Joining device and dissimilar material joining method

Abstract

To provide a joining device to which a molten metal does not adhere to an electrode or a base.SOLUTION: A first end part 31e of a first joined material 31 comprising a first metal having a first melting point and a second end part 32e of a second joined material 32 comprising a second metal having a second melting point lower than the first melting point are made to overlap each other to form an overlapped region 312. A first electrode 41 is formed from a metal having volume resistivity higher than volume resistivity of the first metal, and contacts a surface of the first end part 31e of the overlapped region 312. A second electrode 42 is formed from a metal having volume resistivity which is the same as or lower than the volume resistivity of the first metal, and contacts a surface of the first joined material 31 separated from the overlapped region 312. A pressure device 50 pressurizes the first electrode 41. A power source part 20 electrically conducts between the first electrode 41 and the second electrode 42.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a joining apparatus and a method for joining dissimilar materials. [Background technology]

[0002] There are various types of spot welding (spot joining), such as direct, indirect, and series. When joining dissimilar materials made of metals with different melting points, one of the spot welding methods is used. An example of the dissimilar materials is a copper plate and an aluminum plate. Patent Document 1 describes a series welding method. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-19569 A Summary of the Invention [Problem to be solved by the invention]

[0004] Taking the example of dissimilar materials being copper and aluminum plates, the direct type is a method of joining overlapping copper and aluminum plates by sandwiching them between a pair of electrodes. In the overlapping area where the copper and aluminum plates are overlapped, one electrode contacts the front side of the copper plate, and the other electrode contacts the back side of the aluminum plate. The indirect type is a method of joining the two by contacting one electrode with the surface of the copper plate in the overlapping area, and contacting the other electrode with the surface of the aluminum plate outside the overlapping area. In both the direct and indirect types, the electrode is in contact with the aluminum plate, which has a low melting point, so the aluminum plate may melt and adhere to the electrode.

[0005] The series type is a method in which a pair of electrodes are brought into contact with the surfaces of the copper sheets in the overlapping area to join the two. In the series type, the electrodes do not contact the aluminum sheet, but current flows through both the copper sheet and the aluminum sheet, which can cause the aluminum sheet to melt. The overlapped copper sheet and aluminum sheet are placed on a base with the aluminum sheet facing down. Therefore, when the aluminum sheet melts, it can adhere to the base. It is desirable to develop a joining device and a method for joining dissimilar materials that do not allow molten metal to adhere to the electrodes or base. [Means for solving the problem]

[0006] A first aspect of one or more embodiments provides a joining device comprising: a base material having a first end of a first workpiece made of a first metal having a first melting point and a second end of a second workpiece made of a second metal having a second melting point lower than the first melting point; a first electrode made of a metal having a volume resistivity higher than that of the first metal, the first electrode being brought into contact with a surface of the first end in an overlapping region where the first end and the second end are overlapped; a second electrode made of a metal having a volume resistivity equal to or lower than the volume resistivity of the first metal, the second electrode being brought into contact with a surface of the first workpiece in an area outside the overlapping region; a pressure device that pressurizes the first electrode to apply pressure to a portion of the overlapping region where the first electrode is in contact; and a power supply unit that passes current between the first and second electrodes so that a current flows from the first electrode to the second electrode.

[0007] A second aspect of one or more of the embodiments is a method for bonding a first end of a first material to be bonded, the first end being made of a first metal having a first melting point, and a second end of a second material to be bonded, the second end being made of a second metal having a second melting point lower than the first melting point, and a first electrode made of a metal having a volume resistivity higher than the volume resistivity of the first metal is brought into contact with a surface of the first end in an overlapping region where the first end and the second end are overlapped, and a second electrode made of a metal having a volume resistivity equal to or lower than the volume resistivity of the first metal is placed on the overlapping region. a first electrode is brought into contact with a surface of the first material to be joined in a region outside the overlapping region, and the first electrode is pressed by a pressurizing device to apply pressure to the overlapping region where the first electrode is in contact; a current is passed from the first electrode to the second electrode using the first material to be joined as a conductive path between the first electrode and the second electrode, thereby heating the first electrode, heating the first end with the heat of the first electrode, and heating the second end with the heat of the first end, thereby joining the first end and the second end. Effect of the Invention

[0008] According to the joining apparatus and the method for joining dissimilar materials according to one or more embodiments, molten metal does not adhere to the electrode or the base. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram illustrating a bonding apparatus according to one or more embodiments. [Diagram 2] FIG. 2 is a diagram illustrating a current flow when dissimilar materials are joined by the joining device according to one or more embodiments. [Diagram 3] FIG. 3 is a conceptual diagram showing a state in which resistance heat is generated at the boundary between a first electrode and a first material to be joined when dissimilar materials are joined by a joining device according to one or more embodiments. [Figure 4]FIG. 4 is a conceptual diagram following FIG. 3, illustrating a state in which the first electrode is generating heat when dissimilar materials are joined by the joining device according to one or more embodiments. [Diagram 5] FIG. 5 is a conceptual diagram following FIG. 4, showing a state in which heat from the first electrode is transferred to the first material to be joined when dissimilar materials are joined by a joining device according to one or more embodiments. [Figure 6] FIG. 6 is a conceptual diagram following FIG. 5, showing a state in which heat is generated at the boundary between a first workpiece and a second workpiece when dissimilar materials are joined by a joining device according to one or more embodiments. [Figure 7] FIG. 7 is a diagram showing a series type joining method as a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A bonding apparatus and a method for bonding dissimilar materials according to one or more embodiments will be described below with reference to the accompanying drawings.

[0011] In FIG. 1, the bonding apparatus 100 includes a control unit 10, a power supply unit 20, a first electrode 41, a second electrode 42, a pressure device 50, a radiation thermometer 60, and a measuring instrument 70. A first bonded material 31 and a second bonded material 32, which are different materials, are arranged on a base 43 as base materials to be bonded. The first bonded material 31 is made of a first metal having a first melting point, and the second bonded material 32 is made of a second metal having a second melting point lower than the first melting point. Typically, the first metal is copper or iron, and the second metal is aluminum. The plate thicknesses of the first bonded material 31 and the second bonded material 32 are not limited, but thin plates of 1 mm or less are preferable.

[0012] A first end 31e of the first material to be joined 31 and a second end 32e of the second material to be joined 32 are overlapped. The area where the first end 31e and the second end 32e are overlapped is referred to as an overlapping area 312. The first electrode 41 is in contact with the front surface of the first end 31e in the overlapping area 312. The second electrode 42 is in contact with the surface of the first material to be joined 31 in an area outside the overlapping area 312.

[0013] The first electrode 41 is made of a metal having a volume resistivity higher than that of the first metal. The second electrode 42 is made of a metal having a volume resistivity equal to or lower than that of the first metal. Volume resistivity is the electrical resistance value per unit volume expressed in units of Ω·m. The metal of the first electrode 41 is preferably molybdenum, tungsten, stainless steel, or carbon. The metal of the second electrode 42 is preferably chromium copper or pure copper, taking into consideration the volume resistivity and wear resistance.

[0014] The base 43 has a step corresponding to the plate thickness of the second material 32 below the first material 31 to be joined that is not overlapped with the second material 32 to be joined, but if the plate thicknesses of the first material 31 to be joined and the second material 32 to be joined are thin, such a step need not be provided. The shape of the base 43 is not limited. The base 43 is made of an insulator or a metal.

[0015] The power supply unit 20 and the first electrode 41 are connected by a conductive path 21, and the power supply unit 20 and the second electrode 42 are connected by a conductive path 22. The power supply unit 20 is configured to pass a direct current between the first electrode 41 and the second electrode 42, with the first electrode 41 being a positive electrode and the second electrode 42 being a negative electrode. The power supply unit 20 can be configured as a power supply circuit including a transformer.

[0016] The pressure device 50 applies pressure to the first electrode 41 and the second electrode 42, for example, by an air cylinder. In FIG. 1 and later-described FIGS. 2 to 7, the outline arrows indicate that pressure is being applied. When the first electrode 41 and the second electrode 42 are pressurized, the portion of the first workpiece 31 where the first electrode 41 and the second electrode 42 are in contact is pressurized. The pressure device 50 pressurizes both the first electrode 41 and the second electrode 42, but it may also be possible to pressurize only the first electrode so that only the portion of the overlapping region 312 where the first electrode 41 is in contact is pressurized.

[0017] A current sensor 44 consisting of a toroidal coil is attached to the conductive path 21. The current value detected by the current sensor 44 is supplied to a measuring device 70. The first electrode 41 and the second electrode 42 are connected to the measuring device 70 by a twisted wire or a vinyl electric wire, and the voltage value between the first electrode 41 and the second electrode 42 is supplied to the measuring device 70. The current sensor 44 may be attached to the conductive path 22.

[0018] The radiation thermometer 60 measures the temperature of the first electrode 41 by measuring the intensity of infrared rays emitted from the first electrode 41. The radiation thermometer 60 supplies analog temperature data indicating the temperature of the first electrode 41 to the control unit 10. The control unit 10 supplies the input analog temperature data as is to the measuring instrument 70. The pressure device 50 is equipped with a load cell that converts the load into an electric signal, and a displacement sensor that measures the amount of displacement. The pressure device 50 supplies the measuring instrument 70 with an analog value indicating the applied pressure converted into an electric signal by the load cell. The pressure device 50 supplies the measuring instrument 70 with a digital value indicating the amount of displacement measured by the displacement sensor.

[0019] The control unit 10 controls the power supply unit 20 to pass electricity between the first electrode 41 and the second electrode 42 so that a current of a predetermined current value flows from the first electrode 41 to the second electrode 42 when the first material to be joined 31 and the second material to be joined 32 are joined. The control unit 10 can be configured with a microprocessor.

[0020] The measuring instrument 70 processes the input current value, voltage value, analog temperature data, analog value indicating the applied force, and digital value indicating the amount of displacement, and can display this information on a display unit provided in the measuring instrument 70 in order to monitor this information during the joining of the first material to be joined 31 and the second material to be joined 32. When the amount of displacement reaches a set value, the measuring instrument 70 instructs the control unit 10 to stop the joining. When the control unit 10 is instructed to stop the joining, it controls the power supply unit 20 to stop the current flow between the first electrode 41 and the second electrode 42, and releases the pressure applied by the pressure device 50.

[0021] For some reason, the temperature of the first electrode 41 measured by the radiation thermometer 60 after the start of energization may not increase even after a predetermined time has elapsed. The control unit 10 preferably monitors the temperature of the first electrode 41 based on the analog temperature data output from the radiation thermometer 60, and determines that an error has occurred in the measured temperature when it is assumed that the radiation thermometer 60 has not correctly measured the temperature of the first electrode 41. For example, the control unit 10 determines that an error has occurred in the temperature of the first electrode 41 if the temperature of the first electrode 41 indicated by the analog temperature data has not reached the lowest initial temperature at a time when a predetermined initial time has elapsed after the start of energization.

[0022] When the control unit 10 determines that an error has occurred in the temperature of the first electrode 41, it controls the power supply unit 20 to immediately stop the passage of electricity between the first electrode 41 and the second electrode 42. Furthermore, the control unit 10 controls the pressure device 50 to immediately release the pressure on the first material to be joined 31 and the second material to be joined 32. This makes it possible to prevent the first material to be joined 31, the second material to be joined 32, the first electrode 41, and the second electrode 42 from burning. The control unit 10 may determine that an error has occurred when the temperature of the first electrode 41 becomes abnormally high, and control the power supply unit 20 and the pressure device 50 to stop the passage of electricity between the first electrode 41 and the second electrode 42 and release the pressure on the first material to be joined 31 and the second material to be joined 32.

[0023] Although it is not essential to provide a measuring device 70 in the bonding apparatus 100, it is preferable to provide the measuring device 70 since it enables various information to be monitored during bonding of the first bonded material 31 and the second bonded material 32.

[0024] 2 to 6, a dissimilar material joining method performed using the above-described joining device 100 will be described in detail. In Fig. 2, the second electrode 42 is in contact with the surface of the first material to be joined 31 in a region outside the overlapping region 312, so that only the first material to be joined 31 serves as a conductive path between the first electrode 41 and the second electrode 42. When the power supply unit 20 passes a current between the first electrode 41 and the second electrode 42, the current flows from the first electrode 41 to the second electrode 42 via the first material to be joined 31, as shown by the arrow line.

[0025] Then, as shown in Fig. 3, resistance heat is generated at the boundary between the first electrode 41 and the first material to be joined 31. The hatched horizontally elongated ellipse at the boundary conceptually indicates a heat generating region h1 where resistance heat is being generated. In Fig. 3 and subsequent figures, the arrows indicating the current flowing from the first electrode 41 to the second electrode 42 are omitted, but the current flows from the first electrode 41 to the second electrode 42 via the first material to be joined 31, as in Fig. 2.

[0026] When the boundary between the first electrode 41 and the first material to be joined 31 continues to generate heat, the first electrode 41 generates heat and becomes a heating element h2, as shown in Fig. 4. Then, as shown in Fig. 5, the heat of the heating element h2 is transferred to the first material to be joined 31, and a heating region h3 is generated in the first material to be joined 31 in the overlapping region 312. At this time, the first melting point of the first material to be joined 31 is high, about 1000 degrees for copper and about 1500 degrees for iron, so the first material to be joined 31 does not melt.

[0027] 6, the heat of the heat generating region h3 is transferred to the second material to be joined 32, and a heat generating region h4 is generated at the boundary between the first material to be joined 31 and the second material to be joined 32. Since the melting point of aluminum, which is the second material to be joined 32, is low at 660 degrees, when the temperature of the heat generating region h4 reaches near the melting point of aluminum, the first end 31e and the second end 32e are diffusion bonded. The first end 31e and the second end 32e are bonded to each other at one spot.

[0028] The control unit 10 preferably controls the power supply unit 20 to supply current so that the temperature of the heat generating region h4 (the boundary between the first material to be joined 31 and the second material to be joined 32) is any temperature between 550°C and 660°C. Since the eutectic point of copper and aluminum is 550°C, the lower limit should be 550°C. Since the melting point of aluminum is 660°C, the upper limit should be 660°C, and the temperature of the heat generating region h4 should not exceed 660°C. Even if the temperature of the heat generating region h4 is less than 660°C, which is lower than the melting points of copper and aluminum, the first end 31e and the second end 32e are joined to each other by the eutectic melting phenomenon.

[0029] The control unit 10 cannot directly obtain the temperature of the heat generating region h4, but can estimate the temperature of the heat generating region h4 based on the temperature of the first electrode 41 measured by the radiation thermometer 60, or the time of current flow between the first electrode 41 and the second electrode 42, etc. The control unit 10 only needs to control the power supply unit 20 so that the estimated temperature of the heat generating region h4 is any temperature between 550 degrees or more and 660 degrees or less.

[0030] In this manner, the bonding device 100 causes a current to flow from the first electrode 41 to the second electrode 42 with only the first workpiece 31 as a conductive path, thereby causing the first electrode 41 to generate heat. The bonding device 100 heats the first end 31e by the heat generated by the first electrode 41. The bonding device 100 heats the second end 32e by the heat of the first end 31e, thereby diffusion bonding the first end 31e and the second end 32e.

[0031] Here, the features of the dissimilar material joining method according to one or more embodiments and the effects of the features will be described using a comparative example in which a first material 31 and a second material 32 are joined using a general series joining method shown in Fig. 7. The metals of the first electrode 410 and the second electrode 420 used in the comparative example are selected from, for example, chromium copper, molybdenum, and tungsten. The metals formed for the first electrode 410 and the second electrode 420 are not different. The metals formed for both the first electrode 410 and the second electrode 420 are chromium copper, molybdenum, or tungsten.

[0032] In the comparative example, a first material to be joined 31 and a second material to be joined 32 are overlapped. Both a first electrode 410 and a second electrode 420 are in contact with the surface of the first material to be joined 31 in the overlapping region where the first material to be joined 31 and the second material to be joined 32 are overlapped.

[0033] Therefore, both the first material to be joined 31 and the second material to be joined 32 become a conductive path between the first electrode 410 and the second electrode 420. When a current flows from the first electrode 410 to the second electrode 420, the current flows through the first material to be joined 31 and the second material to be joined 32 as shown by the arrow line. Therefore, the second material to be joined 32, which has a lower melting point, melts. Then, the molten metal of the second material to be joined 32 may adhere to the base located below the second material to be joined 32, which is not shown in FIG. 7. The first material to be joined 31 and the second material to be joined 32 are joined to each other at two spot-like points.

[0034] In contrast, according to the method for joining dissimilar materials according to one or more embodiments, a current flows from the first electrode 41 to the second electrode 42 using only the first material to be joined 31 as a conductive path, so the second material to be joined 32 does not melt entirely. Therefore, the molten metal of the second material to be joined 32 does not adhere to the base 43. Since the first electrode 41 and the second electrode 42 are in contact only with the first material to be joined 31, the molten metal of the second material to be joined 32 does not adhere to the first electrode 41 or the second electrode 42, of course.

[0035] The present invention is not limited to one or more of the embodiments described above, and various modifications can be made without departing from the gist of the present invention. [Explanation of symbols]

[0036] 10 Control section 20 Power supply section 21,22 Conduction path 31 First material to be joined 31e First end 32 Second material to be joined 32e Second end 41 First electrode 42 Second electrode 43 Base 44 Current Sensor 50 Pressure device 60 Radiation thermometer 70 Measuring instruments 312 Overlapped Area

Claims

1. a first end portion of a first material to be joined, the first end portion being made of a first metal having a first melting point, and a second end portion of a second material to be joined, the second end portion being made of a second metal having a second melting point lower than the first melting point, being overlapped with each other; a first electrode made of a metal having a volume resistivity higher than the volume resistivity of the first metal, the first electrode being brought into contact with a surface of the first end portion in an overlapping region where the first end portion and the second end portion are overlapped with each other; a second electrode made of a metal having a volume resistivity equal to or lower than the volume resistivity of the first metal, the second electrode being in contact with the surface of the first workpiece in a region outside the overlapping region; a pressure device that applies pressure to the first electrode so as to apply pressure to the portion of the overlapping region where the first electrode is in contact; a power supply unit that applies current between the first and second electrodes so that a current flows from the first electrode to the second electrode; A joining device comprising:

2. 2. The bonding apparatus according to claim 1, wherein the first electrode is made of molybdenum, tungsten, stainless steel, or carbon.

3. 3. The joining device according to claim 1, wherein the second electrode is made of chromium copper or pure copper.

4. The bonding apparatus according to claim 1 or 2, further comprising a control unit that controls the power supply unit so that a temperature of a boundary between the first workpiece and the second workpiece in the overlapping region is either a temperature higher than the eutectic point of the first and second metals or a temperature lower than the melting point of the second metal.

5. Further comprising a radiation thermometer for measuring a temperature of the first electrode; The control unit monitors the temperature of the first electrode based on the temperature data output from the radiation thermometer, and when it determines that an error has occurred in the temperature of the first electrode, controls the power supply unit to stop the current flow between the first and second electrodes, and controls the pressure device to release the pressure on the overlapping region. The joining device according to claim 4.

6. a first end portion of a first workpiece to be joined, the first end portion being made of a first metal having a first melting point, and a second end portion of a second workpiece to be joined, the second end portion being made of a second metal having a second melting point lower than the first melting point, are overlapped with each other; A first electrode made of a metal having a volume resistivity higher than that of the first metal is brought into contact with a surface of the first end in an overlapping region where the first end and the second end are overlapped, and a second electrode made of a metal having a volume resistivity equal to or lower than that of the first metal is brought into contact with a surface of the first workpiece in a region outside the overlapping region; Pressurizing the first electrode with a pressurizing device to apply pressure to the overlapping region where the first electrode is in contact; a current is passed from the first electrode to the second electrode using the first workpiece as a conductive path between the first electrode and the second electrode, thereby causing the first electrode to generate heat; The first end is heated by the heat of the first electrode, and the second end is heated by the heat of the first end, thereby joining the first end and the second end. Method for joining dissimilar materials.

7. 7. The method for joining dissimilar materials according to claim 6, wherein the first metal is copper or iron, and the second metal is aluminum.

8. 8. The method for joining dissimilar materials according to claim 7, wherein the first electrode is made of molybdenum, tungsten, stainless steel or carbon.

9. 9. The method for joining dissimilar materials according to claim 7 or 8, wherein the second electrode is made of chromium copper or pure copper.

10. 9. The method for joining dissimilar materials according to claim 7 or 8, wherein the temperature of a boundary between the first material to be joined and the second material to be joined in the overlapping region is set to a temperature that is equal to or higher than the eutectic points of the first and second metals and equal to or lower than the melting point of the second metal, thereby joining the first end and the second end by a eutectic melting phenomenon.

11. measuring the temperature of the first electrode with a radiation thermometer; monitoring the temperature of the first electrode based on temperature data output from the radiation thermometer; When it is determined that an error has occurred in the temperature of the first electrode, the current passing between the first and second electrodes is stopped, and the pressure applied to the overlapping area is released. The method for joining dissimilar materials according to claim 7 or 8.

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