JP2015014036A - Electrode for resistance welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for resistance welding which allows welding with the heat generated by itself through electrification even when a to-be-welded material is a hardly weldable material and provides an electrode for resistance welding less reactive with the to-be-welded material.SOLUTION: An electrode for resistance welding uses one or more of metal carbides, nitrides and borides of metals of Groups 4a to 6a, etc. in surfaces of the electrode coming in contact with to-be-welded materials. The materials have relatively high electric resistivity, have a high resistance calorific value when used as an electrode and make hard-to-weld materials easily weldable. Even when the to-be-welded metal is a material easy to deposit on an electrode, e.g. aluminum or magnesium, the electrode causes less deposition owing to low reactivity.

Description

The present invention is a resistance welding used for "resistance welding" in which welding is performed by using the electrical resistance of the material itself or the interface of two or more members by energizing two or more members sandwiched between a pair of electrodes. The present invention relates to an electrode.

  Various materials have been proposed to date as electrodes for resistance welding (hereinafter also simply referred to as “electrodes”).

  Copper alloys such as chromium copper, alumina-dispersed copper, and beryllium copper are most frequently used as resistance welding electrodes. Copper alloys have extremely low electrical resistivity, high thermal conductivity, and high temperature rise and fall, so that productivity can be increased. For example, two or more welded materials (hereinafter referred to as iron materials, stainless steel materials, etc.) to be joined (hereinafter referred to as copper materials) (It is also expressed as “work”) and the reaction is not large, and it is widely used as an electrode for resistance welding.

  However, when the material to be welded is not iron or stainless steel but aluminum, magnesium, titanium, zinc, brass, or the like is resistance-welded, the reaction between the workpiece and the electrode becomes remarkable, and the number of usable times is extremely reduced. At this time, the electrical resistivity changes due to the reactive organism between the workpiece and the electrode, resulting in a problem of unevenness in bonding quality. A metal that takes in oxygen in the atmosphere and easily forms an oxide film on the surface, such as aluminum, has a problem that the workpieces are difficult to weld.

  Moreover, since aluminum, magnesium, zinc and the like have a lower melting point than iron materials, it is necessary to weld them with a large current flowing in a short time. Any material of the electrode will crack on the surface as it is used, but when the material to be welded is aluminum, the reaction between the material to be welded and the electrode is severe, and the electrode and workpiece A phenomenon called “pickup” in which the electrodes are integrated and the electrode lifts the workpiece also occurs. This phenomenon is more likely to occur as the surface state of the electrode becomes rougher, and starts to occur during use.

  In order to solve these problems, various proposals have been made so far.

  Along with the copper material, a material based on W (tungsten) and tungsten is used as an electrode material for resistance welding.

Tungsten has a low melting point, a high melting point, hardness and other mechanical properties, and therefore has excellent properties as a resistance welding electrode, and many types are used.

  Patent Document 1 discloses an electrode in which a core material based on W is embedded in the welding surface of an electrode for resistance welding made of Cu or Cu alloy. In W, a group 2a element, a group 4a element, a group 5a element, An electrode for spot welding in which 0.5 to 10% by volume of fine particles having a melting point of 2400 ° C. or more selected from Group 6a elements, rare earth element oxides, nitrides, carbides and borides is disclosed. By adopting this configuration, even when spot welding is performed under conditions involving pressurization under a large current, it is possible to suppress welding and alloying with the plated metal and to prevent the occurrence of cracks. It is described.

  Patent Document 2 discloses oxides and nitrides of elements such as 2a group, 4a group, 5a group, and 6a group in W or Mo having an aspect with an average particle diameter of 50 μm or more and crystal grains of 1.5 or more. An electrode for fusing welding in which 0.5 to 10 mass% of carbide and boride fine particles are dispersed is disclosed. It is described that this configuration provides a fusing electrode with improved durability.

  Patent Document 3 discloses a thickness of typically 1 to 300 μm in which particles such as oxide, nitride, and carbide are dispersed in a base metal such as Co, Ni, W, and Zr on a base material such as copper. A resistance welding electrode having a coating layer having the following is disclosed. It is described that the welding of the electrode base material for resistance welding and the workpiece is improved and is particularly suitable for spot welding of a galvanized steel sheet.

Patent Document 4 discloses a spot welding electrode in which a base material portion is made of a copper-based material, a tip portion is made of ceramic powder, and a side peripheral surface is made of ZrB ₂ , TiB ₂ , WC, and Mo, and they are integrated and fired. ing. It is described that, by using this electrode, welding of a galvanized steel sheet can be performed with high durability as with iron materials.

  Patent Document 5 discloses a layer made of Ni, Co, Cr, Mo or the like as an intermediate layer on a copper resistance welding electrode, and further particles of oxide, carbide, nitride or the like dispersed in a metal such as W on the electrode. An electrode having a surface layer is disclosed. There is a description that by using this electrode structure, welding is suppressed, the electrode is hardly deformed, and the price is also suppressed. In the embodiment, an example in which a galvanized iron plate is used as a workpiece is shown.

In Patent Document 6, an intermediate layer of Ti, Zr, Hf or the like is coated on a copper or copper alloy substrate, and a surface layer made of a carbide, nitride, or the like of a periodic table 4a, 5a, or 6a group metal is formed in an intermediate layer. An electrode for resistance welding is disclosed.

Many resistance welding electrodes based on copper or tungsten have been proposed as described above, but still have the following problems.
(1) The resistance welding electrode not provided with a coating layer does not have sufficient welding resistance when the workpiece contains a reactive material such as aluminum or zinc. Therefore, a sufficient life is not obtained and the problem of the pickup phenomenon is not solved. Also, the electrode replacement frequency is high and the operating rate of the welding apparatus is not sufficient. (2) A resistance welding electrode provided with a coating layer reaches the end of its life when cracking or welding of the coating layer progresses, and a method such as re-polishing Cannot play with. Therefore, it becomes expensive as an electrode. (3) Tungsten as well as copper have very low electrical resistivity. The electrical resistivity of copper is 1.7 × 10 ⁻⁶ (Ω · cm), and tungsten is about 5.3 × 10 ⁻⁶ (Ω · cm). With such an electrical resistivity, the electrode portion hardly generates heat, and most of the heat is generated at the workpiece joining portion. At this time, the electrode temperature also rises because the heat of the work is transferred to the electrode. At this time, if the electrical resistance of the workpiece is low, heat is not sufficiently generated between the electrode and the workpiece and the electrode, and welding cannot be performed sufficiently. Even if it is possible, a voltage much higher than general conditions is required. For this reason, it may be necessary to replace the apparatus, and it is not easy to introduce it into the apparatus currently in use.

In addition, the types of resistance welding are spot welding that welds only a relatively narrow area of a circular shape, seam welding that welds stacked workpieces in a continuous line, and projections are formed in advance on part of the workpiece. Examples thereof include projection welding in which the portion is energized and welding is performed, butt resistance welding, thermal caulking welding also called fusing welding, and the like. Although these welding methods are different, "appropriate electrical resistance" and "low reactivity with the material to be welded" are required in any method.

JP 2006-102775 A JP 2008-073712 A Japanese Patent Laid-Open No. 02-117780 Japanese Patent Application Laid-Open No. 64-078683 JP-A-60-231597 JP 62-089583 A

The present invention solves the following problems.
(1) For example, even when the workpiece is easily welded or reacted with a conventional electrode such as aluminum, an electrode that is difficult to weld or react is obtained. (2) By means such as re-polishing, the electrode life is compared with the coated electrode. (3) The temperature necessary for welding is obtained by heating the electrode itself (4) Compared to the case of using a conventional electrode such as Cu, the wear resistance of the electrode is improved. Extend life. In addition, the operating rate of the welding equipment is increased accordingly.

  Solved by using as a resistance welding electrode a material that generates more heat when energized (ie, has a higher electrical resistivity) and is less likely to react with the metal component of the workpiece than conventional metal materials used as resistance welding electrodes To do.

  As materials that meet this condition, in the present invention, carbides, nitrides, borides, and any of group 4a, 5a, and 6a metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) of the periodic table are used. Among these solid solutions, ceramics composed of one or more kinds were selected.

  These have higher electrical resistivity than tungsten, and the resistance welding electrode itself generates heat when energized, and the heat can be conducted to the workpiece to heat the workpiece to a temperature required for resistance welding.

The electrical resistivity of the material is in the range of 5 × 10 ⁻⁶ to 1 × 10 ⁻³ (Ω · cm) as a single unit. Even when two or more kinds are mixed, the value of the mixture falls within this range.

The material is ceramic and has low reactivity with metal components, particularly Fe, Al, Ti, Ni, Cu, Zn, and Mg, which are often used as resistance welding workpieces. Since the reactivity is low, welding with the workpiece during welding is unlikely to occur, and the phenomenon of lowering the productivity as in the aforementioned pickup is unlikely to occur.

  In addition to the reaction with the workpiece, the reaction to be careful is the reaction with oxygen, nitrogen, water, etc. contained in the air. The material has a small reaction with these components. For this reason, there is little alteration even in a heated state, and stable electrical resistance and heat generation can be obtained.

  Further, unlike the method of forming a thin film having high welding resistance on a metal electrode as in the technique disclosed in Patent Document 3, for example, re-polishing by grinding or the like is possible. This reduces the cost per electrode.

  Furthermore, the material has high hardness and high wear resistance. Therefore, the amount of wear due to contact with the workpiece is small, and the life of the electrode can be extended.

  There are many types of carbides, nitrides, borides, and any solid solutions of Group 4a, 5a, 6a metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) in the periodic table. An example is given below, but both have low reactivity with metals and the electrical resistivity falls within the above range.

Single metal nitrides TiN, ZrN, HfN, NbN, TaN, Cr ₂ N, CrN, Mo ₂ N, MoN, W ₂ N, WN ₂ , W ₂ N _{3 and} other single metal carbides TiC, ZrC, HfC, VC Borides of simple metals such as TaC, Cr ₃ C ₂ , MoC, WC, W ₂ C TiB ₂ , ZrB ₂ , HfB ₂ , Cr ₃ B ₂ , CrB, NbB, Nb ₃ B ₄ , NbB ₂ , W ₂ B , WB, W ₂ B ₅ , Mo ₂ B, Mo ₃ B ₂ , MoB, MoB ₂ , Mo ₂ B _{5 and} other composite nitrides (Ti · Ta) N, (Ti · Mo) N, (Ti · W) N Single carbonitrides, etc. Composite carbonitrides such as TiCN and ZrCN (Ti · Mo) CN, (Ti · W) CN, etc.

These nitrides, carbonitrides, borides and the like may be one kind or plural. It may be a solid solution or a mixture.
For the following explanation, the above metal nitride, metal carbonitride, metal boride and the like are collectively expressed as “metallized synthetic component”.

By using this metallized synthetic component as an electrode material, it is possible to obtain an electrode for resistance welding which is difficult to weld to a work component and can obtain stable heat generation over a long period of time. Since the metallized composite is uniformly higher in hardness than tungsten, the hardness and wear resistance are enhanced as compared with a resistance welding electrode made of tungsten alone.
As described above, the metallized synthetic component hardly reacts with oxygen in the workpiece or atmosphere. However, if the specific surface area is extremely large at higher temperatures, it will react with them. For this reason, open pores in the electrode are undesirable. This is because the metal and oxygen that have entered through the open pores react inside to consume the electrode. The open pores are almost absent if the relative density is 90%, more desirably about 95% (in other words, the porosity is 10%, 5% or less). Therefore, the relative density of the electrode is preferably 90% or more, and more preferably 95% or more.

On the other hand, the metallized synthetic component has a lower fracture toughness value than tungsten, which is a metal as well as copper. The fracture toughness value represented by K ₁ C is about 3 to 6, and cracking and chipping may not be sufficiently prevented due to impact during use. Therefore, when the electrode material is made of the metallized synthetic component, an electrode shape that eliminates stress concentration and does not provide corners such as edges as much as possible is preferable. For this purpose, it is desirable to use a part of the plane as a welding surface, a shape with a large curved surface, or a structure that is embedded in the metal other than the welding surface.

  The composition of the electrode requires at least 90% by volume of the metallized composition. In other words, the second component may be included as long as it is less than 10% by volume. The second component preferably contains a component having a function as a sintering aid for the metallized synthetic component, such as alumina, spinel, magnesia, yttria and the like. If the second component exceeds 10% by volume, the electrode may become brittle, the electrical conductivity may change greatly, or the dropped component may adhere to the workpiece surface.

Moreover, fracture toughness and thermal conductivity can be improved by selecting less than 5% by volume of tungsten or molybdenum as the second component. You may add together with the said sintering auxiliary agent.

  The resistance welding electrode of the present invention is a sintered body having at least a weld surface with the above composition. For example, a method of applying a thin film such as nitride ceramic as in Patent Document 3 is effective, but the risk of the thin film peeling is high, and if the electrode becomes unusable after a certain number of weldings, the electrode is discarded. There is nothing but a disadvantage in cost. On the other hand, since at least the welding surface of the electrode of the present invention is a sintered body, it is necessary to recycle by reclaiming only the surface layer after use by enlarging the size of the sintered body. Can do. Therefore, the electrode once manufactured can be used until the size becomes extremely small or the sintered body portion is eliminated by re-polishing, which contributes to cost reduction.

  The electrode for resistance welding can use a sintered body of the above-mentioned material only on the welding surface and its vicinity, and other parts can be combined with the shank part. Good. In addition, when using the shank part mentioned later, the part of the said material containing a welding surface is expressed as a "tip part." FIG. 2 shows these schematic diagrams. FIG. 2 (2) is a schematic diagram using the tip portion 1 made of the above material only on the tip portion including the welding surface of the electrode, and FIG. 2 (1) shows the entire resistance welding electrode including the shank portion as the material. The example formed by is shown.

Although various materials can be used for the shank part 2, it is preferable to use copper (pure copper and copper with additives), aluminum, an iron-based material, or the like. These materials have low electrical resistivity, and hardly generate heat in the shank portion when energized. In addition, it is a metal and is not easily damaged during welding. Does not react with oxygen or water in the atmosphere, or stays only on the surface layer. Casting and machining for obtaining a desired shank shape are easy, and the material is also inexpensive.

  In the case of joining the tip part and the shank part, means such as embedded fixing and vacuum brazing can be performed.

  Embedded fixation means that the temperature rises in a state where the chip part is in contact with a low melting point metal (referred to a shank material), and the molten low melting point metal is in contact with part or all of the chip part surface, and the temperature is lowered as it is. In this way, the chip portion and the solidified low melting point metal are integrated. Necessary processing is added to the solidified low melting point metal portion, and a portion having a desired shape becomes a shank portion. It is sometimes referred to as cast-in, cast-in, etc., rather than being buried.

  Vacuum brazing is a method in which a chip portion and a shank portion are joined using a brazing material in a vacuum atmosphere furnace. The brazing material is preferably a brazing material such as AgCuSnTi called an active brazing material.

Further, as shown in FIG. 2 (3), it is also effective to provide a structure in which the tip portion 1 is not removed by making irregularities in the length direction of the electrodes and allowing the shank portion material 2 to enter the concave portions. With such a structure, even if the joining of the electrodes of the tip portion 1 and the shank portion 2 is not complete, there is no problem that the tip portion 1 falls off. Suitable for the production of this structure is the buried fixing method described below.

The resistance welding electrode of the present invention can be used in various forms of resistance welding. For example, spot welding that welds only a relatively narrow area of a circular shape, seam welding that continuously welds stacked plates linearly, and forms a protrusion on a part of the welded material in advance and energizes that part. Examples thereof include projection welding for performing welding, butt resistance welding, and heat caulking welding also called fusing welding. Not limited to these, any welding method "apply current to a pair of electrodes and two or more workpieces sandwiched between the electrodes, raise the temperature, and join the workpieces" It is possible to use.

The electrode for resistance welding according to the present invention has a very small reaction with the workpiece (workpiece). Therefore, the use of the resistance welding electrode of the present invention has the following effects.
(1) There is very little change in electrical resistance due to adhesion of reaction products to the electrodes. Therefore, stable resistance heat generation by application of current can be obtained. The defect rate of the workpiece is suppressed, and the adjustment of the current value and the electrode is small. (2) Since the wear of the welding surface due to the reaction product is extremely small, the shape change of the electrode is small even after repeated welding. Therefore, a longer life than the conventional electrode can be obtained. (3) Mechanical wear due to contact with the workpiece and pressurization can be suppressed. Therefore, a longer life can be obtained than the conventional electrode. (4) The resistance heat generation can be increased, and the “nugget” formed at the time of welding the workpiece is easier to form than the conventional electrode. Since the sintered body is used for the surface, (5) it is possible to use the electrode repeatedly by re-polishing a small amount of the welding surface and its periphery, which is advantageous in terms of cost.

Schematic of the main part of the form using the resistance welding electrode of the present invention for spot welding Example of form of electrode for resistance welding of the present invention (1) The entire electrode is composed of a metallized synthetic component (2) Only the tip portion is composed of a metallized synthetic component (3) The shape of the tip portion and the shank portion is difficult to dissociate Pattern diagram Schematic of the main part of the form using the clamp electrode of the present invention for butt welding

The surface of at least the electrode main body of the resistance welding electrode that abuts the material to be welded is a metallized synthetic sintered body, and the resistance welding electrode of the copper material and the resistance of the W material conventionally used in various resistance welding methods A resistance welding test was conducted together with the welding electrode to investigate the electrode life.
As a result, an electrode for resistance welding having improved weldability with the work, high work appearance quality, and high work joint strength was obtained. It was also confirmed that it was effective in extending the life of resistance welding electrodes.

  The resistance welding electrode of the present invention is obtained by the following method.

  First, a powdered metallized synthetic component is mixed dry or wet. The particle diameter of the powder is not particularly limited, but it is preferable to use an easily available powder of about 0.2 to 10 μm. The blending amount is 90 to 100% by volume of the metallized synthetic component, and 10 vol.

  The mixing may be performed by a known device such as a ball mill, an attritor, a raking machine, or a star mill. A mixed powder is thus obtained.

  Next, the mixed powder is press-molded. The press molding is performed by using a known press apparatus such as a die press machine, a CIP (cold isostatic pressure) apparatus, or a dry rubber press machine, and press-molding the mixed powder at a pressure of 50 to 500 MPa. If necessary, intermediate processing of the molded body is then performed with a lathe, milling machine, machining center or the like. Thus, a molded body is obtained.

The obtained molded body is sintered. All of the metallized synthetic components are difficult to sinter, and high temperatures are required for sintering. Although depending on the component ratio and the type of metallization synthesis, the sintering temperature is suitably 1500 to 2200 ° C. When a suitable sintering aid is added as the second component, the lower limit may be lowered to about 1300 ° C. Further, the atmosphere during sintering needs to be a non-oxidizing atmosphere such as a vacuum atmosphere, an inert gas atmosphere, a nitrogen gas atmosphere, and a hydrogen gas atmosphere. This is because if the metallized synthetic component is an atmosphere containing oxygen at the sintering temperature, it is oxidized from the surface to cause a chemical change, and different oxides are generated. After sintering, it is cooled to obtain a sintered body.

Although the example of the process of sintering after pressing was shown above, the mixed powder is packed in a carbon mold and pressed at a pressure of 1 to 30 MPa with the temperature raised to 1300 to 2100 ° C. to obtain a sintered body. A sintered body can also be obtained by hot pressing.

It can also be produced by a capsule HIP (hot isostatic pressing) method. When capsule HIP is performed, a metal compound powder is packed in a capsule such as titanium, the lid is degassed, and HIP sintering is performed at a temperature of about 50 to 200 MPa and about 1400 to 1700 ° C. can get.

If necessary, the obtained sintered body is machined and electroprocessed to obtain a desired shape. If the entire electrode is formed of the material described above, it is completed.

  On the other hand, when manufacturing the tip part of an electrode with the said material, joining with a shank part is needed after this.

  The shank portion is mainly formed of a metal material as described above, but there are two main means for integration with the tip portion.

One is a method of joining the chip part and the shank part after manufacturing them. A typical method is joining by brazing. Since brazing material uses an active brazing material, brazing in a furnace performed under a low oxygen partial pressure is suitable. By using an active brazing material, even a sintered body with a low W content can be joined to the shank portion.

The other is integration by embedded fixing (or sometimes called casting or casting). Embedded fixing means heating the chip part and a low melting point metal (referred to a shank material) so that the molten low melting point metal is in contact with part or all of the chip part surface, and the temperature is lowered as it is. And a solidified low melting point metal. Necessary processing is added to the solidified low melting point metal portion, and a portion having a desired shape becomes a shank portion.

  After the chip portion and the shank portion are integrated by any method, finishing is completed.

  The metallized composite has a low fracture toughness value, and cracks and cracks are likely to develop under conditions where cracks are likely to occur, as compared with electrodes made of metal. Therefore, the weld surface is flat, the surface is curved with a large curvature, the shape other than the weld surface is embedded in the shank, and there are no steps or edges, so that no chipping or cracking occurs. It is preferable to devise the shape.

The results of actually using the obtained resistance welding electrode will be evaluated in detail in the following examples.

Example 1 Example Used for Spot Welding Electrode Three magnesium plates having a thickness of 0.3 mm were used as workpiece 4 and a welding test was conducted in which the three pieces were integrated. The electrode 20 is a DR type (dome radius type) with a weld surface 3 having a diameter of 8 mm and an overall diameter of 20 mm. An arc having a radius of curvature of 40 mm is applied to a portion having a weld surface diameter of 6 mm and an arc having a radius of curvature of 8 mm is provided to the other portion. did. The manufacturing method is an electrode composed of a tip part 1 and a shank part 2 described in Sample 1 below.

Sample 1
Material of chip 1: 100% by volume of TiN (forming press pressure 150 MPa, sintering temperature 2000 ° C., sintering atmosphere Ar gas)
Material of shank 2: Pure copper (C1020)
Chip 1 and shank 2 bonding method: 950 ° C., embedded in Ar atmosphere

The schematic diagram of the principal part of an electrode is shown in FIG. The magnesium plate 4 which is a material to be welded is welded by a pair of upper and lower electrodes 20.
With the electrode of Sample 1, continuous spot welding was performed under the conditions shown in Table 1. And the formed nugget diameter was measured and the electrode life was calculated | required by making a nugget diameter less than 3 mm into a welding defect. In addition, the surface roughness of the weld surface of the workpiece was observed.
The test was terminated because steps started to occur in the welded portion of the magnesium plate 4 at the time when 10,000 shots were started after welding. The nugget diameter of all the workpieces 4 examined exceeded 3 mm. When the chip part 1 was observed, a part of the chip 1 was chipped. The observation was performed every 500 shots.

  Next, as shown in Table 1, the same test was performed on electrodes with variously changed chip materials.

  The results of tests similar to those for each chip material and sample 1 are shown in the same table.

For comparison, a sample using chromium copper, which is a conventional electrode, is shown as * Comparative Sample No. 101, using a chip material made of tungsten * Comparative sample No. 102.

表１中で「*」のつく試料は、本発明の範囲外の比較試料である

Samples marked with “*” in Table 1 are comparative samples outside the scope of the present invention.

The following was found from the test results.
Chrome copper * comparative sample No. which is a known resistance welding electrode. No. 101 was welded to the workpiece as early as 120 shots, and re-polishing was necessary.

  Tungsten * comparative sample No. which is also a known resistance welding electrode. In No. 102, yellow oxide powder adhered to the entire electrode, and a change (wear) in the electrode shape was observed over the entire exposed portion including the weld surface. Although it can be used by re-polishing, the electrical resistance changes due to wear, and therefore the work of adjusting the energization conditions becomes complicated.

Sample No. which is within the scope of the present invention. As for 1-18, compared with the conventional chromium copper electrode and the tungsten electrode, all were able to extend the lifetime significantly. Each electrode has a life of 5000 shots or more, which is 7 times or more that of a tungsten electrode. The longest life including 1 was about 10,000 shots.
In all the electrodes, the lifetime was reached by causing cracks or chipping due to large cracks in the electrodes. Further, the electrode was hardly welded with magnesium.

Sample 16 is an example in which 5% by volume of Al ₂ O ₃ as a sintering aid was added to the metallized synthesis (95% by volume TiN). This electrode also had a life comparable to that of the sample to which no sintering aid was added. By adding Al ₂ O ₃ and other auxiliary components used for the sintering aid, the sintering temperature at the time of electrode production can be lowered, which is suitable for production. However, if it is added in an amount exceeding 10% by volume, the electrical resistance is affected, which is not desirable.

  Sample 17 has a composition in which MgO as a sintering aid and tungsten are added to the metallized synthetic component. Although a slight amount of oxide was observed on the surface of the electrode during use due to the addition of tungsten, the use was continued as it was because the addition amount was not large. Further, the degree of chipping at the time of life was smaller than that of other electric discharge machining electrodes.

Sample 18 has a composition in which 2% by volume of tungsten is added to the metallized composition. Due to the addition of tungsten, a slight amount of oxide was observed on the surface of the electrode in use. However, since the addition amount was not large, the use could be continued as it was. Further, the degree of chipping at the time of life was smaller than that of other electric discharge machining electrodes.

Example 2 Example Used for Butt Welding The end surfaces of two rod-shaped aluminum members 6 having a diameter of 10 mm were butted together and used as a clamp electrode 30 for “butt welding” in which the end surfaces 7 were welded together. An example is shown. A schematic diagram of the main part of the apparatus is shown in FIG. The clamp electrode 30 clamps a location approximately 10 mm away from the end face 7 to which the aluminum material 6 is welded on a substantially circumference. The two aluminum materials 6 are clamped by the electrodes 30 respectively, and a current is passed between both electrodes, whereby the aluminum materials 6 on both sides of the butting surface 7 having the largest heat generation are resistance welded.
The welding conditions are as shown in Table 2.

The clamp electrode 30 has a ring-like structure having an inner diameter of about 10 mm, a wall thickness of 10 mm, and a width of 20 mm. The clamp electrode 30 is mounted so as to wrap around an aluminum material, and is fixed without screws with a gap.
The material of the clamp electrode 30 is as follows. 51.

Sample No. 51
Electrode material: 98 volume% VC + 2 volume% Y ₂ O ₃ (5 atm argon gas pressure sintering sintering temperature 1900 ° C.)

  Butt welding was performed with the clamp electrode of the sample 51. The electrode life was determined by applying a welded aluminum material to a tensile tester and breaking the welded material along the weld surface. In addition, the clamp electrode was also observed, and when there was a large chip, electrode cracking or welding with the workpiece, the life was determined there.

  When this test was performed using the clamp electrode of the sample 51, it could be used without any problem until the end of 5000 shots. At the time of 5000 shots, the clamp electrode was chipped at the portion where the aluminum material was clamped and became unusable. In the tensile test until chipping occurred, the aluminum material was broken from other than the welded surface.

Next, the same test was performed by changing the material of the clamp electrode from the VC + Y ₂ O _{3 of} Sample 1 to the material shown in Table 3. The results are shown in Table 3.

表３中で「*」のつく試料は、本発明の範囲外の比較試料である

Samples marked with “*” in Table 3 are comparative samples outside the scope of the present invention.

From the results in Table 3, the following was found.
First, the sample No. using the metallized synthetic component of the present invention was used. In any of the electrodes 51 to 69, the lifetime was remarkably longer than those of conventional chromium copper or tungsten electrodes.

  Sample No. Samples containing 10% by volume or less of a sintering aid such as 51, 52, 53, 55, 57, 61, 62, 64 and 67 are easy to make the sintered body dense and have few pores. The degree of electrode chipping was not large. On the other hand, sample No. Samples that did not contain a sintering aid such as 54, 56, 58, 59, 60, 63, 65, and 66 showed a certain life, but pores remained easily, which was likely to be the starting point for electrode cracking. It is thought. In Table 3, breakage that can clamp an aluminum rod is described as “chip”, and breakage that is larger, for example, broken into two, is described as “crack”.

Sample No. 68 is an example of an electrode obtained by adding magnesium oxide and tungsten as sintering aids to ZrN which is a metallized synthetic component. The degree of chipping of this electrode was also small. I think that the effect of tungsten addition comes out together with the sintering aid.
Sample 69 is an example of an electrode in which molybdenum is added to TiB ₂ which is a metallized synthetic component. This electrode is also sample no. Like 68, the lifetime was sufficiently long and the degree of chipping was small.

DESCRIPTION OF SYMBOLS 10 Resistance welding electrode 20 Spot welding electrode 30 Clamp electrode 1 Tip part 2 Shank part 3 Welding surface 4 Workpiece (material to be welded)
5 Nugget 6 Bar-shaped aluminum workpiece 7 Aluminum end face 8 Power supply 9 Conductor

Claims (3)

Resistance comprising at least a portion in contact with the workpiece to be welded with a sintered body made of any one or a mixture of carbides, nitrides and borides of Group 4a to 6a metals of the periodic table, or a solid solution of each other Welding electrode. 90 to 100% by volume of one or more of carbides, nitrides and borides of Group 4a to 6a metals in the periodic table of the sintered body, or a mixture of two or more of them, or a solid solution of each other.
The electrode for resistance welding according to claim 1, comprising 10% by volume or less (excluding 0% by volume) of a sintering aid. Spot welding, projection welding, thermal caulking, seam welding, or butt welding,
The usage method of the electrode for resistance welding of Claim 1 or Claim 2 used for resistance welding in any one of aluminum, copper, magnesium, titanium, brass, and a plated steel plate.

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