JP5873403B2 - Spot welding electrode tips - Google Patents

Description

  The present invention relates to an electrode tip used for spot welding in which two or more stacked metal plates are sandwiched between a pair of electrodes and energized to join the metal plates.

  Spot welding is generally performed by stacking two or more metal plates, sandwiching them between a pair of electrodes from both sides of the overlapped portion, and flowing current to melt the bonding interface of the metal plates by resistance heating. .

  In spot welding, the pressing force, current value, and energization time for pressing the electrode against the metal plate are the three main control factors.

  Of these, the current value is a particularly important factor. When the current value is too low, the diameter of the nugget formed by melting is small and the bonding strength is insufficient. On the other hand, if the current value is too high, dust is generated and the nugget diameter is increased, but this is not preferable because the joint strength varies. For this reason, an appropriate current range (weld lobe) for spot welding is from the current value at which the nugget diameter can be secured to the current value at which dust starts to occur. If this appropriate current range (weld lobe) can be expanded, spot welding is facilitated.

  Conventionally, various proposals have been made as electrode tips (electrodes) that can widen an appropriate current range (weld lobe) for spot welding.

[Prior art 1]
For example, Patent Document 1 discloses a composite electrode for spot welding in which a central portion is made of a copper-based material and an outer edge portion is made of an iron-based material.

  This composite electrode is composed of two kinds of materials with different electrical conductivity so that the applied pressure during welding is received at the outer edge part and the current passes through the center part, and the work piece is energized with high current density. This makes it possible to easily obtain a nugget of the required size, and even if continuous striking is repeated for a long time, the expansion of the diameter of the central portion is effectively suppressed, and a sound welding quality can be maintained, and the electrode The service life is said to be greatly improved.

[Prior Art 2]
Patent Document 2 discloses a spot welding electrode in which a central portion is made of a copper-based material and an outer edge portion is made of ceramics or cermet.

  This electrode is also composed of two kinds of materials having different conductivities so that the applied pressure at the time of welding is received at the outer edge portion and the current passes through the central portion, as in the above prior art 1, Even if it is repeated, the expansion of the diameter of the central part is effectively suppressed, and even if a special large current is not applied, the necessary current density can always be secured, and as a result, a healthy welding quality can be stably maintained. I can do it.

[Prior Art 3]
Further, in Patent Document 3, in the case of resistance spot welding of an aluminum or aluminum alloy plate, a metal plating on these surfaces, or a plated steel plate, the conductivity is 75 when the plate thickness of the plate to be welded is t. (IACS%) or more and having a diameter of 2.5 × t ^1/2 (mm) or more as a core material, the conductivity around the core material is 40 (IACS%) lower than the core material, and the melting point is An electrode for resistance spot welding in which aluminum or an aluminum alloy or a metal higher than the plating metal is coated is disclosed, and in the embodiment, a copper-based material as a core material, iron, stainless steel, titanium, nickel as a coating material, Nickel alloys, molybdenum and tungsten are exemplified.

  As with the prior arts 1 and 2, this electrode is also composed of two kinds of materials having different conductivities so that the applied pressure during welding is received at the outer edge portion and the current passes through the central portion. By preventing this, the electrode life can be dramatically improved.

  The spot welding electrodes of the above-mentioned conventional techniques 1 to 3 are each configured by dividing into a central portion and an outer edge portion, and are common to the spot welding electrode tip of the present invention in that a copper-based material is used for the central portion. doing.

  However, as will be described later, the spot welding electrode tip of the present invention is insulated by interposing a non-conductive film on the joint surface between the central portion and the outer edge portion made of a copper-based material. It is characterized by preventing the occurrence of medium dust by preventing molten metal from jumping out between the parts to be welded, and also preventing the occurrence of surface dust by efficiently cooling from the outer edge of the electrode. It is.

  On the other hand, since the electrode for spot welding disclosed in Patent Documents 1 and 3 uses a metal material for the outer edge portion, its thermal conductivity is sufficiently high. Although it has a function of preventing the occurrence of slag, its insulation is insufficient, so that the nugget region is enlarged and the molten metal cannot be prevented from jumping out, and the generation of middle dust cannot be effectively prevented.

  On the other hand, since the electrode for spot welding disclosed in Patent Document 2 uses ceramics or cermet at the outer edge, its insulation is sufficiently high, so that the molten metal in the nugget region jumps out from between the members to be welded. Although it has a function of preventing the generation of medium dust by blocking the heat, its thermal conductivity is low, so the cooling action from the outer edge is insufficient, and the generation of surface dust cannot be effectively prevented.

  Therefore, there is still room for improvement in the conventional spot welding electrode, and there has been a strong demand for providing an electrode tip for spot welding that can further expand the appropriate current range (weld lobe) of spot welding.

Japanese Patent Laid-Open No. 1-210179 JP-A-1-210180 JP-A-5-318140

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an electrode tip for spot welding that can further expand an appropriate current range (weld lobe) for spot welding.

The invention according to claim 1 is an electrode tip used for spot welding in which two or more stacked metal plates are sandwiched between a pair of electrodes and energized to join these metal plates, both of which are copper the central portion and the outer edge portion made from the system material, interposed these joint surfaces, and the electric resistivity of 1 [Omega · m or more non-conductive film, Ri Tona, further wherein the central portion, the distal end side of the cylindrical portion And the outer edge portion of the outer edge portion is slidably fitted into the cylindrical portion of the central portion via the non-conductive film, and the rear end portion. Since the portion is connected to the flange portion of the central portion via a pressure adjusting member made of an elastic body, the pressure applied by the outer edge portion with respect to the two or more stacked metal plates can be adjusted. sports, characterized in that there An electrode tip preparative welding.

The electrode tip for spot welding according to the present invention is insulated by interposing a non-conductive film on the joint surface between the central portion and the outer edge portion made of a copper-based material, and the pressure applied by the outer edge portion can be adjusted. By configuring, it prevents the molten metal in the nugget region from jumping out between the members to be welded, thereby preventing the generation of medium dust more reliably, and by efficiently cooling from the outer edge of the electrode, It has become possible to prevent the occurrence, and the appropriate current range (weld lobe) for spot welding can be further expanded.

It is a figure which shows schematic structure of the electrode tip for spot welding which concerns on 1st Embodiment of this invention, (a) is a longitudinal cross-sectional view, (b) is an AA arrow directional view in (a). It is a figure which shows schematic structure of the electrode tip for spot welding which concerns on 2nd Embodiment of this invention, (a) is a longitudinal cross-sectional view, (b) is an AA arrow directional view in (a). It is a longitudinal cross-sectional view which shows schematic structure of the electrode tip used in the Example.

  In order to solve the above problems, the present inventors first examined the mechanism of dust generation. In other words, the types of dust include “medium dust” generated between the stacked plates and “surface dust” generated from the surface of the metal plate. Among these, “medium dust” is the result of volume expansion if the melted area (nugget area) becomes too large when energized by pressing the overlapping part of two or more stacked metal plates from the front and back with a pair of electrode tips. This occurs when the distance between the plates in the overlapping portion (hereinafter referred to as “between plates”) is widened, and a part of the melt jumps out from between the plates. On the other hand, “surface dust” occurs when the molten region spreads to the surface of the metal plate (the surface that is not the overlapping surface).

  Therefore, the present inventors pressurize the periphery of the molten region formed by energizing while applying pressure with the electrode tip, thereby preventing a part of the melt from jumping out between the plates. On the other hand, by cooling from the periphery of the electrode tip, it is possible to prevent the occurrence of surface dust by preventing the molten region from spreading to the surface of the metal plate around the electrode tip. I thought.

  In order to simultaneously perform two different actions of preventing the molten material from jumping out between the plates and preventing the molten region from expanding to the surface of the metal plate, specifically, the electrode tip is placed between the central portion and the outer edge. It is configured to be divided into portions and insulated by interposing a non-conductive film on their joint surfaces, and when energizing while pressing the overlapping portion of the metal plate by the central portion, the electrode tip at the outer edge portion It was thought that this could be realized by pressurizing the peripheral overlapping portion.

  Therefore, as a result of conducting a verification test described later in [Example], confirmation was obtained, and further studies were made to complete the present invention.

  Each of the electrode tips for spot welding according to the present invention comprises a central portion and an outer edge portion made of a copper-based material, and a nonconductive film having an electrical resistivity of 1 Ω · m or more interposed between these joint surfaces. It is characterized by that.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

[First Embodiment]
FIG. 1 shows a schematic configuration of an electrode tip for spot welding according to an embodiment of the present invention. Here, reference numeral 1 denotes a central portion, reference numeral 2 denotes an outer edge portion, and reference numeral 3 denotes a non-conductive film.

  First, the structure of the electrode tip may be either an integral type or a cap type. However, since the central portion 1 is energized, it has a structure in which it directly contacts an energizing portion of an adapter or holder of a welding machine (not shown). .

  On the other hand, the outer edge portion 2 is such that part or all of the applied pressure applied from the base side of the electrode tip is transmitted to the outer edge portion 2 directly or indirectly via the central portion 1 and the non-conductive film 3. What is necessary is just a structure. A non-conductive film 3 is interposed on the joint surface between the central portion 1 and the outer edge portion 2, and this non-conductive film 3 is previously coated on the central portion 1 side or the outer edge portion 2 side of the joint surface. Thereafter, the central portion 1 and the outer edge portion 2 may be joined. For this joining, it is sufficient that both are joined to such an extent that the outer edge portion 2 does not fall off by continuous spot welding work, such as fitting by mechanical hammering, screwing by threading to the joining surface, shrink fitting, tacking, etc. Various means can be employed. As the shape of the tip of the electrode tip, a truncated cone type is exemplified in this example, but any shape such as a radius type or a dome radius type may be adopted.

  Next, as the material of the electrode tip, the central portion 1 needs to use a copper-based material having a low electrical resistance, that is, a high conductivity, in order to pass a large current without loss during spot welding. Specific examples of the copper-based material include pure copper, copper-chromium alloy, alumina-dispersed copper, and the like that have improved strength and heat resistance while maintaining electrical conductivity. In addition, when spot welding high-strength steel sheets or the like, it is necessary to increase the pressure in order to bring the joint surfaces into contact with each other. Therefore, it is recommended to select one having high strength and heat resistance.

  In addition, although the outer edge portion 2 is not energized, a copper-based material having excellent thermal conductivity is used to pressurize the periphery of the nugget region and efficiently cool it. As the copper material, in addition to pure copper, copper-chromium alloy, alumina-dispersed copper, etc. with improved strength and heat resistance can be used as well as the central portion 1. The central portion 1 and the outer edge portion 3 do not necessarily need to use the same copper-based material. For example, the central portion 1 is made of pure copper having excellent conductivity, and the outer edge portion 3 is excellent in strength and heat resistance. Copper-chromium alloy or alumina-dispersed copper can also be used.

When spot welding is performed at the center portion 1 of the electrode tip and an electric current flows to the outside of the energized region, and the outer region melts or softens, the pressure of thermal expansion when the nugget region melts The welded metal plate is deformed, and the molten metal is ejected from between the plates to the outside. Therefore, in order to suppress the middle dust, it is only necessary to pressurize the outer peripheral portion of the spot welded portion without energizing to prevent the molten metal in the nugget region from being ejected from between the plates. Therefore, the non-conductive film 3 having high insulation, that is, high electrical resistivity may be disposed on the joint surface between the center portion 1 and the outer edge portion 2. Since the electrical resistivity of the material of the central portion 1 and the outer edge portion 2 (for example, pure copper or copper-chromium alloy) is about 1 × 10 ⁻⁷ Ω · m, the material of the nonconductive film 3 is A material having a significantly high electrical resistivity of 1 Ω · m or more, preferably 1 × 10 ³ Ω · m or more, more preferably 1 × 10 ⁶ Ω · m or more is used. Examples of such materials include ceramics and synthetic resins. More specifically, ceramics include AlN, ZrO ₃ , BeO, and SiC—BeO. Synthetic resins include polyethylene and Teflon (registered trademark). And the like. Further, the thickness of the non-conductive film 3 may be 0.001 mm or more in order to reliably prevent energization from the central portion 1 to the outer edge portion 2, but if the thickness is too large, the cooling action by the outer edge portion 2 is exerted. Since it is killed, the thickness is preferably 1.0 mm or less. The non-conductive film 3 may be formed by, for example, a method in which a film material is deposited on the joint surface between the central portion 1 and the outer edge portion 2 and then heat-treated, or a method in which the film material is plated on the joint surface. Further, it can be easily formed by appropriately selecting and using a well-known method such as a method of attaching a plate-like film material processed in accordance with the shape of the joint surface.

  As described above, the tip of the electrode tip according to the present invention is formed of only a copper-based material except for the thickness of the non-conductive film 3, so that the tip tip is spot-welded for a long time. Even when damaged by the above, there is an effect that the shape of the tip of the chip can be easily reproduced by brushing.

[Second Embodiment]
In the first embodiment, an example is shown in which the non-conductive film 3 is interposed (bonded) to the joint surface between the center portion 1 and the outer edge portion 2 of the electrode tip and is integrated, but as shown in FIG. Further, the center portion 1 is composed of a cylindrical portion 1a on the front end side and a flange portion 1b on the rear end side, and the outer peripheral portion 2 has an inner peripheral portion 2a with the non-conductive film 3 interposed between the center portion 1a and the center portion 1a. The rear end portion 2b is slidably inserted into the cylindrical portion 1a of the portion 1, and the rear end portion 2b is connected to the flange portion 1b of the central portion 1 through a pressure adjusting member 4 made of an elastic body. To do.

  By adopting such a configuration, by changing the type and structure of the elastic body, the pressure applied by the outer edge portion 2 can be adjusted, and generation of medium dust can be prevented more reliably. It is possible to further expand the appropriate current range for spot welding.

  Examples of the elastic body include a coil spring, a leaf spring, rubber, and silicon rubber. However, the elastic body has sufficient strength to withstand repeated repeated spot welding for a long time, and the center portion 1 of the electrode tip and Any material and form may be used as long as a difference in applied pressure can be imparted between the outer edge portion 2 and the outer edge portion 2.

  In the present embodiment, as shown in FIG. 2, an example in which the non-conductive film 3 is covered and insulated on the center portion 1 side is shown, but instead, the outer edge portion 2 side may be covered. Similar insulating action can be obtained. Further, in the present embodiment, as shown in FIG. 2, an example in which insulation is performed by interposing a non-conductive film 3 between the flange portion 1 b of the central portion 1 and the coil spring 4 as a pressure adjusting member is shown. However, when rubber or silicon rubber is used as the pressure adjusting member, since these materials originally have insulating properties, non-conductivity between the flange portion 1b of the central portion 1 and the pressure adjusting member 4 is not possible. The conductive film 3 can be omitted.

  In order to confirm the applicability of the electrode tip for spot welding according to the present invention, a welding test was performed using various electrode tips with a spot welder.

  In this example, a dome radius-shaped cap-type chip was used as the form of the electrode chip.

  FIG. 3 shows a schematic configuration of the electrode tip used in this example. In the same figure, (a) is the whole chip formed integrally with pure copper, (b) is formed by separating the central portion and the outer edge portion with a film, (c) is the central portion and the outer edge portion. Are separated from each other by a membrane, and the outer edge portion is coupled to the center portion by a coil spring (elastic body). In the case of (b), the material of the central part and the outer edge part and the material of the film are changed variously. In the case of (c), the material of the central part and the outer edge part and the material of the film are changed variously. At the same time, a welding experiment was performed by changing the ratio of the applied pressure between the center portion and the outer edge portion by changing the spring constant of the coil spring. In both cases (b) and (c), the material of the central portion and the outer edge portion are the same. The dimensions of each part of the electrode tip are as described in FIG.

The welding conditions are as follows.
・ Total pressure: 400kN
-Electrode holder: Copper-chromium alloy-Initial pressurization time: 0.90 seconds-Energization time: 0.25 seconds-Current value: 4-12 kA
-Steel plate to be welded: Steel type ... JSC980Y
Composition: 0.20C-1.0Si-2.0Mn
Thickness ... 1.2mm
Tensile strength: 1020 MPa

  Then, spot welding is performed by sequentially increasing the welding current from the low current side using each electrode tip on the two steel plates to be welded, and the nugget diameter (unit: mm) is 4√t. The minimum current value (where t: plate thickness [unit: mm]) and the limit current value at which dust starts to occur were determined. Further, the type of dust was identified by observing a cross section of the joint obtained in the test in which the dust was generated. And the case where the range (appropriate current range) from the minimum current value to the limit current value is 3.0 kA or more was judged as a good welding method.

  Table 1 below shows test conditions and measurement results.

  In the same table, test no. Reference numeral 1 is a reference example corresponding to spot welding using a conventional electrode tip in which the entire tip is integrally formed. This reference example had a Chile limit current of 7.0 kA and an appropriate current range of 2.0 kA.

  And test no. 2-5, 8-16 are invention examples that satisfy all the requirements of the present invention. In any of the inventive examples, as a result of the significant increase in the Chile limit current, the appropriate current range reaches 3.0 kA or more, which is significantly wider than the appropriate current range of the reference example.

  In contrast, test no. 6 and 7 are comparative examples that do not satisfy any of the requirements of the present invention. The appropriate current range of these comparative examples is 2.0 to 2.5 kA, which is almost equal to or slightly wider than the appropriate current range of the reference example, and it can be seen that a sufficient improvement effect is not obtained.

  As is clear from the above results, by using the electrode tip for spot welding according to the present invention, it becomes possible to more reliably prevent the occurrence of dust, as a result, the dust limit current is greatly increased, It was confirmed that the appropriate current range (weld lobe) for spot welding can be greatly expanded.

DESCRIPTION OF SYMBOLS 1 ... Center part 1a ... Cylindrical part 1b ... Flange part 2 ... Outer edge part 2a ... Inner peripheral part 2b ... Rear end part 3 ... Non-conductive film 4 ... Pressure adjusting member (elastic body)

Claims (1)

It is an electrode tip used for spot welding to join these metal plates by sandwiching and energizing both surfaces of two or more metal plates sandwiched between a pair of electrodes,
Both the center portion and the outer edge portion made of a copper-based material, interposed these joint surfaces, and the electric resistivity of 1 [Omega · m or more non-conductive film, Ri Tona,
Further, the central portion is composed of a cylindrical portion on the front end side and a flange portion on the rear end side, and the inner peripheral portion of the outer edge portion slides on the cylindrical portion of the central portion via the non-conductive film. It is inserted in a movable manner, and its rear end is connected to the flange portion of the central portion via a pressure adjusting member made of an elastic body, whereby the two or more stacked metal plates An electrode tip for spot welding characterized in that the pressure applied by the outer edge portion is adjustable .