GB2406535A

GB2406535A - A press for cold forging an electrical contact

Info

Publication number: GB2406535A
Application number: GB0322900A
Authority: GB
Inventors: Martin Gaiger
Original assignee: P & B Metal Components Ltd
Current assignee: P & B Metal Components Ltd
Priority date: 2003-09-30
Filing date: 2003-09-30
Publication date: 2005-04-06
Anticipated expiration: 2023-09-30
Also published as: GB2406535B; GB0322900D0

Abstract

A press for cold forging a slug 1, 31 to produce a double-headed electrical contact 11 on a leaf spring blade 17 comprises a first press tool station (Fig 5, 43) to form one or more intermediate heads (Fig 7, 61) and a second press tool station (Fig 8, 60) to form the double-headed electrical contact (Fig 1b, 11). The first press tool station comprises radially movable clamp members 41 which grip a portion (Fig 7, 64) of the shaft 3 of the slug 1 adjacent to the blade 17 to prevent swelling of the portion (Fig 7, 25) of the slug 1 located in the aperture (Fig 7, 15) in the blade 17, to prevent distortion or splitting of the blade 17.

Description

M&C Folio: GBP88174 Document: 931860 Press apparatus and method for cold

forging an electrical contact The present invention relates to a press tool station for cold forging metal, and in particular it relates to a press tool station for cold forging one or more heads on a metal slug which is inserted axially into an aperture in a leaf spring blade to produce an electrical contact and a method of producing a leaf spring blade with an electrical contact fastened to the blade.

Snap-action leaf spring blades are used in electrical switches to switch current between two paths. One end of the blade is fixed while the other end of the blade is movable between two terminals to select an electrical path. A contact is fastened to the movable end of the blade to make effective electrical contact between the blade and a terminal. The contact can be produced by inserting axially a wire of generally uniform cross section into a pre-punched hole in a blade, simultaneously cutting and squeezing the wire in the hole to form a slug which swells to fill the hole and cold forging the ends of the slug to form heads on the end of the slug, thereby producing an effective electrical contact surface on the face of the heads. Another method of mounting an electrical contact on a blade comprises inserting a slug with a pre-formed head and a shaft of generally uniform cross section into the hole and pressing the distal end of the shaft to form a second head on the end of the shaft, thereby forming the double-headed electrical contact on the blade.

The thickness of the leaf spring blade is typically 0.1 mm. The snapaction performance improves when a blade of smaller thickness, say 0.05mm is used, but problems are encountered when mounting the electrical contact on a blade of this thickness. When forming the head on the slug, an axial force is applied and the diameter of the slug increases leading to swelling of the portion of the shaft that is located within the hole. A blade with a thickness of 0.05mm may be unable to provide sufficient resistance to this swelling, and so the blade is deformed, which impedes the snap-action performance. In some cases, the swelling of the slug may split the blade.

This problem can lead to an unacceptably high wastage rate when producing such blades.

Therefore it is an object of the present invention to provide a press tool station to cold forge electrical contacts on a leaf spring blade without distorting or splitting the blade in which it is mounted, by inhibiting swelling of the portion of the shaft that is located in the aperture of the blade.

One aspect of the present invention provides a press tool station for cold forging at least one head on a shaft of a slug which is positioned in an aperture in a member to which the slug is to be fastened, the press tool station comprising radial restraining means forming a cavity to accommodate the shaft of the slug adjacent to the member to which the slug is to be fastened to inhibit radial expansion of the slug within the member during the cold forging operation. The radial restraining means inhibit swelling of the interposing portion of the shaft and consequently inhibit swelling of the adjacent portion of the shaft which is disposed in the aperture of the member to which the slug is to be attached.

In a first embodiment of the present invention, axial support means are provided to support one end of the slug and punch means are provided to impact the other end of the slug to cold forge a head on the end of the slug, the radial restraining means being disposed between the member to which the slug is to be fastened and the punch means.

This embodiment is suitable to cold forge a second head on a singleheaded slug.

In a further embodiment, first and second punch means are provided to impact both ends of the slug to cold forge a head on each end of the slug. Preferably, the first and second punch means, in use, impact substantially symmetrically on the ends of the slug. This embodiment is suitable to simultaneously cold forge two heads on a wire slug of uniform cross-section.

Preferably the radial restraining means comprises a plurality of clamp members.

Preferably one or more of the clamp members are movable from a first position, to allow a slug to be inserted into the press tool station, to a second position where the slug is cold forged.

Preferably the cavity formed by the radial restraining means has a cross section which is substantially identical to the cross section of the shaft of the slug which is being cold forged. The correlation of the diameter of the shaft to the diameter of the cavity defined by the inner surface of the clamp members when urged towards the shaft is determined on a trial and error basis. For example the clamp members may contact the shaft or it may be necessary for the clamp members to pinch the shaft. The precise requirements are believed to vary with the material and thickness of the blade and material of the slug.

Preferably the clamp members comprise a clamp portion and a die portion, wherein the clamp portion inhibits swelling of the interposing portion of the shaft of the slug and the die portion in cooperation with the punch means forms a head when the slug is cold forged. The head which is formed is an intermediate head which is to be pressed again to deform the periphery of the head to cold forge the final head of the electrical contact.

Preferably the height of the clamp portion which contacts the shaft of the slug is less than lmm, further preferably less than 0.2mm and further preferably less than O.lmm.

In one embodiment the member to which the slug is to be fastened is a leaf spring blade. Preferably the thickness of the leaf spring blade is less than or equal to 0. lmm. Further preferably the thickness of the leaf spring blade is less than or equal to 0.05mm.

Another aspect of the present invention provides a method of cold forging at least one head on a shaft of a slug which is inserted axially into an aperture in a member to which the slug is to be fastened, the method comprising providing radial restraining means adjacent to the member to which the slug is to be fastened to inhibit swelling of the interposing portion of the shaft of the slug when cold forging the slug.

In one embodiment of the present invention one end of the slug is axially supported and the other end of the slug is impacted to cold forge a head on the slug.

In another embodiment of the present invention both ends of the slug are impacted substantially symmetrically to cold forge a head.

A further aspect of the present invention provides a method of cold forging an electrical contact on a member, the method comprising cold forging at least one intermediate head on a shaft of a slug which is inserted axially into an aperture in the member to which the slug is to be fastened, removing the radial restraining means from the intermediate head or heads and cold forging the intermediate head or heads to form the electrical contact.

A further aspect of the present invention provides a method of cold forging an electrical contact on a leaf spring blade, the method comprising cold forging at least one intermediate head on a shaft of a slug which is inserted axially into an aperture in the blade to which the slug is to be fastened, removing the radial restraining means from the intermediate head or heads and cold forging the intermediate head or heads to form the electrical contact.

Other aspects and preferred features of the invention will be apparent from the accompanying claims. The invention will be further described by way of example with reference to the accompanying drawings in which: Figure 1 a is a side view of a single-headed slug.

Figure lb is a side view of a double-headed electrical contact fastened to a leaf after cold forging a second head on the single-headed slug of Figure 1 a.

Figure 2a is a perspective view of the single-headed slug of Figure 1 a.

Figure 2b is,a perspective view of the double-headed electrical contact of Figure lb. Figure 2c is a perspective view of a leaf spring with a double-headed electrical contact.

Figure 3 is a cross-sectional view of a prior art press tool station for cold forging the second head of an electrical contact from the singleheaded slug of Figure 1 a.

Figure 4 is a cross-sectional view of a prior art press tool station for simultaneously producing the two heads of a double-headed electrical contact from a wire slug.

Figure 5 is a cross-sectional view of a first embodiment of the present invention showing the single-headed slug of Figure 1 a prior to clamp members gripping the slug.

Figure 6 is a cross-sectional view of the embodiment of Figure 5 after the clamp members have gripped the slug, prior to cold forging an intermediate second head.

Figure 7 is a cross-sectional view of the embodiment of Figure 5 after the intermediate second head has been cold forged.

Figure 8 is a cross-sectional view of a second press tool station for cold forging the final head from the intermediate head of Figure 7, to form the double-headed electrical contact of Figure I b.

Figure 9 is a cross-sectional view of a second embodiment of the present invention showing a wire slug prior to the clamp members gripping the slug.

Figure 10 is a cross-sectional view of the embodiment of Figure 9 after the clamp members have gripped the slug, prior to cold forging intermediate first and second heads.

Figure 11 is a cross-sectional view of the embodiment of Figure 9 after the intermediate first and second heads have been cold forged.

Figure 12 is a cross-sectional view of a second press tool station for cold forging the final heads from the intermediate heads of Figure 11, to form the double-headed electrical contact of Figure lb. Figure 13 is a partial cross-sectional view of the press tool station of Figures 5-7, showing dog-leg cams that urge the clamp members onto the slug, before the dog-leg cams have urged the clamp members onto the slug.

Figure 14 is a partial cross-sectional view of the press tool station of Figure 13, after the dog-leg cams have urged the clamp members onto the slug.

Figure 15 is a perspective view of a clamp member.

Figure la is a side view of a single-headed slug 1 comprising a circular cross- section shaft portion 3 and a head portion 5. The shaft portion 3 protrudes from a face 7 of the head portion 5 which is substantially flat. The single-headed slug 1 of Figure 1 a can be pre-formed by cold forging a blank in a press, as is known in the art. The material of the slug 1 is typically a precious metal such as silver, gold, a combination of one of these metals with another metal, etc.. The cross section of the shaft 3 of the slug 1 is typically circular and uniform along its axial length. The end 9 of the shaft 3 of the single-headed slug 1 can be cold forged to produce a double-headed electrical contact 1 1 mounted on a leaf spring blade 17, as shown in Figure lb. The blade 17 is typically of Beryllium Copper and has a thickness between 0.05 and O. l mm.

In addition to the single headed slug 1 of Figure 1 a, a slug of generally uniform cross section (i.e. with no head) may be cold forged to produce the double-headed electrical contact 11 of Figure lb. Such a slug is typically formed by cutting lengths of a wire and is typically of circular cross section, as in known in the art.

Figure 3 is a cross-sectional view of a prior art press tool station 13 for cold forging the second head of an electrical contact from the singleheaded slug 1 of Figure 1 a. Such a press tool station 13 is used, for example, to produce a leaf spring for an electrical switch, the leaf spring having a double-headed electrical contact. A pre- formed single-headed slug 1 is inserted in a pre-punched hole 15 in a leaf spring blade 17. The end 19 of the shaft 3 of the slug 1 is axially pressed by a press tool die 21 and the slug 1 is deformed to adopt the shape of the face 23 of the press tool die 21 and a double-headed electrical contact 11 is produced. When the slug 1 is deformed, there is a tendency for the portion 25 of the shaft 3 which is located in the aperture 15 to swell due to the force exerted by the press tool die 21. A 0.05mm thick blade 17 provides little resistance to distortion of the portion 25 of the shaft 3 located in the aperture 15 and the diameter of this portion 25 of the shaft 3 may increase, leading to distortion or splitting of the blade 17.

Figure 4 is a cross-sectional view of a prior art method of simultaneously producing the two heads of a double-headed electrical contact 11 from a wire slug 31.

The slug 31 has a generally uniform cross section and is pressed simultaneously on both ends 33 by press tool dies 35 to produce the double-headed electrical contact 11 of Figure lb. As stated above regarding the prior art apparatus for cold forging a single- headed slug 1, the portion 25 of the slug 31 that is located in the aperture 15 of the blade 17 may swell to distort or split the blade 17.

Embodiments of the present invention employ two press tool stations to form a double-headed contact 1 1 on a leaf spring blade 17, as shown in Figure lb, from the single-headed slug 1 of Figure 1 a, or from a wire slug 31. At the first press tool station a slug is cold forged to produce an intermediate head while inhibiting swelling of the portion of the shaft which is located in the hole 1 S of the blade 17. At the second press tool station the intermediate slug is cold forged to produce the double-headed electrical contact mounted on the leaf spring blade.

During the pressing process, the blade 17 forms part of a strip which comprises a plurality of blades 17 which are connected end-to-end. The strip is fed through a multi- station press, operations being performed at each press tool station, as well known in the art. At one press tool station a guide hole (not shown) is punched in the blade 17, which hole is used to advance the blade 17 through the multi-station press. With thin strip material it has been found preferable to pull the strip through the press tool stations, a spike engaging in a hole to index the strip. At another press tool station the blade 17 is punched to produce the hole 15 through which the single headed slug 1 is inserted. The diameter of the hole 15 is 0.08mm greater than the diameter of the shaft 3 of the slug 1, 31 to allow easy insertion of the slug 1 into the hole 15. When the slug 1, 31 is inserted into hole 15, the slug 1, 31 is struck relatively lightly to increase the diameter of the shaft 3 of the slug 1, 31, to hold the slug 1, 31 in place in the hole 15. At other press tool stations the blade 17 is punched to make incisions or to remove a section thereof.

Figure 5 is a cross-sectional view of the first press tool station 43 of a first embodiment of the present invention showing the single-headed slug 1 of Figure 1 a prior to clamp members 41 gripping the slug 1. The press tool station 43 comprises two clamp members 41 (see also Figure 14) which move radially relative to the shaft 3 of the slug 1. The clamp members 41 are in an outer position, such that there is a gap 45 between the clamp members 41 and the shaft 3 of the slug 1.

The press tool station 43 further comprises an axial support 47 which can move axially relative to the slug 1 and which bears on the pre-formed head 5 of the slug 1.

The engaging face 49 of the axial support 47 has a concave surface to accommodate the head 5 of the slug 1 when the shaft 3 of the slug 1 is pressed.

In operation, a blade 17 in the strip of blades is progressed to the position shown and the axial support 47 is moved to bear on the head 5 of the slug 1, as shown. A spacer (not shown) is incorporated in the press tool station 43 so that the minimum distance t between the lower surface 51 of the axial support 47 and the upper surface 53 of the clamp members 41 is nominally greater than the thickness T of the blade 17, thereby isolating the blade 17 from the force exerted by the press tool die 57 when operated. Typically the minimum gap may be equal to the thickness of the blade 17 plus one thousandth of an inch.

Figure 6 is a cross-sectional view of the embodiment of Figure 5 after the clamp members 41 have gripped the slug 1 prior to cold forging an intermediate second head.

The clamp members 41 move parallel to the blade 17 from the outer position shown in Figure 5 to the inner position shown in Figure 6, where the clamp members 41 bear on the shaft 3 of the slug 1. The radial movement of the clamp members 41 is driven by a dog-leg cam, as explained below. When the clamp members 41 are in the position shown in Figure 6, to bear on the shaft 3 of the slug 1, the inner edge 55 of the clamp members 41 defines a cavity with a cross section and diameter which is substantially similar to the cross section and diameter of the shaft 3 of the slug 1. For example, if the shaft 3 of the slug 1 has a generally circular cross section, then the inner surface 55 of the clamp members 41 defines a cavity with a generally circular cross section, of a similar diameter. The correlation of the diameter of the shaft 3 to the diameter of the cavity defined by the inner surface 55 of the clamp members 41 when urged towards the shaft is determined on a trial and error basis. For example the clamp members 41 may contact the shaft 3 or it may be necessary for the clamp members 41 to pinch the shaft 3.

The precise requirements are believed to vary with the material and thickness of the blade and material of the slug. Shims can be used to vary the degree of closing movement of the clamp members. The height of the inner edge 55 is of the order of O.lmm. The inner edge 55 and the sloping die surface 56 ofthe clamp members are highly polished such that when the shaft 3 is deformed, the metal flows smoothly along the die surface 56.

A press tool die 57 has a flat surface 59. The press tool die 57 strikes the end 62 of the slug 1 to cold forge the intermediate head 61 of the intermediate slug 63 as shown in Figure 7. During this process, the shaft 3 of the slug 1 is deformed and the clamp members 41 bear on the interposing portion 64 of the shaft 3 to prevent deformation of this portion 64 of the shaft 3, thereby preventing deformation of the portion 25 of the shaft 3 which is in the hole 15 of the blade 17 so that the blade 17 is not deformed. The intermediate head 61 adopts the shape of the cavity formed by the die surface 56 of the clamp members 41.

Following cold forging of the intermediate head 61, the press tool die 57, the clamp members 41 and the axial support 47 are moved away from the blade 17 to release the blade 17 and intermediate slug 63, and the blade 17 and intermediate slug 63 are moved through the press tool apparatus to the second press tool station 60, shown in Figure 8, where the doubleheaded electrical contact 11 of Figure 1 a is cold-forged. A press tool die 65 moves axially to strike the intermediate head 61 of the intermediate slug 63 to form the double-headed electrical contact 11. During this process, the peripheral portion 69 of the intermediate head 61 is deformed and the portion 25 of the shaft 3 which is in the hole 15 of the blade 17 does not swell appreciably and hence the blade 17 is not deformed. The engaging face 67 of the press tool die 65 is curved with a uniform radius. Subsequent polishing of the surface of the electrical contact may be required to produce a smooth finish.

Figure 9 is a cross-sectional view of the first press tool station 70 of a second embodiment of the present invention showing a wire slug 31 prior to the clamp members 41 gripping the slug 31. In this embodiment, the wire slug 31 has a generally circular cross section. The wire slug 31 is held in the hole 15 by inserting axially a wire of generally uniform cross section into a pre-punched hole 15 in a blade 17, simultaneously cutting and squeezing the wire in the hole 15 to form a slug 31 which swells to fill the hole 15. In this embodiment two sets of clamp members 41 are located, one on each side of the plane of blade 17 and move radially parallel to the blade 17 to bear on the slug 31 prior to cold forging the intermediate first and second heads 73, 75.

Figure 10 is a cross-sectional view of the embodiment of Figure 9 after the two sets of clamp members 41 have gripped the wire slug 31 prior to cold forging the intermediate first and second heads 73, 75. When the clamp members 41 are in the inner position as shown in Figure 10, the cavity defined by the inner edge 55 of the clamp members 41 is substantially similar to the cross section and diameter of the slug 31. The press tool dies 57 move symmetrically towards the ends 33 of the slug 31 so that the ends 59 of the press tool dies 57 strike the ends 33 of the slug 31 substantially simultaneously to deform the end portions 34 of the slug 31 to produce the double- headed intermediate slug 71 of Figure 11, with first and second intermediate heads 73, 75.

During the cold-forging process, the clamp members 41 bear on the interposing portions 64 of the slug 31 to prevent swelling of these portions 64 and to prevent swelling of the portion 25 of the shaft 3 which is in the hole 15 of the blade 17 to avoid deformation of the blade 17. When the clamp members 41 are in the position shown in Figure 10, to bear on the shaft 3 ofthe slug 31, the inner edge 55 ofthe clamp members 41 defines a cavity with a cross section and diameter which is substantially similar to the cross section and diameter of the shaft 3 of the slug 31. For example, if the shaft 3 of the slug 31 has a generally circular cross section, then the inner surface 55 of the clamp members 41 defines a cavity with a generally circular cross section, of a similar diameter. The correlation of the diameter of the shaft 3 to the diameter of the cavity defined by the inner surface 55 of the clamp members 41 when urged towards the shaft is determined on a trial and error basis. For example the clamp members 41 may contact the shaft 3 or it may be necessary for the clamp members 41 to pinch the shaft 3.

The precise requirements are believed to vary with the material and thickness of the blade and material of the slug. Shims can be used to vary the degree of movement of the clamp members. The height of the inner edge 55 is of the order of 0. lmm.

Following cold forging of the intermediate heads 73, 75, the press tool dies 57 and the clamp members 41 are moved away from the blade 17 to release the blade 17 and intermediate slug 71, and the blade 17 and intermediate slug 71 are moved through the press tool apparatus to the second press tool station 80, shown in Figure 12, where the double-headed electrical contact 11 of Figure 1 a is cold forged. Two press tool dies move axially to strike the intermediate heads 73, 75 of the intermediate slug 71 to form the double-headed electrical contact 11. During this process, the peripheral portions 79 of the intermediate head 71 are deformed and the portion 25 of the shaft 3 which is in the hole 15 of the blade 17 does not swell appreciably and hence the blade 17 is not deformed. The engaging face 67 of the press tool dies 65 is curved with a uniform radius. Polishing of the surface of the electrical contact may be required to produce a smooth finish.

Figure 13 is a partial cross-sectional view of the first press tool station 82 of the first embodiment of Figures 5-7, showing dog-leg cams 81 that urge the clamp members 41 onto the slug 1. Two dog-leg cams 81 are provided in this embodiment, disposed on opposing sides of the slug 1. Each dog-leg cam 81 moves axially in an aperture 84 in a respective clamp member 41. Each dog-leg cam 81 has two cam surfaces on opposing sides, being an inner cam surface 85 and an outer cam surface 95. The inner cam surfaces 85 of the two cams 81 face each other. The inner cam surface 85 is comprised of two parallel flat portions 87, 90 and a connecting sloping portion 89. The outer cam surface 95 is comprised of two parallel flat portions 97, 100 and a connecting sloping portion 99 that is parallel to the sloping portion 89 of the inner cam surface 85.

The aperture 84 in the clamp member 41 has a first end 101 and a second end 111, the first end 101 being in the upper surface 53 of the clamp member 41. There is a first sloping surface 103 at the first end and a parallel diagonally opposite second sloping surface 113 at the second end. In use the first sloping surface 103 bears on the sloping portion 89 of the inner cam surface 85 and the second sloping surface 113 bears on the sloping portion 99 of the outer cam surface 95.

One end 105 of the dog-leg cam 81 is on the same side of the press tool station 82 as the press tool die 57. A semi circular rocker 107 is disposed in a rocker housing 117 in which the rocker 107 can slidably rotate. The rocker 107 and rocker housing 117 are located such that the end 105 of the dog-leg cam 81 and the end 109 of the press tool die 57 bear on the ends 115 of the rocker 107. A spring 119 is provided to urge the press tool die 57 against one end 115 of the rocker 107.

In operation, the dog-leg cam 81 is initially in a position such that the inner cam surface 85 is not bearing on the clamp member 41. The dog-leg cam 81 is moved towards the rocker 107 and the sloping portion 89 of the inner cam surface 85 comes into contact with the first sloping surface 103 of the hole 84 of the clamp member 41, and the clamp members 41 begin to move towards the slug 1 until the clamp members grip the slug as shown in Figure 14. The extent of the overlap between the sloping portion 89 of the inner cam surface 85 and the first sloping surface 103 of the hole 84 is such that when the clamp member 41 is in the inner position shown in Figures 14, the sloping portions 89 and the first sloping surface 103 are no longer in contact. As the dog-leg cam 81 further moves in this direction, the rocker 107 rotates in the rocker housing 117 and pushes the press tool die 57 towards the slug 1, until the press tool die 57 strikes the slug 1 to form the intermediate head 61 shown in Figure 7. The dog-leg cam 81 then moves in the opposite direction so that the rocker 107 can rotate back to its initial position as it is driven by the press tool die 57 which is propelled by the spring 119. As the dog-leg cam 81 continues to move in this opposite direction, the sloping portion 99 of the outer cam surface 93 bears on the second sloping surface 113 of the hole 84 of the clamp member 41, to move the clamp member 41 away from the intermediate slug 63, thereby releasing the intermediate slug 63 from the grip of the clamp members 41. The movement of the two clamp members 41 is synchronised by connecting a second dog- leg cam 81 to the first dog leg-cam 81, the second dog-leg cam 81 controlling the movement of the second clamp member 41.

Figure 15 is a perspective view of a clamp member 41. In the first embodiment shown in Figures 5-7 two clamp members 41 are deployed. In the second embodiment of Figures 9-11 four clamp members 41 are deployed, two on each side of the blade.

The shaft 3 of the slug 1, 31 is gripped by the inner edges 55 of two cooperating clamp members 41. The height ofthe inner edge 55 is typically O.lmm.

The sloping die surfaces 56 of two cooperating clamp members 41 form a cavity in which the intermediate head 61, 71 is formed when the slug 1, 31 is cold forged.

Various modifications will be apparent to those in the art and it is desired to include all such modifications as fall within the scope of the accompanying claims.

Claims

CLAIMS: 1. A press tool station for cold forging at least one head on a

shaft of a slug which is positioned in an aperture in a member to which the slug is to be fastened, the press tool station comprising radial restraining means forming a cavity to accommodate the shaft of the slug adjacent to the member to which the slug is to be fastened to inhibit radial expansion of the slug within the member during the cold forging operation.
2. A press tool station as claimed in claim 1, wherein axial support means are provided to support one end of the slug and punch means are provided to impact the other end of the slug to cold forge a head on the end of the slug, the radial restraining means being disposed between the member to which the slug is to be fastened and the punch means.
3. A press tool station as claimed in claim 1, wherein first and second punch means are provided to impact both ends of the slug to cold forge a head on each end of the slug.
4. A press tool station as claimed in claim 3, wherein the first and second punch means, in use, impact substantially symmetrically on the ends of the slug.
5. A press tool station as claimed in any one of the preceding claims, wherein the radial restraining means comprises a plurality of clamp members.
6. A press tool station as claimed in claim 5, wherein one or more of the clamp members are movable from a first position, to allow a slug to be inserted into the press, to a second position where the slug is cold forged.
7. A press tool station as claimed in any one of the preceding claims, wherein the cavity formed by the radial restraining means has a cross section which is substantially identical to the cross section of the shaft of the slug which is being cold forged.
8. A press tool station as claimed in claim 7, wherein the radial restraining means contact the shaft of the slug when the shaft is cold forged.
9. A press tool station as claimed in claim 7, wherein the radial restraining means pinch the shaft of the slug when the shaft is cold forged.
10. A press tool station as claimed in any one of claims 5 to 9, wherein the clamp members comprise a clamp portion and a die portion, the clamp portion inhibiting swelling of the interposing portion of the shaft of the slug and the die portion in cooperation with the punch means forms a head on the slug when the slug is cold forged.
1 1. A press tool station as claimed in claim 10, wherein the height of the clamp portion which contacts the shaft of the slug is less than lmm.
12. A press tool station as claimed in claim 10, wherein the height of the clamp portion which contacts the shaft of the slug is less than 0.2mm.
13. A press tool station as claimed in claim 10, wherein the height of the clamp portion which contacts the shaft of the slug is less than 0. lmm.
14. A press tool station as claimed in any one of the preceding claims, wherein the member to which the slug is to be fastened is a leaf spring blade.
15. A press tool station as claimed in claim 14, wherein the thickness of the leaf spring blade is less than or equal to O. l mm.
16. A press tool station as claimed in claim 14, wherein the thickness of the leaf spring blade is less than or equal to 0.05mm.
17. A method of cold forging at least one head on a shaft of a slug which is inserted axially into an aperture in a member to which the slug is to be fastened, the method comprising providing radial restraining means adjacent to the member to which the slug is to be fastened to inhibit swelling of the interposing portion of the shaft of the slug when cold forging the slug.
18. A method of cold forging as claimed in claim 17, wherein one end of the slug is axially supported and the other end of the slug is impacted to cold forge a head on the slug.
19. A method of cold forging as claimed in claim 18, wherein both ends of the slug are impacted substantially symmetrically to cold forge a head.
20. A method of cold forging as claimed in any one of claims 17 to 19, wherein the restraining means contact the shaft of the slug when the slug is cold forged.
21. A method of cold forging as claimed in any one of claims 17 to 19, wherein the restraining means pinch the shaft of the slug when the slug is cold forged.
22. A method of cold forging an electrical contact on a member, the method comprising cold forging at least one intermediate head on a shaft of a slug which is inserted axially into an aperture in the member to which the slug is to be fastened as claimed in any one of claims 17 to 21, removing the radial restraining means from the intermediate head or heads and cold forging the intermediate head or heads to form the electrical contact.
23. A method of cold forging an electrical contact on a leaf spring blade, the method comprising cold forging at least one intermediate head on a shaft of a slug which is inserted axially into an aperture in the blade to which the slug is to be fastened as claimed in any one of claims 17 to 21, removing the radial restraining means from the intermediate head or heads and cold forging the intermediate head or heads to form the electrical contact.
24. A method as claimed in claim 23, wherein the thickness of the leaf spring blade is less than or equal to 0.1 mm.
25. A method as claimed in claim 23, wherein the thickness of the leaf spring blade is less than or equal to 0.05mm.