GB2278795A

GB2278795A - Apparatus and method for working materials

Info

Publication number: GB2278795A
Application number: GB9312175A
Authority: GB
Inventors: Douglas Roger Hawkey
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-06-12
Filing date: 1993-06-12
Publication date: 1994-12-14
Anticipated expiration: 2013-06-12
Also published as: GB2278795B; GB9312175D0

Abstract

A die for bending sheet metal (19) in combination with a punch (15) has a base (10) containing a pair of elongate rotary sheet support members (12a, 12b) formed as segmental portions of parallel cylinders rotatable about respective longitudinal axes. Each support member lies in a corresponding groove (13a, 13b) in the base. The two grooves are corresponding portions of intersecting parallel cylinders. The cylindrical segments are laterally truncated along a plane of symmetry (14) such that each support member is a mirror image of the other. <IMAGE>

Description

APPARATUS AND METHOD FOR WORKING MATERIALS This invention relates to apparatus and a method for forming materials, particularly but not exclusively for bending sheet metal and the like1 especially in press brake machines.

In order to make a.900 bend in sheet metal on a press brake, a conventional method is to mount a vee die on a die holder, to place the sheet metal over the die, and to make the bend by advancing a punch into the vee die from the other side of the sheet. The punch will have a 90" tip, and the vee die will have an internal angle of 900; or both angles may possibly be slightly less, say 880. The width of the vee will be selected in accordance with the gauge of the sheet metal. For a sheet thickness between 0.5mm and 2.5mm, a die width of 6 times the gauge is normally used; for greater sheet thicknesses, a die width of 8, 10 or even 12 time the gauge may be appropriate.

Many variations of die and punch shape are possible, enabling rounded bends or bends to different angles to be made.

One disadvantage of conventional dies is that they tend to produce bend lines which are formed by the top edges of the vee die digging into the sheet as a fold is made. These bend lines can be reduced but not entirely eliminated by forming a small radius on the top edges of the die. This however has the unwanted effect of increasing the minimum size of flange that can be folded on a particular tool.

An alternative way to control bend lines is to interpose a thin sheet of protective material, such as polyurethane film, between the sheet metal and the die. This film can be separate from or coated on the sheet. In either case, its use adds to the cost of the operation, and if coated on the underside of the sheet it can interfere with other operations such as hole punching in the sheet.

If the formation of bend lines is not prevented during the bending operation, the lines can be removed subsequently by polishing or burnishing the sheet after folding.

Having regard to the relationship between the gauge of the sheet material and the size of the opening of the vee die, it is not always possible to fold a very small flange in one edge of a sheet.

In such case, a larger flange than is necessary is first formed, and the excess material is subsequently cut off. This is obviously undesirable insofar as it requires two operations instead of one and is wasteful of material.

Further, if the sheet material includes holes, notches or other openings close to the intended bend line, these can be dragged or deformed during bending.

It is an object of the invention to provide improved apparatus and methods for working sheet materials and the like, with particular reference to the foregoing problems.

In its broadest aspect, the scope of the invention extends to all novel aspects of the die, tool and method set out below, whether individually or in combination with other features as described herein.

In a particular aspect, the invention provides a die for working sheet metal or the like comprising a side by side pair of elongate rotary sheet support members, each said member being rotatable about a respective longitudinal axis parallel to that of the other.

In a further aspect, the invention provides a forming tool for sheet metal or the like comprising a die as aforesaid, an elongate punch disposed over the adjacent sides of the elongate rotary sheet support members, and means for advancing the punch towards and between the said rotary members.

In a still further aspect, the invention provides a method of working sheet metal or the like comprising supporting a sheet on the pair of rotary sheet support members of a die as aforesaid, punching the sheet along a line between the two rotary members, and allowing the said members to rotate whereby the sheet remains supported in face to face contact with the support members on either side of the said line while the punch forms a fold in the sheet.

For many applications, it will be desirable that the sheet support members have coplanar sheet support faces before they are rotated during use. In a preferred embodiment, the sheet support faces are coplanar in an equilibrium position of the die. The rotary sheet support members may be adapted to return to their equilibrium coplanar position under the influence of gravity after being disturbed therefrom. Alternatively, the die may comprise resilient biasing means adapted to return the faces to the same plane after being disturbed therefrom.

In a preferred embodiment, each of the rotary members comprises a segmental portion of a cylinder. The chordal plane of the segmental portion may suitably form the sheet support surface of the rotary member. The rotary support member suitably rotates about the central longitudinal axis of the cylinder, that is to say about the centre of curvature of the segmental portion of the cylinder. If the chord is a diameter, the centre of curvature of the cylinder lies on the support surface. Alternatively, the centre of curvature of the cylinder may be below the support surface, or it may be above the support surface, in which case it lies outside the segmental portion forming the rotary support member.

Each rotary support member is desirably a laterally truncated segment of a cylinder, and the two members desirably abut one another at their respective truncated faces. The members are suitably mirror images of one another, so that they are equally truncated along a plane of symmetry. The punch may advance in this plane towards the supported sheet, to fold it.

In a particularly preferred aspect of the invention, the cylindrical segments lie in corresponding parallel grooves in a base member. The members rotate slidingly in the respective grooves. At least one of the respective sliding surfaces of a member and its groove may have a low friction coating, for example of polytetrafluoroethylene, or a sleeve of bearing material, such as phosphor bronze, may be interposed between the cylindrical segment and the cylindrical groove.

One embodiment of the invention will now be described by way of example in the accompanying diagrammatic drawings, in which: Figure 1 is an end elevation of a conventional vee die and punch being used to bend a sheet of metal; Figure 2 is a perspective view of a die in accordance with the invention; Figure 3 is an exploded view of the die of Figure 2; Figures 4a and 4b are end views of a rotary support member marked with certain dimensions; Figure 5 is an end elevation of a forming tool in accordance with the invention, just prior to bending a sheet of metal; Figure 6 corresponds to Figure 5 but shows a later stage of the bending operation; and Figure 7 is a perspective view showing the same forming tool and sheet near the end of the bending operation.

Figure 1 shows a die 1 with a vee groove 2. A sheet of metal 3, which was originally flat on the upper surface 4 of the die, is being bent by a punch 5 advancing into the groove 2. The shoulders 6 at the top edges of the groove 2 form bend lines in the sheet being folded.

Figures 2 and 3 show that a die in accordance with the present invention has a base 10 containing a pair of elongate rotary sheet support members 12a, 12b, each formed as a segmental portion of a cylinder and being rotatable about a respective longitudinal axis which corresponds to the centre line of each respective cylinder, the two cylinders being parallel. Each support member lies in a corresponding groove 13a, 13b in the base. The two grooves are corresponding portions of intersecting parallel cylinders. The cylindrical segments 12a, 12b are laterally truncated along a plane of symmetry 14, such that each support member is a mirror image of the other.

As can be seen in Figure 2, the two support members 12a, 12b have respective flat support surfaces 15a, 15b which are coplanar with the remaining upper face 16 of block 10, thus forming an entirely flat support for a sheet of metal to be subsequently folded along its line of intersection with the plane 14.

Figure 4a shows rotary support member 12a having a centre of curvature C in the plane of the top support surface 15a and inset by a distance x from plane 14. Portion A to the left of the centre C is larger than portion B to the right, so the centre of gravity of the member is within portion A and, if free to move, the member will tend to rotate anticlockwise as seen. In this way the two members 12a and 12b will be urged together by their weights to the position shown in Figure 2.

Dimension x corresponds to half the width of a vee die and is selected according to the gauge or thickness of the sheet material to be folded. The effective width of the die is substantially constant in use.

Figure 4b shows a modified rotary support member 12c in which support surface 15c lies above the centre of curvature C' by a distance y. A relieved edge of radius r is provided above the centre C' at 14c to permit rotation of the member clockwise when it is one of a matching abutting pair, the other rotating anticlockwise. Figure 4b also indicates a possible location of the support surface at a distance z below the centre C'. In either of these cases, the effective width of the die varies progressively during the bending operation, becoming respectively smaller (y) or larger (z). This may suit particular forming requirements.

The radius of curvature R of the cylindrical surface of 12c is desirably between 3 and 4 times the dimension x, suitably 32 times.

Figures 5 to 7 show the tool in use to bend a metal sheet 19.

Punch 5 is advanced along plane 14 towards the sheet supported on the upper flat surfaces of members 12a, 12b (Figure 5). After the punch has met the sheet, the pressure of its further advance causes the rotary support members to turn in their respective grooves while keeping their respective faces fully in contact with the workpiece 19, supporting it and spreading the reaction to the force of the punch over a wide area, so as to minimise the risk of marking the sheet. Any holes or notches in the sheet in the region of the bend are also supported, helping to avoid the local distortions which might otherwise result. Perforated or mesh sheets can be successfully folded.

Small flanges can also be reliably formed near sheet edges, equal to half the width of the corresponding vee die, because the illustrated die gives greater support to the sheet edge than does a vee die of corresponding width. Further, smaller vee sizes can be used than with conventional tooling.

The tool can be made in sections, the die for example as shown in Figure 2, so that longer lengths can be made up by placing a plurality of sections end to end. Matching studs and sockets can be provided in opposite ends of the bases to ensure alignment.

Waisted studs can also be provided so that, with corresponding studs in the ends of the rotary supports, elastic tensioners can be carried thereon to bias the supports to their closed positions.

The dies can be made of similar materials to those used for conventional vee dies, namely hardened tempered tool steel. The radiused surfaces of the base may he given a low friction coating, or a bearing sleeve may be interposed.

Claims

ClAIMS

1 A die for working sheet metal or the like comprising a side by side pair of elongate rotary sheet support members, each said member being rotatable about a respective longitudinal axis parallel to that of the other.

2 A die according to claim 1 in which the sheet support members have flat sheet support faces that are coplanar in an equilibrium position of the die, and the rotary sheet support members are adapted to return to their equilibrium coplanar position after being disturbed therefrom.

3 A die according to claim 2 wherein the rotary sheet support members are adapted to return to their equilibrium coplanar position under the influence of gravity, or by resilient biasing means adapted to return the faces to the same plane after being disturbed therefrom.

4 A die according to claim 2 or 3 in which each of the rotary members comprises a segmental portion of a cylinder, a chordal plane of such segmental portion forms the sheet support surface of the rotary member, and the rotary support member rotates about the centre of curvature of the segmental portion of the cylinder.

5 A die according to claim 4 in which each rotary support member is a laterally truncated segment of a cylinder, and the two members abut one another at their respective truncated faces.

6 A die according to claim 5 in which the members are mirror images of one another, being equally truncated at a plane of symmetry.

7 A die according to claim 5 or 6 in which the chordal plane contains a diameter of the cylinder and the centre of curvature of the cylinder lies on the support surface.

8 A die according to claim 5 or 6 in which the centre of curvature of the cylinder lies below the support surface.

9 A die according to claim 8 in which relieved edges are provided to the respective abutting truncated faces of the support members above the centre of curvature.

10 A die according to claim 5 or 6 in which the centre of curvature of the cylinder lies above the support surface, and outside the segmental portion forming the rotary support member.

Ii. A die according to any one of claims 5 to 10 in which the radius of curvature of the cylindrical surface of a support member is between 3 and 4 times the distance of the centre of curvature from the plane at which the truncated faces of the two support members abut.

12 A die according to any one of claims 5 to 11 in which the cylindrical segments lie in corresponding parallel grooves in a base member and are slidingly rotatable in the respective grooves.

13 A die according to claim 12 in which at least one of the respective sliding surfaces of a base member and its groove has a low friction coating.

14 A die according to claim 12 in which a sleeve of bearing material is interposed between the cylindrical segment and the cylindrical groove.

15 A die according to any one of claims 12 to 14 in which the two support members have respective flat sheet support surfaces which are coplanar with an upper face of the base member whereby to form a flat support for a sheet of metal to be folded.

16 A die according to any one of the preceding claims substantially as herein described with reference to and as illustrated in Figures 2 to 7 of the accompanying drawings.

17 A forming tool for sheet metal or the like comprising a die as claimed in any one of the preceding claims, an elongate punch disposed over the adjacent sides of the elongate rotary sheet support members, and means for advancing the punch towards and between the said rotary members.

18 A forming tool according to claim 17 wherein the die comprises a plurality of side by side pairs of elongate rotary sheet support members placed end to end.

19 A forming tool according to claim 18 wherein the sheet support members of the die lie in respectibe base members in accordance with claim 12, and matching studs and sockets are provided in opposite ends of the base members to ensure alignment thereof.

20 A forming tool according to any one of claims 17 to 19 substantially as herein described with reference to and as illustrated in Figures 2 to 7 of the accompanying drawings.

21 A method of working sheet metal or the like comprising supporting a sheet on the pair of rotary sheet support members of a die according to any one of claims 1 te 16, punching the sheet along a line between the two rotary members, and allowing the said members to rotate whereby the sheet remains supported in face to face contact with the support members on either side of the said line while the punch forms a fold in the sheet.

22 A method of folding perforated or mesh metal sheets in accordance with claim 21.

23 A method of folding a sheet in accordance with claim 21 or 22, comprising forming a flange at the sheet edge in a die according to claim 5, and the flange width is equal to the distance of the centre of curvature from the plane at which the truncated faces of the two support members abut.

24 A method of folding perforated or mesh metal sheets according to any one of claims 21 to 23 substantially as herein described with reference to and as illustrated in Figures 2 to 7 of the accompanying drawings.