JP2005288455A - Spot welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method in which welding can be performed without bringing the surface of a planar electrode into direct contact with a workpiece, so that welding is made possible without staining or bending the surface of the planar electrode, in a spot welding method of placing the workpiece on the planar electrode and welding it. <P>SOLUTION: A conductive film 200 made of a conductive material is supplied to the surface of the planar electrode 10 composed of a conductive material. While the workpiece W is placed on this conductive film 200, a welding gun 20 equipped with a welding tip 21 at the tip end is lowered from above, thereby holding the workpiece W between the welding tip and the conductive film 200 and pressurizing/energizing for spot welding. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a spot welding method, and more particularly, to a spot welding method in which spot welding is performed by energizing an object to be welded with a welding gun having a welding tip at the tip thereof on a plate electrode.

  For example, resistance welding is used for joining metal plates such as steel plates, stainless steel plates, and aluminum plates, especially for joining thin metal plates. In resistance welding, a metal plate to be welded (hereinafter referred to as an object to be welded) is overlapped, the overlapped portion is sandwiched between a pair of electrode tips, and energized with pressure, and the resistance heat generated by the energization is heated as a heat source. A method of melting and joining, and the most used of the resistance welding methods is spot welding or spot welding. In spot welding, in order to increase resistance heat as a heat source, the current density is increased by narrowing the cross-sectional area of a pair of electrode tips that pressurize and power the work piece, and a large current is passed in a short time. It melts locally, forms a stone-like nugget and welds it. For this reason, spot welding is widely applied to automobiles, home appliances and other sheet metal products.

  In other words, spot welding has a major drawback in that the temperature of the heat source cannot be adequately controlled because it depends on the physical properties of the material to be welded because the heat source is the Joule heat generated on the contact surface of the work piece. Nevertheless, it does not require a welding rod or flux as in arc welding, and it does not require a large welding machine.

  For this reason, spot welders that perform spot welding can obtain weld joints with considerably high strength, and therefore, a wide variety of products have been proposed depending on the application. However, these spot welders are almost stationary. is there.

  More specifically, in a stationary spot welder, a welding tip having a narrowed cross section is provided at the opposite ends of a pair of welding electrodes in order to weld the overlapped workpieces, and this welding tip is enhanced. A pressurizing device for pressurization is supported by a strong mechanical holding device. The holding device and the pressurizing device are integrally installed at a fixed place.

  For this reason, since a high-pressure force is applied to the stationary spot welder, a high-strength welded joint can be obtained, but the work piece is moved to the welder each time welding is performed. If it is a large structure, its transportation becomes a heavy work, and it is not suitable for manufacturing a metal frame or a metal box of a small rod.

  In addition, when there is a place to be welded inside, there are often places where welding cannot be made, and this place is not preferable because it depends on another welding, such as arc welding. Furthermore, since an electrode tip whose cross section is narrowed to a point is used, a holding jig adapted to the structure of the workpiece to be welded is required to hold the workpiece to be welded at an appropriate position.

  From this point, instead of a pair of welding tips and pressurizers, and at least a stationary spot welder where the pressurizer is installed in a certain place, a portable type welder capable of carrying at least a welding tip is proposed. Has been. The portable type welding machine is configured by separating a welding electrode such as a welding tip from a welding machine main body. However, since it is lightweight as a portable type, an air-cylinder or a hydraulic cylinder cannot be used as a pressurizing device for pressurizing the welding tip, and its use is limited.

  Therefore, the inventors previously proposed a spot welder having a structure shown in Japanese Patent Application No. 05-139543 as a welder capable of welding without moving the work piece. .

  In this spot welder, the upper electrode of the pair of upper and lower electrodes is configured as a rod-shaped welding gun having a welding tip at the tip and a reduced cross section, whereas the lower electrode is made of plate-like copper or an alloy thereof. It is composed of a plate-like electrode made of a conductive material, and is welded by sandwiching an object to be welded between the plate-like electrode and a welding gun and applying a pressurized current. Since the lower electrode of this spot welder is composed of a plate electrode having a wide space, electricity is applied to any part of the surface, and the entire surface can serve as an electrode surface.

However, the previously proposed spot welder can weld an object to be welded on the plate electrode, but has the following drawbacks.
(1) The plate-like electrode as a whole is made of a conductive material, and is made of a conductive material, especially copper or an alloy thereof. Copper has a higher melting point and higher thermal conductivity than other metals, while its electrical resistance is extremely low. For this reason, although it is very suitable as an electrode, there exists a fault that a price is high. For this reason, in order to construct the lower electrode as a plate material having a very wide space, it is inevitably produced by casting as a large structure, which is extremely expensive. Further, a large structure of copper is It becomes heavy and difficult to handle and assemble, and it takes time to replace.
(2) Since the surface of the plate-like electrode forms the electrode as a whole, shunting occurs at the time of welding, current loss increases, and the formed nugget is energized again to impair the properties.
(3) On the surface of the plate-like electrode, the contact portion with the work piece acts as a welding tip during welding. For this reason, it is ideal that the entire surface of the plate-like electrode is used as a welding tip evenly. However, depending on the structure of the workpiece, the frequency of use at a certain place is often extremely high. For this reason, material changes and strains accumulate in the parts that are often used as electrode tips, and the surface of the plate-like electrode is bent. For this reason, it is necessary to grind and flatten the surface warp and the material change portion every time it is used to some extent. In particular, this grinding work needs to be performed with high accuracy up to the so-called mirror finish, and the grinding work takes a long time (one day is taken as a grinding time every week), and the economy and workability are greatly impaired. That
(4) When the frequency of use of the plate electrode used locally as the electrode tip is increased, the material to be welded and the copper of the plate electrode are alloyed and remain attached on the plate electrode. Adheres to the surface of the workpiece when the next workpiece is welded. It takes a lot of work to remove this. In particular, chemical conversion treated steel sheets are used as objects to be welded. Incidentally, bond-treated steel sheets and parkarizing steel sheets are used.
Japanese Patent Application No. 5-139543 and Japanese Patent No. 3445636

  The present invention is a welding method in which one electrode is configured as a plate-shaped electrode having a large area among a pair of electrodes that sandwich and pressurize the workpiece, and in this welding method, mainly as described above. The object is to solve the problems (1), (2), (3) and (4).

  First, in the present invention, a conductive film material made of a conductive material is supplied to the surface of a plate electrode made of a conductive material, and an object to be welded is placed on the plate electrode with the conductive film material interposed. Make it. Subsequently, a welding gun having a welding tip at the tip from the upper part is lowered, and an object to be welded is sandwiched between the welding tip and the conductive film material and subjected to spot welding by applying pressure.

  The conductive film material is supplied as a sheet on the plate electrode and spread or spread.

  The thickness of the conductive film material is 0.1 mm or more, preferably 0.3 mm or more, particularly preferably 0.4 mm or more.

  The conductive film material is copper or an alloy thereof.

  The conductive film material is formed into a continuous web shape, and the conductive film material is supplied continuously or intermittently.

  Since the surface of the plate electrode is covered with the conductive film material, the surface does not directly contact the workpiece during welding. For this reason, the surface of the plate-like electrode is always flat and free from deposits, so that it is not necessary to grind even after repeated use.

  Since the conductive film material is cooled by the plate-like electrode from the back surface to the entire surface, it is immediately cooled even if heat is generated by the contact resistance with the plate-like electrode.

  Since the thickness with the conductive film material is at least 0.1 mm, preferably 0.3 mm or more, heat generation due to contact resistance with the plate electrode can be satisfactorily mitigated.

  Even if the conductive film material is discarded after use for a certain period of time, it is made of copper or an alloy thereof. Therefore, the conductive film material can retain its economic value as a scrap material, and can always be replaced with a new one.

  FIG. 1 is an explanatory diagram of the principle for carrying out the method of the present invention.

  FIG. 2 is an equivalent circuit diagram of electrical resistance between a pair of electrodes when welding is performed by the method of the present invention.

  FIG. 3 is an explanatory view of an example of a spot welder suitable for carrying out the method of the present invention.

  First, FIG. 1 is an explanatory view showing the principle when carrying out the method of the present invention. Although this method can be performed using the spot welder 100 shown in FIG. 3, the principle shown in FIG. 1 can be performed without using such a welder.

  However, in any spot welding machine, the lower electrode of the pair of electrodes is configured as a plate electrode 10 and the other upper electrode is welded with a welding tip 21 at the rod-shaped tip. Configured as a gun 20.

  Further, the downward pressing force by the welding gun 20 configured as the upper electrode can be applied even if the welding gun 20 is held in any welding position. For example, the welding gun 20 can be held in a vertical posture so as to simply move up and down, or the welding gun 20 is held in a horizontal posture, and a welding tip 21 is attached to the tip of the welding gun 20 and is attached to the rear end. When a pressing force such as tension or pressing is applied, a downward pressing force can be applied to the workpiece W by a lever method.

  Next, the conductive film material 200 is supplied onto the plate electrode 10, and the conductive film material 200 is spread or spread on the plate electrode 10 without gaps. In order to spread the gap without gaps, a fixing means is provided on the side edge of the plate electrode 10 and the conductive film material 200 can be pulled and fixed. The conductive film material 200 covers the surface of the plate electrode 10 and directly contacts the workpiece W. Further, since the conductive film material 200 is made of copper or an alloy thereof which is energized through the plate electrode 10 and has excellent conductivity, the conductive film material 200 has an appropriate thickness as will be described later, and the plate electrode 10 from the back surface. Therefore, the conductive film material 200 can be peeled off without being in close contact with the plate-like electrode 10 even when pressed with a high pressure.

  In welding, the workpiece W is placed on the conductive film material 200, and the workpiece W is sandwiched between the conductive film material 200 and the welding gun 20 as the upper electrode, particularly, the welding tip 21 at the tip. Energize and weld. When welding is performed in this manner, the plate-like electrode 10 and the conductive film material 200 are made of a conductive material, and are made of copper or an alloy thereof and have an appropriate thickness. For this reason, the contact resistance between the plate-like electrode 10 and the conductive film material 200 can be relaxed, and welding can be performed with almost no loss of conductivity.

  That is, when welding the workpiece W which overlap | superposed at least two with the plate-shaped electrode 10 interposing the electroconductive film material 200 as a lower electrode, the plate-shaped electrode 10 that works as the lower electrode and the conductive Contact electrical resistance with the conductive film material is generated, and at the same time, the conductive film material 200 is locally subjected to a structural change due to the applied pressure during welding.

As shown in FIGS. 1 and 2, the conductive film material 200 is interposed between the welding tip 21 at the tip of the welding gun 20 and the work W to be welded, and an electrical contact resistance R ₁ is generated on the contact surface. . Welded object W is brought at least two things superimposed occurs electrical contact resistance R ₂ on the contact surface. Welded object W is in contact with the surface of the conductive film material 200 is electrical contact resistance R ₃ occurs in this contact surface. Furthermore, conductive film material 200 is electrical contact resistance R ₄ during this time in contact with the plate-shaped electrode 10 is produced. In addition, the weld object W has inherent electrical resistance R _5. The electric resistance of the current-carrying system at the time of welding is shown as an equivalent electric circuit as shown in FIG.

Further, when these electrical resistances R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are further examined, the electrical contact resistances R ₁ and R ₃ between the welding tip 21 and the conductive film material 200 with respect to the workpiece W are: Since the contact area of the plate-like electrode 10 and the conductive film material 200 is very large compared to the welding tip 21, it is not seen to be the same level.

That is, since the contact area of the workpiece W with respect to the conductive film material 200 increases under a high pressing force, the electrical contact resistance R ₃ decreases with respect to the electrical contact resistance R ₁ and the current density increases. On the other hand, the electrical contact resistance R ₄ depends on the degree of contact between the conductive film material 200 and the plate electrode 10.

From such a point, the actual welding resistance of spot welding varies depending on the electrical contact resistances R ₁ , R ₂ , R ₃ , and R _{4 that} vary depending on the welding mode among the electrical resistances in the welding system. Examination based on the secondary side effective value current of the transformer of the welding power source during welding reveals that when the conductive film material 200 having an appropriately adjusted thickness is interposed, the electrical contact resistance (R ₁ + R ₂ + R ₃ + R ₄ ) is about 20% of the relaxation of the electric resistance of the welding system (R ₁ + R ₂ + R ₃ + R ₄ + R ₅ ), and of this 20%, the ratio of electrical contact resistance (R ₄ ) is slight. Met. In short, it has been found that when the conductive film material 200 is interposed, the key point is the thickness of the conductive film material 200.

  That is, strictly speaking, it is preferable that the conductive film material 200 be in uniform contact with the surface of the plate-like electrode without air or other inclusions interposed therebetween. However, the conductive film material 200 is thin, and it is very difficult to realize this. However, when the thickness of the conductive film material 200 is appropriately adjusted, the current distribution spreads widely in the central portion in the thickness direction, and the contact resistance with the plate electrode 10 becomes extremely small and the influence thereof is reduced. .

  From such a point, the thickness of the conductive film material 200 which can reduce the influence by changing the thickness of the conductive film material 200 and placing it on the plate electrode 10 was obtained.

First, as shown in FIG. 2, the interelectrode pressure and the secondary side current value were determined under the condition of relaxation R of each electric resistance R ₁ , R ₂ , R ₃ , R ₄ , R _{5 being} constant. The secondary current value increased linearly as the interelectrode pressure was increased.

  Next, the electrical resistance relaxation R gradually decreased as the interelectrode pressing force increased.

  Next, welding is performed by changing the thickness of the conductive film material 200 under a high pressure (300 N), and the presence or absence of fusion formed between the conductive film material 200 and the plate electrode 10 is checked with a microscope. As a result of observation, when the thickness of the conductive film material 200 is 0.1 or 0.1 mm or more, there is almost no fusion at a hitting point of about 100, and 0.3 mm or more. When it was 4 mm or more, no fusion was observed even when the pressure was increased.

  More specifically, the conductive film material 200 is placed on the plate-like electrode 10 and directly contacts the workpiece W to work as an electrode surface over the entire surface. On the other hand, even if the surface is deformed and contaminated due to repeated use compared to the expensive plate electrode 10 (for example, contamination formed by alloying with the workpiece), it is discarded as scrap. In terms of economy, it is preferable that the thickness be as thin as possible. Further, when the conductive film material 200 is supplied onto the plate electrode 10 without being manually or continuously supplied, the web-shaped conductive film material 200 wound in a roll shape is supplied by being rewound. It is preferable that the thickness is as thin as possible.

  However, since the conductive film material 200 such as copper is rich in spreadability, it spreads and stretches due to local pressure, changes in material properties, unevenness occurs, contact resistance increases and melts, Often cut. Further, when the conductive film material 200 is spread or spread on the surface of the plate electrode 10, air, an air layer, and dust or other foreign matters are locally interposed therebetween. I can't avoid it.

  In any case, by setting the thin conductive film material 200 on the surface of the plate-like electrode 10, the contact resistance between them is inevitably greatly increased. It happens that the film material 200 cannot be peeled off.

  From such a surface, the conductive film material 200 needs to have a thickness of at least 0.1 mm. Moreover, even if alloying with the electroconductive film material 200 starts locally depending on the material of a to-be-welded object as thickness is 0.3-0.4 mm or more, there is no trouble. In particular, as described above, the ratio of the contact resistance between the conductive film material 200 and the plate electrode 10 is estimated to be approximately 20% of the overall electric resistance, and the conductive film is interposed. Increasing the thickness of the material 200 preferably allows the thickness of the conductive film material 200 to be 0.3 to 0.4 mm or more, as long as it allows an economic disadvantage to be discarded as scrap.

  In FIG. 3, reference numeral 100 denotes a spot welder, 10 denotes a plate electrode, 20 denotes a welding gun, 21 denotes a welding tip, 22 denotes an operation handle, 30 denotes a support post, 40 denotes an air cylinder, and 50 denotes a rotating arm. , 51 is a rotating part, 52 is a presser plate, and 60 is a support column.

  The method of the present invention is a welding method in which a conductive sheet material is interposed between a plate-like electrode that functions as a lower electrode and a welding gun that functions as an upper electrode, and the interposed conductive sheet material is attached or detached. It is freely placed on the plate electrode.

  For this reason, even a steel plate, an aluminum material, a stainless steel plate, or the like that has been subjected to a chemical conversion treatment such as a bond treatment or a parkerizing treatment can be welded.

It is explanatory drawing of the principle at the time of implementing this invention method. It is an equivalent circuit schematic of the electrical resistance between a pair of electrodes at the time of welding by the method of the present invention. It is explanatory drawing of an example of the spot welding machine suitable when enforcing the method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Spot welder 10 Plate electrode 20 Welding gun 21 Welding tip 30 Support post 40 Air-cylinder (pressurizing device)
50 Rotating Arm 200 Conductive Film Material

Claims (6)

  A welding gun which supplies a conductive film material made of a conductive material to the surface of a plate electrode made of a conductive material and places an object to be welded on the conductive film material, while having a welding tip from the top to the tip A spot welding method characterized in that spot welding is performed by applying pressure to the work piece between the conductive film material and lowering the pressure to energize the workpiece.   2. The spot welding method according to claim 1, wherein the conductive film material is supplied as a sheet on the plate electrode.   The spot welding method according to claim 1 or 2, wherein the thickness of the conductive film material is 0.1 mm or more.   The spot welding method according to claim 1 or 2, wherein the thickness of the conductive film material is 0.3 mm or more.   The spot welding method according to claim 1, wherein the conductive film material is a copper or copper alloy film material. 6. The spot welding according to claim 1, wherein the conductive film material is formed into a continuous web shape, and the web-shaped conductive film material is intermittently or continuously supplied onto the plate-like electrode. Law.

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