GB2147231A - Turning over the edge of a sheet metal disc - Google Patents

Abstract

A sheet metal disc 20 is rotatably supported at its centre, and is supported separately near its edge by supports 23, 24. The edge portion of the disc 20 beyond the supports extends initially between two tapered rollers 29, 30. The rollers move in the axial direction of the disc 20 while the disc rotates about its axis, so that the edge portion is turned and comes to lie between one of the rollers 30 and the separate support 23. If the rollers and the separate supports are radially (of the disc) movable with respect to the centre support 21, 22, the apparatus can provide a range of diameters for the disc 20 after turning over. <IMAGE>

Description

SPECIFICATION Turning the edge of a sheet metal disc.

The invention relates to a method of turning the edge of a sheet metal disc, a method of manufacturing a sheet metal disc with a turned edge together with apparatus for use in these methods and sheet metal discs with turned edges produced by these methods.

The present invention uses a method of turning known as forming. Forming is one of the oldest stress free metal working processes. In the present connection the word forming, in analogy with standard NEN 5454-lV 6, means roughly "the gradual shaping of a rotating blank to a hollowed workpiece usually by pressing the former against a rotating mould". In one known type of forming, the sheet material is shaped on a forming lathe by clamping it between a tool (the pattern) and a second rotating component (the model or chuck), so that it can be rotated against the chuck using various forming tools.

Usually it is desired to avoid thinning of the sheet material during forming and it is thus to be distinguished from flow turning in which it is intended that the wall thickness should be reduced.

In practice there is often a small degree of thinning in forming operations.

According to the publication No. 301 "Forming and flow turning of steel" from the Stichting Staalcentrum Netherlands, unamended, sixth edition, Dec. 1980 p 8 ff., forming is frequently done by hand, so that the final result depends on the skill of the operator. Application of hydraulics has made it possible to form large, heavy workpieces and in p 13 ff of the said publication large hydraulic forming machines for manufacture of rocket and satellite components are discussed. Forming and flow turning machines are also shown in FR 1115880 and DE 1900354.

The present invention arises from the need to fabricate rapidly a lid from a disc, the lid being intended as part of the packaging of coiled tin-plate.

Such coils of steel strip, which have come from an electrolytic tinning process, have a diameter varying from 90 to 180 cm. For shipment they are packed in drip proof packaging. By means of the present invention we propose to make such lids of various different diameters but with the same rim depth, by forming. The invention is therefore intended to provide a method for using forming to make from a disc a lid with an abruptly turned-up rim.

According to the present invention a method of turning the edge of a sheet metal disc by forming is provided in which: a central portion of the disc is supported by a first support surface or a first set of support surfaces, for rotation about the axis of the disc; the disc is supported locally against axial pressure at the location where the turn is to be made by a second support surface or set of support surfaces separate from the first; and the edge portion of the disc beyond the second support surface or set of surfaces is initially located between two tapered rollers which move, during the turning operation, in the axial direction of the disc while the disc rotates about its axis; thus the edge portion is turned into a rim.

The invention is also intended to provide a machine or bench upon which this process can be carried out.

Thus the invention provides apparatus having means, which include the said first support surface or set of support surfaces, to hold the central portion of the disc, a rotatable element which includes the or one of the said second support surfaces, the said two rollers, means to rotate the disc about its axis and means to move the rollers in the axial direction of the disc while it rotates so as to turn the edge of the disc about the said element.

The roller which leads during the said axially directed movement is called the support roller, and the roller which follows, and which presses against the edge portion of the disc during the turning operation, is called the forming roller. Preferably the forming roller is motor driven. The said rotatable element is on the same side of the disc as the support roller, so that it resists the pressure of the forming roller on the disc.

In order to make lids for coils of various diameters it is preferred that the rotatable element and the tapered rollers are movable radially of the disc with respect to the holding means for the central portion of the disc. Thus the apparatus may have a horizontal machine bed on which a carriage is mounted, the carriage bearing the said rotatable member and the said rollers.

The gap between the rollers, in which gap the edge of the disc fits initially, is preferably a little wider near the circumference of the disc than at the location of the turn, and is a little larger than the original thickness of the sheet even at its narrowest. This allows a temporary fold along the edge of the disc to be formed to some extent during the turning operation.

The gap between the rotatable element and the rollers, however, is preferably somewhat smaller than the original thickness of the plate, which implies a slight degree of flow turning in the final shaping, although the turning is essentially a forming operation.

Preferably the rotatable element is freely rotata ble and not motor driven. Preferably its axis of rotation makes a slight angle with the axis of the disc, so that it makes essentially only point contact with the disc. This point of contact should be immediately adjacent the rollers. In this case the element should also be tapered.

The invention also concerns the final product, that is a disc with a turned-up rim obtained from a disc using the above described method or employing the above-described apparatus.

Embodiments of the present invention, given by way of example, will now be described with reference to the accompanying drawings in which: Figure 1 shows in schematic section a coil of tinplate positioned on a board and provided with packaging comprising a base, a jacket and a lid with a turned rim; Figures 2, 2A and 2B illustrate a method of turning embodying the present invention; Figure 3 is a side-view, partially in section, of apparatus embodying the invention; Figure 4 is a partial plan view of the apparatus of Figure 3.

Figure 1 shows a coiled strip of tin plate 1 with a core hole 2 which here is vertical. It is packaged with a base or lower cover 3, a jacket 4 and a cap or upper cover lid 5, and these so surround and seal off the coil 1 that together with a water-proof paper wrapping (not shown), a drip proof package is obtained. The coil thus packaged is standing on a pallet or board 6 (shown schematically) and is generally fastened to this with packing tape or sim liar.

The present invention grew from a desire to manufacture both the lower lid 2 and the upper lid 3 from disc shaped sheets of metal by turning the edge of the disc to make a rim at right-angles to the disc plane by forming.

Figure 2 shows part of such a disc 20 still in flat form, with its axis indicated by the dot-dash line aa. This disc 20 is clamped centrally between a mandrel 21 and a head-piece 22, which provide a first set of support surfaces. The head-piece 22 may be self centering. The clamping force is provided by means, e.g. a bellows mechanism, which is not shown. The direction of clamping pressure is given by the arrows d,d. The mandrel 21 can be rotated slowly in the direction indicated by the arrow r using a variable speed d.c. motor. The revolution rate is varied depending on the disc diameter such that the peripheral speed of the disc remains constant.

Near to its circumference the disc 20 is supported axially by a freely rotating but otherwise fixed rotatable element 23 and an opposing and also freely rotating element 24. These provide a second set of support surfaces. The axis 25 of the element 23 in this design sketch forms a small angle of perhaps 10 with the axis a-a about which the disc 20 rotates, but this angle is too small to be shown in the drawing. The angle allows free running during the forming operation. The face 26 of the element 23 may be hollowed so that, together with the oblique orientation of the axis 25, it ensures that only one point 27 (Figure 2B) on its circumference makes contact with the sheet 20.

The forming tool takes the form of two tapered rollers 29, 30 which are rotatably mounted on a carriage 28 which can move parallel to the axis of rotation a-a using a slow driving mechanism (see arrow s). The axis of rotation 31 of support roller 29 forms an angle of about 220 with the surface of the sheet 20 and the axis of rotation 32 of forming roller 30 forms an angle of about 17 with the surface of the sheet. The gap between support roller 29 and forming roller 30 is not of the same width everywhere but is wider on the outside (away from the centre of the disc). The gap is wide enough at its narrowest point to permit passage of the sheet.

In this embodiment both rollers have a double taper. The generator 33 of one 34 of the taper surfaces of support roller 29 forms an angle of about 100 with the surface of the plate 20. The generator 35 of the opposed taper surface 36 of the forming roller 30 forms an angle of 0 with the surface of the sheet. The generator 37 of the other taper surface 38 of the support roller 29 is parallel to the axis a-a. The rotatable element 23, because of the obliqueness of its axis 25, has a slightly tapered surface 39 for which the generator 40 (opposite line 37) is also parallel to the rotation axis a-a, so that between lines 37 and 40 there is a parallelsided gap. The difference in surface speeds of different parts of the rotatable element, caused by the taper and angled axis, is so small that it can be ignored.

The forming roller 30 is driven by a synchronous motor so that it has a constant peripheral speed which is the same as the above-mentioned peripheral speed of the sheet 20 at the point 27 where it contacts the rotatable element 23; the support roller 29, on the other hand, is arranged to rotate freely.

When the sheet 20 rotates and the carriage 28 moves slowly in the direction s as indicated, the rim of the sheet 20 is gradually deformed as shown schematically by the successive broken lines in Figure 2A. The advance of the carriage 28 is deliberately kept slow so that the material of sheet 20 is not deformed too quickly and cracking and embrittlement are avoided. We have determined by experiment that a carriage advance of 4mm per revolution of the sheet 20 is usually suitable.

The tapered rollers 29,30 also act as blank holders and as smoothing rollers for smoothing out folds which may occur during the turning process before the material involved is actually subjected to forming.

Figure 2B, which reproduces the area encircled in Figure 2 on a larger scale, shows the sheet 20 (in section) at the end of the turning operation. The circumferential edge of the disc has been turned up practically at right angles at the point 27 of the freely rotating element 23. The edge of the disc was originally in the gap between the two tapered rollers 29, 30. This gap has a minimum width b which is somewhat larger than the original thickness d of the sheet 20. During the forming operation the edge portion is gradually moved to lie between the forming roller 30 and the rotatable element 23. The width c of the gap between the two tapered rollers 29, 30 on the one hand and the rotatable element 23 on the other is here somewhat less than the original thickness d of the sheet 20, so that here there will be a certain degree of flow turning.

Figures 3 and 4 show a practical forming machine which embodies the present invention. This machine is intended for the manufacture of packaging lids for coils of rolled steel. The machine concerned here also has a facility for cutting a rectangular steel plate of 0.6-2.0mm thickness and 1800mm maximum side into a circular disc of 1800mm max. diam. prior to turning the circumferential edge portion of the disc into a rim.

Another facility offered by this machine is the forming of a central collar with a maximum depth of 65mm surrounding a hole pierced in the sheet at an earlier stage (for the core hole of the coil).

The machine stands on a work floor 50 and a base frame 51, which has a horizontal bed 52. As will appear from the plan view (Fig. 4), the base frame 51 is octagonal with two wings 53 and two posts 54 on the extremities of each of these. On the upper ends of these four posts 54 is mounted a bridge piece 55. A pressure plate 56 hangs from the bridge piece 55 and is freely rotatable around a spindle 57. By means of a cylinder 58 the plate 56 can be pressed against and raised from a lower ring 59.

A sheet to be worked is introduced horizontally and is clamped between the lower ring 59 and the plate 56 which provide a first set of support surfaces for the sheet. The lower ring 59 is mounted on the machine bed 52 and is driven via a drive sprocket from the main drive (not shown) which is mounted in the base from 51 and has a variable speed d.c. motor the rotational speed of which is so adjusted that the peripheral speed of the clamped rotating disc is always the same.

There is an opening 61 in the bed 52 below the lower ring 59. The drive and mechanism for forming a collar with depth 65mm in a disc with central hole, if this should be required, are fitted in the frame 51 below this opening 61. These components are not shown in the drawing since this process is not connected with turning the edge of the disc, but it will be clear that in order to carry out the collar-forming process the pressure plate 56, the lower ring 59 and the drive sprocket 60 are hollow and provide space for the necessary components and the collar.

A sheet or plate introduced into the machine is laid horizontally on the lower ring 59 above the bed 52 and is clamped by actuation of the cylinder 58. Before this is done, however, the disc has to be centered with respect to the vertical axis 62, and in the case of the non-round sheet, e.g. a square or rectangular sheet, a circular disc must first be cut from it.

This cutting is done using a shearing unit 63 (Fig. 3). This unit includes a carriage 64 which can be moved horizontally over the machine bed 52 to and from the vertical rotation axis 62 by means of a cylinder 65. A clamping cylinder 66 is mounted on the carriage 64 so that the carriage 64 can be held fast on the bed 52. The carriage 64 also has a cylinder 67 in order to bring a rotary cutter 68 driven by a motor 69 up to an under cutter 70 which is rotatably mounted on the carriage 64 and driven by a motor 71.

During cutting the sheet is held clamped between the plate 56 and the ring 59. The diameter of the disc to be cut may be from between 900 to 1800mm, this dimension being varied by adjustment of the carriage 64 using the cylinder 65. During the cutting of the disc it is centered on the axis 62.

A disc which has already been cut elsewhere is centered with respect to the rotation axis 62 by means of a centering mechanism which will now be discussed. The frame 51 is provided at the top with four booms 72 projecting radially from the axis 62 and each at an angle of 90 to the next. For the sake of simplicity and clarity only two of these booms are shown.

A number of freely rotating sprockets 73 are mounted on the booms 72 and the frame 51 in the manner shown, with an endless chain 74 running over them, so that the segments of the chain 74 which lie under the booms 72 are radial to the axis 62. A centering cam 75, which can slide along the boom 72, is fitted to each of these radial segments of the chain 74. These can push against the rim of the disc which has been inserted but not yet centered and shift this disc, as the chain 74 moves, towards the unique position concentric with the axis 62. This is done using a coupling chain loop 76 which is actuated by a cylinder 77 with a double piston rod which cylinder 77 is attached to the carriage 64 of the shearing unit 63. This carriage 64 carries two cylinders 77 (Fig. 4) which are naturally operated simultaneously.After centering, the disc is first clamped between the plate 56 and ring 59 and the cylinders 77 put into reverse, after which the forming operation can begin. This centering arrangement is described in more detail in European Patent 0053417.

During the actual forming use is made of the components as already described in connection with Figure 2. These are shown situated to the left of the central axis of rotation 62 in the forming machine shown in Figures 3 and 4.

The support roller 80, forming roller 81 and drive motor 82 are mounted on a carriage 78 which can be moved horizontally above the machine bed 52 by means of a cylinder 79. The carriage 78 is pulled back to its furthest position by the cylinder 79 while cutting or centering of the disc is in progress. By actuating the cylinder 79 in reverse the carriage 78 is brought to the required position. The edge portion of the clamped disc, which portion is to be turned, is thus inserted into the gap between the support roller 80 and the forming roller 81. The assembly of support roller 80, forming roller 81 and the motor 82 is movable vertically on the carriage 78 by means of a vertical worm drive 83 which is driven by an electric motor 84.

On the carriage 78 there is also a clamping cylinder 85 which serves to hold the carriage 78 fast on the machine bed 52 during the turning operation.

Finally the carriage 78 carries the rotatable element 86. This element is mounted so as to rotate freely around an axis 90 which makes an angle of 300 with the axis 62. The element is thus markedly tapered. The element 86 can be raised or lowered on the carriage 78 using a cylinder 87. The rotatable element 86 contacts the disc at the location where the turn is to be made, providing a second support surface for the disc.

The support roller 80 has only a single taper, in contrast to the support roller 29 of Figure 2. Thus it provides a good rolling contact with the unturned edge portion between it and the forming roller 81.

Since the face of the support roller 80 opposed to the rotatable element 86 does not contact the disc, its motion is not important. The forming roller 81 is double tapered, but the tapers are unequal to that it has a good rolling contact with the turned edge portion between it and the element 86, while it has more of a sliding contact with the unturned edge portion between it and the support roller 80.

The rotatable element 86 also makes a good rolling contact with the turned edge portion. As described above, it makes essentially only point contact with the horizontal disc surface.

During forming the support roller 80 and forming roller 81 are moved slowly upward by the motor 84. The material constituting the edge portion of the clamped slowly rotating disc (not shown) and lying in the gap between the rollers is both drawn and upset and the advance rate-independent of the disc diameter-is chosen to be 4mm per complete revolution.

The material, steel sheet with thickness about 1.0mum, has a natural tendency to fold during this operation, and this is also permitted to some extent by the conically widening gap between the forming roller 81 and the support roller 80, which thus act as a blank holder.

As it gradually leaves this gap (with a minimum width b of e.g. 1.2mm) the edge portion of the sheet is flattened again between the rollers 80, 81 by a rolling action at the point of narrowest passage, so that the folds are upset again. The sheet hence becomes locally somewhat thicker.

The distance between the two tapered rollers, i.e.

forming roller 81 and support roller 80, is firm and unchanged during the forming. Adjustment will however be required for a different thickness of sheet.

In addition the width of the gap between the forming roller 81 and the support roller 80 on the one hand and the rotatable element 86 on the other is firm and unchanged during the forming.

The width of this gap must be adjusted when changing to a new sheet thickness as well as to compensate for wear.

In the example given of a sheet thickness d of 1.0mum this gap width (c in Figure 2B) will be 0.8mm, for instance, which implies a certain measure of flow turning. This also means that the depth of the turned up rim of the finished product is somewhat greater than the distance from the point of contact of the rotatable element to the circumference of the sheet in its flat condition. In practice this difference may be 1.5 to 2 cm. For a thicker sheet this rim stretching is naturally greater than with a thin sheet.

It will be seen that in the practical embodiment of the forming maching as shown in Figures 3 and 4 there is no roller (such as roller 24 in Figure 2) opposite to and pressed against the rotatable element 86. This is replaced by a holder 88 fixed to the carriage 78 and holding a rectangular block of wood 89 which can easily be replaced after wear.

In contradistinction to the classical forming process on a rotating jig or chuck, forming with the illustrated apparatus involves: 1) forming against an eccentrically positioned and freely co-rotating element and involving only a small sector of its perimeter (almost a line contact); and also 2) a single continuous movement.

As a result of the conical shape of the rotatable element 86, the contact area between the turned rim of the disc and the surface of the element 86 may have a large radius of curvature, so that the perimeter of the final product is modelled.

After the rim has been formed (having a depth between 0 and 150mm) the disc is brought to a stop. When the rotatable element 86 has been lifted and the carriage 78 with its associated components moved outwards, the clamping on the disc is released and the pressure plate 56 raised sufficiently for the hat-shaped lid to be removed sideways.

A machine as illustrated may be able to form 1 disc per minute, with some extra time requirement for cutting, centering and re-clamping, which gives it a high production capacity.

Claims (14)

1. A method of turning the edge of a sheet metal disc by forming, in which; a central portion of the disc is supported by a first support surface or a first set of support surfaces, for rotation about the axis of the disc; the disc is supported locally against axial pressure at the location where the turn is to be made, by a second support surface or set of support surfaces separate from the first; and the edge portion of the disc beyond the second support surface or set of surfaces is initially located between two tapered rollers which move, during the turning operation, in the axial direction of the disc while the disc rotates about its axis, thus turning the edge portion of the disc into a rim, the said second support surface, or one of the said second set of support surfaces, being on the side of the disc which faces in the said direction of movement of the tapered rollers.

2. A method according to claim 2 in which the said second support surface toward the direction of movement ccontacts the disc substantially at a point, the point being adjacent the said two rollers.

3. Apparatus for carrying out the method of claim 1 or claim 2, the apparatus having: means, which include the said first support surface or set of support surfaces, to hold the central portion of the disc; a rotatable element which includes the or one of the said second support surfaces and is located on the side of the disc which faces in the said direction of movement of the tapered rollers; the two said tapered rollers; means to rotate the disc about its axis; and means to move the rollers in the axial direction of the disc while it rotates so as to turn an edge portion of the disc, initially located between the said rollers, about the said rotatable element.

4. Apparatus according claim 3 for carrying out the method of claim 2 in which the axis of rotation of the said rotatable element is not parallel to, but lies in substantially the same plane as, the axis of a disc the edge portion of which is being turned.

5. Apparatus according to claim 3 or claim 4 in which the rearward (in the said direction of axial movement) said roller (the forming roller) is double tapered, the edge portion of a disc initially lying between the other said roller (the support roller) and a first taper surface of the forming roller before the turning operation, and finally lying between the said rotatable element and a second taper surface of the forming roller after the turning operation.

6. Apparatus according to any one of claims 3 to 5 having drive means to rotate the rearward (in the said direction of axial movement) said roller.

7. Apparatus according to claim 6 having a horizontal machine bed and a carriage movable with respect to the machine bed, the carriage carrying the rotatable element, the tapered rollers, and the said drive means for the rearward roller.

8. Apparatus according to any one of claims 3 to 7 in which the said rotatable element is not driven.

9. Apparatus according to any one of claims 3 to 8 in which the said rotatable element is tapered.

10. A method according to claim 1 or claim 2 in which the gap between the tapered rollers, into which the edge portion of the disc fits initially, is widened towards the circumference of the disc, and is wider than the thickness of the disc even at the location where the turn is to be made.

11. A method according to any one of claims 1, 2, and 10 in which the gap between the rotatable element and the tapered rollers is less than the original thickness of the disc, so that the turning operation involves a degree of flow turning.

12. A method of turning the edge portion of a disc of sheet metal substantially as herein described with reference to and as illustrated in Figs.

1,2,2A and 2B of the accompanying drawings.

13. Apparatus for turning the edge portion of a disc of sheet metal substantially as herein described with reference to and as illustrated in Figs.

3 and 4 of the accompanying drawings.

14. A disc having a turned edge portion turned by a method according to any one of claims 1,2,10,11 and 12 or by means of apparatus according to any one of claims 3 to 9 and 13.