Lower electrode for nut welding

Abstract

This provides a lower electrode for nut welding with a significantly extended service life. [Solution] This is a lower electrode 11 for nut welding used when welding a weld nut 50 to a metal plate 30, characterized in that a guide pin insertion hole 17 is formed in the center of the electrode body 16 which is made of a block of chromium zirconium copper, and the upper surface 15 of the electrode body 16 which serves as the support surface for the metal plate 30 is a forged hardened surface with a Rockwell hardness (HRBS) of 82 to 90.

Description

Technical Field

[0001] The present invention relates to a lower electrode for nut welding that is used by being incorporated into a welding machine for welding a weld nut to the surface of a metal plate.

Background Art

[0002] Many weld nuts (nuts for welding) have welding protrusions on their seating surfaces and are used by being welded to the surface of a metal plate typified by a steel plate. A pilot hole is formed in the metal plate in advance, and welding is performed with the center of the weld nut and the center of the pilot hole aligned.

[0003] For this welding, a welding machine including a lower electrode unit 10 and an upper electrode 20 as shown in FIG. 1, for example, is used. The lower electrode unit 10 includes a lower electrode 11, a lower electrode holder 12, and an elevating guide pin 13, and a compressed air supply port 14 is formed in the lower electrode holder 12. As shown in FIG. 1, with the guide pin 13 raised from the lower electrode 11 by compressed air, the pilot hole 31 of the metal plate 30 is aligned by passing it through the guide pin 13, and the metal plate 30 is placed on the upper surface 15 of the lower electrode 11. Further, from above, the weld nut 50 is placed on the tip of the guide pin 13 by a nut feeder or manually.

[0004] Next, as shown in FIG. 2, the upper electrode 20 is lowered to push down the weld nut 50 with its lower surface, pressing the welding protrusion 51 protruding from the lower surface of the weld nut 50 against the upper surface of the metal plate 30 and pressing the lower surface of the metal plate 30 against the upper surface 15 of the lower electrode 11. At this time, the guide pin 13 is pushed down together with the weld nut 50. When a welding current is passed between the upper electrode 20 and the lower electrode 11 in this state, the welding current concentrates and flows through the portion of the welding protrusion 51 of the weld nut 50, melting the welding protrusion 51 and welding the weld nut 50 to the surface of the metal plate 30. Although the structure is somewhat different in Patent Document 1, the above-described procedure is disclosed.

[0005] In the welding process for such nuts, the weight of the metal plate 30 and the load when the upper electrode 20 descends all act on the upper surface 15 of the lower electrode 11, which is the support surface for the metal plate 30. Since the lower electrode 11 is a small component with a diameter of about 20 mm, the area of ​​the upper surface 15 is also small, and large compressive stresses are repeatedly generated with each welding. Moreover, the material of the lower electrode 11 is a copper alloy with excellent conductivity, which is a much softer and more easily deformed metal than steel. For this reason, the lower electrode 11 currently in use is a consumable item with a short service life and has the problem of having to be replaced frequently. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-320288 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Therefore, the objective of the present invention is to solve the above-mentioned problems of the conventional invention and to provide a lower electrode for nut welding that has a significantly longer service life than conventional electrodes without impairing the conductivity which is important for welding. [Means for solving the problem]

[0008] The inventors of this invention have conducted extensive research to find a solution to the above problems. As a result, they have found that conventional lower electrodes for nut welding are manufactured by machining copper material, and therefore the hardness and strength of the upper surface of the electrode body, where large compressive stresses occur during welding, are determined by the material properties of the copper material itself. Furthermore, since the lower electrode is a component that conducts welding current between it and the upper electrode, it is not easy to increase its hardness and strength through surface treatment. However, they have discovered that by adding an unprecedented process of forging to the lower electrode, it is possible to increase the hardness and strength of the upper surface of the electrode body without impairing conductivity, or even slightly increasing conductivity.

[0009] The lower electrode for nut welding of the present invention was completed based on the above findings, and is a lower electrode for nut welding used when welding a weld nut to a metal plate, characterized in that a guide pin insertion hole is formed in the center of the electrode body which is made of a chromium zirconium copper block, and the upper surface of the electrode body which serves as the support surface for the metal plate is a forged hardened surface with a Rockwell hardness (HRBS) of 82 to 90.

[0010] Furthermore, it is preferable that the outer circumference of the cylindrical portion formed at the bottom of the electrode body be a threaded surface, and that the electrode body be made of chromium zirconium copper having a composition of Cr: 0.4~1.00%, Zr: 0.03~0.15%, and the remainder being Cu. [Effects of the Invention]

[0011] According to the invention of claim 1, the hardness and strength of the upper surface of the electrode body of the lower electrode can be increased, thereby improving the service life of the lower electrode. Moreover, as shown in the data of the examples, it is also possible to increase the conductivity by several percent.

[0012] According to the invention of claim 2, by machining the male thread for screwing the electrode body into the lower electrode holder, a highly accurate male thread can be made, and compressed air supplied from the lower electrode holder will not leak.

[0013] According to the invention of claim 3, a lower electrode with excellent conductivity and hardness can be obtained. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view of a key part of a nut welding machine, showing the upper electrode in a raised position. [Figure 2] This is a cross-sectional view of a key part of a nut welding machine, showing the upper electrode in a lowered position. [Figure 3] The images show a plan view (A), a front view (B), and a cross-sectional view (C) of the lower electrode. [Modes for carrying out the invention]

[0015] Preferred embodiments of the present invention are shown below, and in the following description, the same reference numerals as those used in Figures 1 and 2 will be used. Figure 3 shows the structure of the lower electrode for nut welding in this embodiment. The lower electrode 11 is made entirely of a copper alloy block with excellent conductivity, and in this embodiment, the lower electrode 11 is made of a chromium zirconium copper block with excellent conductivity and strength.

[0016] The electrode body 16 of the lower electrode 11 has a shape that is flattened on both sides when viewed from above, and a guide pin insertion hole 17 is formed in the center into which a guide pin 13 can be inserted. In addition, a male thread 18 is formed on the outer circumference of the cylindrical part formed at the bottom of the electrode body 16, and the surface is machined for the male thread. This male thread 18 is for screwing the electrode body 16 into the lower electrode holder 12 as shown in Figure 1, and the flat parts 19 on both sides of the electrode body 16 are for engaging a tool such as a wrench when attaching or detaching the lower electrode 11.

[0017] While the shape of the lower electrode 11 is conventional, conventional products were manufactured by machining copper material. In contrast, the lower electrode 11 of the present invention has at least its upper surface 15 as a forged hardened surface. Since forging pressure is applied by a press machine to forge the upper surface 15, it is not possible to forge only the upper surface 15, and the forging pressure is applied to the entire electrode body 16. Furthermore, since forming the male thread 18 by forging is costly, machining is performed after forging, and this part becomes a male thread machined surface with excellent dimensional accuracy.

[0018] In this embodiment, the surface hardness of the chromium zirconium copper before forging is specified by the manufacturer to have a Rockwell hardness (HRBS) of 65 or more. However, as shown in the data of the examples, the measured value was in the range of 72 to 78. On the other hand, the upper surface 15 of the electrode body 16 of the present invention has been forged to form a forged hardened surface with a Rockwell hardness (HRBS) of 82 to 90. That is, the average value has a hardness increase of about 15% compared to the conventional product. As a result, the hardness and strength of the lower electrode 11 are increased, and its service life can be extended to more than twice that of the conventional product.

[0019] As the chromium zirconium copper, those having a composition of Cr: 0.4 to 1.00%, Zr: 0.03 to 0.15%, and the balance being Cu are preferable. Cr and Zr are components that improve the strength of the copper alloy. However, exceeding the above range causes a decrease in conductivity, which is not preferable. Conversely, if it is less than the above range, it approaches pure copper and the strength required for use as the lower electrode 11 cannot be obtained. There are various types of copper alloys, but from the viewpoint of achieving both conductivity and strength, chromium zirconium copper is considered to be the most suitable as the material of the lower electrode 11.

[0020] As described above with respect to FIGS. 1 and 2, this lower electrode 11 is screwed into the lower electrode holder 12 and incorporated into the welding machine, and is used to weld the weld nut 50 to the metal plate 30 typified by the steel plate. Since the upper surface 15 of the electrode body 16 serving as the support surface of the metal plate 30 is a forged hardened surface with a Rockwell hardness (HRBS) of 82 to 90, wear and deformation are suppressed, and the service life can be extended.

[0021] The Rockwell hardness (HRBS) is used for measuring the hardness of relatively soft materials. A steel ball with a tip of 1 / 16 inch is pressed against the surface of the object to be measured with a load of 100 kgf, and the hardness is calculated from the size of the indentation. The details of the measurement method of Rockwell hardness are specified in JIS Z2245 (2016). According to the published conversion table, Rockwell hardness (HRBS) 82 to 90 is converted to Vickers hardness (HV) 160 to 196.

[0022] In the present invention, the Rockwell hardness (HRBS) of the upper surface of the electrode body 16 was set to 82 to 90. However, if the hardness is below this range, it approaches the conventional product and the effect of extending the service life becomes weak. Increasing the hardness beyond this range is preferable for extending the service life. However, when the material is chromium zirconium copper with excellent conductivity, it is not easy to further increase the hardness by forging, and this range is considered preferable from the perspective of manufacturing cost.

Example

[0023] Examples of the present invention are shown below. A lower electrode similar to the conventional one was manufactured by cutting a chromium zirconium copper material. Also, this conventional product was forged using a press machine to manufacture a lower electrode with the upper surface being a forged hardened surface. When the composition of this chromium zirconium copper was analyzed, it was Cr: 0.69%, Zr: 0.07%, and the balance was Cu.

[0024] The hardness and conductivity of the upper surfaces of these conventional products and the products of the present invention were measured. For the hardness measurement, an Akashi AR-20 Rockwell hardness tester was used. After calibration using a Rockwell hardness standard piece, the hardness at two points on the left and right of the guide pin insertion hole on the upper surface of the lower electrode was measured. Two conventional products and six products of the present invention were measured. The measurement results are summarized in Table 1 below. The conductivity (%IACS) shown in Table 1 is a value based on an international standard that expresses the conductivity of pure copper as 100%.

[0025]

Table 1

[0026] As shown in Table 1, the hardness of the forged hardened surface on the upper surface of the lower electrode was approximately 15% higher than that of the conventional product manufactured by cutting. Moreover, although they are made of the same material, the conductivity also increased by a few percent. This is presumably due to the densification of the metal structure by forging. It was confirmed that not only the hardness and strength increase by forging, but also the conductivity, which is an important property as an electrode, improves by about a few percent.

[0027] When the lower electrode of the present invention described above was set in a nut welding machine and its service life was measured, it was confirmed that the average of six electrodes was more than twice that of the conventional product.

[0028] As described above, the present invention makes it possible to provide a lower electrode for nut welding with a significantly longer service life than conventional products. [Explanation of Symbols]

[0029] 10 Lower electrode unit 11 Lower electrode 12 Lower electrode holder 13 Guide pins 14 Compressed air supply port 15 Top side 16 Electrode body 17 Guide pin insertion hole 18 male thread 19 Flat area 20 Upper electrode 30 metal plate 31 Pilot hole 50 Weld Nuts 51 Welding protrusions

Claims

1. A lower electrode for nut welding used when welding a weld nut to a metal plate, A guide pin insertion hole is formed in the center of the electrode body, which is made of a chromium zirconium copper block, A lower electrode for welding nuts, characterized in that the upper surface of the electrode body, which serves as the support surface for the metal plate, is a forged hardened surface with a Rockwell hardness (HRBS) of 82 to 90.

2. The lower electrode for nut welding according to claim 1, characterized in that the outer circumference of the cylindrical portion formed at the bottom of the electrode body is a threaded surface.

3. The lower electrode for nut welding according to claim 1 or 2, characterized in that the electrode body is made of chromium zirconium copper having a composition of Cr: 0.4 to 1.00%, Zr: 0.03 to 0.15%, and the remainder being Cu.

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