GB2057316A - Bending sections - Google Patents

Abstract

The present invention provides a method of bending a bar in a single plane, e.g. to form a ring by successive bends performed along an L-section 22, such that a simple bend in the required plane would bow the section out of that plane, which method comprises, bending the bar in the required plane and in the same linear press motion bowing the bar out of the plane, in order to compensate for the bow that is induced in the bar by bending in that plane. The invention further provides a set of press tools 15, 16 arranged to bend the bar in two dimensions, upon movement of the tools in one dimension. The method is applicable to bending of an asymmetrical section, or to bending a symmetrical section, e.g. rectangular into a conical ring. <IMAGE>

Description

SPECIFICATION Compound bending This invention relates to compound bending and, in particular, to the bending of bars by pressing.

One method of forming rings from rectangular or square bar is to use a pin bending machine in which a male press tool is supported on a pin and a female press tool is supported on the cross head of a press, so that it may be moved towards and away from the male press tool. The metal bar is fed between the male and female press tools and is gradually bent around the pin, to form a ring.

This process can also be used for form rings of other sections and also to form conical rings.

However, difficulties arise when, for example, bend ing a bar of L-shaped cross-section into a right angled cylindrical ring, because as the bar is bent in the plane of the ring, the unbalanced nature of the cross-section of the bar will cause it also to bow out of the plane of the ring. Similar problems arise when forming a conical ring of rectangular or square cross-section.

In the past this problem has been overcome by pre-bowing the bar in the opposite direction so as to compensate for the bow which will be induced when forming the ring. This process is, however, time consuming and it is considerably difficult to assess the degree of pre-bowing required to arrive at a flat ring. The only alternative to this method, however, has been to form a cylindrical ring of square or rectangular section and subsequently machine the ring to the desired cross-section, eg. L-shaped or conical, which is extremely time and material consuming and thus expensive.

The problem described above arises whenever a metal bar is bent about an axis which is non-parallel to a neutral plane of the bar, that is, to a longitudinal plane through the bar about which the cross-section of the bar is balanced and which is perpendicular to a plane in which the bar may be bent using uni-directional forces.

The present invention provides a one-stage process of producing flat rings where a neutral plane of the bar (as hereinbefore defined) is inclined to the axis of curvature of the ring.

According to one aspect of the present invention, a method of bending a bar in a single plane about an axis which is not parallel to a neutral plane of the bar (as hereinbefore defined) comprises feeding the bar between a pair of press tools which are mounted in a press for relative linear reciprocating movement in or parallel to said plane, the opposed surfaces of said press tools being contoured to bend the bar in said plane and in the same press tool movement, to bow the bar out of the plane in which the bar is bent to a sufficient extent to compensate for the bowing that is induced in the bar by the linear movement of the press, so that as the bar is fed between and released from the press tools, it is bent in a single plane, to the required curvature.

As the metal bars that are bent using the present method have elastic properties, allowances must be made in the configuration of the press tools to accommodate a degree of spring back when the press is released. The bending of the bar in a plane substantially perpendicular to the movement of the press, in order to compensate for the induced bow must, therefore, be equal to the degree of induced bow but in the opposite direction, so that when the bar springs back, the resultant bend will be in a single plane. The combination of bending and bowing of the bar will cause it to take up a conical configuration and consequently when forming, for example, a right angled cylindrical ring, it is neces sary to arrange the press tools in a slightly conical arrangement, so that the spring back of the bar will bring the ring back into a right angled cylindrical shape.

Similarly when forming conical rings, the cone angle defined by the press tools must be slightly greater than that required for the final ring.

According to another aspect of the present invention, a set of press tools for use in a pin bending machine to bend a bar in a single plane, about an axis which is not parallel to a neutral plane of the bar (as hereinbefore defined) comprises, a male and female press tool, said male and female press tools having part cylindrical first surfaces corresponding to the inner and outer bends of the bar respectively and part annular second surfaces extending laterally from the first surfaces and corresponding to the annular or part annular surfaces of the bent bar, said second surfaces being curved out of the plane in which the bar is to be bent, from the central portion to the outer-most points of the press tool, this curvature of the second surfaces being equal and opposite to the bow induced in the bar by bending the bar to the first surfaces of the press tools.

The invention is now described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows diagrammatically a pin bending machine, of known design, which is used in accordance with the present invention; Figure 2 shows a plan view of the male and female press tools used to form a right angled cylindrical ring of L-shaped cross-section, in accordance with the present invention; Figure 3a illustrates the profile of the male and female press tools, along the centre line a-a in Figure 2; Figure 3b illustrates the profiles of the male and female press tools, along the line b-b in Figure 2; Figure 4a shows a view similar to Figure 3a, illustrating the profile of the male and female press tools used to form a conical ring of rectangular cross-section, in accordance with the present invention; and Figure 4b shows a view similar to Figure 3b of the male and female press tools illustrated in Figure 4a.

The pin bending machine illustrated in Figure 1 is of conventional design and comprises a table 11, having a pin 12 which is located in a fixed position perpendicular to the table. A cross-head 13 is mounted upon a pneumatic ram 14for movement in the plane of the table 11 towards and away from the pin 12. A male press tool 15 is clamped to the pin 12 and a female press tool 16 is clamped to the cross-head 13, so that the male and female press tools 15 and 16 may be brought together to act on opposed sides of a metal bar 17 which is fed between them.The co-operating contoured surfaces 20 and 21 of the male and female press tools 15 and 16 respectively, are radiused in the plane of the table 11 so that a metal bar 17 may be gradually fed between the male and female press tools 15 and 16, to progressively bend the bar 17 into a ring 18.

Because of the elastic nature of the metal bar 17, the radius of the contoured surfaces of the male and female press tools 15 and 16 must be slightly smaller than the radius required for the ring 18, in order to allow for spring back of the metal bar as it is released from the press tools 15 and 16.

The apparatus described thus far, is perfectly adequate for forming rings of balanced crosssection, that is, for bending bars about an axis which is parallel to the neutral plane (as hereinbefore defined) of the bar. When, however, it is desired to form a ring by bending a bar about an axis which is non-parallel to the neutral plane of the bar, for example, when forming a right angled cylindrical ring from an L-shaped bar, as illustrated in broken line in figure 3a or when forming a conical ring from a rectangular section bar, when the bar is released from the press tools, it will tend not only to spring back to form a larger diameter bend, but will also spring back out of the plane of the table.

Figures 2, 3a and 3b illustrate a male 15 and female press tool 16 which are adapted to produce a flat ring of L-shaped cross-section in which the flange of the L-shaped section extends into the bore of the ring. As illustrated in Figure 2, the contoured surfaces 20 and 21 of the male and female press tools 15 and 16 respectively are radiused in the horizontal plane to a curvature which, allowing for spring back of the metal bar, will provide a ring of the required diameter. In the horizontal plane (as illustrated in Figures 3a and 3b) the contoured surfaces 20 and 21 have pressing surfaces 23, 24, 25 and 26 which when the press tools are brought together, constrain the metal bar 22.As illustrated by Figures 3a and 3b, the contours defining faces 25 and 26 are gradually swept up from the central point of the press tools shown in Figure 3a to the outer regions of the press tools shown in Figure 3b, so that these surfaces differ in height by a distance x between the central point and the outer points of the tools, (this distancex has been exaggerated in the drawings in order to illustrate clearly the principle of the invention). The contoured face 21 of the female press tool 16 is shaped to define a leading lower edge 27 having a pair of lugs 28, positioned on each side of the portion of the female press tool 16 which is engaged by the male press tool 15.This leading edge 27 and the lugs 28 are tapered to form a lead in so that as the male and female press tools 15 and 16 are brought together about the metal bar 22, the flange portion of the bar 22 first engages the face 25 of the male press tool 15 at the central point (line a-a). As the male and female press tools 15 and 16 continue to move together, the lower edge of the bar 22, at the outer portions of the male and female press tools 15 and 16, gradually rides up the tapered lead in surface of the leading edge 27 and lugs 28 of the female press tool 16 and the bar is thus gradually bowed in a substantially vertical plane as it is bent in the horizontal plane, until the press tools 15 and 16 are brought firmly together when the pressed portion of the metal bar conforms to the contours of the male and female press tools 15 and 16 defined by faces 23, 24, 25 and 26, as described hereinbefore. Alternatively lead in formations may be provided on the male press tool or on both press tools.

The compound bending produced by the press tool design of the present invention, causes the metal bar to take up a conical configuration. Consequently, if the faces 23 and 24 of the male and female press tools 15 and 16 were vertical, upon release of the bar 22 from the press tools 15 and 16, spring back of the bar 22 would cause itto take up a conical configuration with the flange portion at the larger diameter end. The faces 23 and 24 of the male and female press tool 15 and 16 are consequently inclined at a small angle H to the vertical so that the metal bar 22 is pressed at a slight conical angle with the flanged portion of the bar at the smaller diameter end, in this way upon spring back of the metal bar 22, it will take up the desired right angled cylindrical ring configuration.The faces 25 and 26 are also inclined at an angle H to the horizontal, so as to conform with the inclination of the metal bar 22 against faces 23 and 24.

By means of the above described press tools 15 and 16, an L-shaped bar 22 may be gradually fed between the press tools and bent into a flat rightangled ring having a flange directed into the bore.

Figures 4a and 4b illustrate the profiles of male and female press tools 30 and 31 for bending a rectangular bar 32 into a flat conical ring. The faces 33,34,35 and 36 which engage the bar 32 when the male and female press tools 30 and 31 are brought together, differ in height by distance x between the central portion defined by line a-a and the outer portions of the press tools defined by line b-b, in the same manner as the press tools described with reference to Figures 3a and 3b. The press tools illustrated in Figures 4a and 4b function in the same manner as those described with reference to Figures 3a and 3b, to bend the rectangular bar 32 in both the horizontal plane and the plane which is substantially in the conical plane of the ring required. Again, in order to allow for closing of the cone angle upon spring back of the bar 32 when the male and female pressed tools 30 and 31 are released, the angle of inclination of the faces 33 and 34 to the vertical and faces 35 and 36 to the horizontal are equal to the desired cone angle 0 plus a small angle H.

Claims (16)

1. A method of bending a bar in a single plane about an axis which is not parallel to a neutral plane of the bar (as hereinbefore defined) comprising; feeding the bar between a pair of press tools which are mounted in a press for relative linear reciprocating movement in or parallel to said plane, the opposed surfaces of said press tools being con toured to bend the bar in the said plane and in the same press tool movement to bow the bar out of the plane in which the bar is bent, to a sufficient extent to compensate for the bowing that is induced in the bar by the linear movement of the press, so that as the bar is fed between and released from the press tools, it is bent in a single plane, to the required curvature.

2. A method according to Claim 1 in which the bar is fed between the press tools, so that its cross-section is inclined at a small angle to the desired configuration taken up by the bar after bending, so that upon spring back of the bar after it is released from the press tools, the bar will take up its desired configuration.

3. A method according to Claim 1 or 2 in which the cavity formed between the press tools defines substantially the cross-section of the bar, the press tools being arranged to abut both the inner and outer cylindrical or part cylindrical surfaces of the bar and also the lateral annular or part annular surfaces of the bar, the surfaces of the press tools abutting the lateral surfaces of the bar being curved, out of the plane in which the bar is to be bent, from the central portion of the press tools to the outermost points of the press tools, so as to bow the bar out of the plane in which the bar is bent.

4. A method according to Claim 3 in which a tapered lead in portion is provided on the surface of one or both press tools which abuts the lateral surface of the bar, this lead in portion serving to bend the bar to the contour of the surfaces of the press tools abutting the lateral surfaces of the bar, upon linear closing of the press tools.

5. A method according to Claim 4 in which the surfaces of the press tools abutting the lateral surfaces of the bar, are arranged to engage the bar initially at the central portion, tapered lead in portions being provided on the outer portions of the press tools which, as the press tools are closed, causes the bar to be bowed to the contour of the lateral surface abutting portion of the press tools.

6. A method according to any one of the preceding claims in which the bar is progressively fed between the press tools to give up to 360 degrees curvature.

7. A set of press tools for use in a pin bending machine to bend a bar, in a single plane, about an axis which is not parallel to a neutral plane of the bar (as hereinbefore defined) comprising a male and female press tool, said male and female press tools having part cylindrical first surfaces corresponding to the inner and outer bends of the bar respectively and part annular second surfaces extending laterally from the first surfaces and corresponding to the annular or part annular surfaces of the bent bar, said second surfaces being curved out of the plane in which the bar is to be bent, from the central portion to the outermost points of the press tools, this curvature of the second surfaces being equal and opposite to the bow induced in the bar by bending the bar to the first surfaces of the press tool.

8. A set of press tools as claimed in Claim 7 in which the first surfaces and second surfaces are inclined slightly to the configuration of the cylindrical or part cylindrical and annular or part annular surfaces required in the final bar, in order to allow for spring back of the bar when it is released from the press tools.

9. A set of press tools as claimed in Claim 7 or 8 in which tapered lead in portions are provided on one or both of the second surfaces, so that linear movement of the press tools in the plane in which the bar is to be bent will cause the bar to be bent out of that plane and to the curvature of the second surfaces.

10. A set of press tools substantially as described herein, with reference to and as shown in, Figures 2, 3a and 3b of the accompanying drawings.

11. A set of press tools substantially as described herein, with reference to and as shown in Figures 4a and 4b of the accompanying drawings.

12. A method of bending a bar substantially as described herein with reference to the accompanying drawings.

13. A bar bent by a method according to any one of Claims 1 to 6 or 12.

14. A bar bent on a set of press tools according to anyone of Claims 7 to 11.

15. A ring formed by bending a bar by a method according to anyone of Claims 1 to 6 or 12.

16. A ring formed by bending a bar on a set of press tools according to anyone of Claims 7 to 11.