JP2005313221A - Welding electrode for spot welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pair of welding electrodes, at the time when resistance welding is performed with the lapped parts of the materials to be welded sandwiched, capable of performing the welding without being subjected to dressing treatment. <P>SOLUTION: In the welding electrodes 100 with which resistance spot welding is performed with the lapped parts of at least the two materials to be welded sandwiched, electrode caps 120, 120 each surrounding the tip thereof and matching thereto are provided. In the electrode caps 120, 120 the parts abutted on the materials to be welded sandwiched from both the sides are provided with hard parts 121 having more hardness compared with the other parts, and, as cooling water is fed to the back surfaces of the hard parts, water cooling is performed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a welding electrode for spot welding, and more specifically, spot welding is performed by pressurizing and energizing a material to be welded such as a steel plate or other metal material made of a conductive material such as copper or an alloy thereof. The present invention relates to a welding electrode.

  For example, spot welding is used for joining metal plates such as steel plates, stainless steel plates, and aluminum plates, especially for joining thin metal plates. In spot welding, a metal plate to be welded (hereinafter referred to as a material to be welded) is overlapped, the overlapped portion is sandwiched between a pair of welding electrodes, and energized with pressure. It is welding which heat-melts the welding part of and joins. Also, spot welding is a welding method in which the welded portion is formed as a spot or a spot. In particular, in order to increase the resistance heat as a heat source, pressurization energization is performed across the material to be welded. By narrowing the cross-sectional area of a pair of welding electrodes, the current density is increased, a large current is passed in a short time, and in this way, the joint portion of the welded material is locally heated and melted to form a stone-like nugget And is widely applied to automobiles, home appliances and other sheet metal products.

  That is, spot welding is Joule heat generated by a heat source on the contact surface of the workpiece. For this reason, there is a drawback that the temperature of the heat source cannot be adequately controlled depending on the physical properties of the material to be welded. Nevertheless, spot welding is widely used because it has the advantage that it can be joined without requiring a welding rod or flux, such as arc welding.

  For this reason, a wide variety of spot welders have been proposed depending on the application, but the most popular of these spot welders is a welder called a stationary type, which is a spot welder. That said, the stationary type is immediately associated.

  More specifically, in the stationary spot welding machine, a pair of welding electrodes are arranged facing each other in order to weld the overlapped workpieces, and the tip of each welding electrode is narrowed in cross section. The pressurizing device configured to pressurize each welding electrode is supported by a strong mechanical holding device, and the upper and lower welding electrodes are installed in a certain place together with the holding device and the pressurizing device.

  For this reason, the use of a stationary spot welder has the great advantage that a high-strength weld joint can be obtained because a high pressure is applied, and the welded material is moved to the welder each time welding is performed. However, it is applied from the manufacture of small rod metal frames and metal boxes to the welding of large structures.

  However, if the frequency of use of the welding electrodes used as the upper and lower electrodes in this stationary spot welder increases, the metal component of the material to be welded will alloy with the copper component of the tip of the welding electrode to form the tip of the welding electrode. It adheres, the weldability is impaired, and this deposit adheres to the surface of the next material to be welded and is contaminated, which takes much time to remove. In particular, recently, various types of chemically treated steel sheets are used as materials to be welded. Incidentally, bond-treated steel sheets and parkerizing steel sheets are used, and aluminum materials having higher electrical conductivity and thermal conductivity than steel sheets are used. Therefore, improvement of this point is demanded.

  From this point of view, a resistance welding method and apparatus as described in JP-A-4-32280 have been proposed. However, this welding method and apparatus is a technique for welding by interposing a conductive tape such as copper continuously fed between a welding electrode and a material to be welded, and interposing the conductive tape. This complicates the structure of the apparatus, which is not preferable.

  That is, this method is a resistance welding method in which a conductive tape made of copper or the like is continuously supplied between an electrode and a material to be welded, and welding is performed via this conductive tape. An apparatus for carrying out the method includes a feed roll, a support roll, a winding roll and an electrode, and the conductive tape fed from the feed roll is supported by the support roll. However, it is continuously supplied between the electrode and the material to be welded.

This welding apparatus is provided with a feed roll and a support roll of a conductive tape such as copper, and a conductive material is supplied between the electrodes. Because of such a structure, the structure becomes complicated, which is not preferable from an economical point of view. Further, the conductive tape cured at the time of welding has a hindrance to continuous and smooth winding.
JP-A-4-32280

  The object of the present invention is to solve the above-mentioned drawbacks. In particular, any welding material can be spot welded regardless of the type, material, etc. by simply attaching it to the welding electrode of an existing welding machine during welding. We propose an electrode cap that is easy to handle.

  That is, the present invention provides a welding electrode that is resistance-welded across the overlapped portions of at least two materials to be welded, and is provided with an electrode cap that surrounds the welding electrode so as to align with at least the tip of the welding electrode. A hard portion is provided at a contact portion with the material to be welded.

  The hard portion provided on the electrode cap is configured to be water-cooled from the back surface.

  This electrode cap is comprised from an oxygen-free copper plate, a tough pitch copper plate, or phosphorus deoxidized copper, and is comprised as a work hardening part which worked and hardened the contact part with a to-be-welded material by a forge process.

  Moreover, the hard part of the contact part with a to-be-welded material is comprised, for example from the copper alloy containing precipitation hardening components, such as chromium and belium, and this hard part is hardened by forging, heat processing, etc., and is comprised.

  As described above, the present invention surrounds at least the tip portion of the welding electrode that is resistance-welded across the overlapped portions of at least two workpieces with the electrode cap, and the contact portion of the surrounding electrode cap with the workpiece to be welded Are provided with hard parts. Therefore, it is the electrode cap that abuts the material to be welded during welding and applies a high pressure, and a wide variety of materials to be welded can be welded regardless of the type by simply changing the electrode cap.

  In addition, since it is not necessary to polish or cut the tip of the welding electrode by dressing or the like, it is not necessary to take a dressing allowance on the welding electrode, and a cooling water cooling passage can be formed up to the tip surface of the welding electrode, improving the cooling effect. be able to.

  Furthermore, the electrode cap is made of an oxygen-free copper plate, a tough pitch copper plate or phosphorous deoxidized copper, and even if the hard part is formed by forging the contact part with the material to be welded, it is almost directly from the back side. Since it can be cooled with water, the degree of curing hardly returns.

  Furthermore, the welding electrode does not necessarily need to be composed of an expensive precipitation-hardened copper alloy, and can be composed of an inexpensive oxygen-free copper plate, tough pitch copper plate or phosphorous deoxidized copper, and the copper plate close to pure copper is conductive. The current loss can be greatly reduced due to excellent heat conductivity and thermal conductivity.

  FIG. 1 is an explanatory view of a welding electrode for spot welding according to one embodiment of the present invention.

  FIG. 2 is a front view showing, in section, a part of the tip body of the main body of the welding electrode shown in FIG.

  FIG. 3 is a longitudinal sectional view of an example of an electrode cap in the welding electrode shown in FIG.

  First, in FIG. 1, reference numeral 100 denotes a welding electrode according to one embodiment of the present invention. The welding electrode 100 generally forms a pair of upper and lower parts, and a welded material (not shown) is interposed between the welding electrodes 100. ) Is spot welded by sandwiching and applying pressure. The pair of welding electrodes 100 have substantially the same structure, and can be configured as a welding electrode attached to what is called a stationary type.

  That is, as shown in FIG. 1, the welding electrode 100 is coupled via the taper 103 so that the welding tip 101 does not leak cooling water to the shank 102, and the shank 102 is connected via the taper 104 to the shank holder. The welding tip 101 can be coupled via the taper surface 103 for polishing and cutting when the frequency of use during welding increases. However, since the present invention does not require dressing processing such as cutting and polishing as will be described later, these can also be configured integrally.

  Further, in spot welding, a welding target material (not shown) in which steel plates or other metal plates are superimposed is sandwiched between welding electrodes 100 arranged above and below, and the overlapped portion is joined to the upper and lower welding electrodes 100, 100 is applied with pressure from both sides and spot welding is performed.

  Next, the welding electrodes 100, 100 arranged one above the other as described above are usually configured in the same structure, and each welding electrode 100 is provided with a tip body 110, and the tip of the tip body 110 is aligned with it. An enclosing electrode cap 120 is fitted. That is, even if each of the upper and lower welding electrodes 100 is a stationary spot welder of a conventional example, the welding electrode 100 is configured by fitting the electrode cap 120 to the tip of the welding electrode and combining them.

  In other words, a spot welding machine of a conventional example, particularly a welding electrode of a spot welding machine called a stationary type can be used as the chip body 110 as it is.

  More specifically, necessary welding force and welding current are transmitted to the workpiece to be spot welded by the upper and lower welding electrodes 100, 100. However, unlike the conventional example, the welding electrodes 100 and 100 shown in FIG. 1 are configured by combining the tip body 110 with the electrode cap 120. In particular, the electrode cap 120 is directly brought into contact with the material to be welded and pressurized and energized for welding, and the heat generated at the interface between the material to be welded and the electrode cap 120 is quickly removed and high pressure is applied. Need to be configured to withstand

  For this reason, the welding electrode 100 can be composed of a chromium copper alloy containing about 1% of chromium as a precipitation hardening type component as in the conventional example. However, the welding electrode 100 has a higher conductivity and thermal conductivity than the chromium copper alloy. One feature is that it can be made of oxygen-free copper, tough pitch copper, or phosphorous deoxidized copper close to pure copper. Thus, if the chip body 110 itself is made of a material close to pure copper, heat dissipation from the chip body 110 is promoted without any loss of thermal conductivity, and the cooling effect can be sufficiently exerted. For this reason, as will be described later, even if a hard portion is provided and hardened by work hardening the bottom portion of the electrode cap 120, work hardening in the hard portion hardly disappears due to heating during welding.

  Further, the chip body 110 can be configured to adopt an internal cooling system. For example, as shown in FIGS. 1 and 2, a cooling pipe 111 is arranged in the axial direction of the shank 102 and the chip body 110, cooling water is sprayed from the tip of the pipe 111, and the tip of the chip body 110 is moved from the inner surface. It can be configured to cool from the inside.

  As described above, the cooling pipe 111 is provided inside the chip body 110, and the cooling water sprayed from the tip of the cooling pipe 111 is configured to return through the annular passage on the outer periphery of the cooling pipe 111 in the chip body 110 after cooling. If a cooler or the like is interposed in the middle, the electrode cap 120 aligned with the chip body 110 can be cooled, and the life can be greatly improved.

  That is, the tip portion is configured to be cooled by cooling water from the inside of the chip body 110 as described above, but as in the conventional example, if the tip end of the chip body 110 is directly pressed against the workpiece and welded, There are the following obstacles, and when a surface-treated steel plate, an aluminum material or the like is used as a material to be welded, the life of the welding electrode is shortened, which becomes a serious problem.

  That is, the contact between the tip of the tip body 110 and the material to be welded causes the copper component and the component compatible therewith to alloy with each other, and the alloy layer moves to the welding electrode side. For this reason, the tip of the welding electrode, that is, the tip of the tip body is worn or consumed. On the other hand, in the material to be welded, the nugget diameter of the welded portion is decreased, and the shear strength and tensile strength of the formed nugget are decreased, which is not preferable. In particular, the wear and consumption of the tip end portion are increased at the center of the welding electrode tip end, and the tip shape becomes concave. Even if the welding electrode is pressed with such a shape, a desired nugget diameter cannot be obtained, and a decrease in the nugget diameter causes a decrease in strength such as shearing or tension.

  In order to remove such a place, as described above, in the welding electrode of the conventional example, the tip shape is cut or polished (in short, dressing), and then returned to the regular shape and welded again. Yes.

  However, performing polishing and dressing reduces the welding efficiency. In particular, in the case of surface-treated steel sheets and aluminum materials that have been used recently, the frequency of this polishing and dressing increases, and the tip of the welding electrode needs to take a dressing allowance in anticipation of cutting or polishing by dressing. There is always a thick. For this reason, even if the temperature and flow rate of the cooling water are adjusted, the cooling of the tip becomes insufficient, and problems such as wear and wear of the welding electrode tip cannot be solved.

  Therefore, the welding electrode 100 according to the present invention is configured by combining the tip body 110 and the electrode cap 120, and conventionally, the portion left as a dressing allowance can be thinned to enhance the cooling effect.

  In addition, the electrode cap 120 combined with the chip body 110 is brought into direct contact with the material to be welded, and the hard portion 121 is provided at the contact portion in direct contact. The hard cap 121 of the electrode cap 120 is configured so that a sufficient pressing force is applied to the material to be welded.

  When the welding electrode 100 is such that the electrode cap 120 is combined with the tip body 110 as described above, the tip body 110 is made of a chromium copper alloy containing about 1% of chromium, similarly to the welding electrode of a normal spot welder. However, since it does not press directly against the work piece, it can be made of oxygen-free copper, tough pitch copper, or phosphorous deoxidized copper, which is close to pure copper, to increase the electrical conductivity and thermal conductivity of the electrode. Can do. Incidentally, when the conductivity of those close to pure copper is 100%, the conductivity of the chromium copper alloy is about 80%, and the current loss can be reduced.

  On the other hand, the electrode cap 120 can also be formed by deep-drawing a precipitation hardening type copper alloy plate containing about 1% of copper, but its formability is somewhat hindered. However, since the electrode cap 120 is provided with a hard portion 121 at the bottom, the electrode cap 120 is formed by deep drawing an oxygen-free copper plate, a tough pitch copper plate, or a phosphorous deoxidized copper plate into a container shape, and a part thereof is locally The hard portion 121 can be formed by work hardening by forging or the like.

  With this configuration, it is possible to draw the metal properties close to pure copper with almost no other alloy components, that is, the characteristics as a face-centered cubic lattice metal, and use high conductivity and thermal conductivity. Furthermore, the hard part 121 can be formed in the bottom part by utilizing the fact that the work hardening of copper is extremely high by repeatedly forging the bottom part.

  In general, it is known that copper has a low electric resistance and allows a current to pass through, has a heat conductivity next to that of silver, and is easy to extend as a face-centered cubic lattice metal, and has excellent workability. Copper has an extremely high work-hardening property, and a blade having a sharp blade using this has been known since ancient times. However, such a property appears most highly in copper containing no alloying elements or impurities, and when alloying components are contained, it decreases accordingly. For example, the conductivity corresponding to the electrical resistance is 80% that of chromium copper containing only about 1% of chromium compared to the conductivity of oxygen-free copper, tough pitch copper, phosphorous deoxidized copper, etc., which are almost similar to pure copper. The electrical conductivity of the copper alloy containing other components such as beryllium is further reduced. On the other hand, from the viewpoint of workability, chrome copper is a precipitation hardening type alloy by quenching and tempering, so that the softening temperature is as high as about 500 ° C. and it can withstand high temperatures. The degree of work hardening, that is, work hardenability is also reduced.

  From these points, the electrode cap 120 is made by deep drawing a plate made of almost copper, such as tough pitch copper and oxygen-free copper, and the bottom portion thereof is further press-rolled to work and harden it. Form as part. When the hard part is formed in this way, if it is oxygen-free copper or tough pitch copper, which is almost copper, its work hardening rate is much higher than that of iron or steel, and higher than that of aluminum or even chromium copper or other copper alloys Therefore, the hard part 121 can be formed without impairing the conductivity and thermal conductivity. Furthermore, the electrode cap 120 is configured as a cylindrical body that matches the shape of the chip body 110, and in particular, the cylindrical side wall portion 122 has a reduced drawing margin, and can maintain a certain degree of ductility and elasticity (spring hack). By utilizing this, the chip body 110 can be aligned and held.

  As described above, when the hard portion 121 is formed by work hardening the bottom portion of the electrode cap 120, the hard portion 121 is easily softened by being heated during welding.

  The present inventors examined this point by actually carrying out spot welding, and it was found that the energization time was extremely short in spot welding, and when the cooling capacity was increased by adjusting the amount of cooling water, the hard part 121 of the electrode cap 120 was made copper. Even if it is raised above the recrystallization temperature (about 200 ° C.), it is very short to be maintained at this temperature, and the recrystallization speed does not become a time that can sufficiently overcome the work hardening. It was confirmed that it could be maintained sufficiently.

  In addition, in connection with work hardening, the electrode cap 120 supports a load at a high temperature during welding, and may be subjected to both work hardening and annealing. This creep behavior (strain becomes stress and time at high temperature). It is necessary to consider the phenomenon). Considering this point, it is sufficient to predetermine a standard for the life of the electrode cap 120 and replace it when the standard is reached.

Judgment criteria used as a temporary guide in this electrode cap replacement are as follows.
(1) The number of consecutive hits until the nugget diameter or shear strength is below a specified value,
(2) An alloy layer of the electrode cap and the welded material is formed on the bottom surface of the electrode cap, which is transferred to the welded portion of the welded material and the appearance of the welded portion is impaired, and continuous hitting until the pickup phenomenon occurs Points,
(3) The number of continuous hit points before the phenomenon occurs when the electrode cap is welded to the workpiece,
It is.

  As described above, the welding electrode according to the present invention can be widely used in the field of spot welding and is not only called a stationary type as a welding machine, but also industrially referred to as so-called sheet metal work in addition to automobiles and electrical products. It can also be used in other fields.

It is explanatory drawing of the welding electrode for spot welding which concerns on one Example of this invention. It is a front view which shows a part of chip | tip main body of the main body in the welding electrode shown in FIG. It is a longitudinal cross-sectional view of an example of the electrode cap in the welding electrode shown in FIG.

Explanation of symbols

100 Welding electrode 110 Chip body 111 Cooling pipe 121 Hard part

Claims (8)

  An electrode cap is provided in a welding electrode that is spot-welded by sandwiching at least two overlapped parts of the welded material, and is in contact with the welded material in the electrode cap. A welding electrode for spot welding, characterized in that a hard part is provided in the part.   The welding electrode for spot welding according to claim 1, wherein the hard portion of the electrode cap is water-cooled from the back surface thereof.   The welding electrode for spot welding according to claim 1 or 2, wherein the electrode cap is made of an oxygen-free copper plate, a tough pitch copper plate, or phosphorous deoxidized copper.   The spot welding welding electrode according to claim 1 or 3, wherein the hard portion of the electrode cap is formed as a work-hardened portion obtained by work hardening by forging.   The welding electrode for spot welding according to claim 1, wherein the hard portion of the electrode cap is made of a precipitation hardened copper alloy.   6. The spot welding according to claim 1, 2, 4 or 5, wherein the welding electrode is made of a precipitation hardening copper alloy and a cooling water flow passage for cooling at least the hard part of the electrode cap is provided. Welding electrode.   The spot welding welding electrode according to claim 1 or 2, wherein the electrode is made of a precipitation hardened copper alloy, and the electrode cap is made of an oxygen-free copper plate, a tough pitch copper plate, or phosphorous deoxidized copper. The electrode cap is formed into a cylindrical container by deep-drawing an oxygen-free copper plate, a tough pitch copper plate or a phosphorus deoxidized copper plate, and the hard portion is formed by forging and processing the bottom of the cylindrical container. The spot welding welding electrode according to claim 1.

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