GB2203075A

GB2203075A - Method of manufacturing a screw head with crossed slots

Info

Publication number: GB2203075A
Application number: GB08711935A
Authority: GB
Inventors: Luciano Salice
Original assignee: Arturo Salice SpA
Current assignee: Arturo Salice SpA
Priority date: 1987-03-23
Filing date: 1987-05-20
Publication date: 1988-10-12
Also published as: EP0283669A2; GB8711935D0; EP0283669A3; DE3709513A1

Description

METHOD OF MANUFACTURING A SCREW HAVING A SCREW HEAD WITH CROSSED SLOTS This invention relates to a method of manufacturing a screw having a screw head with crossed slots, the sides of which are of an undercut configuration, in which pressure acting in the axial direction is applied to the screw head with a deforming tool.

Screw heads having crossed slots which are provided with an undercut configuration are known and permit a cross-head screwdriver to be fitted therein at an angle to the vertical so that the screws can be turned even when the screwdriver cannot be introduced into the crossed slots in alignment with the shank of the screw. In that case the undercut sides of the slots prevent the screwdriver from slipping off the sides of the slots when inserted in the screw head at an inclined angle, and also prevent the screwdriver from not being firmly engaged in the crossed slots.

German utility model No. 81 14 236 discloses a method on which the screw is made by die casting, wherein the die portions which form the mutually crossing undercut slots have to be withdrawn laterally from the head of the screw. This known method of manufacturing screws with undercut crossed slots is therefore very complicated and expensive.

In a manufacturing method disclosed in British patent specification No. 2 149 348, a screw with a screw head with crossed slots is produced by a casting process, wherein the screw blank which is cast from a cold-workable material has crossed slots with mutually parallel straight sides, and a partspherical cap portion. The parts of the part-spherical cap portion which laterally delimit the crossed slots are then pressed inwardly by a punch in such a way as to provide a head which is approximately in the form of a portion of a cylinder, with crossed slots which have an undercut configuration. That method of manufacturing a screw is also relatively expensive as firstly a screw blank has to be cast and the screw blank than has to be given the appropriate shape by means of a punch.

There is thus a need for a generally improved method of manufacturing a screw with a crossed slotted head, which in a simpler and more economical fashion can produce screws with screw heads having crossed slots provided with undercut configurations.

According to the present invention there is provided a method of manufacturing a screw having a screw head with crossed slots, the sides of which are of an undercut configuration, in which a substantially cylindrical portion of wire or the like is fitted as a screw blank into a die and pressure is applied to a head region thereof in the axial direction of the blank by at least one deforming punch so that, by thrust deformation, a central recess which is of round cross-section and two intersecting slots which cross therethrough are firstly formed in the head region of the screw blank, and then the head portions which are separated from each other by the more deeply impressed slots and which are in profile substantially in the form of a quarter of a circle, are formed with a part-spherical shape having inner rounded-off edges outwardly curving.

With the method of the invention, the screw shank can be provided, substantially in one working step by thrust deformation using a punch of suitable configuration, with a screw head whose crossed slots have undercut configurations, the shape of which approximately corresponds to the inside walls of the edge region of a space delimited by a flattened hollow sphere.

The undercut configuration permits a cross-head screwdriver to be inserted at an inclined angle without the screwdriver slipping out when the turning torque is applied because the overhanging upper co-operating sides provide the screwdriver with the necessary hold.

The undercut configurations which prevent a screwdriver from slipping out are formed, in accordance with the method of the invention, in the region in which the slots cross, by the head portions which are firstly separated by the mutually crossing slots, of a cross-section substantially in the form of a quarter of a circle, being displaced outwardly, wherein the upper inner edge regions are pressed inwardly and the inner rounded-off edges thereof are curved outwardly. The undercut regions are therefore not formed directly at the sides of the cross slots but at the rounded-off inner edges of the quarter circle profile portions between the crossed slots.

Preferably, the pressure is applied with a deforming punch having a bowl-shaped recess containing a cross-shaped web protuberance with a central projecting mandrel portion, in such a way that the substantially quarter-spherical portions which are of enlarging configuration and which are separated by the web portions forming the cross-shaped protruberance, bear with their heads against the bottom, which is curved in a dome-like configuration, of the bowl-shaped recess, and are curved outwardly forming a space which is overhung by the tips of the quarter-spherical portions, in the form of a flattened hollow sphere.

Advantageously, the head region of the screw blank is shaped substantially as a truncated cone in a first step by means of a punch. After this first thrust deformation step, further deformation of the head region is then carried out in the above-described manner.

A screw head manufactured in accordance with the above-described method has outwardly curved edge regions in the region of the bottom of the mutually crossing web portions. Conveniently therefore, in a third step, the screw head is provided with a cut which separates off the edge region. That cut can be made by means of a pressing or stamping tool. The cut separates an outer annular region from the screw head so that that region is of a more attractive appearance with a lower region in the form of a cylindrical disc.

An apparatus for carrying out the method according to the invention, includes a die and a punch, wherein the punch has a bowl-shaped recess with a bottom which is curved in a dome-like configuration and which is, subdivided by a cross-shaped protruberance consisting of mutually crossing web portions, the end faces of which are disposed in a plane in the boundary region between the dome-like curved bottom and an outer region delimited by a substantially cylindrical wall, and has a projecting mandrel, provided with a flat tip, at the crossing region of the web portions.

According to a further aspect of the present invention, there is provided a screw having a head which under a part-spherical region has a region which is substantially in the form of a cylindrical disc and which is provided with mutually crossing slots which divide substantially quarterspherical portions, wherein the inwardly bent, rounded-off inner tip regions of the quarter-spherical portions overhang recess portions which are in the form of annular grooves and which are disposed in the base regions and whose peripheral angle is about 450 and which delimit a space divided by the slots, approximately in the form of a flattened hollow sphere.

The inner upper tip regions of the quarter-spherical portions of the screw head preferably are chamfered in a substantially hollow-cone configuration. The chamfers promote inclination of the screwdriver when fitted at an inclined angle. In manufacture by means of the apparatus according to the invention, in accordance with the method of the invention, the chamfers are formed by a shallow-conical tip of the central mandrel portion of the punch.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a side view of a screw of the invention in which the head which is provided with a cross slot is shown partly in section, Figure 2 is a plan view of the head of the screw shown in Figure 1, Figure 3 is a view from below or a punch for manufacturing the screw shown in Figures 1 and 2, and Figure 4 to 9 show in part section different successive deformation operations in the head region of the screw blank up to the formation of the screw head according to the method of the invention.

A screw shown in Figures 1 and 2 has a screw head 1 and a shank 2 which includes a screwthreaded portion 3 and a screwthread-free portion 4 between the screwthread and the head 1. The head 1 has an upper partspherical portion 5 forming a cap, and a region 6 which adjoins same and which is approximately in the form of a cylindrical disc. The screw head is provided with slots 7 and 8 which cross each other at right angles and which are formed by grooves having mutuallly parallel sides which are at right angles to the floor of the grooves. The screw head is provided on the axis of the screw in a recess 9 which is of a round cross-section and which the slots cross or intersect. The slots 7 and 8 subdivide the upper region of the screw head into four substantially quarter-spherical portions 10.The inner tip regions 11 of the quarter-spherical portions 10 are bent or deformed inwardly and they accordingly overhang recess portions 12 in the form of an annular groove which are formed in the base regions thereof. The peripheral angles of the inner edges of the recess portions 12 are about 450. The recess portions 12 delimit a space which is divided by the slots, by bulgedout portions and which is approximately in the shape of a flattened hollow sphere. The upper inner tip regions of the quarter-spherical portions are provided with hollow-conical chamfers 14 above the annular groove-like recess portions 12.

The screw shown in Figures 1 and 2 is produced from a substantially cylindrical portion of wire or the like, which forms a screw blank.

A die 15 which is indicated in Figures 4 to 9, and a punch 16, are used to manufacture the screw head.

The punch 16 has a bowl-shaped recess 17 with a bottom 18 which is curved in a dome-like configuration. The bowl-shaped recess 17 is subdivided by a mutually crossing web protruberance consisting of mutually crossing or intersecting web portions 19. The end faces of those web portions 19 are dispose in one plane in the boundary region between the dome-like curved bottom of the bowl-like recess and an outer region delimited by a substantially cylindrical wall. Provided in the region in which the portions 19 cross is a central projecting mandrel portion 20 with a flat sided conical tip. The tip of the mandrel portion 20 is disposed approximately in the region of the plane of the flat edge of the punch 16.

The individual steps during the method of the invention for deforming the head region of the screw blank to provide the screw head are shown in Figures 4 to 9.

The screw blank is fitted into a blind hole-like recess in the die 15.

In a first deformation step, the head region of the screw blank is deformed to a truncated cone shape, by a punch which is not shown in the drawing.

The increased-width portion truncated cone is shown at 21 in Figure 4.

Further deformation of the truncated cone shaped head region, to form the screw head, is carried out by the punch 16. Firstly, as the punch 16 is lowered, the flat sided conical tip of the central mandrel portion 20 engages the centre of the upper circular surface of the truncated cone shaped portion 21. Then, the mutually crossing web portions 19 of the punch also engage the portion 21 as the punch and the mandrel portion 20 are further pressed in. The mutually crossing portions 19 separate portions of a substantially quarter-circular cross-section, and bend them outwardly in the manner shown in Figure 6.As the punch 16 is moved further downwardly, those portions of quarter-circular cross-section bear against the dome-like curved bottom of the recess in the punch 16 and are thereby displaced outwardly, while the inner edges of said portions are increasingly bulged out in the manner shown in Figures 7 and 8. When the punch has been moved completely down, as shown in Figure 8, the portions of substantially circular cross-section have been deformed to provide substantially quarter-spherical portions. In that respect, formed in the inner edge region of said quarter-sperical portions is a space whose shape approximately corresponds to a flattened hollow sphere. Chamfers 14 have been formed by the shallow-conical tip of the mandrel portion 20.

After the head has been shaped with the punch 16, the outer edge of the screw head is punched or stamped away by means of a punching or stamping tool, so that the edge regions which are pressed out of the outer ends of the mutually crossing slots are removed and the screw head has a bottom flat-cylindrical region.

The shank of the screw blank, which is provided with a screw head in the above-indicated manner, is then provided with a screwthread in the usual fashion.

Claims

1. A method of manufacturing a screw having a screw head with crossed slots, the sides of which are of an undercut configuration, in which a substantially cylindrical portion of wire or the like is fitted as a screw blank into a die and pressure is applied to a head region thereof in the axial direction of the blank by at least one deforming punch so that, by thrust deformation, a central recess which is of round cross-section and two intersecting slots which cross therethrough are firstly formed in the head region of the screw blank, and then the head portions which are separated from each other by the more deeply impressed slots and which are in profile substantially in the form of a quarter of a circle, are formed with a partspherical shape having inner rounded-off edges outwardly curving.

2. A method according to claim 1, in which the pressure is applied with a deforming punch having a bowl-shaped recess containing a cross-shaped web protruberance with a central projecting mandrel portion, in such a way that the substantially quarter-spherical portions which are separated off between the web portions forming the cross-shaped protruberance and which are of an enlarging configuration bear with their heads against the bottom, which is curved in a domelike configuration, of the bowl-shaped recess, and are curved out-wardly, forming, in the vicinity of the intersection of the slots, a space, which is overhung by the tips of the quarter-spherical portions, in the form of a flattened hollow sphere.

3. A method according to claim 1 or claim 2, in which the head region of the screw blank is shaped as a truncated cone in a first step by means of a punch.

4. A method according to any one of claims 1 to 3, in which the screw head is provided in a third step with a cut which separates off the edge region.

5. Apparatus for carrying out the method according to claim 1, including a die and a punch wherein the punch has a bowl-shaped recess with a bottom which is curved in a dome-like configuration and which is subdivided by a cross-shaped protruberance consisting of intersecting web portions, the end faces of which are disposed in a plane in the boundary region between the dome-like curved bottom and an outer region delimited by a substantially cylindrical wall, and has a projecting mandrel, provided with a flat tip, at the intersection of the web portions.

6. A screw having a head which under a part-spherical region has a region which is substantially in the form of a cylindrical disc and which is provided with mutually crossing slots which divide substantially quarterspherical portions, wherein inwardly bent, rounded-off, inner tip regions of the quarter-spherical portions overhang recess portions which are in the form of annular grooves and which are disposed in the base regions and whose peripheral angle is about 450 and which delimit a space divided by the slots, approximately in the form of a flattened hollow sphere.

7. A screw according to claim 6, wherein the inner upper tip regions of the quarter-spherical portions are chamfered in a substantially hollow-cone configuration.

8. A method of manufacturing a screw having a screw head with crossed slots, substantially as hereinbefore described with reference to the accompanying drawings.

9. Apparatus for manufacturing a screw having a screw head with crossed slots, substantially as hereinbefore described with refernce to the accompanying drawings.

10. A screw having a screw head with crossed slots, substantially as hereinbefore described with reference to the accompanying drawings.