GB2181082A - Production of metal cans - Google Patents

Abstract

In a die-ring assembly (10) for carrying out a drawing and wall ironing process, a coolant fluid is directed under pressure towards a metal can (14, 16, 24, 26, 28) as it passes through each work- performing die-ring (12, 18, 20, 22), said coolant fluid being directed at said metal can from a position (30A) disposed downstream of said die-ring or a position (30B) disposed upstream of said die-ring, or from both such positions, and said coolant fluid being directed in such manner as to create a vortex of coolant fluid swirling around the metal can. Downstream of each die-ring is a guide ring (12G, 18G, 20G, 22G) having a small radial clearance over the workpiece arriving from that die-ring. Downstream of each die-ring and before the next die-ring is a can punch damping ring (12P, 18P, 20P). Coolant fluid flowing over the can through said damping rings exerts hydrodynamic damping forces which tend to damp and restrain the can and punch (36) against transverse vibration. <IMAGE>

Description

SPECIFICATION Production of metal cans The invention relates to the production of thin-walled metal cans by the so-called draw ing and wall ironing process. That process will be referred to hereafter, for the sake of sim plicity, as the "DWl Process".

In a first stage of that process a flat circular blank is drawn to form a shallow cup, and thereafter the cup, mounted on the free end of a close-fitting ram or punch, is subjected to a second, "wall-ironing" stage, by being pushed through one or more annular "wallironing" dies for the purpose of effecting by means of each such die an elongation of the wall of the cup.

Such elongation is produced by virtue of a very high, radial compression that is gradually built up in each successive transverse section of the said wall as that wall is pulled progressively through the throat of the annular die.

The shaping of the longitudinal radial section of the throat of the die is such as to cause such gradually increasing compression to be exerted.

British patent specification 1345227 and US patent specification 4109502 and 4173882 relate to this DWl process and disclose apparatus for carrying out this process.

In carrying out the DWI process, a large proportion of the input energy is converted into heat energy, with the consequence that the temperatures of the dies and the ram or punch would rise to a very high value if no adequate cooling means is provided. Hence, it has been normal practice, as evidenced by the disclosures of the said prior patent specifications, to supply to the entry sides of the dies a liquid coolant, which coolant has also operated as a lubricant for the opposing, working surfaces of the dies and the longitudinal wall of the metal cup and a means for flushing away debris formed during the process.

The most common form of tool operating this process is the so-called rigid type, in which type the ironing die-rings together with other rings (for example drawing and guiding rings) associated with them have been rigidly mounted as an assembly on a machine bed, for operation with a horizontally-disposed, cantilever-mounted punch, which has been arranged for movement in a horizontal direction along the machine bed to and from the rigid die-ring assembly.

It has been found that satisfactory operation of the DWI process can be upset or prevented by deflections of the cantilevered punch caused by uneven distribution of temperature around the ram surface. These rises have been found to occur non-uniformly in the transverse cross-section of the punch, with the consequence that the punch does not merely increase in overall horizontal length, but also deflects from its desired true alignment with the longitudinal axis of the die assembly.

According to the present invention in a diering assembly for performing the DWI process, there are provided at the exit side, and preferably also at the entry side, of the or each work-performing die-ring coolant flow passages for directing, when in operation, coolant fluid under pressure at a workpiece at the position or positions at which the said workpiece emerges from or enters the said die-ring.

By this means the workpiece and punch are more effectively cooled, so that undue and uneven temperature rises in the punch are avoided.

Preferably, each said coolant passage is arranged to direct said coolant fluid in a direction having a substantial transverse component as well as a longitudinal or axial component; in a preferred arrangement said coolant passages have a transverse component that is substantially greater than the said longitudinal component; and advantageously, said coolant passages are arranged to direct coolant tangentially relative to the outer surface of the workpiece, whereby, when in operation, to create a vortex of coolant fluid swirling around each of the exit and entry sides of each such die-ring.

According to another preferred feature of the present invention said work-performing die-rings are spaced apart so as to ensure engagement of only one such die-ring at a time with the workpiece, and between one die-ring and the next there is provided a workpiece/punch damping ring or sleeve arranged to have a bore of diameter such as to just clear the outer surface of a workpiece passing therethrough from the preceding work-performing die-ring, but such as to provided by virtue of the presence and flow of said coolant fluid a damping (and in appropriate cases a centring) action on said workpiece punch.

Such a said centring action would arise from hydrodynamic forces acting radially between opposing surfaces on said damping ring and said workpiece and punch.

Preferably, the assembly has no coolant exits other than that provided by the central bore of the assembly. This ensures a maximum flow of coolant fluid through the fine passageways between the workpiece and punch on the one hand and the damping ring on the other hand. An improved coolant flow may be obtained if the diameter of the punch is reduced upstream of the workpiece-carrying head thereof.

Said coolant flow passages for directing coolant fluid at the entry side of a work-performing die-ring may be formed in a said punch damping ring laying immediately upstream of said die-ring.

According to another preferred feature of the present invention there is provided imme diately downstream of each said work-performing die-ring a guide ring, which is preferably generally similar to its preceding work-performing die-ring, and which has a throat-diameter slightly greater than that of the said preceding work-performing die-ring, so that in operation there is a slight radial clearance between the guide ring throat and the outer surface of the workpiece. This avoids the unnecessary generation of heat at the and each guide ring.

Each work-performing die-ring is positioned in relation to the preceding guide ring such that the workpiece is still encompassed by a guide ring at the time the workpiece enters the next work-performing die-ring.

Such radial clearance between a guide ring throat and a workpiece passing therethrough is sized so as to limit to safe values any transverse deflection to which said workpiece and the punch carrying it may be subjected on emerging from an upstream die-ring or entering a downstream die-ring.

According to a second aspect of the present invention, a method of performing a DWI process includes the step of directing a coolant fluid under pressure towards the workpiece as it emerges from the or each workperforming die-ring. Preferably such method also includes the step of directing coolant fluid under pressure towards the workpiece as it enters the or each work-performing die-ring.

Preferably, in such a method said coolant fluid is directed towards said workpiece in a direction that is substantially tangential to the outer surface of said workpiece, thereby to create a vortex of coolant fluid swirling around said workpiece adjacent to the associated diering.

Advantageously, such a DWI method also includes the step of passing the workpiece, on emerging from a die-ring, through a guide ring having a throat diameter sufficient to give radial clearance from the outer surface of the workpiece, said clearance being sufficient to protect the workpiece and the punch carrying it against excessive transverse deflections as the workpiece leaves the upstream die-ring or enters the downstream die-ring.

Other features and advantages of the present invention will appear from the description that follows hereafter, and from the claims that are appended at the end of the description.

One die-ring assembly, according to the present invention, for use as a DWI tool of the said rigid type, will now be described by way of example, and with reference to the accompanying drawings, in which: Fig. 1 shows a central, vertical section through the whole assembly; Figs. 2A and 2B show two fragmentary central, vertical sections of an upper part of the assembly, to indicate the spatial relationship of a guide ring in that assembly to workperforming die-rings lying up- and downstream respectively of that guide ring; Fig. 3 shows a further fragmentary central, vertical section of a part of the die assembly illustrating the function of a said guide ring; Fig. 4 shows and and side views of a workpiece/punch damping ring incorporated in the assembly, showing the positioning of typical coolant flow passages formed in that ring;; Fig. 5 shows pictorially part of the die-ring assembly with certain parts removed to show, in terms of coolant fluid flow, the application of the main inventive concept.

Referring now to the drawings, a die-ring assembly 10 includes, proceeding from the punch entry end of the assembly (at the righthand side of Fig. 1) towards the exit end, a series of axially-spaced, work-performing annular dies comprising (a) a re-draw die-ring 12 for reducing the diameter of a shallow cup 14 (the workpiece) to form a re-drawn cup 16, and (b) 1st, 2nd and 3rd ironing die-rings 18, 20 and 22 for successively ironing the longitudinal wall of the re-drawn cup whereby to successively elongate that wall and thereby produce in turn Ist, 2nd and 3rd ironed cups 24, 26 and 28 of progressively greater wall lengths.

Immediately following each work-performing die ring on its downstream side is a coolant supplying spacer ring 12C, 18C, 20C and 22C in which are formed coolant supply passages 30A for directing coolant fluid under pressure longitudinally and tangentially at the cup end as it emerges from the exit side of each of the work-performing die-rings.

Immediately following each said coolant supplying spacer ring on its downstream side is a guide ring 12G, 18G, 20G and 22G, which is intended to provide guidance and support as necessary for a cup workpiece as it moves from one work-performing die-ring to the next.

Immediately following each of the guide rings 12G, 18G and 20G is a workpiece/punch damping ring 12P, 18P and 20P in which are formed coolant supply passages 30B for directing coolant fluid under pressure longitudinally and tangentially at the workpiece end as it enters each of the associated workperforming die-rings.

The assembly of die-rings and associated rings described above is secured rigidly together by fluid-pressure operated means (now shown), and the rigid assembly so formed is mounted securely on the bed of a DWI processing machine, with its longitudinal axis horizontally disposed.

Secured to said assembly, upstream of the re-draw die-ring 12, is a nest ring 32 which is intended to co-operate in the re-drawing stage with a blank holder 34 which is provided for holding the shallow cup blank 14 in the "advanced" position shown in the figure, that is adjacent the re-draw die-ring 12. The blank holder has a bore 34B through which a punch or ram 36 of the DWI machine is horizontally movable to convert the shallow cup workpiece 14 into the desired can form (third ironed cup) 28 in the die-ring assembly 10.

A wall support ring 38 is mounted at the entry side of the nest ring 32, to provide support for the cylindrical wall of the cup workpiece 14 during the initial re-drawing stage. That stage may involve a bend-stretch process as described in our co-pending UK patent application 7937773, filed 31st October 1979, in which process as the punch advances the longitudinal wall is drawn along a path which in longitudinal radial section is of S-shaped configuration and which is formed by the radiused end 34A at the downstream end of the blank holder and a radiused entrance to the throat 12T of the re-draw diering 12. For details of that process, the reader's attention is directed to the specification of the above-mentioned patent application.A coolant fluid is mist-sprayed into the metalflow passageways formed between the nest ring, the blank holder, and the re-draw die ring through ducts which are not shown in the drawings.

The respective work-performing die-rings are provided with hard-wearing annular inserts of tungsten carbide which form the respective work-performing throats of the die-rings; and the respective guide rings are likewise provided internally with similar annular inserts of a hardwearing material such as tungsten carbide.

The workpiece/punch damping rings have internal annular inserts or sleeves of a tough material that is compatible with the tungsten carbide of the punch, so as to minimise metal pick-up. For example, a heavy duty bronze may be used.

The respective coolant flow passages 30A and 30B are in each case arranged to open into the bores of the respective coolant supplying spacer rings and punch damping rings, and to communicate at their opposite ends with annular coolant supply passages 30C that are formed in the respective constituent components of the die assembly and that connect in their turn, via radial and axial conduits, with coolant supply ports 30D, to which in operation a supply source of coolant fluid under suitable pressure is connected.

The coolant flow passages 30A and 30B are oriented so as to direct coolant fluid (a) longitudinally towards a workpiece emerging from or entering the associates work-performing die-ring, and in addition (b) in a direction substantially tangential to the outer surface of that workpiece, as shown in the Figures 4A and 4B.

Such orientation is intended to subject the workpiece and the encompassing work-performing die-ring, both as the workpiece enters and leaves that die-ring, to a series of tangentially directed high pressure jets which create at each such entry and exit position a vortex of coolant swirling circumferentially around the workpiece, as well as an axial flow of such coolant through the assembly, as illustrated in the Figure 5.

This coolant fluid flow arrangement has for its objective the removal rapidly of the highest possible amount of heat from the workpiece and the punch carrying it, and the flushing away of debris formed in the work-performing operation. The flow of coolant is also intended to extract and carry away heat from the die-ring assembly, so that the temperature of that assembly, as well as that of the workpiece and punch, can be kept at moderate levels.

Although the assembly is provided with specific passages for supplying cooling to the bore of the disc assembly, no specific exit passages are provided in the body of the assembly to enable the escape of coolant fluid therefrom. As a result, coolant fluid admitted to the bore of the assembly has to force its way longitudinally of the assembly between the external surfaces of the workpiece and punch and the opposing surfaces of the various rings constituting the assembly. The outer surfaces of the workpiece and punch are thus subjected to radially directed hydro-dynamic forces which tend to damp transverse vibrations of the punch and its workpiece within the bore of the assembly, and thereby limit the amplitude of any such vibrations that are set up in those members.The rate of flow of coolant fluid is maintained at a level such as to keep the radial gaps between the workpiece and punch on the one hand and the bore of the damping rings on the other hand full.

The inner surface of the punch damping rings or sleeves may have suitably raised areas to enhance the hydro-dynamic action resulting from the flow of coolant fluid.

This punch damping action is of considerable assistance during the faster return stroke of the punch after the workpiece has been removed from its end at the exit end of the assembly, in avoiding damage to the punch surface during that return stroke. Moreover, if on such return stroke the punch starts to vibrate, the punch damping rings tend to take most of the radial vibration loads, so that the guide and ironing rings are thereby protected from damage due to such vibration.

The lack of coolant escape passages in the assembly ensures that the debris produced in the metal deformation processes are flushed away ahead of the workpiece and punch, that is the assembly is self-cleaning. The flow of coolant lengthwise through the whole of the assembly moreover tends to maintain the temperature differences along the length of the assembly at a low level.

Whereas, in the past it has been considered desirable to have the bore of each guide ring throat the same as that of its associated (upstream) ironing ring, it has now been appreciated that with such an arrangement the consequent engagement of the workpiece with the and each guide ring serves principally to convert frictionally more of the input energy into useless heat energy, without providing any appreciable wall-ironing action or other benefit, and to increase the power input required to drive the punch.

Hence, in the present die-ring assembly, the guide rings are sized so that, in operation, the guide rings have a small radial clearance from the outer surface of the workpiece. This contributes to the avoidance of undue temperature rises in the punch, workpiece and die assembly. Furthermore, this arrangement has the merit that when the guide rings are of the same construction as their associated (upstream) wall-ironing rings, in the course of time such ironing rings which have become worn can be used subsequently as guide rings working in association with new wall-ironing rings.

The Figure 2A shows the radial clearance of a typical guide ring over the ironed wall of a cup workpiece that is emerging from the associated upstream die-ring, whereas in the Figure 2B the positioning, and function, of a guide ring in relation to the next downstream die-ring is shown.

Figure 3 shows how such a guide ring (despite its working radial clearance over the workpiece) functions to protect the punch and workpiece from undue transverse deflection by a lopsided workpiece, i.e. where one side of the longitudinal wall of a workpiece extends further than the opposite part, so that the ironing ring continues to engage the workpiece at the long side, whilst being clear of the guide ring on the short side. In this event, the guide ring functions on the said short side of the workpiece wall to limit the deflection of the punch made possible by the movement of the workpiece beyond the ironing ring on the said short side.

By causing the coolant fluid to flow axially through the whole die-ring assembly, and by maintaining the spaces between the workpiece/punch and the rings of said assembly full of such fluid, it has been found possible to obtain better and more effective cooling of all such working parts, and moreover with a much reduced coolant fluid flow rate as com pared with that required for a die-ring as sembly having substantially only transverse (as opposed to axial) coolant fluid flow therethrough.

The axial flow of coolant fluid is consider ably improved by providing the punch, up stream of a can-carrying head portion thereof, with a shank portion having a diameter slightly less than that of the said head portion.

In addition, by supplying coolant fluid simultaneously to both upstream and downstream sides of each work-performing die-ring, it is possible to keep the temperature difference axially of each such ring to a low value, so that differential thermal expansion in each such ring should be substantially reduced, and likewise mechanical failures of such rings due to excessive thermal cycling should be reduced.

Claims (21)

1. A die-ring assembly for use in carrying out a DWI process (as hereinbefore defined), said assembly including at least one work-performing die-ring, and in which assembly there is provided for the or each said die-ring, on the downstream side thereof, a coolant supply means having coolant supply passages for directing a coolant fluid, when in operation, towards said die-ring and a workpiece emerging from said die-ring.

2. A die-ring assembly according to Claim 1, wherein there is provided for the or each said die-ring, on the upstram side thereof, a coolant supply means having coolant supply passages for directing a coolant fluid, when in operation, towards said diering and a workpiece entering said die-ring.

3. A die-ring assembly according to Claim 1 or Claim 2, wherein each said coolant supply passage is arranged to direct said coolant fluid in a direction having a substantial component (the "transverse component") in a direction transverse to the axis of movement of said workpiece through said assembly, as well as a component (the "longitudinal component") in a direction along the said axis.

4. A die-ring assembly according to Claim 3, wherein said transverse component is substantially greater than said longitudinal component.

5. A die-ring assembly according to Claim 4, wherein each said coolant supply passage is arranged to direct said coolant fluid in a direction that is substantially tangential to the outer surface of a workpiece that is entering or emerging from (as the case may be) a said die-ring, thereby to create, when in operation, a vortex of said coolant fluid swirling around the said workpiece adjacent said die-ring.

6. A die-ring assembly according to any preceding claim, including a plurality of said dierings axially spaced apart so as to ensure engagement of only one such die-ring at a time with a said workpiece passing through the assembly, and wherein there is provided in the or each space between a die-ring and an adjacent one a workpiece damping ring having a bore of diameter such as to provide a small radial clearance gap between said bore and the outer surface of a workpiece passing through said bore after emerging from the preceding die-ring, said gap being sized and pro portioned such that coolant fluid passing through said gap as said workpiece is ad vanced through said assembly by a punch ex erts on the workpiece and punch hydro-dynamic, damping forces which tend to damp and thereby limit any transverse vibrations set up in said workpiece and punch.

7. A die-ring assembly according to Claim 6, wherein said assembly has no coolant fluid escape path other than that provided through the bores of the die and other rings constituting said assembly.

8. A die-ring assembly according to Claim 6 or 7, wherein said coolant supply passages for directing coolant fluid towards a workpiece entering a die-ring are formed in a workpiece damping ring disposed adjacent the die-ring on the upstream side thereof.

9. A die-ring assembly according to any preceding claim, wherein a guide-ring is disposed downstream of the or each said diering, the or each said guide-ring having a throat diameter that is slightly greater than that of the associated die-ring disposed upstream thereof, whereby, in operation, there exists a small radial clearance gap between the throat of the guide-ring and the outer surface of a workpiece, said clearance gap being sized so as to limit to safe values any transverse deflection to which said workpiece and a punch carrying it may be subjected on emerging from an upstream die-ring or on entering a downstream die-ring.

10. A die-ring assembly according to Claim 9, wherein the or each said guide-ring is spaced from the associated upstream die-ring by a coolant supply ring in which are formed said coolant supply passages for directing coolant fluid at the exit side of said associated die-ring.

11. A die-ring assembly according to any preceding claim, wherein there is provided a succession of said die-rings spaced part and having their respective throats shaped and proportioned for ironing the longitudinal wall of a workpiece in a series of successive ironing stages.

12. A die-ring assembly according to Claim 11, wherein there is provided, upstream of said succession of wall-ironing die-rings, a redrawing die-ring for reducing the diameter of a longitudinal wall of a workpiece blank having the form of a shallow cup.

13. A DWI method (as hereinbefore defined) of working a workpiece blank, in which method a coolant fluid is directed under pressure towards the workpiece as it emerges from the or each workperforming die-ring.

14. A method according to Claim 13, wherein a coolant fluid is directed under pressure towards the workpiece as it enters the or each work-performing die-ring.

15. A method according to Claim 13 or 14, wherein said coolant fluid is directed towards said workpiece in a direction that is substantially tangential to the outer surface of said workpiece, thereby to create a vortex of coolant fluid swirling around said workpiace adjacent to the associated die-ring.

16. A method according to Claim 12, 13 or 14, wherein a said workpiece emerging from a die-ring is passed through a guide ring having a throat diameter sufficient to give a radial clearance from the outer surface of the workpiece, said clearance being sufficient to protect the workpiece and a punch carrying said workpiece against excessive transverse deflections as the workpiece leaves the upstream diering or enters the downstream die-ring.

17. A method according to any one of the Claims 13 to 16, wherein said workpiece, after emerging from one said die-ring and before entering a next said die-ring, passes through a workpiece damping ring and is subjected therein to hydro-dynamic damping forces which tend to damp and thereby limit any transverse vibrations set up in said workpiece and a punch carrying it, said damping forces being produced by the flow of coolant fluid through said damping ring in a radial clearance gap that separates that ring from the workpiece.

18. A die-ring assembly for use in carrying out a DWI process (as hereinbefore defined), said assembly including at least one work-performing die-ring, and in which assembly there is provided for the or each said die-ring, on either or both of the downstream and upstream sides of the die-ring, a coolant supply means having coolant supply passages for directing a coolant fluid, when in operation, towards said die-ring and a workpiece passing therethrough, and in such manner as to create a vortex of coolant fluid swirling around the workpiece adjacent the die-ring on the downstream side or the upstream side thereof, or on both said sides.

19. A DWI method (as hereinbefore defined) of working a workpiece blank, in which method a coolant fluid is directed under pressure towards the workpiece as it passes through the or each workperforming die-ring, said coolant fluid being directed at said workpiece from a position disposed downstream of said die-ring or a position disposed upstream of said die-ring, or from both such positions, and said coolant fluid being directed in such manner as to create a vortex of coolant fluid swirling around the workpiece adjacent the die-ring on the downstream side or the upstream side thereof, or on both said sides as appropriate.

20. An apparatus according to any one of the Claims 1 to 12 and 18 substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

21. A method according to any one of the Claims 13 to 17 and 19, substantially as herein before described with reference to and as illustrated by the accompanying drawings.