JP2010131666A - Electrode for spot welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for spot welding capable of forming a nugget having a large diameter and the high tension shear strength. <P>SOLUTION: An electrode 1 for spot welding has such a structure that a center part near the tip end of the electrode is provided with a cylindrical hollow part 1a which is not abutted against a material to be welded 2, and only a peripheral part 1b of the cylindrical hollow part is abutted against the material to be welded. Since a nugget with a large diameter is obtained by a spot welding using this electrode, the tension shear strength per welding spot becomes high, so that the sheet thickness of the material to be welded can be made thin and weight reduction can be achieved. Moreover, since a nugget with high tension shear strength is obtained only by replacing the electrode, the current welding equipment can be used without any remodeling and the total costs of equipment can be reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode suitable for spot welding that is widely used in the manufacture of automobiles, aircraft, railway vehicles, and other household items.

  Resistance welding represented by spot welding can heat the material in a very short time, so the molten metal is less likely to be adversely affected by oxygen and nitrogen in the air, so the weld must be specially shielded with a neutral gas. It has the feature that there is no. In addition, resistance welding has high working efficiency and has been used in a wide range of fields such as the automobile industry, aircraft industry, railway vehicle industry, and household goods industry.

  In spot welding, two pieces of metal to be welded (materials to be welded) are overlapped, a cylindrical electrode is brought into contact with the welded portion from the top and bottom, and a current is passed for a very short time while applying pressure, so that the resistance of the current path This is to form a welded portion (nugget) using resistance heating (joule heat) generated by the above, and is one type of resistance welding method using melt solidification.

  Specifically, as shown in FIG. 3, the electrodes 31 and 31 are brought into contact with the workpieces 32 and 32 from above and below, and a current is passed from the welding transformer 33 while the pressure P is applied to form a nugget 34. The nugget 34 begins to melt gradually on the surface where the workpieces are in contact with each other, and grows to a predetermined size. A broken line 35 indicates a current path.

  Since the spot welding electrode is repeatedly energized for a very short time, it is frequently exposed to an environment of high heat and high load. Therefore, if it is used for a long time, deformation is likely to occur and work efficiency is lowered. In order to avoid such a situation, various contrivances have conventionally been made regarding the shape of the electrodes.

  Conventionally used shapes include a R type (radius type) having a curved surface at the tip, a DR type (dome radius type), and a CF type (conical frustum type) having a flat tip. .

  Further, for example, a core material made of W as a base material is embedded in a contact surface of the electrode surrounding material made of Cu or Cu alloy that is in contact with the material to be welded (for example, see Patent Document 1). A spherical concave portion having a diameter exceeding 1/2 of the diameter of the corresponding contact surface is provided at the center of the contact surface of the electrode tip in contact (for example, refer to Patent Document 2), or the tip surface of the electrode is centered and peripheral. The central portion is a convex portion having a small curvature radius, and the peripheral portion is a convex portion having a large curvature radius, a tapered surface having a large inclination angle, or a flat surface orthogonal to the axial direction (see, for example, Patent Document 3) ) Etc. are also known.

JP 2006-102775 A JP 2006-130514 A JP 2007-307588 A

  As described above, electrodes having various shapes have been used in the past. For nuggets formed using such electrodes, the tensile shear strength per welding spot is increased as the plate thickness of the material to be welded is reduced. It is desirable to increase the height. One method for increasing the tensile shear strength of the nugget is to increase the nugget diameter.

  However, to increase the nugget diameter, it may be possible to increase the welding current, increase the energization time, or increase the pressure applied to the material being welded. If the pressure is increased, the temperature rises from the center of the nugget, causing the center to boil, making it easier for blowholes (bubbles) to form in the nugget, and causing inconveniences such as burr around the nugget. There was a problem that the nugget was not formed in the disk shape but only on the outer periphery.

  Such welding defects are generally called donut nuggets, and the nugget diameter may be substantially reduced due to phenomena such as uneven nugget width and thickness, and nugget breaks. The tensile shear strength was extremely reduced, which caused a significant deterioration in the strength of the weld.

  The present invention has been made to solve the above-mentioned problems, and provides a spot welding electrode capable of forming a nugget having a large diameter and obtaining a high tensile shear strength.

  In order to solve the above problems, a first aspect of an electrode for spot welding according to the present invention is an electrode used for spot welding, and is a cylindrical hollow portion that is not brought into contact with a material to be welded at a central portion near the tip of the electrode Is provided, and has a structure in which only the peripheral portion of the cylindrical hollow portion is in contact with the material to be welded.

  The second aspect of the spot welding electrode according to the present invention is characterized in that, in the first aspect, the diameter of the cylindrical hollow portion is 20 to 50% of the diameter of the electrode.

  Furthermore, the third aspect of the electrode for spot welding according to the present invention is characterized in that, in the first aspect or the second aspect, the surface of the electrode that comes into contact with the workpiece is flat.

  The fourth aspect of the electrode for spot welding according to the present invention is characterized in that, in the first aspect or the second aspect, the surface of the electrode that comes into contact with the material to be welded is curved.

  According to the present invention, the contact portion between the welded material and the electrode is only the peripheral portion of the electrode, and the welded material and the electrode are not in contact with each other at the center. Therefore, the nugget has a hollow shape with a hollow center.

  The hollow nugget by the electrode of the present invention has a uniform nugget width and thickness unlike the doughnut-shaped nugget which is a poorly welded shape formed by a conventional electrode. Therefore, if the diameter of the electrode of the present invention is increased, thereby forming a hollow nugget having a large diameter, the tensile shear strength is higher than that of a conventional disk-shaped nugget (wire nugget) having no open center. Obtainable.

  Moreover, according to the spot welding electrode of the present invention, a nugget having a higher tensile shear strength per welding hit point can be obtained as compared with the prior art, so that the thickness of the material to be welded can be reduced and the weight can be reduced. It becomes possible.

  Furthermore, according to the electrode for spot welding of the present invention, a nugget having high tensile shear strength can be obtained only by replacing the electrode, so that it can be used without improving the existing welding equipment, and the overall equipment cost is reduced. Can be achieved.

  Hereinafter, preferred embodiments of an electrode for spot welding according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing the situation of spot welding using the spot welding electrode of the present invention. In FIG. 1A, the spot welding electrodes 1 and 1 of the present invention are brought into contact with the workpieces 2 and 2 from above and below, and a welding current is passed from the welding transformer as indicated by an arrow while applying a pressure P. Form. A broken line 4 indicates a current path. In FIG. 1, the welding transformer is not shown.

  The spot welding electrode 1 of the present invention is provided with a cylindrical hollow portion 1a in the center near the electrode tip, and only the peripheral portion 1b of the cylindrical hollow portion 1a is brought into contact with the workpiece 2 to be welded. It has become so. As shown in FIG. 1B, the nugget 3 formed by such electrodes has a circular and hollow shape when viewed from the pressing direction.

  The hollow nugget formed by such an electrode of the present invention is different from a doughnut-type nugget that is poorly welded, the nugget has a uniform width and thickness, and its shape does not change even when the diameter is increased, and is high. Has tensile shear strength.

  In addition, the contact surface of the peripheral part 1b which contact | abuts to-be-welded material of the electrode 1 for spot welding of this invention may be made flat, and may be curved. When spot welding is performed using the electrode of the present invention, it is possible to select the most suitable contact surface shape.

  Here, as for the electrode 1 for spot welding of this invention, as shown in FIG. 2, it is preferable that the diameter d (mm) of the cylindrical hollow part 1a is 20 to 50% of the diameter D (mm) of an electrode. . A hollow nugget formed of electrodes in such a range has a larger diameter and higher tensile shear strength than a disk-shaped nugget formed by conventional wire welding.

  The reason why the above range is preferable for the shape of the electrode is that if the diameter d of the cylindrical hollow portion 1a is less than 20% of the diameter D of the electrode 1, the width W of the nugget (see FIG. 1B) becomes too thick. This is because there is no significant difference in effect as compared with the conventional disk-shaped nugget, and when the diameter d of the cylindrical hollow portion 1a exceeds 50% of the diameter D of the electrode 1, This is because the width W becomes too thin and the desired tensile shear strength cannot be obtained, and on the contrary, the tensile shear strength may be lowered.

The normal nugget diameter is required to be 4 × t ^1/2 or more when the total thickness of the materials to be welded is t as shown in FIG. Therefore, also in the present invention, as shown in FIG. 1B, the nugget diameter X satisfies the above-mentioned conditions, and the ratio of the diameter d of the cylindrical hollow portion to the diameter D of the electrode is 20 to 50%. What is necessary is just to determine the shape of an electrode suitably.

  As described above, when the spot welding electrode of the present invention is used, a hollow nugget having a large diameter and a uniform nugget width and thickness can be formed. Tensile shear strength higher than that of nuggets (wire-welded nuggets) can be obtained.

  Therefore, when spot welding is performed using the electrode of the present invention, a nugget having a higher tensile shear strength per welding spot can be obtained as compared with the conventional method, so that the thickness of the material to be welded can be reduced and the weight can be reduced. Can be realized.

  Furthermore, since a nugget having a high tensile shear strength can be obtained only by exchanging the electrodes, the existing welding equipment can be used without improvement, and the overall equipment cost can be reduced.

It is the figure which showed the condition of the spot welding using the electrode for spot welding of this invention. It is the figure which showed the electrode for spot welding of this invention. It is the figure which showed the condition of the spot welding using the conventional electrode for spot welding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrode for spot welding 1a ... Cylindrical hollow part 1b ... ...... Peripheral part 2 ......... Welding material 3 ... Nugget 4 ...・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Current path

Claims (4)

  An electrode used for spot welding is provided with a cylindrical hollow portion that is not in contact with the material to be welded at the center near the tip of the electrode, and only the peripheral portion of the cylindrical hollow portion is the material to be welded. An electrode for spot welding characterized by having a structure to be brought into contact.   The spot welding electrode according to claim 1, wherein the diameter of the cylindrical hollow portion is 20 to 50% of the diameter of the electrode.   The spot welding electrode according to claim 1 or 2, wherein a surface of the electrode that comes into contact with a workpiece is flat.   The spot welding electrode according to claim 1 or 2, wherein a surface of the electrode that comes into contact with a workpiece is curved.

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