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(11) | EP 0 044 764 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method for manufacturing a center electrode for use in a spark plug |
| (57) A method for manufacturing an inconel and copper electrode for use in a spark plug
characterized bythe steps of lubricating a piece of inconel wire prior to forming
the inconel into a cup-shaped piece (3) having a copper core (9) extending from only
one end of the inconel. |
[0002] Spark plugs are used in internal combustion engines to ignite the fuel in the combustion chamber: Hence, the electrodes .of a spark plug are subject to. intense heat and an extremely corrosive atmosphere. To provide some degree of longevity for the spark plug, the center electrode is made from a good heat conducting material such as copper surrounded by a jacket of a corrosion resistant material such as nickel.
[0003] The.manufacture of copper and nickel electrodes for spark plugs has been accomplished in a variety of ways. For instance, U.S. Patent 3,803,892 issued April 16, 1974 and entitled "Method of Producing Spark Plug Center Electrode" describes a method of extruding-copper and nickel electrodes from a flat plate of the two materials. U.S. Patent 2,261,436 issued November 4, I941 and entitled "Spark Plug and Method of Making the Same" illustrates how copper and nickel is swaged into a single long wire and then cut to smaller lengths for use as electrodes in a spark plug. Finally, U.S. Patent 3,548,472 issued December 22, 1970 and entitled "Ignition Plug and Method for Manufacturing a Center Electrode for the Same" illustrates a method of cold forming an outer nickel cup shaped sleeve by several steps and then inserting a piece of copper wire into the cup and then lightly pressing the two materials together.
[0004] The invention proposes :
A method for manufacturing a center electrode for use in a spark plug characterized in that it comprises the steps of :
- coating a piece of corrosion resistant metal wire with a lubricant ;
- inserting the piece of corrosion resistant metal wire into a first die ;
- striking the wire in said die once with a first punch to form a recess at one end and a taper at opposite end of the wire ;
- inserting the member into a second die ;
- striking the member in the second die once with a second punch to form an elongated cupped shaped member havirg a tapered end portion ;
- inserting a piece of metal wire into the cup, said wire havirg a thermal conductivity greater than the thermal conductivity of said corrosion resistant wire ;
- inserting the mated pieces into a third die ; and
- striking the mated pieces in the third die with a third punch to form said heat conducting wire and said corrosion resistant cup into an integral body with the heat conduction wire exposed at only one end of the corrosion resistant member.
[0005] The invention is a method for manufacturing an inconel and copper electrode for use in a spark plug. The method is characterized by the steps of lubricating an inconel wire beforeit is formed into a cup-shaped member in two steps, inserting a piece of copper wire into the inconel cup and into a die, and:then striking the mated pieces with a punch to form an electrodeTwith the copper exposed at only one end of the inconel. The method is further characterized by the use of a bolt making machine which appliesthe necessary force behind the punch striking the metal in the die.
[0006] An advantage of this invention is that it provides a process that permits the cold working of inconel.
[0007] Another advantage of the invention is that it provides a simple method of forming inconel into a cup shaped member.
[0008] Another advantage of this invention is that a large number of center electrodes can be produced with a minimum number of manufacturing steps.
[0009] Another advantage of this invention is the method provides a spark plug electrode having good heat conductivity and increased corrosion resistance which increases the useful life and effectiveness of the spark plug.
[0010] Another advantage of this invention is that the lubricant prevents bonding of the punch to the inconel wire during the process of shaping the inconel wire into a cup-shaped member.
[0011] The invention will now be described with reference to the accompanying drawings wherein :
FIGURE 1 illustrates a piece of inconel wire ready to be formed.;
FIGURE 2 illustrates the first shape of the piece of inconel wire formed by the punch and die shown ;
FIGURE 3 is an enlarged view of the piece inconel shown in FIGURE 2 ;
FIGURE 4 illustrates the second shape of the inconel wire formed by the punch and die shown ;
FIGURE 5 is an enlarged view of the piece of inconel shown in FIGURE 4 with a copper wire insert ;
FIGURE 6 illustrates the step of coining together the inconel cup and the copper ;
FIGURE 7 illustrates the copper wire coined to the inconel cup ;
FIGURE 8 illustrates the completed electrode formed by the die and punch shown ; and
FIGURE 9 is an enlarged view of the completed electrode shown in FIGURE 8.
[0012] Referring now to the drawings FIGURE 1 illustrates a piece of corrosion resistant metal wire having a diameter of about 0,360 cm. A preferred corrosion resistant alloy is inconel which is an iron alloy containing Nickle and Chromium. One such inconel metal, known as Hoskins Alloy 831, contains 75 % Nickle, 15 % Chromium and 7 % Iron. Before placing a piece of inconel wire into a die it is coated with a standard cold heading lubricant. Such a lubricant is a lubricating oil with extreme pressure additives : sulphur, chlorine and neutral animal fat. It is most often a combination of sulphrized fat and a chlorine additive and is available from a good number of lubricant manufacturers. Lubrication is vital in cold heading to reduce die wear, promote good finishes and eliminate galling, scratching and seizing of the work piece by preventing pickups by the dye. During the cold heading operation, the sulphur and chlorine components of the lubricant form ferrous sulphides and chlorides which prevent welding of the die to the workpiece and act in the same way as a solid lubricant. An example of one such lubricating oil is TUF-DRAW I.F. 2885 made by Franklin Oil Corporation of Ohio.
[0013] FIGURE 2 illustrates the die 10 and punch 30 which forms the inconel wire 2 into a predetermined shape. The die 10 is mounted in a housing 20 which also includes a spring 21 actuated knockout pin 40 for removing the incmel wire 2 after the punch 30 has struck the wire and withdraws from the die 10.
[0014] FIGURE 3 illustrates the shape to the inconel wire 2 after removal from the die. The inconel 2 is formed so that there is a recess 22 at one end. and a tapered portion 23 at the opposite end. This shape helps to facilitate forming the inconel into a cup-shaped member in the next step shown in FIGURE 4.
[0015] FIGURE 4 illustrates the die 11 and punch 31 which forms the elongated cup-shaped inconel member 3 having a 0,264 cm diameter hole about 0,577 cm deep. To obtain the necessary force to form the inconel cup-shaped member the die and punch are located in a bolt making machine. One such bolt making machine suitable for driving the punch and mountiigthe die is a National Machinery 1/4 inch boltmaker which operates at about 85 strokes per minute and will apply a pressure from the punch to the workpieces greater than 15,000 Kg/cm2. Because of the high pressure between a workpiece, a die and a punch, it is important that the die and punch be comprised of a material such as carbide.
[0016] FIGURE 5 illustrates a piece of copper wire 9 inserted into the elongated cup-shaped member 3. When the wire 9 is inserted into the inconel cup 3 there is a void 8 between the copper and inconel wire. It is preferred that this void be eliminated to increase the efficiency of thermal conductivity between the copper wire 9 and inconel cup 3.
[0017] FIGURE 6 illustrates a punch 32 and die 12 for securing together (coining) the copper wire 9 to the inconel cup 3. This step minimizes any void between the copper wire 9 and inconel cup 3.
- coating a piece of corrosion resistant metal wire (1) with a lubricant ;
- inserting the piece of corrosion resistant metal wire (1) into a first die (10) ;
- striking the wire in said die (10) once with a first punch (30) to form a recess (22) at one end and a taper (23) at the opposite end of the wire (2) ;
- nserting the member (2) into a second die (11) ;
- striking the member in the second die once with a second punch (31) to form an elongated cupped shaped member (3) having a tapered end portion;
inserting a piece of metal wire (9) into the cup (3), said wire having a thermal conductivity greater than the thermal conductivity of faid corrosion resistant wire ;
- inserting the mater pieces (9.3) into a third die (13, 14) ; and
-striking the mated pieces (9.3) in the third die (13, 14) with a third punch (33) to form said heat conducting wire and said corrosion resistant cup into an integral body with the heat conducting wire (9') exoosed at only one end of the corrosion resistant member (3').