and display multiple reflected waves from the welding part even more clearly. Inner hole cone angle α=90±10 degrees Outer wall cone angle β≧180−α degrees

[0006]

[Problem to be Solved by the Invention] However, in the ultrasonic welding inspection method using a waveguide, the corona bond part, which should originally be rejected, is judged to be a welding pass by combining it with the nugget part of the welding good part. , there is a problem that the corona bond part, which should be excluded from the weld sound part, is added to the pass judgment factor. This can be explained as follows. 11 shows a case where the welded part is larger than the diameter G of the ultrasonic absorber 4 in FIG. 10 and includes a corona bond part and a nugget part, and the horizontal axis of adjacent reflected waves is the thickness of the upper plate 31. t1
and the thickness t2 of the lower plate 32. on the other hand,
FIG. 12 shows the ultrasonic absorber 4 of the waveguide 6 in FIG.
This is a display when the welded part is smaller than the diameter G of the upper plate 31 and reflected waves from the bottom surface of the upper plate 31 are being received, and the horizontal axis of adjacent reflected waves corresponds to the thickness t1 of the upper plate 31. As described above, the prior art does not take into consideration the fact that the welded portion is composed of the nugget diameter DN and the corona bond diameter Dc and must be divided. The joining strength of the corona bond part is much lower than that of the nugget part (particularly when welding Zn-plated steel sheets), so even if the corona bond diameter is large, if the nugget diameter is small, sufficient welding strength cannot be obtained. However, the device disclosed in Japanese Patent Publication No. 59-14187 may end up determining that the test is acceptable even in such a case.

Furthermore, in the case of Japanese Patent Publication No. 59-14187, the pass/fail judgment is made by visually confirming the waveform displayed on an oscilloscope or the like, and therefore inspection requires skill. Furthermore, since it is done visually, false judgments are likely to occur and the work is tiring.

The present invention focuses on the above-mentioned problem, and makes it possible to reliably determine whether a reflected wave is generated at the nugget portion or the corona bond portion, and to directly display the result of welding pass/fail. The purpose of the present invention is to provide a spot welding inspection device that is capable of inspecting spot welding.

[0009]

[Means for Solving the Problems] A spot welding inspection device according to the present invention in accordance with this object includes an ultrasonic probe provided with a waveguide having an ultrasonic absorber capable of contacting a spot welded portion of an object to be inspected. A spot welding inspection device comprising a probe and a calculation processing means electrically connected to the ultrasonic probe. an ultrasonic transmitter/receiver that outputs ultrasonic waves to the probe and receives reflected waves of the ultrasonic waves from the object to be inspected; and stores reflected waves of the spot weld based on signals from the ultrasonic transmitter/receiver. a waveform storage processing unit;
a nugget discriminator for determining the degree of attenuation of the reflected wave based on the information from the waveform storage processing section and discriminating the nugget in the spot weld; It consists of a pass/fail determining section that determines the pass/fail of welding by comparison with a reference nugget, and a display section that displays the pass/fail result based on information from the pass/fail determining section.

0010

[Operation] In the spot welding inspection device configured in this way, the ultrasonic waves output from the ultrasonic probe toward the spot weld are reflected inside the spot weld, and
The reflected waves are input to the ultrasound probe. The reflected waves input to the ultrasound probe are stored in the waveform storage processing section. Next, the nugget discrimination section determines the degree of attenuation of the reflected wave based on the waveform information stored in the waveform storage processing section, and determines whether the reflected wave is generated at the nugget section or at the corona bond from this attenuation degree. It becomes possible to determine whether the When the nugget portion is determined, the pass/fail judgment section judges whether the diameter of the nugget portion determined by the degree of attenuation of the reflected wave is larger than the reference nugget, and the judgment result of the pass/fail judgment section is displayed on the display section. Is displayed. In this way, the nugget part of the spot weld and the corona bond part can be reliably distinguished based on the determined degree of attenuation of the reflected wave, so the corona bond part will no longer be considered as a factor in determining acceptance. . Therefore, the reliability of determining whether the spot weld is acceptable is increased, and the required strength of the weld is reliably maintained. Also,
Since the determination result is displayed as is on the display section, there is no need to judge pass/fail on the display section. Therefore, the level of skill required for pass/fail judgment is not required, and the inspection effort is also reduced compared to the conventional method.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the spot welding inspection apparatus according to the present invention will be described below with reference to the drawings. Figure 1
6 to 6 show an embodiment of the present invention. Figure 1 shows the entire spot welding inspection device, and the object to be inspected and the ultrasonic probe are the same as in the prior art, so they will be explained using the same symbols as in the prior art. . In FIG. 1, the object to be inspected 3 is composed of an upper plate 31 and a lower plate 32. As shown in FIG. The upper plate 31 is a thin steel plate with a thickness T1, and the lower plate 32 is a thin steel plate with a thickness T2. Upper plate 3
1 and the lower plate 32 are joined by spot welding, and a nugget part 1 and a corona bond part 2 are formed at the spot weld. The nugget portion 1 has a metal structure mainly composed of dendrites that have been melted and resolidified, and the corona bond portion has a metal structure that has only been solid-phase bonded.

The spot welded upper surface of the upper plate 31 has
The ultrasonic probe 7 is in contact with it. A waveguide 6 having an ultrasound absorber 4 is attached to the tip of the ultrasound probe 7 . When the ultrasonic probe 7 is pressed against the upper plate 31, the ultrasonic absorber 4 is in close contact with the spot-welded upper surface. Further, the outer diameter of the ultrasonic absorber 4 for detecting reflected waves is G. The ultrasonic probe 7 is electrically connected to the arithmetic processing means 15 via a cable 9.

[0013] The arithmetic processing means 15 includes an ultrasonic transmitting/receiving section 10
, a waveform storage processing section 11, a nugget discriminating section 12, a pass/fail determining section 13, and a display section 14. The ultrasonic transmitter/receiver 10 is connected to the ultrasonic probe 7 and has a function of outputting ultrasonic waves toward an upper plate 31 and a lower plate 32 as objects to be inspected. It also has a function of inputting reflected waves input to the ultrasonic transmitter/receiver 10. The waveform storage processing section 11 has a function of storing the reflected waves of the spot weld based on the signal from the ultrasonic transmitting/receiving section 10. The nugget discriminating section 12 has a function of determining the degree of attenuation of the reflected wave based on the information from the waveform storage section 11 and discriminating the nugget section 1 in the spot weld section.

The pass/fail determining section 13 has a function of determining pass/fail of welding by comparing the size of the nugget portion 1 based on the information from the nugget discriminating section 12 with a preset reference nugget. The display unit 14 has a function of displaying pass/fail results based on information from the pass/fail determining unit 13. Waveform storage processing section 11, nugget discriminating section 12, and pass/fail determining section 13
is composed of programs stored in, for example, a microcomputer system. The display unit 14 is composed of, for example, a CRT (cathode ray tube) of a microcomputer system.

Next, the inspection procedure and operation of the spot welding inspection apparatus described above will be explained. First, when inspecting spot welds, as shown in Figure 1, the upper plate 3
The ultrasonic probe 7 is selected based on the plate thickness T1 of the first plate 32 and the plate thickness T2 of the lower plate 32. In this case, a waveguide 6 is selected that has an ultrasonic absorber 4 having a diameter G of the tip portion that should be the same as the diameter DN of the nugget portion 1 that is required as a reference for the diameter of the welded portion. Next, an ultrasonic transmission medium (not shown) is applied between the waveguide 6 and the ultrasonic probe 7 to facilitate the transmission of ultrasonic waves and to obtain clear signals.

Next, the ultrasonic probe 7 on which the waveguide 6 is set is brought into contact with the welded surface of the upper plate 31 of the object to be inspected 3, and the upper plate 31 and the ultrasonic absorber 4 are brought into close contact. state. In this state, the ultrasonic transmitting/receiving section 10 emits ultrasonic waves. The ultrasonic waves transmitted to the object to be inspected 3 bounce back as reflected waves within the welding area, and are stored in a waveform storage processing section 11 having a wave memory. Here, Figures 11 and 12
If the diameter of the welded portion is smaller than the diameter G of the ultrasonic absorber 4 inside the waveguide 6, multiple reflected waves from the bottom surface of the upper plate 31, that is, the waveform shown in FIG. vice versa,
If it is larger than the diameter G of the internal ultrasonic absorber 4 of the waveguide 6, multiple reflected waves will be generated from the welded part of the upper plate 31 and the lower plate 32,
That is, the waveform shown in FIG. 11 is stored in the waveform storage processing section 11.

Next, the processing procedure in the nugget discriminator will be explained based on the flowchart of FIG. In FIG. 2, processing for determining the nugget portion is started in step 51, and the process proceeds to step 52, where it is determined whether multiple reflected waves have been captured. Here, if it is determined that the multiple reflected waves have not yet been captured, the process proceeds to step 60 and the process is completed. If it is determined in step 52 that multiple reflected waves have been captured, the process proceeds to step 53. Here, as shown in FIG. 3, the surface wave S and the lower plate 3
m-th reflected wave B2-m from the surface wave S in the reflected wave of 2
and the n-th reflected wave B2-n, respectively.
By setting s, Gm, and Gn and holding the peak, the heights of the respective reflected waves Ps, Pm, and
Pn is calculated. When the process of step 53 is completed,
Proceeding to step 54, the m-th reflected wave B2-m,
The delay time Tmn of the n-th reflected wave B2-n is determined. That is, Lmn, which indicates from which bottom surface of the plate the ultrasonic wave is reflected by the distance between adjacent reflected waves, is determined. This Lmn is expressed by the following formula.

[0018]

[Math 1]

Here, Lmn, Tmn, n, m, and Vo are defined as follows. Lmn: Distance between adjacent reflected waves, equivalent to plate thickness Tmn: Time n of m-th and n-th reflected waves from surface wave S, m: Integer n>m Vo: Speed of ultrasonic longitudinal wave

The determination in step 55 is made as follows. First, in the case of Lmn,t1, if it is smaller than the diameter G of the internal absorber 4 of the waveguide 6, it is naturally determined that the reflected wave is a reflected wave from the bottom surface of the upper plate 31. . Also, t1 ≦Lmn≦t1
In the case of +t2, it is a reflected wave from either the nugget portion 1 or the corona bond portion 2, and it is necessary to determine which one.

[0021] Now, if we look at the degree of attenuation of the reflected wave, we can see Figure 5.
As shown in FIG. 6, the degree of attenuation is large in the nugget portion, and the degree of attenuation is small in the corona bond portion, as shown in FIG. Causes of ultrasonic attenuation in metals include diffusion loss due to the spread of the wavefront of the ultrasonic wave, scattering attenuation due to grain boundaries and structure boundaries, viscous attenuation due to internal friction, and even dislocation movement. Examples include attenuation. Here, if we compare the nugget part and the corona bond part, we can see that the nugget part is made of metal with a structure mainly composed of melted and resolidified dendrites, whereas the corona bond part is simply solid phase bonded. Therefore, there is no significant change in the structure, and the metal has a structure mainly in a normalized state, and it is thought that such a difference in structure is reflected in the difference in attenuation between the two. As described above, in this embodiment, the degree of attenuation of the reflected wave is determined, and depending on the relationship between the degree of attenuation and the threshold value for this, it is determined whether the reflected wave is generated at the nugget portion 1 or the corona bond portion 2. It is determined.

Specifically, t1 <Lmn≦t1 +t
In case 2, the sum of the welded portions of the nugget portion 1 and the corona bond portion 2 is larger than the diameter G of the internal absorber of the waveguide 6, and multiple reflected waves are stored in the waveform storage processing unit 11. As shown in FIGS. 3 and 4, from the surface wave S, the height Pm of the reflected wave B2-m from the bottom surface of the m-th lower plate 32, and the reflected wave B2-n from the bottom surface of the n-th lower plate 32. The height Pn and B
The interval time Tmn between 2-m and B2-n is calculated. In actual measurement, m is 1, n is 2, and the height P of the first reflected wave B2-1 from the bottom surface of the lower plate 32 is
1 and the reflected wave B2- from the bottom surface of the second lower plate 32
Normally, the interval time T12 of 2 is calculated.

The height Pm of the reflected wave already obtained in this way
, Pn, Tmn, the attenuation degree α of the reflected wave from the lower plate
Calculate mn. In other words, from the wave height of B2-m to B2
As a measure of the attenuation to the wave height of −n, the attenuation degree αm
n is determined as shown in the following equation (1).

[0024]

[Math 2]

In formula (1), Vo is the velocity of the ultrasonic longitudinal wave in a solid related to the bulk modulus, rigidity, and density of the solid, and although it is originally different between the nugget part 1 and the corona bond part 2, , for convenience of calculation, a predetermined constant is used. Moreover, Lmn means the transmission traveling distance from the m-th reflected wave to the n-th reflected wave when the ultrasonic wave passes through the weld while reflecting on the upper and lower surfaces of the weld. The attenuation degree αmn can be determined by the above formula (1), and the value of this attenuation degree αmn differs between the nugget portion 1 and the corona bond portion 2. Therefore, the threshold value αs of the degree of attenuation is determined in advance, and as shown in step 50,
By comparing the value of αmn with the threshold value αs, it is possible to determine whether the nugget portion 1 or the corona bond portion 2 is present. That is, if it is determined in step 56 that αs>αmn, it is determined that not only the nugget portion 1 but also the corona bond portion 2 is included. Therefore, if it is determined that αs>αmn, the information is not suitable as information for determining pass/fail, and the process proceeds to step 59 and ends.

If it is determined in step 56 that αs≦αmn, the process proceeds to step 57, where the pass/fail determining unit compares the size of the nugget portion 1 based on the information from the nugget determining unit 12 with a preset reference nugget. It is carried out by 13. Here, if the size of the nugget portion 1 determined by the nugget discriminator 12 does not reach the size of the reference nugget, the process proceeds to step 59, where the display unit 14 displays a message indicating that the welding has failed, and the process proceeds to step 60. reach. In step 57, if the size of the nugget portion 1 determined by the nugget discriminator 12 has reached the size of the reference nugget, the process proceeds to step 58, where the display unit 14 displays a message indicating that the welding has been passed, and the process proceeds to step 60. reach. In this way, the determination of pass/fail of welding is directly displayed on the display unit 14, so there is no need to make a determination by looking at the display on the display unit, and the determination of pass/fail is facilitated. In this embodiment, the display section is made up of, for example, a CRT (cathode ray tube), but it may be configured to notify the inspector using a display lamp, a buzzer, or the like.

[0027]

As explained above, when using the spot welding inspection device according to the present invention, the degree of attenuation of reflected waves of ultrasonic waves is determined by the arithmetic processing means, and from this degree of attenuation, the reflected waves are generated at the nugget portion. Since it is determined whether the weld is caused by a corona bond or not, the corona bond part, which should be excluded from the weld sound part, is no longer taken into account as a factor in determining whether the weld is acceptable. Therefore, the reliability of determining whether the spot weld is acceptable or not is increased, and it becomes possible to reliably maintain the required strength of the weld. Further, since the determination result is displayed as is on the display section, there is no need to make a pass/fail determination on the display section. Therefore, the level of skill required for pass/fail judgment is not required, and inspection labor is also reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a spot welding inspection device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure for inspecting a welded part by the apparatus of FIG. 1;

FIG. 3 is a waveform diagram of a gate output for determining a welded portion and a non-welded portion in FIG. 1;

FIG. 4 is a waveform diagram showing the degree of attenuation of reflected waves in FIG. 1;

FIG. 5 is a waveform diagram showing the degree of attenuation of multiple reflected waves in the nugget portion of FIG. 1;

6 is a waveform diagram showing the degree of attenuation of multiple reflected waves at the corona bond portion in FIG. 1. FIG.

FIG. 7 is an enlarged sectional view of the vicinity of a spot weld.

FIG. 8 is a schematic configuration diagram of a conventional spot welding inspection device.

FIG. 9 is a perspective view of the waveguide in FIG. 8;

FIG. 10 is a cross-sectional view of the waveguide of FIG. 9;

FIG. 11 is a waveform diagram showing a received waveform of ultrasonic waves in a specific area of a spot weld.

FIG. 12 is a waveform diagram showing the received waveform of ultrasonic waves in another specific area of the spot weld.

[Explanation of symbols]

1 Nugget part 2 Corona bond part 3　Object to be inspected 4 Ultrasonic absorber 6 Wave guide 7 Ultrasonic probe 10 Ultrasonic transmitter and receiver 11 Waveform storage processing unit 12 Nugget discrimination section 13 Pass/fail judgment section 14 Display section 15 Arithmetic processing means

Claims (1)

[Claims] 1. An ultrasonic probe provided with a waveguide having an ultrasonic absorber capable of contacting a spot welded portion of an object to be inspected, and an arithmetic processing means electrically connected to the ultrasonic probe. A spot welding inspection device comprising: the arithmetic processing means connected to the ultrasonic probe;
An ultrasonic transmitter/receiver unit that outputs ultrasonic waves to the ultrasonic probe and receives reflected waves of the ultrasonic waves from the object to be inspected; a waveform storage processing unit that stores the waveform storage processing unit; a nugget determination unit that determines the degree of attenuation of the reflected wave based on the information from the waveform storage processing unit and determines the nugget portion in the spot weld; It is composed of a pass/fail judgment section that judges pass/fail of welding by comparing the size of the nugget portion with a preset reference nugget, and a display section that displays the pass/fail result based on information from the pass/fail judgment section. Features of spot welding inspection equipment.