JP2007111707A - Spot welding method of titanium plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the spot welding method of a titanium plate, with which welding phenomenon between a spot electrode and the titanium plate can be suppressed and a nugget of a sufficient size can be formed. <P>SOLUTION: In the titanium plate spot-welding method in which generation of a spot electrode welding phenomenon is suppressed, the titanium nitride plate in which a nitride layer having a thickness of >5 to <10 μm is formed on the surface of the titanium plate by a nitriding treatment is used, and the nitride layer of the titanium nitride plate and a spot electrode are brought into pressurized-contact with each other for spot welding. Also, in the titanium nitride plate, contact resistance between the spot electrode and the titanium plate is >0.01 and <0.2 mΩ. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spot welding method for a titanium plate, and more particularly to a spot welding method for a titanium plate that suppresses the occurrence of a welding phenomenon between a spot electrode and a titanium plate at the time of spot welding and obtains an excellent spot welding nugget. .

  The titanium plate spot welding method is a commonly used technique, in which a titanium plate, which is an object to be welded, is inserted between a pair of opposed spot electrodes, and a welding current is supplied in a state where an electrode pressing force is applied, This is a welding method in which a titanium plate as a workpiece is melted by raising the temperature by Joule heat generation. As an application example of spot welding of this titanium plate, for example, when manufacturing a casing for a small electronic device product consisting of an exterior cover and an interior case, after forming the exterior cover and the interior case from a titanium material, Some of them are overlapped and integrated by spot welding (for example, see Patent Document 1).

  However, spot welding of titanium plates has the following differences compared to spot welding of steel plates.

  When spot welding a steel sheet, using the same welding electrode, using the same welding electrode, and increasing the welding current in the same energization time, (1) a meteorite-like molten part called a nugget is formed, (2) So-called dust is generated in which molten metal that has become excessively large from the plate to the plate is scattered from the plate to the plate, and (3) the welding result changes in the order of welding of the electrode and the plate. At this time, the dust generation current becomes the upper limit of the welding current proper range. On the other hand, when spot welding a titanium plate, if the welding current is increased, (1) a meteorite-like melted part called a nugget is formed, (2) the electrode and the plate are welded, and (3) plate-plate The welding results change in the order that dust occurs from the beginning. At this time, the welding current becomes the upper limit of the appropriate welding current range.

  Considering this welding result in which the order of dust generation and welding is reversed, in the case of a titanium plate, the contact resistance between the electrode and the plate is higher than in the case of the steel plate, and the temperature between the electrode and the plate easily rises. It can be qualitatively understood that the electrode and the plate are seized and lead to welding.

  In the case of spot welding of steel plates, so-called dust generation in which nuggets are formed between the plates and excessively large molten metal scatters between the plates dominates the upper limit of the appropriate current. On the other hand, in the case of spot welding of a titanium plate, since the electrode-plate is welded before a nugget of an appropriate size is obtained between the plates, the upper limit of the appropriate current is controlled by the welding. That is, in the case of spot welding of a titanium plate, a smaller welding current, that is, a welding current at which a sufficiently large nugget is formed dominates the welding result. If a welding current exceeding the welding current is supplied to generate a nugget of sufficient size, welding occurs between the electrode and the plate, the electrode tip wears out, the electrode life is shortened, and workability is deteriorated. There is a problem that the quality of the surface of the spot welded portion is also deteriorated. For this reason, the present condition is that the spot welding method which can supply the welding current which can form a nugget of sufficient size is calculated | required.

  The gist of the present invention is to suppress a welding phenomenon between a spot electrode and a titanium plate by nitriding a titanium plate as a workpiece. As a technique related to the nitriding treatment of the titanium plate, a titanium nitride plate in which a nitride layer having a thickness of 0.1 μm or more and 1.0 μm or less is formed on the surface is proposed. Furthermore, a titanium nitride plate having a nitride layer with a thickness of 0.5 μm or more and 5.0 μm or less formed on the surface has been proposed (for example, see Patent Documents 2 and 3). These titanium plates are intended to make the surface of the titanium plate difficult to be wrinkled during processing. Further, it has been proposed to form a nitride layer having a thickness of 10 μm to 15 μm to form a titanium nitride plate having excellent wear resistance (see, for example, Patent Document 4). However, none of these techniques solves or suggests the problems of the spot welding method for titanium plates.

JP 2003-283150 A Japanese Patent Laid-Open No. 10-60620 Japanese Patent Laid-Open No. 10-204609 JP-A 64-10883

In view of the above situation, an object of the present invention is to provide a spot welding method for a titanium plate that can suppress a welding phenomenon between a spot electrode and a titanium plate and can form a sufficiently-sized nugget.

  The originator can improve the surface lubricity and reduce the contact resistance between the spot electrode and the titanium plate by nitriding the surface of the titanium plate used for spot welding. As a result, it was found that a sufficiently large nugget can be formed by suppressing welding phenomenon between the spot electrode and the titanium plate and increasing the welding current.

  The gist of the present invention is as follows.

  (1) Titanium plate that suppresses the occurrence of a spot welding phenomenon characterized in that spot welding is performed using a titanium plate having a nitride layer having a thickness of more than 5 μm and less than 10 μm on the surface in a spot welding method of a titanium plate. Spot welding method for plates.

  (2) Use of a titanium plate having a nitride layer having a contact resistance between the spot electrode and the titanium plate of more than 0.01 mΩ and less than 0.2 mΩ, and suppressing the occurrence of the spot welding phenomenon as described in (1) above Spot-welding method for titanium plate.

  (3) The titanium plate is a titanium plate in which a nitride layer is formed on a surface of the titanium plate by nitriding the surface, and the occurrence of the spot welding phenomenon described in (1) or (2) is suppressed. Spot welding method for titanium plate.

  (4) Spot welding of a titanium plate that suppresses occurrence of the spot welding phenomenon according to any one of (1) to (3), wherein the nitride layer of the titanium plate and a spot electrode are brought into pressure contact. Method.

  (5) The spot of the titanium plate that suppresses the occurrence of the spot welding phenomenon according to any one of (1) to (4) above, wherein the titanium plate is a nitrided titanium plate or a titanium alloy plate Welding method.

  According to the spot welding method of the titanium plate of the present invention, the welding phenomenon between the spot electrode and the titanium plate can be suppressed, a sufficiently-sized nugget can be formed, and not only the life of the spot electrode can be extended but also the welded portion appearance can be welded. Departmental quality can be improved.

  Hereinafter, a titanium plate spot welding method according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory view showing an example of a state in which a spot welding method using a nitrided titanium plate according to the present invention is performed. FIG. 2 is an explanatory view showing an example of a state in which an ordinary spot welding method for titanium material is performed. FIG. 3 is an explanatory view showing spot proper welding conditions for a nitriding titanium plate and a normal titanium plate.

  As shown in FIG. 2, in the spot welding of a titanium plate, a titanium plate 2, 2 ′, which is an object to be welded, is inserted between a pair of opposed spot electrodes 1, 1 ′ and an electrode pressure is applied. The nugget 3 is formed by supplying a welding current and increasing the temperature by Joule heat generation to melt a titanium plate as a workpiece.

  However, when trying to spot weld a titanium plate, the weld between the spot electrode and the plate is welded before the nugget of an appropriate size is obtained between the plate and the plate, and the welding required to form a sufficiently large nugget. The current cannot be supplied. If we try to supply a welding current that exceeds the welding current to create a nugget of sufficient size, welding occurs between the electrode and the plate, the electrode tip wears out, the electrode life is shortened, and workability is deteriorated. There is a problem that the quality of the surface of the spot welded portion is also deteriorated.

  Therefore, the inventor has intensively studied a spot welding method for a titanium plate capable of supplying a welding current capable of forming a nugget having a sufficient size. As a result, the surface of the titanium plate used for spot welding is nitrided to form a nitride layer, thereby improving surface lubricity and reducing the contact resistance between the spot electrode and the titanium plate. Since the spot electrode welding phenomenon can be suppressed by suppressing heat generation, the present invention has been completed by finding that a sufficient size of nugget can be formed by increasing the welding current.

  In the spot welding method for titanium plates of the present invention, as shown in FIG. 1, titanium plates 5 and 5 ′ (hereinafter sometimes referred to as titanium nitride plates) having a titanium nitride layer 4 on the surface as a workpiece are spot electrodes. It is inserted between 1 and 1 'for spot welding. The titanium nitride plate used in the present invention can be obtained by a nitriding method such as a gas nitriding method or a liquid nitriding method in which nitrogen is diffused and permeated into the surface layer of the titanium plate to form a nitride layer.

  By using a titanium nitride plate, the contact resistance between the plate and the plate and the contact resistance between the spot electrode and the plate are significantly lower than the contact resistance between the plate of the titanium plate and the contact resistance between the spot electrode and the plate. A confirmation test was conducted.

  That is, as shown in FIG. 2, when a normal titanium plate was inserted between the spot electrodes, the plate-plate contact resistance was 0.074 mΩ, and the electrode-plate contact resistance was 0.718 mΩ. .

  On the other hand, as shown in FIG. 1, when titanium nitride plates 5 and 5 ′ having a titanium nitride layer 4 having a thickness of 9.8 μm are inserted between the spot electrodes 1 and 1 ′ as a work piece, The contact resistance was 0.047 mΩ, and the contact resistance between the spot electrode and the plate was 0.149 mΩ.

  Compared to the fact that the plate-to-plate contact resistance of the titanium plate was 0.074 mΩ and the electrode-plate contact resistance was 0.718 mΩ, the contact resistance of the titanium nitride plate was the plate-to-plate contact. The resistance is about 1/2 and the electrode-plate contact resistance is about 1/4. This indicates that the surface lubricity is enhanced by nitriding the surface of the titanium plate to form a nitrided layer, and the familiarity between the plate and the plate and between the electrode and the plate is improved.

  When the nitride layer is formed on the titanium plate in this manner, the contact resistance between the spot electrode and the titanium plate is lowered, the current path area in spot welding is increased, and a larger nugget can be formed while preventing welding.

  FIG. 3 is a diagram showing the relationship between the welding current and the nugget diameter in a titanium plate and a titanium nitride plate having a thickness of 1 mm.

  As shown in FIG. 3, the nugget diameter tends to increase proportionally as the welding current increases, but welding (indicated by the arrow) occurs between the spot electrode and the titanium plate even if the welding current is increased. Therefore, the welding current cannot be supplied beyond the welding current when the welding occurs. The welding current of the titanium plate was 6.8 kA. In contrast, the welding current of the titanium nitride plate was 9.2 kA.

  At this time, the nugget diameter in the titanium plate is 3.4 mm, the nugget diameter in the titanium nitride plate is 5.0 mm, and there is a clear difference in the nugget diameter between the two. It is clearly higher than the board.

  Note that the titanium nitride plate, which is a test material used in the welding test shown in FIG. 3, was brightly annealed at an annealing temperature of 650 ° C. and an annealing time of 60 minutes in an air atmosphere to form a titanium nitride layer (nitride layer). ) Was used on the surface.

  In the present invention, the titanium nitride plate having a nitride layer having a thickness of more than 5 μm and less than 10 μm on the surface and the reason for limiting the thickness of the nitride layer will be described. The thickness of the titanium nitride layer on the surface of the titanium plate is 5 μm or less. However, the occurrence of welding cannot be sufficiently suppressed. On the other hand, if the thickness of the titanium nitride layer is 10 μm or more, it takes too much time for nitriding, which is not industrial. In order to obtain a titanium nitride layer having such a predetermined thickness, for example, in the case of a gas nitriding method, nitriding is performed by performing bright annealing in an air atmosphere at an annealing temperature of 650 ° C. for an annealing time of 5 minutes to 120 minutes. A titanium layer is obtained.

  As a method for simply evaluating the spot weldability of a titanium nitride plate obtained by nitriding the surface, there is a contact resistance measurement. This can be calculated by applying a current of 1 A with two electrodes pressed with an electrode pressing force of 250 kgf and a CF tip diameter of 5.0 mm, and measuring the voltage between the spot electrode and the titanium plate at this time. When the surface nitride layer thickness exceeds 5 μm, the contact resistance is less than 0.2 mΩ, and the surface nitride layer is less than 10 μm and the contact resistance exceeds 0.01 mΩ. Therefore, in the present invention, a titanium nitride plate having a contact resistance between the spot electrode and the titanium plate of more than 0.01 mΩ and less than 0.2 mΩ is used.

  Furthermore, as a method of measuring the thickness of the nitrided layer, the thickness of the nitrided layer is measured by embedding a sample of a nitrided titanium nitride plate in a synthetic resin, polishing the cross section, and then measuring by EPMA line analysis. did.

  In addition, although the flat plate was demonstrated as a titanium nitride plate used by this invention, what shape | molded the plate may be used. The titanium plate to be nitrided is not limited to a titanium plate, and may be a known titanium alloy plate containing an alloy component.

  Hereinafter, the present invention will be described in detail based on examples.

  Table 1 shows the results of investigating the effect of suppressing the occurrence of the spot electrode welding phenomenon by using a titanium nitride plate having a nitride film when spot welding the titanium plate. The spot welding conditions were a welding current of 7 kA, an electrode pressing force of 250 kgf, a CF type tip diameter of 5.0 mm electrode, and an energization time of 12 cycles.

  Note that the contact resistance between the spot electrode and the plate was measured by measuring the voltage between the titanium plates when a constant current of 1 A was passed in a state where two samples were placed between the CF electrodes facing each other and an electrode pressing force of 200 kgf was applied. And calculated from Ohm's law.

  Moreover, the titanium nitride plate which is a test material used in the welding test was a titanium plate that was brightly annealed at each annealing temperature and annealing time shown in Table 1 in an air atmosphere.

  As shown in Table 1, the spot electrode welding phenomenon occurred in Comparative Examples 1 and 2 at a welding current of 7 kA, but in the inventive examples 1 to 9, the spot electrode welding phenomenon was suppressed and a sufficiently sized nugget was formed. The welding strength was also good. As is clear from these examples, it was found that the lower limit of the titanium nitride film thickness is preferably more than 5.0 μm and the upper limit is preferably less than 10.0 μm. It was also found that the upper limit of the contact resistance between the spot electrode and the plate is preferably less than 0.2 mΩ, and the lower limit is preferably in the range of more than 0.01 mΩ from the measurement accuracy.

  Comparative Examples 1 and 2 are untreated titanium plates. Comparative Example 1 has a surface roughness Ra of 0.5 μm, and Comparative Example 2 has a surface roughness Ra of 0.35 μm, which is the same untreated material, but has a different contact resistance. Yes.

  When spot electrode welding occurs during spot welding, the spot electrode and the titanium plate are fixed and peeled off, so that the wear of the spot electrode is remarkable, the life of the spot electrode is extremely shortened, and workability is deteriorated. Furthermore, since the surface of the titanium spot welded portion becomes rough, the weld appearance quality is also deteriorated. In any of the inventive examples, such a spot electrode welding phenomenon did not occur.

It is explanatory drawing which shows one Example of the spot welding arrangement | positioning of a titanium nitride material. It is explanatory drawing which shows one Example of the spot welding arrangement | positioning of a normal type titanium material. It is explanatory drawing which shows the welding current appropriate range of a titanium nitride material and a normal type titanium material.

Explanation of symbols

1, 1 'electrode 2, 2' titanium plate 3 nugget 4 nitride coating 5, 5 'titanium nitride plate

Claims (5)

  In a spot welding method for a titanium plate, spot welding is performed by using a titanium plate having a nitride layer having a thickness of more than 5 μm and less than 10 μm on the surface. Spot welding method.   2. A titanium plate having a spot electrode-titanium plate contact resistance, wherein the titanium plate has a nitride layer having a contact resistance of more than 0.01 mΩ and less than 0.2 mΩ, and the spot electrode welding phenomenon is suppressed. Spot welding method.   The spot welding of the titanium plate which suppressed the generation | occurrence | production of the spot electrode welding phenomenon of Claim 1 or 2 characterized by the above-mentioned. The said titanium plate is a titanium plate which nitrided the titanium plate surface, and formed the nitride layer on the surface. Method.   4. The spot welding method for a titanium plate with suppressed occurrence of the spot electrode welding phenomenon according to claim 1, wherein the nitride layer of the titanium plate is brought into pressure contact with the spot electrode.   5. The spot welding method for a titanium plate that suppresses the occurrence of a spot electrode welding phenomenon according to claim 1, wherein the titanium plate is a nitrided titanium plate or a titanium alloy plate.

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