JPS5914189B2 - 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, non-destructive 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 detect multiple reflection waveforms that appear on a cathode ray tube. Since the state of the weld 15 was determined by observation, a large amount of time was consumed in the inspection, and since it was not a quantitative determination method, there was a drawback that the determination differed between inspectors.

In addition, the conventional method of performing in-process non-destructive 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. 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. Also,
Another method is the transducer reflection method, in which a transducer for transmitting and receiving 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 surface or the contact surface between the material to be welded and the electrode are used, the accuracy of determining the welding state is extremely low. 35 Therefore, as a method to improve these problems, one electrode was equipped with a transducer for both transmitting and receiving purposes to send out pulsed ultrasonic waves, which were then reflected by an ultrasonic reflecting surface provided on the other electrode. A device has been developed that detects ultrasonic waves and detects changes in the wave height value to quantitatively determine the welding state.

First, the conventional ultrasonic inspection apparatus described above will be explained. 1st
The figure shows the arrangement of electrodes, ultrasonic transducers, and materials to be welded, and the progress state of ultrasonic waves during welding with a conventional ultrasonic inspection device. Figure 2 shows the progress of ultrasonic waves detected by the transducer and displayed on the cathode ray tube. , a diagram showing multiple reflection waveforms, 1 is an electrode, 2 is an ultrasonic transducer for both transmitting and receiving purposes, and 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 welding material 9 with the tip surface 7 of the electrode 4; 13 drives the ultrasonic vibrator 2; and detects an electric signal converted when an ultrasonic reflected wave is input to the ultrasonic vibrator 2. It is a transmitting and receiving device.

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.
, 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. After the ultrasonic waves transmitted through the surfaces 10, 11 and 12 are reflected by the ultrasonic reflecting surface 51, the ultrasonic waves pass through the contact surfaces 10, 11 and 1 again.
This is a reflected wave that has passed through the oscillator 2 and reached the oscillator 2. The main component of the first reflected wave B1 is the reflected wave from the contact surface 11 and the tip surface 6 of the electrode 1, and as the energization time elapses, the contact state between the contact surface 11 and the electrode 1 improves and the contact area increases. Therefore, the reflected wave B1 decreases monotonically.

Further, the reflected wave B2 changes almost similarly to the reflected wave B1. On the other hand, the reflected wave C from the reflecting surface 51 passes through the weld twice and is affected by changes in physical properties due to the temperature rise of the welding materials 8 and 9, so it becomes monotonous like the reflected waves Bl and B2. There will be no changes.

FIG. 3 is a diagram showing the relationship between the contact 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 T, 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 welding surfaces 10, 11, and 12 increases as the welding time passes, and the contact condition improves. Further, as the welding 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 T2
In the process leading to this, 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 T3 of the energization time of the reflected wave C.
This is a diagram showing the relationship between the difference H2-H1 between the peak value H2 at time T2 and the peak value H at time T2 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 the gate circuit, and the peak value H2 of the reflected wave at the end of the energization time T3 and the time T2 are detected.
By detecting the peak value H, of I can do it. By the way, in spot welding, the electrode is a consumable item, so it is necessary to replace it with another electrode after several points have been struck.

In this case, in a static state (state where the material to be welded is not pressurized), the relative values of the first fundamental wave and the second fundamental wave will vary depending on the mounting state of the electrode, etc.

This is experimentally clear. The second point is that when welding for a long time, the electrode tip deforms and the conversion efficiency of ultrasonic waves to the vibrator etc. deteriorates, so the relationship between the amount of ultrasonic transmission and the nugget area deviates, so this needs to be calibrated. It was hot.

Since there was no way to cover such variations and always make a one-to-one correspondence between the amount of ultrasonic transmission and the nugget area, the conventional method has been used to It was necessary to find the relationship between areas.

The present invention has been made to solve these problems, and a block diagram of an ultrasonic inspection apparatus according to the present invention will be shown below.

In FIG. 4, 14 is a melting part, 15 is a transmitting circuit for intermittently applying voltage to the ultrasonic transducer 2 to transmit pulsed ultrasonic waves at the same time as receiving the energization time start signal, 1
Reference numeral 6 denotes a receiving circuit that receives the ultrasonic reflected wave from the ultrasonic transducer 2, amplifies and outputs the signal converted into an electrical signal, and 17 is a gate circuit, which uses the ultrasonic reflecting surface of the electrode 4 as the output voltage of the receiving circuit 16. 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; 19 is a welding time A display device 20 that displays the output voltage from the detection/holding circuit 18 holds 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. , and a holding circuit that outputs this peak value H2, 21 is a detection/holding circuit 1
The output of 8 is a differential amplifier circuit which outputs the difference H2-H1 between the turtle pressure H1 and the output voltage H2 of the holding circuit 20. 22 is a differential amplifier circuit that outputs the difference H2-H1 between the turtle pressure H1 and the output voltage H2 of the holding circuit 20; A gate circuit 3 holds and outputs the peak value, and calculates the ratio H2-H, /B2 of the electrical signal to the B2 echo generated from the gate circuit 22 and the value of the output [12-H] of the differential amplifier circuit 21. The arithmetic circuit 24 is a display device that displays the arithmetic results of the arithmetic circuit 23.

As described above, by calculating the ratio of the difference signal H2-H and the electric signal B2 corresponding to the B2 echo in an arithmetic circuit, and making the value of this ratio correspond to the nugget area, the area can be obtained. Since the echo is used as the sensitivity standard, the relationship between the amount of ultrasound transmitted and the nugget area can be kept constant.

This is clear from the practical example described below.

Figure 5 shows the ultrasonic transmission amount △H (H2-H) obtained by the conventional method.
, ) and the nugget area when the first bottom wave B is kept constant.

According to the experiment, the shapes of the electrodes and vibrators used were all the same, the material to be welded was 1.6m10spcc, and the welding conditions were a pressure of 350k9 and a welding current of 8.8KA1. The contact time is 6 to 18 cycles. Therefore, as is clear from FIG. 5, when B and echo are used as a reference, the amount of ultrasound transmission and the nugget area do not correspond one-to-one. They have a very skewed relationship. Figure 6 shows B under the same conditions as Figure 5.
2 is a diagram showing the relationship between the amount of ultrasound transmitted and the nugget area according to the present invention when the echoes are held constant.As is clear from FIG. 6, the relationship between the amount of ultrasound transmitted and the nugget area is almost constant. .

Therefore, if the electrodes have the same shape and vibrator, etc., the ratio of the amount of ultrasound transmitted and the B2 wave has a certain constant relationship. Like this B2
If the echo is kept constant for each electrode, even if the electrodes are replaced, the relationship between the size of the weld and the amount of ultrasonic transmission can be placed on a single straight line when welding the same plate thickness and material.

With this method, even when the electrodes are replaced, the nugget area and the amount of ultrasound transmission always correspond one-to-one, so it is possible to calibrate the difference in the amount of ultrasound transmission for each electrode, and the amount of ultrasound transmission can be adjusted every time the chip is replaced. It is no longer necessary to calculate the relationship between quantity and nugget area.

As is clear from the above description, this invention is for welding stacked materials to be welded by sandwiching them between electrodes from both sides and applying pressure and current. The ultrasonic wave is transmitted through the welding material, and the reflecting surface formed on the other electrode reflects the ultrasonic wave that has propagated through the welding material, and the reflected wave passes through the welding material again and returns to the ultrasonic vibrator. When determining the size of the molten part formed in the welded material from the change in the peak value of the reflected wave detected during the ultrasonic transmission, the bottom surface of the electrode in a static state. The above determination is made using the second wave reflected from the wave.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the configuration of the main parts of the welding equipment and its operating principle, Figure 2 is the waveform of the ultrasonic reflected wave detected by the ultrasonic transducer, and Figure 3 is information about this detection method. A characteristic diagram showing the change in the peak value of the ultrasonic reflected wave C, which is a medium, and Fig. 5 shows the ultrasonic change amount H2 when the first bottom wave of the electrode is kept constant without applying pressure to the welded material. - Figure 6, a special diagram of the relationship between H1 and the area of the molten zone, shows the amount of change in ultrasonic waves H when the second bottom wave of the electrode is kept constant when the material to be welded is not pressurized.
FIG. 4, which is a characteristic diagram of the relationship between the peak and the area of the melted part, does not show the structure of a complete embodiment of the present invention.

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 through the material to be welded between the two electrodes, 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; a first sending circuit that detects a minimum value of a peak value during the energization time for the reflected wave detection from the output signal of the receiving circuit and sends out an electrical signal H_1 corresponding to the minimum value; A second sending circuit that detects the peak value of the output signal after passing through the peak value and sends out an electrical signal H_2 corresponding to the peak value, and the output of the receiving circuit are introduced, and the output of the ultrasonic transducer is Electric signal B_2 corresponding to the reflected wave that passed twice between the electrode surfaces of the attached electrodes that are in contact with the welded material.
a gate circuit that sends out the electrical signals H_1 and H_2;
a differential amplifier circuit that outputs a difference signal H_2-H_1, and an arithmetic circuit that calculates a ratio H_2-H_1/B_2 between the value of the electrical signal B_2 generated from the gate circuit and the value of the difference signal H_2-H_1, A resistance spot weld where the size of the fusion zone formed in the welded material is determined based on the value of H_2-H_1/B_2, and the quality of the welding state of the welded material is determined from this value. ultrasonic inspection equipment.