JPS5914188B2 - Ultrasonic inspection device for resistance spot welds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic inspection device for resistance welds.

Generally, nondestructive ultrasonic testing of spot welds is performed in a separate process from the welding process, and an ultrasonic flaw detector is used to place a probe on the weld and observe the multiple reflection waveforms that appear on the cathode ray tube. Since the 10 welding states were determined by
In addition to requiring a lot of time to conduct the inspection, this method also had the disadvantage of causing differences in the judgments of different inspectors because it was not a quantitative judgment method.

In addition, the conventional method of performing in-process nondestructive testing using ultrasonic waves during welding involves attaching a transmitting transducer to one end of a pair of electrodes and a receiving transducer to the other, and Ultrasonic waves were transmitted through the device, and changes in the amount of ultrasound transmitted were observed on a cathode ray tube (transmission method).

This method reduces inspection time and dramatically improves inspection reliability, but requires two transducers for transmitting and receiving, and unlike series spot welding, the electrode is only on one side. The drawback is that it cannot be applied to anything that exists. Another method is the transducer reflection method, in which a transmitting/receiving transducer is attached to one side of the electrode, and a non-destructive inspection is performed using the reflection method. Since the reflected waves from the tip end surface of the electrode or the contact surface between the welded material and the electrode are used, the accuracy of determining the welding state is extremely low. 90 So,
As a method to improve these problems, one electrode is equipped with a transducer for both transmitting and receiving purposes to send out pulsed ultrasonic waves, and the ultrasonic waves reflected by the ultrasonic reflecting surface attached to the other electrode are absorbed. A device has been developed that quantitatively determines the welding condition by detecting the change in the peak value.

First, the conventional ultrasonic inspection apparatus described above will be explained. to 0
- Figure 1 shows the arrangement of electrodes, ultrasonic transducers and materials to be welded, and the progress of ultrasonic waves during welding using a conventional ultrasonic inspection device. In the diagram showing a multiple reflection waveform, 1 is an electrode, and 2 is an ultrasonic transducer for both transmission and reception, which is attached to the inner end surface 31 of a hole 3 made in the electrode 1.

Reference numeral 4 denotes the other electrode facing the electrode 1, 5 a hole formed in the electrode 4, and 51 an inner end surface of the hole 5 forming an ultrasonic reflecting surface.

6 is the tip surface of electrode 1, 7 is the tip surface of electrode 4, 8 and 9
are the materials to be welded, 10 is the contact surface of the materials 8 and 9 to be welded,
11 is a contact surface of the material to be welded 8 with the tip surface 6 of the electrode 1; 12;
13 is the contact surface of the contact member 9 with the tip surface 7 of the electrode 4, and 13 is the contact surface for driving the ultrasonic transducer 2, and the electrical signal that is converted when the ultrasonic reflected wave is input to the ultrasonic transducer 2. This is a transmitting/receiving device to be detected.

T is a transmitted wave, B1 is a first reflected wave that is a combination of the reflected waves of the transmitted wave T reflected at contact surfaces 10, 11, and 12 and input to the vibrator 2, and B2 is a first reflected wave B.
1 is reflected by the inner end surface 31 of the hole 3 of the electrode 1, and then travels toward the electrode 4 again, and is reflected and synthesized from the contact surfaces 11 and 12, respectively, resulting in a second reflected wave. C is the contact wave of the traveling wave T. The ultrasonic wave transmitted through the surfaces 10, 11, and 12 is reflected by the ultrasonic reflecting surface 51, and then transmitted through the contact surfaces 10, 11, and 12 again to reach the vibrator 2. 1st
The main component of the reflected wave B1 is the reflected wave from the contact surface 11 and the tip surface 6 of the electrode 1, and the contact state between the contact surface 11 and the electrode 1 improves as the energization time elapses, and the contact area increases. The reflected wave B1 monotonically decreases.

Further, the reflected wave B2 changes almost similarly to the reflected wave B1. On the other hand, since the reflected wave C from the reflecting surface 51 passes through the contact area twice, it is affected by the change in temperature due to the temperature rise of the welded materials 8 and 9, so the reflected waves B, , B2, etc. There are no monotonous changes.

FIG. 3 is a diagram showing the relationship between the welding time and the peak value of the reflected wave C, where T is the time at which the welding current begins to flow.

From then until a certain point t1, the peak value of the reflected wave C increases monotonically as the welding time elapses. The reason for this is that the temperature of the contact surfaces 10, 11, and 12 increases as welding time progresses, and the contact condition improves. Furthermore, as the contact time elapses, it rapidly decreases from time t1 to time T2. When the cross section of the welded part is inspected, from time t1 to time T
In the process of reaching No. 2, minute melted areas (nuggets) begin to form. That is, the change from time t1 to time T2 is considered to be due to rapid attenuation of the ultrasonic waves when the metal near the bonding surface 10 undergoes a phase change from a solid phase to a liquid phase.
Therefore, by detecting this time point T2, it is possible to detect whether or not a melted portion is formed. As the energization time further elapses, the peak value of the reflected wave C increases again, and the energization ends at time T3. Figure 3 shows the end point T of the energization time of the reflected wave C.
The peak value H2 at time 3 and the peak value H1 at time T2
This is a diagram showing the relationship between the difference H2-H1 and the diameter of the melted part, and a good correlation is obtained between the two.

Therefore, the reflected wave C is selectively detected by a gate circuit, the peak value H2 of the reflected wave at the end of the energization time T3 and the peak value H1 at time T2 are detected, and the difference H2-H is calculated. Since it is possible to know the diameter of the welded part formed by this, it is possible to make a highly reliable estimate of the quality of the welded part from this. By the way, in the conventional ultrasonic inspection method for resistance welds, when welding workpieces of the same material and thickness with the same electrode under different welding conditions, the change in the amount of ultrasonic transmission H2-H and the molten area The relationship diagram of the size (area) of will vary greatly depending on the welding conditions.

This is clear from experiments. Therefore, in the conventional method, it can be said that the diagram of the relationship between the change H2-H1 in the amount of ultrasonic transmission and the size (area) of the melted part is effective only under constant contact conditions. In this way, it was necessary to reduce changes in the relationship diagram between the amount of ultrasonic transmission and the size (area) of the fused portion due to welding conditions and the like.

The present invention has been made to solve these problems, and the ultrasonic inspection apparatus according to the present invention will be described in detail below.

In FIG. 4, 14 is a melting part, 15 is a transmitting circuit for intermittently applying a voltage to the ultrasonic transducer 2 to send out pulsed ultrasonic waves at the same time as receiving the energization time start signal;
6 is a receiving circuit that receives the ultrasonic reflected wave from the ultrasonic transducer 2, amplifies and outputs the signal converted into an electric signal, and 17 is a gate circuit that uses the ultrasonic reflection of the electrode 4 as the output voltage of the receiving circuit 16. 18 is a circuit for selecting the peak value of the reflected wave from the surface 51; 18 is a detection/holding circuit for detecting and holding the minimum value of the output voltage of the receiving circuit 16 and outputting this peak value H1; A display device 20 displays the output voltage from the detection/holding circuit 18 during welding time, and displays the output voltage of the receiving circuit 16 at the time of receiving the energization time end signal only when the output voltage H1 is received from the detection/holding circuit 18. A holding circuit that holds and outputs this peak value H2, 21 is a detection/holding circuit 1
8 is a differential amplification circuit that outputs the difference H2-H1 between the output voltage H and the output voltage H2 of the holding circuit 20, and 28 is a constant A, B, which is necessary to calculate the size of the melted part. 27 is the output H from the differential amplification circuit 21.
2-A calculation circuit that calculates the size of the melted portion based on H1, the output H1 from the detection/holding circuit 18, and the outputs A2B and C' from the holding output circuit 28; 22 is the calculation result of the calculation circuit 27; It is a display device for displaying images.

As described above, the size (area) of the molten part is determined by the difference signal H2-H1, the peak value H of the minimum value, and constants A, B, and C' determined by the thickness and material of the workpiece to be welded, etc., which will be described later. can be calculated.

Further, according to this method, variations depending on welding conditions can be eliminated. This is clear from the practical example described below.

One example of this, shown in Fig. 5, shows a plate thickness of 1.6 m77! FIG. 2 is a diagram showing the relationship between the change H2-H in the amount of ultrasonic transmission and the size (area) of the fusion zone obtained by welding the Spcc material of 1. As is clear from FIG. 5, when the contact conditions (welding torrent, pressurization) are changed, the relationship between the amount of ultrasonic transmission H2Hl and the size of the molten zone shifts in parallel. In other words, welding conditions (welding current,
When the amount of applied pressure is changed, the amount of change in ultrasound transmission amount H2-H
When 1 is zero, the size (area) of the molten part takes on various values. FIG. 6 is a diagram showing the relationship between the magnitude of H1 when the amount of change in the amount of ultrasonic transmission is zero among the data in FIG. 5, and the size (area) of the melted part at that time.

As is clear from this, there is a good proportional relationship between the peak value H of the ultrasonic transmitted wave at the minimum point and the size of the fused zone. FIG. 7 is a diagram showing the relationship between FIG. 5 and FIG. 6 described above.

The horizontal axis shows the amount of ultrasonic transmission (relative frequency), and the vertical axis shows the size (area) of the fusion zone. Straight line 2 in the figure shows the relationship between H1 and the area of the fusion zone at the minimum point. The lines A, C, C, etc. indicate the relationship between H2-H1 and the area of the molten zone.In other words, the relationship between the amount of ultrasonic transmission and the size of the fused zone is determined by the welding conditions at the minimum point. Although it corresponds one-on-one regardless of
After passing the minimum point, it separates into straight lines A, C, and C depending on the welding conditions. The relationship shown in FIG. 7 above can be expressed as the following equation.

S-A-H1+B・(H2-H1)+CI-(1)A:
It is the slope of straight line 2, and is the ratio of the area of the melted part to the amount of ultrasound transmission H1 at H2-H1-0.

B: The slope of straight lines A, C, etc., and the amount of ultrasound transmission (H
2-H1) Increase in the area of the melted part.

C: Constant depending on the material to be welded.

By using the above equations, if the constants A, B, and C' are determined in advance for each plate thickness and material, it is possible to measure the size of the fused zone while reducing variations due to welding conditions, etc. can.

As is clear from the above description, the present invention is applicable to welding by sandwiching stacked materials to be welded from both sides between electrodes and applying pressure and current, in which an ultrasonic vibrator disposed on one electrode is driven. The ultrasonic wave is transmitted in a pulsed manner, and the ultrasonic wave that has propagated through the welding material is reflected by the reflecting surface formed on the other electrode, and this reflected wave passes through the welding material again and then The return to the ultrasonic transducer is detected during the ultrasonic wave transmission, and among the changes in the peak value of the reflector that is detected, the peak value of the reflected wave at the minimum point and the reflection at the end of the welding current are detected. From the value of the difference between the peak value of the wave and the peak value of the reflected wave at the minimum point, etc.,
The area of the melted portion formed in the above-mentioned welding material can be calculated.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view to explain the configuration of the main parts of the welding equipment and its operating principle, Figure 2 is a waveform diagram of the ultrasonic reflected waves detected by the ultrasonic transducer, and Figure 3 is a diagram for this inspection. A characteristic diagram showing changes in the peak value of the reflected wave C, which is the information medium of the method, FIG. 4 is a plotter diagram showing the configuration of an embodiment of the present invention, and FIG. Amount of change in wave C (H2-H
, ) and the size of the molten part (SH2-H1) of the welding material. Figure 6 shows the amount of change in the reflected wave C and the molten part of the welding material when welding conditions are changed. FIG. 7 is a characteristic diagram that combines the characteristics shown in FIGS. 5 and 6 into one. In the figure, 1 and 4 are electrodes, 2 is an ultrasonic vibrator, 3 and 5 are holes, 51 is an ultrasonic reflecting surface, 8 and 9 are materials to be welded, 10 and 1
1 and 12 are contact surfaces of each member forming an ultrasonic reflecting surface, 1
3 is a transmitting/receiving device, 14 is a melting part, 15 is a transmitting circuit, 1
6 is a receiving circuit, 17 is a gate circuit, 18 is a detection and holding circuit, 19 and 22 are display devices, 20 is a holding circuit, 21 is a differential amplification circuit, 27 is an arithmetic circuit, and 28 is a holding/output circuit.

Claims (1)

[Claims] 1. A device for sandwiching a material to be welded between an electrode to which an ultrasonic vibrator is attached and an electrode on which an ultrasonic reflecting surface is formed, and passing a welding current between the two electrodes through the material to be inspected, and the vibrator. a transmitting circuit for driving the ultrasonic waves to send out ultrasonic waves in a pulsed manner; and detecting ultrasonic reflected waves from the ultrasonic reflecting surface with the vibrator during the ultrasonic sending pause time and extracting them as electrical signals. a receiving circuit, and detecting the minimum value of the peak value during the energization time for the reflected wave detection from the output signal of the receiving circuit and generating a corresponding electric signal H_1;
a first sending circuit that sends out the electrical signal; a second sending circuit that detects the peak value of the output signal after passing through the minimum value and sends out an electrical signal H_2 corresponding to the peak value; Difference signal between H_1 and H_2 H_2-H_1
and a differential amplification circuit that outputs a molten material formed on the welded material based on the electric signal H_1 from the first sending circuit and the difference signal H_2-H_1 from the differential amplification circuit. An ultrasonic inspection device for a resistance point welded part, which determines the size of the welded part and determines the quality of the melted state of the welded material based on the value of the size.