JPS61173481A - Manufacture of composite center electrode for superplug - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a spark plug electrode, and more particularly to a composite center for a spark plug of the type consisting of a corrosion-resistant portion forming one end of a spark gap and an adhesive terminal wire. The present invention relates to an improved method of manufacturing electrodes. Each particular internal combustion engine design operates most effectively with a spark plug having a selected thermal range for such engine. Various factors determine the thermal range of a spark plug, including the thermal properties of the insulator and center electrode, and the length of the insulator ignition tip extending from the insulating sheet. For example, if the insulator ignition tip is too short, the center electrode and insulator will operate at very low temperatures and will tend to become fouled with combustion deposits. On the other hand, if! ! If the edge or center electrode is too far away from the insulating sheet, the center electrode will overheat and cause premature ignition. By providing the center electrode with a thermally conductive core, heat is dissipated from the electrode more quickly, so long electrodes and insulator noses can be used without premature ignition. This, in turn, increases the amount of contamination paths and deposits that can be tolerated without causing defects.

In one type of spark plug, the center electrode portion located within and projecting from the insulator nose consists of a cladding made of a corrosion-resistant nickel alloy and surrounding a thermally conductive steel core. An iron terminal wire is welded to the inner end of this electrode. The iron terminal wire extends through the compacted powder seal in the insulator hole and connects directly to the high voltage terminal for the spark plug or, for example, to the ignition noise suppressor and (
or) connected to the high voltage terminal through an auxiliary spark gap. When making the electrode, the steel core must be completely enclosed within the nickel cladding so that the copper is not exposed to the combustion gases in the combustion chamber and the solid nickel end is welded to the iron wire.

BACKGROUND OF THE INVENTION Various methods of making highly thermally conductive spark plug center electrodes are known in the prior art, such as electrodes having a nickel coating surrounding a steel core. One commercial method for making such electrodes consists of placing a copper billet within a nickel cap that has a cylindrical sidewall and a closed end and an open end. The copper billet is recessed from the open end of the cap, and the open end is rolled to partially surround the copper billet. The resulting composite billet is
First, the sealed end is partially pushed through an extrusion orifice. When the resulting extrudate is pushed back and withdrawn from the orifice, the sealed lower end forming one side of the firing gap in the finished spark plug, with the nickel extending over and surrounding the copper, dia. This results in an electrode with a large upper end. Iron terminal wire is then welded to the nickel coating so that it extends concentrically from the larger diameter end of the extruded electrode. When assembling the spark plug, the center electrode is inserted into the stepped hole in the spark plug insulator until the larger diameter portion contacts the step of the hole. The seal is conventionally placed between the iron terminal wire and the insulator in a tubular space above the enlarged diameter portion of the electrode.

In an improved prior art method for manufacturing this type of spark plug electrode, a composite billet is formed by inserting a copper billet into a sealed bottom nickel cap.

The nickel billet ends are rolled to hold the copper billet within the cap, and the composite billet is extruded first through an extrusion orifice with the open end. During the extrusion operation, the nickel wall at the open end of the cap is sealed over the steel core. The extrudate is then removed from the extrusion orifice, and the remaining large diameter shoulder is sheared off the extrudate to form a head on the extruded end of the extrudate, to which the iron wire is welded. Ru. In a modification of this method, a copper billet is placed within a nickel cap so that it is recessed from the open end of the cap;
The end of the iron terminal wire is held within the nickel cap while pushing the nickel cap open end first. During the extrusion operation, the terminal wire ends within the cap deform to form mechanical contact with the nickel cap.

The electrode is then completed by forming a suitable shoulder for facing the step of the insulator hole. Although each of these methods produces high quality electrodes, the electrode manufacturing process is particularly difficult for electrodes where the terminal wire must be welded to the extrusion.
Becomes relatively expensive.

DISCLOSURE OF THE INVENTION The present invention provides an improved method for manufacturing spark plug electrodes of the type having inexpensive terminal wires bonded to the upper or inner ends of the electrodes. A composite billet is initially formed by placing a copper billet within a nickel alloy camp. An extruded electrode blank is formed by passing at least a portion of the composite billet through an extrusion orifice having a diameter smaller than the outer diameter of the cap. One end of the electrode blank formed entirely of nickel makes one side of the spark gap;
The other or inner end of the electrode blank is connected to an inexpensive iron terminal wire to complete the electrode. The terminal wire is made into a cap at the inner end of the electrode blank, the end of the electrode wire is positioned within the molded cap, and the cap wall is deformed inwardly relative to the terminal wire to mechanically connect the terminal wire and the electrode blank. and attached to the electrode blank by electrically interconnecting. If desired, a slightly larger diameter flange or head can be formed at the end of the wire to strengthen the connection between the terminal wire and the electrode blank before inserting the wire with the head into the camp. can. The improved electrode made by the method of the present invention connects the electrode wire to the electrode blank without the need for welding at the connection point or for the steel core to be completely encapsulated within a nickel alloy cap. This method can also be used, for example, to attach a terminal wire to the headed end of a nickel alloy solid electrode without welding. As a result, the cost of electrode manufacturing is reduced compared to prior art manufacturing weld center electrodes.

[Best mode of carrying out the invention]

Referring to the drawings, and in particular to FIG. 1, a cap 15 is shown made of a corrosion resistant material such as a nickel alloy. The cap 15 is made with a tubular sidewall 16, a closed end 17 and an open end 18.

The side wall 16 and end 17 of the cap have a right cylindrical opening 19.
is limited. A billet 20 of a highly thermally conductive metal such as copper is placed within the opening 19 of the cap. Billet 1
-20 is slightly smaller than the inner surface of the cap end 17 and the tubular side wall 16, and is formed to roughly match therewith.

However, since the billet 20 is made to have a vertical length shorter than the vertical length of the cap opening 19, when the billet 20 is placed in the opening 19, the upper end 21 of the billet 20
are spaced on the inside of the cap open end 19.

After the billet is inserted into the cap opening 19, pressure is preferably applied to the billet end 21 to expand the billet 20 into contact with the cap sidewall 16, thereby retaining the billet 20 within the camp 15. The assembled cap 15 and billet 20 form a composite billet 22 as shown in FIG. Optionally, a crimp 23 is made in the portion of the cap sidewall 16 overlying the billet end 21 and adjacent the open end 18.

Crimp 23 slightly reduces the diameter of the open end;
The copper billet 20 is held within the cap 15 more reliably. After the composite billet 22 is completely formed, it is inserted into the closed sowing holes 24 of the extrusion die 25 as shown in FIG. 3, either with the open end first as shown or with the closed end first. Insert a composite billet into the upper end. Hole 24 has a diameter slightly larger than the outside diameter of billet 22, restricting billet 22 to slide axially within hole 24. Extrusion orifices 26 of reduced diameter are located within the bore 24 and are spaced apart from the die 25 at intervals greater than the height of the composite billet 22.
is away from the top surface 27 of.

After inserting the composite billet 22 into the hole 24, a tool or extrusion punch 28 having a flat end 29 is inserted into the hole 24 until the end 29 contacts the flat closed end 17 of the composite billet 22. The planar end 29 of the punch has a diameter only slightly smaller than the diameter of the hole 24, so that the punch fits into the hole 24.
The inside of the billet can be advanced and pressure applied across the closed end 17 of the billet.

The punch 28 is advanced through the extrusion die hole 24, forcing the bulk of the composite billet 220 through the extrusion orifice 26, as shown in FIG. Compound throat 22 is passed through extrusion orifice 26 to form extruded electrode blank 30. Since the punch 28 is larger in diameter than the extrusion orifice 26, the entire composite billet 22 is inserted through the orifice 2.
6, leaving a large diameter tubular butt 31 at the closed end 32 of the electrode blank 30.

After extrusion, the punch 28 is extracted from the die hole 24 and the electrode blank 30 is pushed back out of the orifice 26 by a suitable brush jar (not shown) and removed from the hole 24.

During the extrusion operation, the corrosion-resistant metal present in the crimp 23 of the cap portion of the billet 22 is collected at one end 33 of the electrode blank 30, and a core 34 made from the copper billet 20 is collected at one end 33 of the electrode blank 30.
completely surround. Core 34 has an end 35 adjacent the closed end of electrode blank 30 which is somewhat flat. This arrangement is provided to provide better heat flow from the electrode than is achieved in prior art bridges in which the sealed end 17 of the composite blank electrode is first passed through the extrusion orifice 26. By first passing the open end 18 of the composite blank 22 through the orifice 26, the position of the core end 35 is more easily adjusted than in prior art methods.

After removing the electrode blank 30 from the extrusion die 25, a large diameter butt 31 is sheared from the electrode blank 30, as shown in FIG. Initially, when extruding the closed end of the billet 22, it may not be easy to fin the batt 31. The resulting electrode blank 30 is of uniform diameter throughout its length and has a flat end 32 extending perpendicular to the axis of the electrode blank 30 to create one side of the spark gap in the spark plug. There is.

As shown in FIGS. 6 to 8, a head 36 is formed at the end 33 of the electrode blank 30. As shown in FIGS.

The head 36 is of a larger diameter than the shank portion 37 of the electrode blank 30 and defines a shoulder 38 for seating in a stepped hole in the spark plug insulator (not shown). Furthermore, the head 36 defines a cap 39 to which an iron terminal wire 40 is attached, as shown in FIG. FIG. 6.7 shows the first forming step on the end 33 of the extruded blank 30. Electrode blank 30 is inserted into opening 41 of die 42 so that electrode blank end 32 contacts ejector end 43 . Forming the electrode blank end 33 into a slightly planar end 36' with a shape intermediate to straight sides and a head 36 that will eventually be made on the electrode blank. The forming end 44 of the bunch 45 is advanced to the upper end 46 of the die opening 41 having a larger diameter. In addition, the electrode blank 30 has an opening 4 in the die 48, as shown in FIG.
7, the stepped end 49 of the punch 50 is advanced to the larger diameter upper end 51 of the gouer opening 47, and the formation of the electrode blank head 36 is completed.

Referring to FIG. 9, the terminal B 40 is attached to the electrode blank 30 by placing the end 32 of the electrode blank 30 within the opening 52 in the die 53 with the electrode blank shoulder 38 abutting the die surface 54. One end of the terminal wire 40 is placed within the cap 39 and the tool 56 is advanced toward the die surface 54 to radially pleat the sidewall 57 of the cap 39 inwardly against the terminal wire end 55 . The tool 56 is then withdrawn and the completed composite electrode 58 is removed from the die 53.

FIG. 10 is a fragmentary enlarged view showing details of the completed composite electrode 58. Closed end 32 of electrode blank 30
forms the lower end of the composite electrode that forms one side of the spark gap when the composite electrode is assembled into a spark plug. The lower end of composite electrode 58 has a coating or outer surface 59 made of a corrosion-resistant material, such as a nickel alloy, which originally formed cap 15 in FIG. Core 34 is made from a thermally conductive material, such as copper, that originally formed billet 20 in FIG. The open end 18 of the composite billet 22 is first inserted into the extrusion orifice 2
By extruding the electrode blank in the direction past 6, the position of the lower end 35 of the steel core 34 relative to the lower end 32 of the composite electrode 58 is adjusted very precisely. Composite electrode 5
8, the above method of manufacturing electrode lower end 32 and shoulder 38
You can also precisely adjust the spacing between.

Pressing the camp sidewall 57 inwardly against the terminal wire end 55 applies enough force to slightly deform the terminal wire, creating a strong mechanical lock between the terminal wire end 55 and the deformed cap sidewall 57. I will provide a. Therefore, the electrode wire 40
is attached to the extruded electrode blank 30 without welding as in the prior art. The resulting composite electrode is less expensive to manufacture than similar electrodes in which the terminal wire is welded to the electrode blank; Better coaxial alignment than electrodes is achieved.

FIG. 11 shows an improved method of attaching a terminal wire 60 to an extruded electrode blank 61 to create a composite center electrode for a spark plug. The electrode blank 61 is the electrode blank 37 described above.
For example, it is made by the method shown in FIGS. 1-8. The electrode blank 61 has a shoulder portion 65 that is connected to the die 6.
The die 64 is placed in the opening 63 of the die 64 so as to be in contact with the surface of the die 64 . Terminal wire 60 is made with a headed end 67 having a diameter slightly larger than the diameter of the remainder of wire 60. The headed wire end 67 is placed within the molded opening upper end 68 of the cap of the extruded electrode blank 61 and the tool 69 is inserted into the die 64.
Move the electrode blank upper end 68 forward toward ! 6
0 and deforms inward so as to cover the headed wire end 67. After that, the tool 69 is removed,
Composite electrode 62 is complete.

FIG. 12 is an enlarged view showing details of the composite electrode 62.

Composite electrode 62 has a lower end 69 that creates one side of the spark gap when electrode 62 is assembled to a spark plug insulator (not shown). The lower electrode end 69 is made of a corrosion-resistant material such as a nickel alloy and consists of a tubular sheath surrounding a thermally conductive core 71 made of copper, for example.

The shoulder 65 is spaced apart from the lower electrode end 69 by a predetermined distance. At the top of the shoulder 65, the headed wire end 67 is mechanically attached to the extruded electrode blank 61 by nickel molded inwardly against the shank of the wire 60 and over the headed wire end 67. Locked. Therefore, there is no need to weld the extruded electrode blank 61 and the terminal wire 6.
A strong coupling with 0 is obtained.

13-15 shows an extruded electrode blank 7 formed from a cap 76 made of a corrosion-resistant metal such as a nickel alloy and a billet 77 made of a highly thermally conductive metal such as copper.
5 shows a modified sequence of steps for manufacturing 5.

The billet 77 is - initially inserted into the open lower part 8 of the cap and placed facing the closed lower end 79 of the cap.

Additionally, optionally, the billet 77 is hammered into the cap 76 to remove the billet 77 from the cap 76 during subsequent operations.
held within.

The assembled cap 76 and billet 77 form a composite billet 80, which is inserted into an opening 81 that typically passes through an extrusion die. Composite billet 80 and aperture 81 are of substantially the same diameter, with only a slight clearance to allow composite billet 80 to be received within aperture 81 and to allow axial movement therein. Composite billet 80 has ends 79
is moved downwardly within opening 81 until it contacts extrusion orifice 83 of limited diameter. As shown in FIG. 14, core 77 of composite billet 80 has an upper surface 84 that is recessed from open upper portion 85 of cap 76. As shown in FIG. The punch 86 has a stepped lower end 87 molded to match the upper end of the composite billet 80 so that the lower surface 88 of the punch 86 contacts the core surface 84 and the punch 86
The surface 89 of is in contact with the cap end 85. Thereafter, the punch 86 is advanced downwardly to push the main body portion of the composite billet 80 through the extrusion orifice 8, as shown in FIG.
3 to make an extruded electrode blank 75. punch 8
6 stops just before the extrusion orifice 83. When the punch 86 is extracted from the die opening 81 and the extruded electrode blank 75 is taken out from the die 82, the obtained electrode blank 75 has a diameter slightly smaller than the outer diameter of the lower handle portion 92 of the electrode blank 75 that has passed through the extruded orifice 83. Camp molded upper end 9 with a small diameter internal opening 91
It has 0. For example, the handle portion 9 of the electrode blank 75
2 has a diameter of 0.254 cm (0.1 inch), then the cap opening 91 has a diameter of 0.228 cm (0.090 cm).
0.02 inch diameter to accommodate iron terminal wire
It would be about 28 am (0,092 inches). The terminal wire can be attached to the extruded electrode blank 75 in either of the ways shown in FIGS. 9 and 11.

A shoulder 93 is created on the electrode blank between the lower end 90 and the lower handle portion 92. Because the punch stops at a precise location within die 82, the length between shoulder 93 and lower end 94 will vary depending on the metal volume within core 77 and variations in camp 76 within standard manufacturing tolerances. Therefore, it is necessary to flake off the electrode blank end 94 to obtain the desired spacing between shoulder 93 and end 94.

16-19, the extruded electrode blank 98 and the terminal wire 99 (FIG. 16) are combined into a composite center electrode 10 for a spark plug.
0 (Figure 19) shows an improved method for assembly. The electrode blank 98 may be of a solid material, such as a nickel alloy, or may include an outer surface 101 of a hard, corrosion-resistant material, such as a nickel alloy, and a core 102 of a highly thermally conductive material, such as copper. It may also have the following.

The terminal wire 99 is made of an inexpensive material such as iron. Electrode blank 98 has an enlarged diameter cap molded end 103 with an opening 104 sized to receive end 105 of terminal wire 99 . A step 106 is created in the electrode blank 98 in which the cap molded end 1
03 is joined to the handle portion 107 of the electrode blank 98.

17, electrode blank 98 is shown placed within opening 108 of die 109. Referring to FIG.

Die opening 108 is sized to accommodate handle portion 107 and step 106 abuts die surface 110. Thus, the cap opening 104 faces away from the goo surface 110. Terminal wire 99 is placed in axial alignment with electrode blank 98 by a suitable mechanism not shown. Tool 111 has a stepped opening 112 spaced from end 113 of terminal wire 99 opposite end 105 . The tool opening 112 is also axially aligned with the terminal cotton 99 and the electrode blank 98 .

Tool 111 moves parallel to and toward die surface 110 and has a surface 114 that attaches terminal wire 99 to electrode blank 98 to form composite center electrode 100. As the tool 111 is advanced toward the die 109, the opening 1
12 accommodates the terminal wire 99. At face 114 , end 115 of aperture 112 is of a diameter sized to accommodate the diameter of cap molded end 103 of electrode blank 98 . Adjacent to open end 115 , aperture 112 has an inwardly curved conical portion 116 . The conical section 116 preferably has a bevel angle of about 30" to facilitate metal flow. Inwardly from the conical section 116 is a wire that is larger than the terminal wire 99 and smaller than the cap molded end 103 of the electrode blank 9. There is a diameter expansion area 117. The opening 112 has a long portion 118 inside the expansion area 117, which is large enough to accommodate the terminal wire 99.1
At the inner end of the section 18, the opening 112 has another inwardly tapered conical section 119 forming a chamfer at the end 113 of the terminal wire 99. The conical portion 119 preferably has a bevel angle of about 30'' to facilitate metal flow. The inner end of the opening 112 is adjacent to the ejector bin 120.

As tool 111 is advanced toward die 109 , terminal wire end 113 passes through tool open end 115 , conical section 116 , enlarged region 117 , and enters open section 118 . When the terminal wire end 113 reaches the conical portion 119, further advancement of the tool 111 causes the terminal wire end 105 to enter the cap opening 104 of the electrode blank 98. Further advancement of the tool 111, where the cap end 103 also passes through the tool open end 115, causes the cap end to extrude along the terminal, %I*99, as shown in the fragmentary enlarged cross-sectional view of FIG. enters the expanded region 117 of the opening 112 and connects the terminal &
A connection 121 connecting 199 to electrode blank 98 is formed.

When the advance of the tool 111 approaches the final stage, the terminal wire end 105
abuts interior end 122 in camp opening 104.

When the tool 111 is finally advanced, the terminal wire cannot be moved and its end 113 is in the conical end area 1 of the tool opening 112.
19, and a chamfered surface 123 is formed on the end 113 of the terminal wire 99.
form.

Therefore, a separate manufacturing step for creating the chamfered surface 123 on the terminal wire 99 is eliminated. Chamfered surface 123 helps align center electrode 100 during spark plug assembly.

After advancing the tool 111 until the tool surface 114 contacts the goo surface 110, the center electrode 100 is completed and the tool 111 is removed. When the tool 111 is separated from the die 109, the ejector bin 120 in the tool 111 and the die 10
Ejector bin 124 in 9 ejects composite center electrode 100 from apertures 108 and 112. Obtained center electrode 10
0 has a higher degree of concentricity and is much cheaper to manufacture than similar composite center electrodes in which the terminal wire is welded to the electrode blank.

The invention has been described for a type of spark plug electrode having a core made of a highly thermally conductive material. In its broadest concept, the invention is equally applicable to attaching terminal wires to solid electrodes made, for example, of nickel alloys. for example,
A cap is formed within the end of a solid iron or wire made of the material by the method shown in Figures 6-8. The welding is then removed in order to attach the terminal wire by the method shown in FIGS. 9 or 11.

Various modifications and changes may be made to the preferred method described above without departing from the spirit and scope of the claims.

[Brief explanation of drawings]

1 is a vertical cross-sectional view showing a corrosion-resistant metal cap and a cylindrical billet of highly thermally conductive metal before being inserted into the cap according to the first step of the method of the invention; FIG. , the composite billet after inserting the thermally conductive billet into a corrosion-resistant cap, bulging or pegging in the correct position, and diamond-shaping the edges of the cap inward to hold the copper billet in the correct position. FIG. 3 is a fragmentary cross-sectional view showing the position of the composite billet within the hole of the extrusion die before extrusion, and FIG. 4 is similar to FIG. FIG. 5 is a fragmentary cross-sectional view showing the billet in the extrusion die at the end of extrusion; FIG. FIG. 6 is a fragmentary cross-sectional view showing the electrode blank placed in a first die to initially form the top or inner end of the electrode blank; FIG. and FIG. 7 is a fragmentary cross-sectional view showing the punch advanced to initially shape the inner end of the electrode blank and the electrode blank in the first die of FIG. Figure 9 is a fragmentary cross-sectional view through the second die showing completed cap formation at the inner end of the electrode blank; Figure 9 is a fragmentary cross-sectional view showing one method of attaching the terminal wire to the electrode blank; 10 is a fragmentary cross-sectional view through a completed electrode made by the method shown in FIGS. 1 to 9, and FIG. 11 shows an improved method for attaching terminal wires to an electrode blank. FIG. 12 is an enlarged fragmentary cross-sectional view of an electrode made by the method shown in FIGS. 1-8 and FIG. 11, and FIG. 14 is a vertical cross-sectional view showing a cylindrical billet of highly thermally conductive metal before being inserted into a corrosion-resistant metal cap to make an electrode blank according to an embodiment; FIG. 15 is a fragmentary cross-sectional view similar to FIG. 14 showing the composite billet in the extrusion die upon completion of extrusion; FIG. , FIG. 16 is a cross-sectional view of the extruded electrode blank and terminal wire before assembly according to an improved embodiment of the present invention, and FIG. 17 is a cross-sectional view of the extruded electrode blank of FIG. 16 placed in a die and FIG. 18 is a fragmentary cross-sectional view showing the electrode blank and the linearly arranged terminal wires before the tool is advanced to attach the terminal wires to the electrode blank; FIG. 19 is a cross-sectional view of a composite electrode produced by the die and tool of FIG. 17. FIG. -2F'IG, 6 -FIG 7-:=
YoF"IG, 8 =MoF1choG,
9(IG, 12 -f'I6. 14 12F'IG, 15

Claims (7)

[Claims] (1) forming a metal electrode blank having a corrosion-resistant surface and first and second ends; when the electrode is assembled into a spark plug, the second end defines one end of the spark gap; forming a cap on an end of a first blank; positioning an end of a terminal wire within the blank cap; advancing a punch having a forming hole over the terminal wire and the blank cap; deforms the wall of the blank cap so that metal flows inward and into contact with the terminal wire, and then flows along the terminal wire away from the end of the terminal wire, causing metal to flow along the terminal wire and away from the terminal wire end. A method of manufacturing spark plug electrodes consisting of providing a strong mechanical and electrical connection between blanks. (2) a tubular side portion of a predetermined outer diameter from a corrosion-resistant first metal;
A cap is fabricated having an open first end and a closed second end, the cap being partially filled with a second metal having high thermal conductivity, the second metal contacting at least an inner surface of the closed end. spaced inwardly from the open end, at least a partially filled portion of the cap passing through an extrusion orifice having a diameter smaller than an outer diameter of the cap;
creating an electrode blank having first and second ends made from a corresponding opening and said sealed end, creating a cap within said first blank end, and locating an end of a terminal wire within said blank cap; and deforming the blank cap wall so that metal flows inwardly into contact with the terminal wire and away from the terminal wire end and along the terminal wire to contact the terminal wire and the electrode. A method of manufacturing a composite spark plug electrode comprising providing a strong mechanical and electrical connection between blanks. (3) said partially filled cap first passes a portion of its open end through said extrusion orifice; 3. A method as claimed in claim 2, including the step of deburring the diameter of the removed portion. (4) said partially filled cap advances a punch having a shaped end to initially pass a portion of its closed end through said extrusion orifice, and said partially filled cap partially passes said extrusion orifice; 3. The method of claim 2, wherein as it passes, said punch-formed end forms a cap within said first blank end. (5) The inward deformation of the blank cap wall also slightly deforms the terminal wire end, providing a strong mechanical and electrical connection between the terminal wire and the electrode blank. The method according to claim 2. (6) Claim 2 further includes the step of forming a chamfered surface on a second end of the terminal wire opposite to the terminal wire end, and simultaneously deforming the blank cap. Method described. (7) further comprising forming a head on the terminal wire end, the wire head being positioned within the blank cap, the blank cap wall being deformed inwardly over the wire head, and the terminal wire 3. A method according to claim 2, characterized in that a strong mechanical connection is provided between the electrode blank and the electrode blank.