Resistance welding equipment

Abstract

To make it possible to stably ensure a desired joint strength between two components to be joined by projection welding.SOLUTION: In a resistance-welding device 1 which flows welding-current between a pair of positive and negative electrodes 2, 3 via a welding transformer 12 in the state two components 21, 22 interposed between the pair of electrodes 2, 3 are pressurized by a pressurization mechanism 6, a plurality of conductive members 14a, 14b, in which the welding-current flows, are electrically connected to at least the positive electrode 3 of the pair of electrodes 2, 3, and the plurality of conductive members 14a, 14b are arranged at equal intervals along a circle with an axis of the positive electrode 3 as a center.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a resistance welding device. [Background technology]

[0002] Resistance welding is a method in which, for example, one of a pair of electrodes, one positive and one negative, is arranged coaxially opposite each other across two members to be joined (welded objects) while applying pressure to the other. Joule heat is generated at the contact point between the two members, causing the metal at the contact point to melt and solidify (to form a nugget) and join the two members together. One type of resistance welding is projection welding, in which a projection (protrusion) is provided on one of the two members, the tip of which contacts the other (see, for example, Patent Document 1). Projection welding has the advantage of allowing welding to be performed efficiently in a short time, preventing deterioration in appearance quality due to thermal deformation, etc.

[0003] In a resistance welding device used for projection welding, a pair of electrodes is usually 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, which 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-217854 Summary of the Invention [Problem to be solved by the invention]

[0005] In a resistance welding device for projection welding, the current paths formed by electrically connecting a welding transformer and 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 called "bus bars" or "bus bars" that are made of a material with high electrical conductivity, such as copper, copper alloy, or aluminum alloy, and that can carry large currents. However, as schematically shown in Figure 5, the above-mentioned current path 103 formed using conductive member 102 is typically only one, connecting welding transformer 100 and electrode 101 over the shortest distance, mainly from the perspective of reducing costs.

[0006] However, when current path 103 is provided in the above manner, a larger amount of welding current flows through a region of electrode 101 (particularly the positive electrode located upstream in the direction of flow of the welding current) that is closer to welding transformer 100 (the right half of the region in the illustrated example) than through a region farther from 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 along the circumferential direction of electrode 101 (the direction along a circle centered on the axis of electrode 101) on one of the two members to be joined, differences in melting behavior (e.g., melting amount per unit time) occur among the multiple projections 105. Such differences result in differences in the quality of the nugget formed between the two members as the projections 105 melt and solidify, which may make it difficult to consistently ensure the desired joint strength.

[0007] In view of the above circumstances, an object of the present invention is to provide a resistance welding apparatus that can stably ensure a desired joint strength between two members to be joined by projection welding. [Means for solving the problem]

[0008] The present invention, which was invented to achieve the above-mentioned object, comprises 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 pressurizes one of the pair of positive and negative electrodes toward the other member, and while the pressure mechanism pressurizes the two members interposed 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, and is characterized in that a plurality of 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 plurality of conductive members are arranged at equal intervals along a circle centered on the axis of the positive electrode.

[0009] With the 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 along the direction in which the workpiece is clamped between the pair of electrodes (the axial direction of the electrodes), to vary around the electrodes. Therefore, for example, if one of the members is provided with multiple protrusions (welding protrusions) spaced apart around the electrodes, it is possible to uniformize the melting pattern of the multiple protrusions (e.g., the melting amount per unit time), and ultimately to stably ensure the desired joint strength between the two members to be joined.

[0010] In the above configuration, the conductive members may have the same dimensions in the direction of the welding current flow, which makes it possible to equalize the amount of welding current supplied to multiple locations around the circumferential direction of the positive electrode via each conductive member, which is advantageous in terms of uniform melting of the multiple protrusions. [Effects of the Invention]

[0011] As described above, the resistance welding apparatus according to the present invention makes it possible to stably ensure a desired joint strength between two members to be joined by projection welding. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a resistance welding device. [Figure 2] FIG. 1(a) is a partially enlarged view of the resistance welding device in which the workpieces to be welded are set, and FIG. 1(b) is a plan view of the second member shown in FIG. [Figure 3] 2 is a schematic diagram for explaining a characteristic configuration employed in the resistance welding apparatus of FIG. 1. FIG. [Figure 4] 1. FIG. 4 is a schematic diagram for explaining a modification of the characteristic configuration employed in the resistance welding apparatus of FIG. [Figure 5] 1 is a schematic diagram for explaining problems with a conventional resistance welding device. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings (FIGS. 1 to 4).

[0014] 1 shows a schematic diagram of a resistance welding apparatus 1 according to one embodiment of the present invention. The resistance welding apparatus 1 shown in the figure is used to join two metal members by projection welding, which is a type of resistance welding, and mainly includes a pair of electrodes 2 and 3, a pressure mechanism 6, a power supply unit 10, and a control unit 15.

[0015] 2(a), an example of two members (workpieces to be welded) to be joined by the resistance welding apparatus 1 of FIG. 1 will be described. The workpieces to be welded shown in FIG. 2(a) consist of a first member 21 having a circular hole 21a and an annular second member 22 that is placed on top of the first member 21 and welded around the hole 21a of the first member 21. As also shown in FIG. 2(b), one end face of the second member 22 (the face facing the first member 21) has a plurality of (eight in the illustrated example) protrusions 23 provided at equal intervals (45° pitch) along the circumferential direction thereof. The second member 22 is placed on top of the first member 21 with the tip ends of the protrusions 23 in contact with the upper end face of the first member 21.

[0016] 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 a coolant flowing inside while the workpieces are being welded.

[0017] The pressure mechanism 6 of this embodiment 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 to be applied to the workpiece placed between the electrodes 2 and 3. Here, 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 that 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 formed from a metal material with high electrical conductivity such as copper or a copper alloy, and 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.

[0018] 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 a low current (e.g., a current of about tens to hundreds of amperes) output from the power source 11 into a large current (e.g., a current of about several thousand amperes) suitable for resistance welding. An 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 a 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. Hereinafter, for convenience 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.

[0019] As illustrated in FIG. 3, electrical connection means 14 electrically connecting positive electrode 3 and the positive terminal of welding transformer 12 has a plurality of (here, two) conductive members 14a, 14b electrically connected to positive electrode 3 via lower holding member 5, and these two conductive members 14a, 14b are arranged facing each other with positive electrode 3 (lower holding member 5 holding it) therebetween in the radial direction. In other words, two conductive members 14a, 14b are arranged at equal intervals (180° pitch) along a circle centered on the axis of positive electrode 3. Note that both conductive members 14a, 14b are formed from a material with high electrical conductivity, such as copper, copper alloy, or aluminum alloy, and are formed from a material (commonly referred to as a "bus bar" or "bus bar") that can pass a large current output from welding transformer 12.

[0020] Although not shown in the figure, the electrical connection means 13 that electrically connects the negative electrode 2 and (the negative terminal of) the welding transformer 12 also has a configuration similar to the above-mentioned electrical connection means 14. That is, the electrical connection means 13 has a plurality of conductive members electrically connected to the negative electrode 2 via the upper holding member 4, and the plurality of conductive members are arranged at equal intervals along a circle whose center is the axis of the positive electrode 3 (negative electrode 2).

[0021] Control unit 15 includes first control unit 16 and second control unit 17. First control unit 16 is electrically connected to power source 11 and controls the amount of welding current flowing between positive electrode 3 and negative electrode 2 in accordance with a predetermined current pattern determined in advance according to the configuration of the workpieces to be welded. Second control unit 17 is electrically connected to electric motor 7 that constitutes pressurizing mechanism 6 and controls the operation of electric motor 7 in accordance with a predetermined pressurizing pattern determined in advance according to the configuration of the workpieces to be welded.

[0022] The resistance welding apparatus 1 of this embodiment has roughly the above-mentioned configuration. With this resistance welding apparatus 1, projection welding is performed on the workpieces to be welded as follows.

[0023] First, as shown in FIG. 2( a), a workpiece consisting of a first member 21 and an annular second member 22 disposed above the first member 21 with the tips of the projections 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. The negative electrode 2 moves downward, and the workpiece is sandwiched between the negative electrode 2 and the positive electrode 3. After the workpiece is sandwiched, 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 generated at the position where the protrusion 23 was located.

[0024] 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 a pressure mechanism 6, and then passes a welding current between the pair of electrodes 2, 3 via a welding transformer 12. The positive electrode 3 is electrically connected to a plurality (two) of conductive members 14a, 14b, through which the welding current flows, 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 FIG. 3).

[0025] 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 toward 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), if multiple (eight in the illustrated example) protrusions 23 are provided on the annular second member 22 at equal intervals around its circumference, it becomes possible to uniformize the melting behavior of 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. This enhances the effect of uniformizing the melting behavior of the protrusions 23.

[0026] Therefore, according to the resistance welding apparatus 1 of this embodiment, it is possible to stably ensure a desired joint strength between the two members 21, 22 to be joined by projection welding, which is a type of resistance welding.

[0027] Although the resistance welding apparatus 1 according to one embodiment of the present invention has been described above, various modifications can be made to the resistance welding apparatus 1 without departing from the gist thereof.

[0028] For example, three or more conductive members electrically connected to the positive electrode 3 for passing the welding current can be arranged at equal intervals along a circle centered on the axis of the positive electrode 3. Figure 4 shows an example in which four conductive members are arranged at 90° intervals along the circle (14a to 14d). This is advantageous in that the amount of welding current flowing from the positive electrode 3 to the negative electrode 2 can be made uniform in the circumferential direction of the electrodes 2, 3, compared to when two conductive members are arranged at 180° intervals (see Figure 3).

[0029] In this case, since 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 the welding current (the longitudinal direction of the conductive members) by, for example, making conductive members 14a (14b), 14c, and 14d different in shape and length. This makes it possible to equalize the amount of welding current supplied (input) to multiple locations around the positive electrode via each conductive member, thereby uniforming the melting state of each protrusion 23.

[0030] 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 use the lower electrode 2 as the negative electrode and the upper electrode 3 as 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 the configuration shown in Figures 3 and 4. This allows the same effects as those of the above embodiment to be achieved. [Explanation of symbols]

[0031] 1 Resistance welding equipment 2 electrodes 3 electrodes 6 Pressure mechanism 11 Power supply 12 Welding transformer 13 Electrical connection means 14 Electrical connection means 14a, 14b, 14c, 14d Conductive members 21 First member 22 Second member 23 Protrusion

Claims

[Claim 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.

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