GB2141654A

GB2141654A - Method of forming spark plug shells

Info

Publication number: GB2141654A
Application number: GB08412273A
Authority: GB
Inventors: Gregory Lynn Heminger; Louis Charles Linenkugel
Original assignee: Champion Spark Plug Co
Current assignee: Federal Mogul Ignition Co
Priority date: 1983-06-20
Filing date: 1984-05-14
Publication date: 1985-01-03
Also published as: JPS6035487A; ZA843953B; IT8421497A0; BE899929A; GB8412273D0; IT1174040B; DE3418218A1; AU2890784A; BR8402704A; FR2548090A1

Abstract

A method of forming by cold extrusion a spark plug shell (72) (Fig. 7) with a high insulator seat (76) (Fig. 7). A cylindrical blank (66) is cut from a steel rod and is subjected to a series of cold extrusions in a seven-station, six die cold forming press. The steps of the method include piercing out the web (56) across the cavity in the blank (66) to form a hollow cylinder and then extruding a ring (76) around the inside of the cavity (52) which serves as an insulator seat. <IMAGE>

Description

SPECIFICATION Method of forming spark plug shells BACKGROUND OF THE INVENTION This invention relates generally to a method of manufacturing spark plug shells or bodies, and more specifically to a method of forming by cold extrusion a spark plug shell with a high insulator seat.

Due to differing requirements of various engines, it is necessary to provide spark plugs with different heat ranges. In this regard, the heat range of a spark plug is determined, in part, by the volume of the chamber surround ing the insulator tip of the spark plug. This chamber is defined by the spark plug shell and the insulator tip. Generally, the volume of the chamber is determined by the location of the insulator seat within the spark plug shell.

That is, a spark plug shell with a high insulator seat will provide a chamber having a relatively large volume as compared to a spark plug shell having a low insulator seat.

Spark plug shells having low insulator seats are readily manufactured by known cold extrusion methods. However, until our invention, it was not possible to manufacture spark plug shells having insulator seats having a bottom edge located more than 0.3 inches (0.762 cm.) from the bottom of the spark plug shell without using an extra machining step which added cost and resulted in some waste material.

BRIEF SUMMARY OF THE INVENTION The invention provides a method of forming by cold extrusion a spark plug shell with a high insulator seat in which a cylindrical blank is cut from a steel rod and is subjected to a series of cold extrusions in a seven-station, six die cold forming press.

According to the preferred embodiment of the invention, the steps of the method include piercing out the web across the cavity in the blank to form a hollow cylinder with an open top end and an open bottom end and then forcing a punch into the hollow cylinder past the open top end to extrude a ring around the inside of the cylinder so that the bottom edge of the ring is more than 0.3 inches (0.762 cm.) from the open bottom end.

It is a principal object of our invention to provide a method of manufacturing spark plug shells with high insulator seats which is lower in cost than previously-used methods of manufacture.

Further, it is an object of our invention to provide a method of manufacturing spark plug shells having high insulator seats which utilizes fewer machining steps and involves less waste than previously-known methods.

The above and other objects, features and advantages of our invention will become apparent to persons skilled in the art upon consideration of the detailed description together with the appended drawing.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1-6 represent longitudinal sections through a series of dies in which a blank is successively cold extruded in accordance with the method of our invention.

FIG. 7 is a longitudinal section of a basic spark plug shell produced by the method of our invention.

FIG. 8 is a fragmentary, partially-sectioned view of a finished spark plug utilizing a shell produced by the method of our invention.

FIG. 9 is a longitudinal section of a spark plug shell produced by the previously-known method of manufacture.

DETAILED DESCRIPTION OF THE PRE FERRED EMBODIMENT Referring to FIGS. 1-6, a cylindrical blank is cut from a coil of steel wire and is subjected to a series of cold extrusions in a sevenstation, six die cold forming press. The press includes an array of six cold extrusion stations, each of which has a die and a punch for forcing a blank into the die, the punches being positioned on one side of the machine and the dies being positioned on the other side of the machine. A transfer mechanism operates to index blanks cut from the steel rod successively through the six stations.

At the first station, illustrated in FIG. 1, the punch 10 forces a cylindrical blank cut from the steel rod into a first die 1 2 having a recess 14. The resulting blank 1 6 is removed from die 1 2 by means of a kick-out pin 1 8 which is held rigid during movement of punch 10 into die 1 2, and is transferred to die 20 at the second station (FIG. 2) by the transfer mechanism (not shown).

At the second station, blank 1 6 is subjected to both forward and rearward extrusion in recess 22 by a punch 24 to form a modified blank 26 which includes a hexagonal portion 28 and a shallow cavity 30. After punch 24 is withdrawn, blank 26 is injected from die 20 by means of a kick-out pin 32, and is transferred to die 34 at the third station (FIG. 3).

In die 34 at the third station, blank 26 is subjected to a further rearward extrusion by a punch 36 which changes the shape of the blank to the shape of blank 38 by providing a cavity 40 of increased volume. Blank 38 then is ejected from die 34 by a kick-out pin 42 and transferred to die 44 at station four (FIG.

4).

Blank 38 then is subjected primarily to backward extrusion into recess 46 of die 44 by a punch 48 which results in a blank 50 having a cavity 52 with an open top end 54 and a web 56 across cavity 52 at the bottom end of blank 50. After punch 48 is withdrawn, blank 50 is ejected from die 44 by a kick-out pin 58 and transferred to a die 60 at station five (FIG. 5).

There is no further extrusion of blnkk 50 at station five. Rather, punch 62 is actuated to pierce out web 56 in cooperation with pierce out sleeve 64 to provide a new blank 66 which, in addition to having a cavity 52 and an open top end 54, has an open bottom end 68 so that blank 66 is in the form of a hollow cylinder. Blank 66 is ejected from die 60 by means of pierce out sleeve 64 which also functions as a kick-out pin, and then is transferred to a die 70 at station six (FIG. 6).

At station six, blank 66 is further modified into a final blank or spark plug shell 72 by means of a punch 74 having a small diameter portion 75 and a large diameter portion 77 which extrudes some metal along the inside of cavity 52 to form a ring 76 around the inside of the cavity which serves as an insulator seat.

Because a two diameter punch is used, the specific size of the inner diameter of ring 76 is assured, as well as the concentricity of ring 76 relative to cavity 52. Blank 72 then is ejected from die 70 by a kick-out pin 78.

The blank or spark plug shell 72 which is produced after the final extrusion step shown in FIG. 6 can be seen in more detail in FIG.

7. Shell 72 is generally a hollow cylinder and includes a cavity 52 which runs the length thereof between an open top end 54 and an open bottom end 68. Located in cavity 52 is a ring 76 which serves as a seat for the insulator which is inserted in spark plug shell 72 at a later stage of the manufacturing process.

Referring now to FIG. 8 there is shown a portion of a completed spark plug utilizing a spark plug shell 72 of the type shown in FIG.

7. As will be noted, shell 72 has been subjected to some further manuffacturing steps by having threads 80 rolled onto it and a side electrode 82 welded to the bottom end of it.

Also, it can be seen that an insulator 84 which carries a center electrode 86 has been inserted in cavity 52 of shell 72 and abuts ring or seat 76.

At this point, it can be seen that insulator 84 includes a tapered tip portion 88 which defines with the lower end of cavity 52 below ring 76 a chamber 90 which tends to trap gaseous vapor and aids in establishing the flame front when the spark plug is fired during engine operation.

FIG. 9 shows a spark plug shell 92 manufactured according to the prior known pm cess. In order to provide a high insulator seat or ring 94, the shell 92 first was extruded with a relatively wide shoulder and then had excess material at 96 counterbored or cut away by a machining step in order to leave a cavity that would define with a spark plug tip a chamber of essentially the same volume as that shown as chamber 90 shown in FIG. 8.

This method of manuffacture not only results in extra cost due to the extra machining step involved in cutting away the excess material at 96, but the waste material also adds to the increased cost for this method of manuffacture. As can be seen, without a machining operation, the previous method of manufacture permitted location of the bottom edge of the insulator shoulder upwardly from the open bottom end 98 of shell 92 by a distance of no more than 0.3 inches (0.762 cm.).

While only a single embodiment of our improved method has been described, it will be understood that various changes and modifications can be made to it without departing from the spirit and scope of our invention Further, while our improved method has been described in conjunction with the manufacture of a spark plug shell, it is not so limited.

Thus, the limits of our invention should be determined from the claims when construed in light of the prior art.

Claims

1. A method of forming by cold extrusion a spark plug shell with an insulator seat comprising the steps of: forcing a metal blank into a first die to form a cylindrical blank having a cavity with a web across the bottom of said cavity; piercing out said web from said cylindrical blank: and forcing a punch into said cavity to extrude a ring around the inside of said cavity which functions as an insulator seat.

2. The method as set forth in claim 1, wherein said punch has a first diameter and a second smaller diameter to assure that said ring is concentric relative to said cavity and that said ring has a specific inner diameter.

3. A method of forming by cold extrusion a spark plug shell with a high insulator seat comprising the steps of: forcing a metal blank into a first die to form a cylindrical blank having a first open end and a cavity with a web across the bottom of said cavity; piercing out said web from said cylindrical blank to provide said cylindrical blank with a second open end; and forcing a punch into said cavity to extrude a ring around the inside of said cavity which serves as an insulator seat.

4. The method as set forth in claim 3, wherein said punch is forced into said cavity past said first open end and the bottom edge of said ring is located more than 0.3 inches (0.762 cm.) from said second open end.

5. The method as set forth in claim 4, wherein said punch has a first diameter and a second smaller diameter to assure that said ring is concentric relative to said cavity and that said ring has a specific inner diameter.

6. A method of cold extruding an article comprising the steps of: forcing a metal blank into a first die to form a blank having a cavity with a web across the bottom of said cavity; piercing out said web from said blank; and forcing a punch into said cavity to extrude a ring around the inside of said cavity.

7. The method as set forth in claim 6, wherein: said blank has first and second open ends after said web is pierced out; said punch is forced into said cavity past said first open end; and the bottom edge of said ring is located more than 0.3 inches (0.762 cm.) from said second open end.

8. The method as set forth in claim 7, wherein said punch has a first diameter and a second smaller diameter to assure that said ring is concentric relative to said cavity and that said ring has a specific inner diameter.

9. A method of cold extruding an article substantially as described.