GB2073076A

GB2073076A - A Preformed Blank for a Hexagon Head Screw or a Hexagonal Nut Having a Supporting Collar or Flange

Info

Publication number: GB2073076A
Application number: GB8103786A
Authority: GB
Original assignee: WAELZLAGER KOM VEB
Current assignee: WAELZLAGER KOM VEB
Priority date: 1980-04-02
Filing date: 1981-02-06
Publication date: 1981-10-14
Also published as: JPS56154242A; DE3045152A1; DD150701A1

Abstract

A preformed blank 4 is characterised by its geometrical shape which is a frustum of a hyperboloid of revolution of one sheet. It has in the direction of the subsequent bearing surface (flange or collar) of the final shape 5 a constant increase in diameter as far as the maximum diameter D2 of the blank 4. The diameter D2 is adjoined by a frusto- conical bevel 9 until a maximum height Hz of the blank 4 is reached. This height Hz is smaller than the final height H of the screw head. The diameter D1 of the outer end face 10 of the blank 4 corresponds or substantially corresponds to the corner dimensions of the final shape 5 of the hexagon. A shaping tool for the further processing of the preformed blank 4 comprises a hollow shaping ram 6 and a die 7. The ram 6 has an inner hexagonal surface 13 and an outer annular projection which corresponds to a recess 11 in the die 7. The inner surface of the projection 12 is constructed in the direction of the inner hexagonal surface 13 in the form of a gransitional cone 14. The angle a of the cone lies substantially in a range from 55 DEG to 80 DEG . <IMAGE>

Description

SPECIFICATION A Preformed Blank for a Hexagon Head Screw or a Hexagonal Nut Having a Supporting Collar or Flange This invention relates to a preformed blank for further processing to produce a hexagon head screw or a hexagonal nut having a supporting collar, more particularly a flanged screw, and also relates to a shaping tool for producing the final shape of the screw or nut.

It is known in flanged screws to start from a cylindrical intermediate blank and then produce the hexagon head with flange by upsetting (K. W.

Michler: Economic Manufacture of Screws, published in "Draht" (Wire), Coburg, 23, (1972), 5, Pp. 250-253). The cylindrical intermediate blank from which the flanged screw head is produced by upsetting has a somewhat smaller diameter than the width across flats to be upset.

For the satisfactory shaping of the hexagon, in upsetting extremely high forces are required, which result in the pressed tool element becoming unusable after being used only for a short time. If the forces are not high enough, the hexagon edges are inadequately shaped, resulting in a reduction of the possible tightening torque.

Moreover, the inadequately shaped hexagon corner can cause accidents, since a spanner can easily slip off.

Another prior art method starts from a cylindrical intermediate blank and pre-shapes the hexagon edge in an additional stage, by reduction or upsetting, then producing the final shape in a further stage by upsetting the hexagon and the flange (K. Sieber: Bases for Designing of Tools for the Cold Pressing of Shaped Parts, preferably on Multi-stage Presses, published in "Draht" (Wire), Coburg, 17, (1966), 4, pp. 196-205). Apart from the necessity of an additional re-shaping stage and a securely positioned transfer of the hexagon from pre-shaping to final shaping, this method has the same disadvantages as those found in upsetting flanged screws from a cylindrical blank in a re-shaping stage.

It has also been suggested to produce flanged screw heads by extrusion moulding from a cylindrical intermediate blank, whose diameter is equal to the flange diameter (Federal German Patent Specification 1 022 882). A disadvantage of this method is a considerabie formation of burr on the bearing surface of the flange and the drawing of the screw shank into the flanged screw head, something which results in an annular fold at the transition between the shank and the flange. the annular fold reduces the properties of use of the flanged screw.It has also been suggested to start from a cylindrical intermediate blank and then use a hollow ram having an inlet cone to produce the screw heads and nuts with supporting collar, with convex and concave curves instead of the hexagon (Federal German Offenlegungsschrift 1625 467, German Auslegeschrift 1 728 574). This method cannot be used to make hexagon head screws with supporting collars.

It is an object of the invention to produce flanged screws or flanged nuts with hexagon corners shaped with the sharp edges, without the use of additional re-shaping stages and with relatively low re-shaping forces.

The problem which the invention aims at solving is to provide a preformed blank, necessary for re-shaping to produce a hexagon with supporting collar, and a shaping tool suitable for the further processing of the preformed blank, in dependence on the geometrical design and dimensions of the intermediate blank from the final shape.

The technical reasons for the disadvantages of the inadequately shaped hexagon corners produced by the methods described hereinbefore lie in the flow and stressing conditions present when upsetting or press-moulding cylindrical intermediate blanks into hexagons. The lower the re-shaping forces, the less sharp-edged are the corners formed. The higher the re-shaping forces, the shorter is the tool life.

In the known extrusion moulding of a flanged screw head it is necessary to exceed the limits of the method. This is the technical reason for the heavy burr formation and the drawing of the screw shank into the flanged screw head (funnel formation), resulting in the formation of an annular fold which reduces the properties of use of the flanged screw.

The unusability of the method of making hexagon head screws with supporting collars disclosed in German Offenlegungsschrift 1625 467 is due to the differently shaped screw head.

Any attempt to produce hexagon head screws by that method results in undesirable deformations (overlappings, cracks, burr).

The present invention consists in a preformed blank for a hexagon head screw of a hexagonal nut having a supporting collar, from which in a subsequent processing stage the final shape of the screw or nut is produced, the head of the screw or the nut having a geometrical shape of a frustum or a hyperboloid of revolution of one sheet, which has in the direction of the subsequent bearing surface of the final shape a constant increase in diameter as far as the maximum diameter (D2) of said blank, which diameter is adjoined by a frusto-conical bevel until a maximum height (Hz) of the blank is reached which is smaller than the final height (H) of the screw head or the nut, the diameter (D,) of the outer end face of the blank corresponding or substantially corresponding to the corner dimension of the final shape of the hexagon.

The shaping tool for the further processing of the preformed blank to produce the final shape comprises a hollow shaping ram and die, the ram having an inner hexagonal surface and an outer annular projection corresponding to a recess in the die, characterised in that the inner surface of the projection of the shaping ram is constructed in the direction of the inner hexagonal surface, in dependence on the shape of the preformed blank, in the form o a transitional cone, the angle (α) of the transitional cone lying substantially in a range from 55 to 80 .

In order that the invention may be more readily unclerstood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Fig. 1 shows a shaping tool with the starting blank before the pressing of the preformed blank, Fig.2 2 shows the shaping tool with the preformed plank after pressing, Fig.3 shows another shaping tool with the preformed blank before the final pressing, and Fig.4 shows the shaping tool with finally shaped workpiece after the final pressing.

A starting blank 1 (Fig. 1) for producing a hexagon head screw with a supporting collar or flange, is formed in known manner by upsetting, extrusion moulding or reduction, and is re-shaped in a first method step ofthe re-shaping process by the @ working stroke of a shaping ram 2 and a die 3 to such an extent that a preformed blank 4 is produced, due to the engraving worked into the shaping ram 2 and die 3 (Fig. 2). The geometric configuration of the preformed blank 4 is the precondition for a final shape 5 (Fig. 4) which is to be produced in the subsequent step of the method and which is produced by a superimposed reducing-upsetting operation carried out by the working stroke of a hollow shaping ram 6 and a die 7.Features of the preformed blank 4 according to the invention are that its geometrical configuration corresponds to a hyperboloid of revolution of one sheet which has in the direction of the shank 8 of the screw a continuous increase In diameter. The maximum diameter D2 of the preformed b!ank 4 is adjoined by a frusto-conical bevel 9 as a transition to the shank 8 of the screw, i.e. to a shank-side diameter D3 of the preformed blank.

The diameter D1 of end face 10 of the preformed blank 4 corresponds to the corner dimension of the finished pressed hexagon of the final shape 5 of the flanged screw and is dimensioned in dependence on the width S across the flats.

For the further pt-ocessing of the preformed blank 4 in the second step of the method, the shaping ram 6 has a shoulder 12 which corresponds to a recess -i 1 in the die 3 and which partially penetrates. into the recess 11 during the pressiny operation. In dependence on the shape of the preformed blank 4, the inner surface of the shaping ram 6 is formed as a transitional cons in the direction of the inner hexagon surface 13. The base diameter D4 of The transitional cone 14 is dimensioned in dependence on the width S across the flats. The angle a of the transitional cone 14 lies substantially in a range from 55 to 80 .

The shaping rams 2. 6 and dies 3, 7 are constructed in accordance with the geometry of the preformed blank 4 and the final shape 5 to be achieved. The dimensions of this geometry are determined in dependence on the screw dimensions. The functional interrelations required for the dimensions of the final shape 5 are expressed in the foilowing relationships: D1, D4=f(s) D1 > S, D4 > S D2=f(DF, S) D2 < DF, D2 > S D32=f(d, D2) D32=d...D2 Hz=f(H, d, a) Hz < H R=f(D1, D2) R > 0,5 s The preformed blank 4 and finally shaped workpiece 5 are ejected by known die-side and ram-side ejectors 15, 16, 17. The geometric configuration of the preformed blank 4 in the form of a hyperboloid of revolution of one sheet, described in the embodiment disclosed, may alternatively be a frustum with small screw head heights.

Similarly, the configuration of the preformed blank and of the shaping tool described for the flanged screw in the exemplary embodiment may also he used for producing a flanged nut.

Claims

1. A preformed blank for a hexagon head screw or a hexagonal nut haviiig a supporting coilar, from which in a subsequent processing stage the final shape of the screw or nut is produced, the head of the screw or the nut having a geometrical shape of a fruetjm or a hyperboloid of revolution of one sheet, which has in the direction of the subsequent bearing surface of the final shape a constant increase in diameter as far as the maxlirium diameter (D2) of said blank, which diameter is adjoined by a frusto-conical bevel until a maximum heiglt ii2) of the blank is reached which is smaller than the final height (H) of he screw head or the nut, the diameter (D1) of the outer end face of the blank corresponding or substantially cerresponding to the corner dimension of the final shape of the hexagon.

2. A preformed blank, substantially as herein described vith- reference to and as shown in Fias.

2 and 3 of the accompanying drawings.

3. A shaping tool For the further processing of the preformed blank claimed in claim 1, comprising a ho@ow shaping rem and a die, the ram having an inner hexagonal surface and an outer annular projection corresponding to a recess in the rlie, characterised in that the inner surface of the projection or the shaping ram is constructed in the direction of the inner hexa 30nel surface, in dependence on the shape of the preformed blank, in the form of a transitional cone, the angle (a) of the transitional cone lying substantially in a range from 55 to 80 .

4. A shaping tool, substantially as herein described with reference to and as shown in Figs.

3 and 4 of the accompanying 1-awings.