The invention finds a use in the cold forming of fasteners, in particular the heads of fasteners. For convenience, the present invention is described in relation to the production of a slot in a blank screw head, but is equally applicable to other types of fasteners such as bolts .

BACKGROUND ART The conventional methods used in forming a slot in a blank screw head have evolved around the idea of cutting or grinding the appropriate slot shape into the screw head. Where, for example, a slot having a base wall was required, the blank screw head was held in position in a die or vice or the like which was then in turn moved relative to a flat or circular saw or grinding wheel. The alignment of the blank screw head held within the die, vice or the like with respect to the saw or grinder was critical as the placement and depth of the slot base in the screw ⁷ head was dependent upon the manner in which the screw head moved relative to the saw or grinder. The width of. _. the saw or grinder was such as to provide a slot of width 0.05 inches. Accordingly, the saw or grinder was usually constructed of special materials to compensate for its narrow width. Further, if a plurality of slots in either one or various directions across the screw head was desired, the screw head was required, for example, to make a number of passes in the same or different directions over the saw or grinder, or more sophisticated and expensive cutting or grinding procedures were necessary. The present invention has been found to alleviate or at least minimize the problems found in the conventional methods for forming a slot and it is simple to use and convenient in operation.

DISCLOSURE OF THE INVENTION One aspect of the present invention provides a punch and die assembly.

In the invention, the punch for forming into a fastener head an open-ended slot having side walls and a base wall; comprises a body portion having an end face; and a working tongue extending from the end face, said tongue having two sets of opposed side faces, each side face extending from the end face of the body portion and terminating at or near an end section, one set of opposed sides faces being relatively wide when compared to the other "edge" set of opposed side faces; the construction and arrangement being such that when in use, the relatively wide side faces form the side walls of the slot in the fastener head and the base wall of the slot conforms to the shape of the end section.

In the invention, the die for supporting a fastener blank having a shank and a head into which a slot is to be formed, at one end of the shank; comprises a body portion having a working face; a bore located within the body portion and comprising a fastener- head receiving recess and a shank receiving portion, the fastener head receiving recess communicating with and extending between the shank receiving portion and the working face of the body portion and having greater cross-section than the shank receiving portion, the fastener head receiving recess Being generally of complimentary shape to the fastener head but having further at least two cavities, each defined by a wall or walls extending inwardly into the body portion; the construction and arrangement being such that .the cavities will receive burrs when formed from the fastener head during a slot forming operation.

In a further aspect of the invention there is provided a method for forming into a fastener head an open- ended slot having side walls and a base wall using the punch and die assembly the method comprising supporting the fastener head in the die; and working the fastener head with the working tongue of the punch to form the slot in the

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fastener head.

Preferably the body portion of the punch is in the form of an elongated member. The member may be of any suitable transverse cross-sectional shape, for example, circular or rectangular, but a substantially cylindrical elongated member will be hereinafter described. In one form, the cylindrical elongated member has an end face receivable in the die. Preferably, the end face is flat and has substantially upwardly extending peripheral side walls which are continuous and capable of being received in the die. The working tongue extends from the end face in the opposite direction to the side walls and is preferably integral with the face. The working tongue may take many but preferably has a substantially rectangular cross- section formed by the two sets of opposed side faces which extend from the end face of the body portion and terminate at or near the end section of the tongue.

Several alternative forms of working tongue are conveniently described in terms of the appearance of the broad side i.e. one of the relatively wide faces of the tongue across the longitudinal axis of the punch. The end section may be of substantially flat configuration with the edge faces of the tongue substantially normal to the end section giving the appearance of a rectangular tongue or with the edge faces diverging away from the end section giving the appearance of a frusto conical tongue. Alterna¬ tively, the end section may have a concave recess, preferably centrally disposed between the edge faces , and again these edge faces may be normal to, or diverge from, the end section toward the end face of the body portion. The concave recess may be angular, thereby giving the tongue a W-shaped appearance, or smoothly curved.

In a further embodiment the end section may be in the form of an inverted channel section recess by formed extending the edge faces and adjacent relatively wide faces of the working tongue to form outwardly extending teeth, having inner and outer edge faces , the outer edge faces of the teeth being continuous extensions of the working tongue

edge faces and the inner edge faces of the teeth being parallel to each other and merging with a substantially flat or concave, base of the channel.

When using a punch having a working tongue with an end section of flat configuration, a substantially flat slot base wall is obtained while a concave end section yields a base wall of substantially convex configuration when the base wall is viewed from the head of the screw along the longitudinal axis of the screw shank. The length of the end section of the working tongue of the punch may be equal to, greater than, or less than the largest diameter of the screw head into which the slot is to be formed. It is preferable that the length of the end ^" section where it is of the inverted channel shape be less than the largest diameter of the screw head.

The punch of the present invention can be secured to a punch support means which means can move relative to the die into which the punch is received.

The punch can be made of any suitable material, preferably it is composed of known hard tooling steel.

The die of the present invention has a body ^' portion into which the punch is received. Preferably, the body portion is in the form of an elongated member which may be of any suitable transverse cross-sectional shape such as circular or rectangular, but a substantially cylindrical elongated member will be hereinafter described.

The elongated die member preferably has the fastener head receiving recess and shank receiving portion forming a bore suitably located along its longitudinal axis and more preferably centrally located in the elongated member. The shank receiving portion and the fastener head receiving recess are of sufficient cross-section to receive the shank of the blank screw and the head of the screw which is to be slotted. The shank receiving portion and/or fastener head receiving recess may be lined with a suitable wear resistant material, such as tungsten carbide and are preferably adapted to receive a replaceable sleeve made of suitable wear resistant material.

The elongated member of the die preferably has a working face adapted to receive and/or engage the punch. In one form the- shank receiving portion is of constant cross-section while the fastener head receiving recess has a cross-section which expands in the direction towards the working face of the die to form a stepped hollow for cooperating the end face and working tongue and/or the side walls of the punch. Preferably, the stepped hollow is comprised of two recesses. In this preferred form the fastener head receiving recess communicates with the shank receiving portion and has a complimentary shape to that of the desired screw head into which a slot will be formed. The fastener, head receiving recess may have substantially diverging side walls emanating ^■ from the walls of the shank receiving portion thus accommodating a blank for a countersunk screw head. It is preferred that the maximum diameter of the fastener head receiving recess is equal to or greater than the maximum diameter of the blank screw head. There are also provided in the fastener head receiving recess at least two cavities which are preferably diametrically opposed one another and spaced around the fastener head receiving recess and preferably adapted to receive the or part of the working tongue of the punch and large enough to receive any burrs formed when forming the slot. Preferably the cavities lie between the junction of the shank receiving portion and the fastener head receiving recess and the working face of the die. The cavities also preferably extend outwardly and diverge away from or near the junction. Each of the cavities is defined by a wall or walls which extend inwardly into the body portion of the die. Preferably, that part of the cavity-defining body portion wall most closely adjacent to the shank receiving portion of the bore extends initially parallel with the shank receiving portion. The second of the preferred two recesses preferably communicates with the fastener head receiving recess and has its base wall substantially normal with respect to the shank receiving portion walls. The second recess is also provided

with side walls which are preferably perpendicular to its own base wall and which are substantially normal with respect to the working face of the die. When viewed along the longitudinal axis of the die, the base wall of the second recess can be of any peripheral shape which will accommodate the punch. Preferably, it is circular.

The base wall of the second recess may be lined with a suitable wear resistant material or in another preferred form, a wear resistant ring of desired config- uration can be housed within the base and side walls of the second recess. Preferably, those edges of the wear ring remote from the base and side walls of the second recess are chamfered to guide the punch or its end face when entering the die. The presence of the wear resistant ring is found to assist in aligning the working tongue of the punch with the cavities in the fastener head receiving recess of the die. The area of the base wall of the second recess exposed to the punch is preferably sufficient to accommodate the end face of the punch. The die can also be supported by a die support means which means can be movable with respect to the punch and/or the punch support means.

The die can be made of any suitable materials, preferably it is composed of known hard tooling steel. The screw blank can be inserted and removed from the die of the invention by any of the methods currently employed in the known cutting or grinding procedures . Further, it is found that ^" the slot can be formed in the blank screw head before or after a thread is rolled onto the screw shank.

The present invention finds particular use with respect to the method given in my International Patent Application Number PCT/AU 80/00043 which relates to Australian Patent Specification Number 43831/79. The subject matter of this International and Australian Appli¬ cation is incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of

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example with reference to the accompanying diagrammatic drawings in which:-

Fig. 1 is a perspective view of a punch.

Figs. 2 and 3 are fragmentary side views of a punch with other embodiments of the working tongue of the punch.

Fig. 4 is a perspective view of a die.

Fig. 5 is a perspective view of another embodiment of die.

Fig. 6 is a cross-section view along line VI-VI in Fig. 4

Fig. 7 is a top plan view of the die in Fig. 5.

Fig. 8 is a cross-section view along line VIII- VIII in Fig. 7.

In Figs. 1, 2 and 3, there are illustrated punches 9 having a cylindrical bodies 10 and an end faces 11, with working tongues 12. The working tongue in Fig. 1 has. relatively wide faces 13, set of opposed "edge" side faces 14 and an end section 15. Teeth 16 extend outwardly from the end section 15, and are formed by extensions of the opposed relatively wide faces 13 and edge faces 14. Each of the teeth 16 has an inner edge face 17.

Fig. 2 illustrates a side view of the working tongue 12 of the punch 9. The relatively wide faces 18 of the tongue are substantially parallel while the edge faces 19 diverge away from end section 20 toward the end face 11 of the punch. Fig. 3 is a similar view to Fig. 2 but illustrates a substantially "W" shaped working tongue 21, having an end section 22 of concave configuration with edge faces 23 which diverge away from the end section toward the end face 11 of the punch.

In Fig. 4 and Fig. 5, the elongated die 50 comprises a cylindrical body 51 with a working face 52, with a mould 53 having a countersunk recess 54 for receiving a fastener head to be slotted by a punch; cylindrical bore 55 for receiving the fastener shank and cavities 56 which are large enough to receive part of the working tongue of a punch and/or burrs formed when working a fastener head with the punch. The die of Fig. 5 has the same construction as

that of Fig. 4 except that the working face 57 is stepped, a best shown in Fig. 8., to accommodate a wear resistant ring 58.

Fig. 6 and Fig 8. illustrate diametrically opposed cavities 56 spaced from the junction of the recess 54 and bore 55 and lying between that junction and the working face 52 of Fig. 4 and Fig. 6 or working face 57 of Fig. 5 and Fig. 8. Each cavity 56 is defined by walls extending inwardly into the cylindrical body 51 of the die. That part 60 of the cavity-defining body portion wall 59, most closely adjacent to the cylindrical bore 55 extends initiall parallel with the cylindrical bore 55. Each cavity 56 can be provided with an air inlet hole (not shown) to aid in reήioving burrs captured in the cavity during the formation of the slot into the fastener head.

In use, a fastener head blank is held in the die recess 54 and with its shank in bore 55, the working tongue 12 of the punch is brought into contact with and works upon the fastener head blank, so that the teeth 16 of the tongue pass through the head blank producing burrs upon the edge face 14 of the tongue which are received in the cavities 56 of the die. Pressure is applied to the working tongue 12 through the punch 10 until the inner edge faces 17 of the teeth 16 of the tongue move past the walls 60 and into the cavities 56 to shear off burrs formed during the initial working operation. While the teeth 16 are shearing off the burrs, the end section 15 of the tongue is forming the base wall of the slot and the relatively wide faces are forming the slot side walls of the fastener head. It has been found with the present invention that a single slot or a number of slots having a desired base and side wall configuration can be formed using the punch and die of the present invention.

Finally, it is to be understood that various alterations, modifications and/or additions may be introduce into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

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