JP5560084B2 - Spot welding torch - Google Patents

Description

  The present invention relates to a spot welding torch used for spot welding.

Conventionally, as the torch used in the above spot welding, a torch body having a cylindrical shape with one end portion as a bottom portion and a tapered opening formed at the other end portion as an electrode tip mounting portion, Some have a water supply pipe arranged in the hollow part.
This torch has a water supply pipe coaxially arranged in the hollow part of the torch body, and the inside of the water supply pipe is formed as a water supply channel and the outside is formed as a drainage channel, and the cooling water supplied to the torch main body from the outside is The electrode tip is cooled by being sprayed to the back surface of the electrode tip attached to the electrode tip mounting portion through the water supply channel.

  When performing spot welding, a pair of the above-mentioned torches are arranged coaxially, and two or more metal plates to be joined are inserted between the electrode tips facing each other, and between the electrode tips of both torches. By applying a current while applying a predetermined load (generally about 200 kgf), a nugget is generated between the metal plates in close contact with each other, thereby joining the metal plates together.

  The quality determination of the joint between the metal plates joined by such spot welding is generally performed after spot welding is completed, and if a defect is found in the joint, the process returns to the previous step. Since spot welding must be performed again, time and cost are increased accordingly.

  As a technique for dealing with such a problem, for example, as in a welding operation monitoring device disclosed in Patent Document 1, an ultrasonic generator-side transducer is arranged on one torch for spot welding. On the other hand, there is a type in which a transducer on the ultrasonic reception side is arranged on the other torch and both the transducers are configured to generate a torsional waveguide between these torches.

  In this welding motion monitoring device, the quality level of the joint generated during welding is compared by comparing the data corresponding to the extracted torsional waveguide from the ultrasonic equipment with the profile corresponding to the acceptable quality level. Is to ask for.

JP 2007-90435 A

  However, in the past, the data of the quality of the joint is obtained by adopting a sensitive torsion mode guide wave generated between one torch and the other torch by a vibrator. There is a problem that the analysis becomes complicated, and it has been a conventional problem to solve this problem.

  The present invention has been made paying attention to the above-described conventional problems, and provides a spot welding torch that realizes easy data analysis and enables real-time quality evaluation of joints by spot welding. It is an object.

As described above, when spot welding is performed, two or more metal plates to be joined are inserted between two electrode tips and sandwiched between them, and then generally about 200 kgf between the electrode tips of both torches. Apply the load of and adhere. At this time, a compressive stress of about 10 kgf / mm ² is applied to the joint between the metal plates that are in close contact with each other.

Here, when an ultrasonic wave is passed through a joint between metal plates that are in close contact with each other by applying compressive stress, a transmitted sound pressure (echo) is obtained. As shown in FIG. 3, the transmitted sound pressure is higher at a low frequency such as 2 MHz or 5 MHz than at a high frequency such as 10 MHz. Therefore, a metal plate to which a compressive stress σ (kgf / mm ² ) is applied. It is considered that the degree of adhesion between the metal plates can be evaluated from the transmitted sound pressure (%) when a longitudinal wave of an ultrasonic wave having a low frequency is passed through the joint between them.

Next, when a current is passed between the electrode tips in this state, the temperature of the joint between the metal plates that are in close contact with each other increases, and the metal at the joint melts to produce nuggets.
At this time, since the degree of adhesion between the metal plates is improved due to the decrease in the yield strength of the metal accompanying the increase in the temperature of the joint portion, the transmitted sound pressure increases, but with the formation of this nugget, the ultrasonic wave is solid-liquid (Molten metal)-Permeate in the order of solid. In general, the speed of sound in molten metal is 1/3 to 1/4 of the speed of sound in a solid, and the acoustic impedance is also reduced to 1/3 to 1/4. Therefore, as described above, ultrasonic waves are solid-liquid (melted). When propagating in the order of (metal) -solid, the amplitude value of the transmitted wave decreases.

When the nugget is solidified, the ultrasonic wave propagates in the order of solid-solid-solid, so that the transmitted sound pressure increases again.
In other words, when an appropriate nugget is formed at the joint between the metal plates that are in close contact with each other, the amplitude value of the transmitted wave temporarily decreases due to melting of the metal, and the amplitude of the transmitted wave is solidified with the solidification of the molten metal. The value will start to rise again.

  On the other hand, the thickness of the nugget and the transmitted sound pressure when ultrasonic waves pass through the nugget have frequency dependence. For example, when ultrasonic waves with a frequency of 0.5 MHz are used, the thickness of the nugget 4 and the transmitted sound pressure are as shown in the graph of FIG. As shown in the graph of FIG. 4, even when the nugget is formed, when the penetration is shallow or the thickness of the nugget is thin, the change in the transmitted sound pressure due to the melting of the metal is small.

  That is, when the nugget is not formed or when the nugget is thin, the amplitude value of the transmitted wave increases as the load is applied between the electrode tips, and the temperature of the joint between the metal plates increases. As a result, the amplitude value further increases, but the amplitude value of the transmitted wave does not decrease or slightly decreases.

  In this way, the present inventors propagate ultrasonic waves in a longitudinal wave mode in which data analysis is simple and perform changes in the amplitude value of transmitted waves during spot welding. Thus, it was found that the joint of spot welding can be evaluated.

  As described above, the spot welding torch has a double pipe structure in which a water supply pipe having a diameter of about 5 mmφ is coaxially arranged in the hollow portion of the bottomed cylindrical torch body, and the water supply inside the water supply pipe The water passing through the path is sprayed on the back surface of the electrode chip attached to the electrode chip mounting portion of the torch body.

  Therefore, the present inventors conducted a test to confirm whether the ultrasonic wave propagates through the water in the water supply channel inside the water supply pipe arranged in the hollow portion of the torch without any trouble.

  Specifically, first, a thin tube having an inner diameter of 5.8 mm, an outer diameter of 10.5 mm, and a length of 107 mm is submerged in water, a transmitting-side vibrator is disposed at one end of the thin tube, and a receiving-side vibrator is disposed at the other end. Arranged. Next, ultrasonic waves with three frequencies of 1.0 MHz, 2.25 MHz, and 5.0 MHz were transmitted and received through both vibrators.

  At this time, transducers with diameters of 25.0 mmφ and 12.5 mmφ that can emit ultrasonic waves with frequencies of 1.0 MHz, 2.25 MHz, and 5.0 MHz were employed as the transmitter-side transducers. Employed a transducer for a frequency of 5.0 MHz having a diameter of 10.0 mmφ smaller than that of the transmission-side transducer. This is because if the dimensions of the receiving-side transducer are determined in accordance with the frequency of the transmitting-side transducer, the outer diameter of the narrow tube exceeds 10.5 mm, and there is a possibility of receiving ultrasonic waves propagating outside the narrow tube. Because.

  In the above test, it was possible to confirm the signal that ultrasonic waves having frequencies of 1.0 MHz, 2.25 MHz, and 5.0 MHz were transmitted through the inside of the thin tube, and the sound pressure of the transmitted ultrasonic waves was measured. The present inventors have obtained the knowledge that any of the sound pressures applied can be applied to the monitoring of a spot welding joint.

That is, the invention according to claim 1 of the present invention is a spot welding torch used for spot welding in which two or more metal plates are sandwiched and welded between a pair of electrode tips, with one end portion as a bottom portion and A torch having a water supply portion and a drainage portion that has a cylindrical shape with the other open end as a mounting portion of the electrode tip, and supplies and drains cooling water to a hollow portion between the bottom portion and the tip mounting portion. The main body and the cooling water that is disposed in the hollow portion of the torch main body are guided to eject the cooling water supplied from the water supply unit to the electrode chip attached to the chip mounting unit, and the cooling water ejected to the electrode chip is A water supply pipe that forms a drainage channel that leads to the drainage section, and an ultrasonic wave that is disposed in the main body of the torch and that transmits and receives ultrasonic waves to the joint between the metal plates through the water supply pipe and the electrode tip. Includes a sonic sensor, the end portion facing the ultrasonic sensor of the water supply pipe is formed in a funnel-shaped end portion progressively diameter increases toward the ultrasonic sensor, the water supply unit, the funnel of the water supply pipe The drainage portion is disposed on the peripheral wall between the funnel-shaped end portion of the water supply pipe and the tip mounting portion of the torch body. configurations and to have, and a means for solving the conventional problems described above spot welding torch of this configuration.

  In the spot welding torch according to the first aspect of the present invention, a pair of spot welding torches arranged coaxially and two or more metal plates to be joined between electrode tips attached to each torch body When spot welding is performed with sandwiching water, supplying and draining cooling water to both torches and sending and receiving ultrasonic waves between both ultrasonic sensors makes it possible to obtain an appropriate nugget at the joint between the metal plates that are in close contact with each other. In this case, the amplitude value of the transmitted wave once decreases, but the amplitude value of the transmitted wave starts to increase again. In some cases, the amplitude value of the transmitted wave that rises as the temperature of the joint between the metal plates rises hardly decreases or only slightly decreases.

  In this way, longitudinal wave mode ultrasonic waves from the ultrasonic sensor are propagated to the joint between the metal plates, and the change in the sound pressure of the transmitted wave at the time when the ultrasonic wave passes through the joint between the metal plates is measured. As a result, it is possible to determine the weld quality of the joint in real time, that is, the weld quality determination of the joint can be performed in real time without requiring complicated data analysis.

Further, in the torch for spot welding according to claim 1 of the present invention, since Ru said end facing the ultrasonic sensor of the water supply pipe and the funnel-shaped end portion progressively diameter increases toward the ultrasonic sensor Tei, ultrasound incident on the side surface of the end portion facing the ultrasonic sensor of the water supply pipe, it Does not easily transmitted to the water supply pipe itself beyond the critical angle, so that the transmission and reception of ultrasonic waves are performed efficiently.

At this time, as shown in FIG. 5, when the sound speed in water is Vw and the sound speed transmitted through the water supply pipe is Vp, the critical angle θcr of the ultrasonic wave obliquely incident on the side surface of the water supply pipe is cos ⁻¹ (Vw / Vp). On the other hand, the taper angle θ at the funnel-shaped end of the water supply pipe is (D−d) / (tan θ) = (D + d) / (D, where d is the diameter of the water supply pipe and D is the diameter of the transducer of the ultrasonic sensor. tan2θ).

Therefore, in the spot welding torch according to claim 2 of the present invention, the sound velocity in water is Vw, the sound velocity transmitted through the water supply pipe having the diameter d is Vp, and the critical angle of the ultrasonic wave obliquely incident on the side surface of the water supply pipe is θcr. In this case, the taper angle θ at the funnel-shaped end of the water supply pipe is θ <θcr = cos ⁻¹ (Vw / Vp), and the diameter D of the vibrator of the ultrasonic sensor , (D−d) / (tan θ) = (D + d) / (tan 2θ).

Furthermore, in the spot welding torch according to claim 3 of the present invention, ultrasonic waves are transmitted between the end of the water supply pipe facing the ultrasonic sensor and the ultrasonic sensor between the central axis and the water supply pipe. In this case, the acoustic lens that is focused near the ultrasonic sensor of the water supply pipe is difficult to be transmitted to the water supply pipe itself beyond the critical angle. Therefore, transmission / reception of ultrasonic waves is efficiently performed.

Furthermore, in the spot welding torch according to claim 4 of the present invention, the frequency of the ultrasonic wave transmitted and received by the ultrasonic sensor is 0.5 MHz to 2.0 MHz, and the diameter of the water supply pipe is set to the wavelength of the ultrasonic wave. The configuration is three times or more.

As described above, in spot welding, a compressive stress of about 10 kgf / mm ² is generally applied to the joint between the metal plates that are in close contact with each other. The transmitted sound pressure (echo) obtained when ultrasonic waves flow through the joint between the metal plates increases as the compressive stress increases, and the tendency is more pronounced as the frequency decreases. Is 0.5 MHz to 2.0 MHz, and the diameter of the water supply pipe is set to be three times or more the wavelength of the ultrasonic wave, it is easy to flow low-frequency ultrasonic waves that can provide a large echo to the water supply pipe.

Furthermore, in the spot welding torch according to claim 5 of the present invention, the ultrasonic sensor is an ultrasonic sensor directly attached to the torch body with a soft metal. For this ultrasonic sensor, it is desirable to use a high-temperature ultrasonic probe previously developed by the applicant of the present invention.
In the spot welding torch having this configuration, peeling due to deterioration of the sensor mounting portion can be avoided in an underwater environment in the torch body.

  Since the spot welding torch according to claim 1 of the present invention has the above-described configuration, it is excellent in that it enables real-time quality evaluation of a joint by spot welding after facilitating data analysis. Effect.

In addition, since the spot welding torch according to claims 1 to 3 of the present invention has the above-described configuration, it is possible to efficiently transmit and receive ultrasonic waves.
Furthermore, since the spot welding torch according to claim 4 of the present invention has the above-described configuration, it is easy to flow low-frequency ultrasonic waves capable of obtaining a large transmitted wave echo to the water supply pipe. Since the spot welding torch according to Item 5 has the above-described configuration, the sensor can be prevented from peeling off in the underwater environment in the torch body.

It is a section explanatory view of the spot welding torch concerning one example of the present invention. FIG. 2 is a configuration explanatory diagram of a spot welding monitoring device in which the spot welding torch shown in FIG. 1 is employed. It is a graph which shows the influence of the compressive stress which acts on the transmitted sound pressure (echo) in the case of flowing an ultrasonic wave in the junction part between metal plates. It is a graph which shows the relationship between the thickness of a nugget at the time of an ultrasonic wave permeate | transmitting a nugget, and transmitted sound pressure. It is a figure explaining the relationship between the taper angle in the funnel-shaped end part of the water supply pipe of the spot welding torch shown in FIG. 1, and the diameter of the vibrator.

Hereinafter, the present invention will be described with reference to the drawings.
1 and 2 show an embodiment of a spot welding torch according to the present invention. In this embodiment, the spot welding torch according to the present invention is employed in a system for monitoring a spot welding joint. Will be described as an example.

  As shown in FIG. 2, the joint monitoring system includes a pair of spot welding torches 1 and 1 having a cylindrical shape in which electrode tips C and C are attached to tip portions that are coaxially arranged and face each other. In addition, an evaluation unit 3 that determines the quality of welding at a joint when welding by sandwiching two metal plates W between the electrode tips C, C of the pair of spot welding torches 1, 1, The monitor 4 which displays the evaluation result by this evaluation part 3 is provided.

  As shown in FIG. 1, the spot welding torch 1 has one end portion as a bottom portion 2 a and the other open end portion (tip portion) as a mounting portion 2 b for the electrode tip C, and the bottom portion 2 a and the tip mounting portion. A torch body 2 having a water supply portion 2c and a drainage portion 2d for supplying and discharging cooling water to and from the hollow portion between the portions 2b is provided, and a water supply device (not shown) is provided in the water supply portion 2c and the drainage portion 2d of the torch body 2 And a waste water treatment device are connected to each other.

  On the axial center of the hollow portion of the torch body 2, the cooling water supplied from the water supply part 2 c is guided to the electrode chip C attached to the chip mounting part 2 b and jetted, and the cooling jetted to the electrode chip C is jetted. A water supply pipe 5 that forms a drainage channel 2f that guides water to the drainage unit 2d is disposed. At this time, air bubbles generated in the torch main body 2 due to the temperature rise during spot welding are suppressed to a small amount, and the generated air bubbles are prevented from entering the water supply path (ultrasonic propagation path) inside the water supply pipe 5 to the drainage path 2f. For guidance, the water supply pipe 5 is constructed and arranged.

  Longitudinal wave mode ultrasonic waves are emitted to the torch body 2 of one torch 1A of the pair of spot welding torches 1 and 1 through the water supply pipe 5 and the electrode tip C toward the joint Wa between the metal plates W and W. The transmission side ultrasonic sensor 6 is disposed, and the torch body 2 of the other torch 1B receives the ultrasonic wave from the transmission side ultrasonic sensor 6 that has passed through the joint Wa through the electrode chip C and the water supply pipe 5. The ultrasonic sensor 7 is arranged, and the ultrasonic sensors 6 and 7 are both directly attached to the bottom 2a of the torch body 2 by brazing. For these ultrasonic sensors 6 and 7, it is desirable to use a high-temperature ultrasonic probe previously developed by the applicant of the present invention.

In this case, the end of the water supply pipe 5 in the one torch 1 </ b> A facing the transmission-side ultrasonic sensor 6 is a funnel-shaped end 5 a that gradually increases in diameter toward the transmission-side ultrasonic sensor 6. Specifically, as shown in FIG. 5, when the sound speed in water is Vw, the speed of sound transmitted through the water supply pipe 5 having a diameter d is Vp, and the critical angle of the ultrasonic wave obliquely incident on the side surface of the water supply pipe is θcr, The taper angle θ at the funnel-shaped end portion 5a of the water supply pipe 5 is smaller than the critical angle θcr (θ <θcr = cos ⁻¹ (Vw / Vp)), and the diameter D of the vibrator of the transmission-side ultrasonic sensor 6 is included. On the other hand, (D−d) / (tan θ) = (D + d) / (tan 2θ) is set.

  In addition, between the funnel-shaped end portion 5a of the water supply pipe 5 facing the transmission-side ultrasonic sensor 6 in the one torch 1A and the transmission-side ultrasonic sensor 6, ultrasonic waves are transmitted between the central axis of the water supply pipe 5 or its An acoustic lens 8 for focusing in the vicinity is installed.

  In this embodiment, the frequency of the ultrasonic wave transmitted and received between the transmission-side ultrasonic sensor 6 and the reception-side ultrasonic sensor 7 of the pair of spot welding torches 1 and 1 is 0.5 MHz to 2.0 MHz. The diameter d of the tube 5 is set to 3 times or more of the wavelength of the ultrasonic wave.

  The evaluation unit 3 is a joint at the time when transmission / reception of ultrasonic waves is performed between the transmission-side ultrasonic sensor 6 and the reception-side ultrasonic sensor 7 while supplying / draining cooling water to / from the pair of spot welding torches 1, 1. The change in the sound pressure of the transmitted wave of Wa is measured, and from this measurement result, the welding quality of the joint Wa is determined and displayed on the monitor 4.

  In the spot welding joint monitoring system having such a configuration, two metal plates W to be joined between the electrode tips C and C attached to the torch bodies 2 and 2 of the pair of spot welding torches 1 and 1. , W, when spot welding is performed, first, a current P is applied while applying a load P of about 200 kgf between the pair of spot welding torches 1, 1 to bring them into close contact with each other.

  During this welding, ultrasonic waves are transmitted and received between the transmission-side ultrasonic sensor 6 and the reception-side ultrasonic sensor 7 while supplying and draining cooling water to and from the torch bodies 2 and 2 of both spot welding torches 1 and 1. Make it.

  When an appropriate nugget is formed at the joint Wa between the metal plates W and W that are in close contact with each other, the amplitude value of the transmitted wave temporarily decreases due to melting of the metal, As the solidification occurs, the amplitude value of the transmitted wave starts to rise again.

  On the other hand, when the nugget is not formed or when the nugget is thin, the amplitude value of the transmitted wave increases as the load P is applied between the electrodes C and C, and the metal plates W and W are joined. As the temperature of the portion Wa increases, the amplitude value further increases, but the amplitude value of the transmitted wave does not decrease or decreases slightly.

  As described above, the spot welding torch 1 having the above-described configuration is employed, and the ultrasonic wave in the longitudinal wave mode from the transmission-side ultrasonic sensor 6 is propagated to the joint Wa between the metal plates W and W. If the evaluation unit 3 measures the change in sound pressure of the transmitted wave at the time when it passes through the joint Wa between the metal plates W and W, the weld quality determination of the joint Wa can be performed in real time. While facilitating data analysis, it is possible to determine whether the joint Wa is good or bad in real time.

In the spot welding torch 1, the end of the water supply pipe 5 of one torch 1 </ b> A facing the transmission-side ultrasonic sensor 6 is directed to the transmission-side ultrasonic sensor 6 as a funnel-shaped end 5 a that gradually increases in diameter. In other words, the relationship between the taper angle θ of the funnel-shaped end 5a and the diameter D of the vibrator included in the transmission-side ultrasonic sensor 6 is θ <θcr = cos ⁻¹ (Vw / Vp) and ( Since D−d) / (tan θ) = (D + d) / (tan 2θ), the ultrasonic wave incident on the side surface of the end of the water supply pipe 5 facing the transmission-side ultrasonic sensor 6 exceeds the critical angle θcr. It becomes difficult to be transmitted to the tube 5 itself, and as a result, transmission / reception of ultrasonic waves is efficiently performed.

  Further, in the spot welding torch 1, since the acoustic lens 8 is installed between the funnel-shaped end 5 a of the water supply pipe 5 and the transmitting-side ultrasonic sensor 6 in one torch 1 A, the ultrasonic welding Transmission / reception is performed more efficiently.

  Furthermore, in the spot welding torch 1, the frequency of the ultrasonic wave transmitted and received between the transmission side ultrasonic sensor 6 and the reception side ultrasonic sensor 7 is set to 0.5 MHz to 2.0 MHz, and the diameter of the water supply pipe 5 is set. Since d is set to be three times or more of the wavelength of the ultrasonic wave, a low frequency ultrasonic wave is obtained through the water supply pipe 5 so that a large echo can be obtained when the ultrasonic wave is applied to the joint Wa between the metal plates W and W. It becomes easy.

  Furthermore, in the spot welding torch 1, both the ultrasonic sensors 6 and 7 are directly attached to the bottom 2 a of the torch body 2 by brazing. Therefore, in the underwater environment in the torch body 2, the sensor attachment part It is possible to avoid peeling due to deterioration.

  Further, in the above-described embodiment, the case where the spot welding torch according to the present invention is employed in a spot welding joint monitoring system and two metal plates are welded is described as an example. However, the present invention is not limited thereto. However, the present invention can be applied to spot welding of two or more metal plates W.

  The configuration of the spot welding torch according to the present invention is not limited to the configuration of the above-described embodiment.

1 (1A, 1B) Spot welding torch (one torch, the other torch)
2 Torch body 2a Bottom 2b Tip mounting part 2c Water supply part 2d Drainage part 2f Drainage channel 5 Water supply pipe 5a Funnel-shaped end part of water supply pipe 6 Transmission side ultrasonic sensor 7 Reception side ultrasonic sensor 8 Acoustic lens C Electrode chip W Metal plate Wa joint

Claims (5)

A spot welding torch used for spot welding in which two or more metal plates are sandwiched and welded between a pair of electrode tips,
A cylindrical shape having one end as a bottom and the other open end as a mounting portion for the electrode chip, and supplying and draining cooling water to a hollow portion between the bottom and the chip mounting portion. A torch body having a water supply portion and a drainage portion;
The cooling water that is disposed in the hollow portion of the torch main body and that guides the cooling water supplied from the water supply unit to the electrode chip attached to the chip mounting unit, and jets the cooling water sprayed to the electrode chip to the drainage unit. A water supply pipe that forms a drainage channel leading to
An ultrasonic sensor that is disposed in the torch body and transmits and receives ultrasonic waves to and from the joint between the metal plates through the water supply pipe and the electrode tip ;
The end of the water supply pipe facing the ultrasonic sensor is formed in a funnel-shaped end that gradually increases in diameter toward the ultrasonic sensor,
The water supply portion is disposed on a peripheral wall between the funnel-shaped end portion of the water supply pipe and the bottom portion of the torch main body, and the drainage portion is disposed on the funnel-shaped end portion of the water supply pipe and the torch main body. A spot welding torch arranged on a peripheral wall between the tip mounting portion . The taper angle at the funnel-shaped end of the water supply pipe, where Vw is the speed of sound in water, Vp is the speed of sound transmitted through the water supply pipe having the diameter d, and θcr is the critical angle of the ultrasonic wave obliquely incident on the side of the water supply pipe θ is θ <θcr = cos ⁻¹ (Vw / Vp), and (D−d) / (tan θ) = (D + d) / (D with respect to the diameter D of the vibrator of the ultrasonic sensor. 2. The spot welding torch according to claim 1, which has a relationship of tan 2θ). Wherein said end portion facing the ultrasonic sensor of the water supply pipe, between the ultrasonic sensor, any claim 1-2 which is installed an acoustic lens for focusing an ultrasonic wave to the central axis or its vicinity of the water supply pipe The spot welding torch according to any one of the items. Wherein the frequency of the ultrasonic waves to be transmitted and received by the ultrasonic sensor and 0.5MHz～2.0MHz, the diameter of the water supply pipe to any one of claims 1 to 3 which is three times or more a wavelength of the ultrasonic The described spot welding torch. The spot welding torch according to any one of claims 1 to 4 , wherein the ultrasonic sensor is an ultrasonic sensor directly attached to the torch body with a soft metal.

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