JP7777910B2 - Resistance welding equipment - Google Patents

Description

The present invention relates to a resistance welding device.

Resistance welding is a method in which, for example, one of a pair of electrodes, one positive and one negative, is positioned coaxially opposite each other across the two components to be joined (welded objects) while applying pressure to the other. A welding current is passed between the pair of electrodes, generating Joule heat at the contact point between the two components, melting and solidifying the metal at the contact point (forming a nugget) and joining the two components together. One type of resistance welding is projection welding, in which a projection (protrusion) is provided on one of the two components, the tip of which contacts the other (see, for example, Patent Document 1). Projection welding has the advantage of allowing for efficient welding in a short time, as the welding current is concentrated at the protrusion when current is passed between the electrodes, preventing deterioration in appearance quality due to thermal deformation.

In resistance welding equipment used for projection welding, a pair of electrodes is typically electrically connected to a power source via a welding transformer. As a result, even if the welding current output from the power source is low, on the order of tens to hundreds of amperes, and is unsuitable for resistance welding, the welding transformer can convert this low current into a large current of the order of thousands of amperes, which is suitable for resistance welding.

JP 2014-217854 A

In a resistance welding device used for projection welding, the current paths formed by electrically connecting a welding transformer to a pair of electrodes (the current path connecting the positive terminal of the welding transformer to the positive electrode, and the current path connecting the negative terminal of the welding transformer to the negative electrode) are typically formed using conductive members known as "bus bars" or "bus bars" that are made of highly electrically conductive materials such as copper, copper alloys, and aluminum alloys and are capable of carrying large currents. However, as shown schematically in Figure 5, the above-mentioned current path 103 formed using conductive member 102 is typically formed using only one path connecting the welding transformer 100 to the electrode 101 over the shortest distance, primarily to keep costs down.

However, when the current path 103 is set up in the above manner, more welding current flows through the region of the electrode (particularly the positive electrode located upstream in the direction of welding current flow) 101 that is closer to the welding transformer 100 (the right half of the region in the illustrated example) than through the region farther from the welding transformer 100 (the left half of the region in the illustrated example). Therefore, when multiple projections 105 for projection welding are provided at intervals around the circumference of the electrode 101 (the direction along a circle centered on the axis of the electrode 101) on one of the two components to be joined, differences in the melting behavior (e.g., melting amount per unit time) between the multiple projections 105 occur. When such differences occur, differences also occur in the quality of the nugget formed between the two components as the projections 105 melt and solidify, which may make it difficult to consistently achieve the desired joint strength.

In light of the above situation, the present invention aims to provide a resistance welding device that can stably ensure the desired joint strength between two components joined by projection welding.

The present invention, which was devised to achieve the above-mentioned objective, is a resistance welding device comprising a pair of positive and negative electrodes arranged coaxially opposite each other across two members, one of which has the tips of multiple protrusions on the other member in contact with the other member, and a pressure mechanism that presses one of the pair of positive and negative electrodes toward the other member. While the pressure mechanism presses the two members sandwiched between the pair of positive and negative electrodes, a welding current is passed between the pair of positive and negative electrodes via a welding transformer. In this device, multiple conductive members through which the welding current flows are electrically connected to at least the positive electrode of the pair of positive and negative electrodes, and the multiple conductive members are arranged at equal intervals along a circle centered on the axis of the positive electrode.

With a resistance welding device having the above configuration, the welding current output from the positive terminal of the welding transformer can be equally divided and supplied (input) to multiple locations around the positive electrode. This reduces the amount of welding current flowing from the positive electrode to the negative electrode, i.e., the amount of welding current flowing in the direction in which the workpiece is clamped between the pair of electrodes (the axial direction of the electrodes), which varies less around the electrode. Therefore, for example, by providing multiple protrusions (welding protrusions) spaced apart around the electrode on one of the components, it is possible to uniformize the melting pattern of the multiple protrusions (e.g., the amount of melting per unit time), thereby consistently ensuring the desired joint strength between the two components to be joined.

In the above configuration, the multiple conductive members can be made to have the same dimensions in the direction in which the welding current flows. This makes it possible to equalize the amount of welding current supplied to multiple locations around the positive electrode via each conductive member, which is advantageous in ensuring uniform melting of the multiple protrusions.

As a result, the resistance welding device according to the present invention makes it possible to stably ensure the desired joint strength between two components joined by projection welding.

FIG. 1 is a schematic diagram of a resistance welding device. 1A is a partially enlarged view of a resistance welding device in which a workpiece to be welded is set, and FIG. 1B is a plan view of a second member shown in FIG. 1A. 2 is a schematic diagram for explaining a characteristic configuration employed in the resistance welding apparatus of FIG. 1. FIG. 1. FIG. 4 is a schematic diagram for explaining a modification of the characteristic configuration employed in the resistance welding apparatus of FIG. 1 is a schematic diagram for explaining problems with a conventional resistance welding device.

The following describes an embodiment of the present invention with reference to the drawings (Figs. 1 to 4).

Figure 1 shows a schematic diagram of a resistance welding device 1 according to one embodiment of the present invention. The resistance welding device 1 shown in the figure is used to join two metal members using projection welding, a type of resistance welding, and mainly comprises a pair of electrodes 2, 3, a pressure mechanism 6, a power supply unit 10, and a control unit 15.

Based on Figure 2(a), an example of two members (workpieces to be welded) joined using the resistance welding apparatus 1 of Figure 1 will be described. The workpieces shown in the figure consist of a first member 21 having a circular hole 21a and an annular second member 22 placed on top of the first member 21 and welded around the hole 21a of the first member 21. As also shown in Figure 2(b), one end face of the second member 22 (the face facing the first member 21) has multiple (eight in the illustrated example) protrusions 23 equally spaced (at 45° intervals) along its circumferential direction, and the second member 22 is placed on top of the first member 21 with the tip of each protrusion 23 in contact with the upper end face of the first member 21.

The pair of positive and negative electrodes 2, 3 are arranged coaxially, one above the other, with their tips facing each other, and are constantly cooled by the coolant flowing inside while the workpiece is being welded.

In this embodiment, the pressure mechanism 6 adjusts the vertical position of the upper electrode 2 to apply pressure (clamp) from above and below the workpiece placed between the pair of electrodes 2 and 3. The pressure mechanism 6 can precisely adjust the downward (upward/downward) movement of the electrode 2, i.e., the pressure applied to the workpiece placed between the electrodes 2 and 3. In this example, an electric (linear) actuator is used, which includes an electric motor 7, such as a servo motor, that generates a rotational driving force, and a ball screw 8 as a motion conversion mechanism that converts the rotational motion of the output shaft of the electric motor 7 into linear motion (linear motion in the vertical direction). An upper holding member 4, which holds the upper electrode 2, is attached to the tip of the output shaft 9 of this electric actuator. Meanwhile, the lower electrode 3 is held by a lower holding member 5 attached to the structure of the resistance welding apparatus 1. Both the upper holding member 4 and the lower holding member 5 are made of a metal material with high electrical conductivity, such as copper or a copper alloy. The upper electrode 2 is held by the upper holding member 4 in a state where it can be electrically connected to the upper holding member 4, and the lower electrode 3 is held by the lower holding member 5 in a state where it can be electrically connected to the lower holding member 5.

The power supply unit 10 includes a power source 11 and a welding transformer 12 electrically connected to the power source 11. The welding transformer 12 converts the low current (e.g., a current of tens to hundreds of amperes) output from the power source 11 into a large current (e.g., a current of several thousand amperes) suitable for resistance welding. The upper electrode 2 is electrically connected to the negative terminal of the welding transformer 12 via electrical connection means 13 and an upper holding member 4, and the lower electrode 3 is electrically connected to the positive terminal of the welding transformer 12 via electrical connection means 14 and a lower holding member 5. Therefore, in this embodiment, the upper electrode 2 constitutes the negative electrode, and the lower electrode 3 constitutes the positive electrode. For ease of explanation, the upper electrode 2 and the lower electrode will also be referred to as the "negative electrode 2" and the "positive electrode 3," respectively.

As shown in FIG. 3 , the electrical connection means 14 electrically connecting the positive electrode 3 and the positive terminal of the welding transformer 12 includes multiple (here, two) conductive members 14a, 14b electrically connected to the positive electrode 3 via the lower holding member 5. These two conductive members 14a, 14b are arranged facing each other, radially sandwiching the positive electrode 3 (or the lower holding member 5 that holds it). In other words, the two conductive members 14a, 14b are arranged at equal intervals (180° pitch) along a circle centered on the axis of the positive electrode 3. Both conductive members 14a, 14b are made of a highly electrically conductive material such as copper, copper alloy, or aluminum alloy, and are capable of carrying the large current output from the welding transformer 12 (components commonly referred to as "bus bars" or "bus bars").

Although not shown in the figure, the electrical connection means 13 that electrically connects the negative electrode 2 to the welding transformer 12 (the negative terminal thereof) also has a configuration similar to the electrical connection means 14 described above. That is, the electrical connection means 13 has multiple conductive members electrically connected to the negative electrode 2 via the upper holding member 4, and the multiple conductive members are arranged at equal intervals along a circle centered on the axis of the positive electrode 3 (negative electrode 2).

The control unit 15 includes a first control unit 16 and a second control unit 17. The first control unit 16 is electrically connected to the power source 11 and controls the amount of welding current flowing between the positive electrode 3 and the negative electrode 2 according to a predetermined current pattern determined in advance according to the configuration of the workpieces to be welded. The second control unit 17 is electrically connected to the electric motor 7 that constitutes the pressure mechanism 6 and controls the operation of the electric motor 7 according to a predetermined pressure pattern determined in advance according to the configuration of the workpieces to be welded.

The resistance welding device 1 of this embodiment has roughly the above configuration. With this resistance welding device 1, projection welding is performed on the workpiece as follows.

First, as shown in FIG. 2(a), a workpiece consisting of a first member 21 and an annular second member 22 positioned above the first member 21 with the tip of the protrusion 23 in contact with the first member 21 is placed between the electrodes 2 and 3. Preferably, the second member 22, the hole 21a formed in the first member 21, and the electrodes 2 and 3 are coaxially arranged. After the workpiece is placed between the electrodes 2 and 3, the electric motor 7 constituting the pressure mechanism 6 is driven based on an operation command output from the second control unit 17 of the control unit 15. This causes the negative electrode 2 to move downward, and the workpiece is clamped from above and below between the negative electrode 2 and the positive electrode 3. After the workpiece is clamped, pressure is applied to the workpiece from above and below according to a pressure pattern previously stored in the second control unit 17, while a welding current is passed between the electrodes 2 and 3 (the workpiece) according to a current pattern previously stored in the first control unit 16. As a result, the protrusion 23 that is in contact with (pressed against) the first member 21 melts, and a joint (nugget) that joins the first member 21 and the second member 22 together is created at the position where the protrusion 23 was located.

The resistance welding device 1 of this embodiment described above applies pressure to one of the pair of positive and negative electrodes 2, 3 (negative electrode 2) toward the other electrode (positive electrode 3) using the pressure mechanism 6, and then passes a welding current between the pair of electrodes 2, 3 via the welding transformer 12. The positive electrode 3 is electrically connected to multiple (two) conductive members 14a, 14b, each of which passes a welding current, and these two conductive members 14a, 14b are arranged at equal intervals along a circle centered on the axis of the positive electrode 3 (see Figure 3).

This configuration allows the welding current output from the positive terminal of the welding transformer 12 to be equally divided and supplied (input) to two locations around the positive electrode 3. This reduces the amount of welding current flowing from the positive electrode 3 to the negative electrode 2, i.e., the amount of welding current flowing along the clamping direction of the electrodes 2, 3 around the workpieces (first member 21 and second member 22). Therefore, as shown in FIG. 2(b), by providing multiple (eight in the illustrated example) protrusions 23 at equal intervals around the circumference of the annular second member 22, it is possible to uniformly melt the multiple protrusions 23. In particular, in this embodiment, two conductive members through which the welding current also flows are electrically connected to the negative electrode 2, and these two conductive members are equally spaced along a circle centered on the axes of the electrodes 2, 3, thereby enhancing the uniformity of the melting behavior of each protrusion 23.

Therefore, the resistance welding apparatus 1 of this embodiment makes it possible to stably ensure the desired joint strength between the two members 21, 22 to be joined by projection welding, which is a type of resistance welding.

The above describes a resistance welding device 1 according to one embodiment of the present invention, but various modifications can be made to the resistance welding device 1 without departing from the spirit of the device.

For example, three or more conductive members electrically connected to the positive electrode 3 for carrying the welding current can be arranged evenly along a circle centered on the axis of the positive electrode 3. Figure 4 shows one example, with four conductive members arranged at 90° intervals along the circle (14a-14d). This is advantageous in terms of making the amount of welding current flowing from the positive electrode 3 to the negative electrode 2 uniform around the circumference of the electrodes 2, 3, compared to when two conductive members are arranged at 180° intervals (see Figure 3).

In this case, however, because conductive member 14d is connected to lower holding member 5 at a position farther from welding transformer 12 than conductive member 14c, there is a concern that the amount of welding current input to positive electrode 3 via conductive member 14d may be significantly reduced compared to the amount of welding current input to positive electrode 3 via conductive member 14c. Therefore, although not shown, it is preferable to make conductive members 14a-14d the same in the direction of welding current flow (the longitudinal direction of the conductive members) by, for example, making the shapes and lengths of conductive members 14a (14b), 14c, and 14d different from one another. This will equalize the amount of welding current supplied (input) to multiple locations around the positive electrode via each conductive member, thereby uniforming the melting pattern of each protrusion 23.

In addition, in the embodiment described above, the upper electrode 3 connected to the pressure mechanism 6 is the negative electrode, and the lower electrode 2 is the positive electrode. However, it is also possible to reverse this and have the lower electrode 2 be the negative electrode and the upper electrode 3 be the positive electrode. However, even in this case, the electrical connection means (13) that electrically connects the electrode 3 to the positive terminal of the welding transformer 12 should have a configuration such as that shown in Figures 3 and 4. This allows for the same operational effects as the above embodiment to be achieved.

REFERENCE SIGNS LIST 1 resistance welding device 2 electrode 3 electrode 6 pressure mechanism 11 power supply 12 welding transformer 13 electrical connection means 14 electrical connection means 14a, 14b, 14c, 14d conductive member 21 first member 22 second member 23 projection

Claims (1)

A resistance welding device comprising: a pair of positive and negative electrodes arranged coaxially opposite each other across two members, one of which has tips of a plurality of protrusions in contact with the other member; and a pressure mechanism for applying pressure to one of the pair of positive and negative electrodes toward the other member, wherein the two members interposed between the pair of positive and negative electrodes are pressed by the pressure mechanism, and a welding current is passed between the pair of positive and negative electrodes via a welding transformer,
A resistance welding device characterized in that a plurality of conductive members through which the welding current flows are electrically connected to at least the positive electrode of a pair of positive and negative electrodes, and the plurality of conductive members are arranged at equal intervals along a circle centered on the axis of the positive electrode.