METHOD AND APPARATUS FOR PRODUCING TWO-PIECE CAN BODIES FROM A LAMINATED METAL SHEET AND A TWO-PIECE CAN BODY PRODUCED THEREBY

Abstract

A method and apparatus for producing two-piece can bodies by drawing and ironing a laminated metal sheet, and more particularly to a processing method which prevents abrasion damage or scuffing of the laminate layer on the can body during its ironing, and a drawn and ironed two-piece can body produced thereby.

Claims

1. A method for producing can bodies comprising a base and a tubular body for two-piece cans, from a laminated metal sheet by deep drawing and wall-ironing, wherein a disc is produced from the laminated metal sheet, which is deep-drawn into a cup, followed by redrawing the cup and subsequently forming the redrawn cup into a can body by wall ironing, wherein the wall ironing taking place in a single stroke by punching the redrawn cup through one or more wall-ironing rings by means of an internally cooled punch assembly, wherein the punch assembly comprises: a ram, a punch which is attached to the ram, the punch assembly comprising an internal annular cavity below the surface of the punch between a position near the distal end of the punch and a position near the proximal end of the punch, a plurality of cooling fluid inlets for supplying a cooling fluid into the internal annular cavity and a plurality of cooling fluid outlets for removing the cooling fluid from the internal annular cavity, wherein the internal annular cavity is provided with means for improving the efficiency of the internal cooling of the punch, wherein the means for improving the efficiency of the internal cooling of the punch consist of obstacles in the internal annular cavity to increase the turbulence in the cooling fluid during its travel from the cooling fluid inlets to the cooling fluid outlets and to provide a larger cooling surface for extracting heat from the punch, wherein the obstacles consist of: discontinuous obstacles such as chevrons, cylinders, or of continuous obstacles in the form of a plurality of adjacent helical walls delimiting a plurality of helical cooling channels in the internal annular cavity to conduct the cooling fluid from the cooling fluid inlets to the cooling fluid outlets, the ram comprising means for supplying cooling fluid to the cooling fluid inlets and removing cooling fluid from the cooling fluid outlets, to efficiently internally cool the punch during the production of the can bodies to prevent abrasion damage or scuffing of the laminate layer on the tubular body of the can body, wherein a. the cooling fluid inlets are arranged nearer the distal end of the punch and wherein the cooling fluid outlets are arranged nearer the proximal end of the punch, or wherein b. the cooling fluid inlets are arranged nearer the proximal end of the punch and wherein the cooling fluid outlets are arranged nearer the distal end of the punch, or wherein c. the cooling fluid inlets of part of the helical cooling channels are arranged nearer the distal end of the punch and wherein the corresponding cooling fluid outlets are arranged nearer the proximal end of the punch, and wherein the cooling fluid inlets of the other helical cooling channels are arranged nearer the proximal end of the punch and wherein the corresponding cooling fluid outlets are arranged nearer the distal end of the punch, so that some of the helical cooling channels conduct cooling fluid from the distal end to the proximal end of the punch and the other cooling channels conduct cooling fluid from the proximal end to the distal end of the punch.

2. The method according to claim 1, wherein the punch comprises at least three adjacent helical cooling channels.

3. The method according to claim 1, wherein each helical cooling channel is provided with its own cooling fluid inlet and its own cooling fluid outlet.

4. The method according to claim 1, wherein the redraw ring and the one or more ironing rings also have internal cooling channels, which cool the outside laminate layer of the can body during the deep drawing and wall-ironing.

5. The method according to claim 1, wherein the temperature of the punch assembly is controlled by means of a temperature control unit and wherein the temperature control unit is able to control the temperature of the punch by adapting the speed of production of can bodies and/or by adapting the flow rate of the cooling fluid entering the internal annular cavity and/or by adapting the temperature of the cooling fluid entering the internal annular cavity.

6. An internally cooled punch assembly for use in the method according to claim 1, wherein the punch assembly comprises: a ram, a punch attached to the ram, the punch assembly comprising an internal annular cavity below the surface of the punch between a position near the distal end of the punch and a position near the proximal end of the punch, a plurality of cooling fluid inlets for supplying a cooling fluid into the internal annular cavity and a plurality of cooling fluid outlets for removing the cooling fluid from the internal annular cavity, wherein the internal annular cavity is provided with means for improving the efficiency of the internal cooling of the punch, wherein the means for improving the efficiency of the internal cooling of the punch consist of obstacles in the internal annular cavity to increase the turbulence in the cooling fluid during its travel from the cooling fluid inlets to the cooling fluid outlets and to provide a larger cooling surface for extracting heat from the punch wherein the obstacles consist of: discontinuous obstacles or of continuous obstacles in the form of a plurality of adjacent helical walls delimiting a plurality of helical cooling channels in the internal annular cavity to conduct the cooling fluid from the cooling fluid inlets to the cooling fluid outlets, the ram comprising means for supplying cooling fluid to the cooling fluid inlets and removing cooling fluid from the cooling fluid outlets, to efficiently internally cool the punch during the production of the can bodies to prevent abrasion damage or scuffing of the laminate layer on the tubular body of the can body, wherein a. the cooling fluid inlets are arranged nearer the distal end of the punch and wherein the cooling fluid outlets are arranged nearer the proximal end of the punch, or wherein b. the cooling fluid inlets are arranged nearer the proximal end of the punch and wherein the cooling fluid outlets are arranged nearer the distal end of the punch, or wherein c. the cooling fluid inlets of part of the helical cooling channels are arranged nearer the distal end of the punch and wherein the corresponding cooling fluid outlets are arranged nearer the proximal end of the punch, and wherein the cooling fluid inlets of the other helical cooling channels are arranged nearer the proximal end of the punch and wherein the corresponding cooling fluid outlets are arranged nearer the distal end of the punch, so that some of the helical cooling channels conduct cooling fluid from the distal end to the proximal end of the punch and the other cooling channels conduct cooling fluid from the proximal end to the distal end of the punch.

7. The punch assembly according to claim 6, wherein the punch comprising the internal annular cavity with the obstacles or the plurality of adjacent helical cooling channels is a product of additive manufacturing.

8. The punch assembly according to claim 7, wherein the punch comprises a punch sleeve and an insert which, when assembled, form the punch with the internal annular cavity with the obstacles.

9. The punch assembly according to claim 8, wherein the insert with the obstacles a product of additive manufacturing.

10. The punch assembly according to claim 9, wherein the material of the insert is a machined tool steel, wherein the obstacles are machined in the insert.

11. The punch assembly according to claim 6, wherein the plurality of continuous obstacles forming the helical cooling channels runs between a position near the distal end of the punch to a position near the proximal end of punch and wherein the helical cooling channels run below the surface of the punch, and wherein the punch comprises at least three adjacent helical cooling channels.

12. The punch assembly according to claim 6, wherein the plurality of continuous obstacles forming the helical cooling channels runs between a position near the proximal end of the punch to a position near the distal end of punch and wherein the helical cooling channels run below the surface of the punch, and wherein the punch comprises at least three adjacent helical cooling channels.

13. The punch assembly according to claim 6, wherein the temperature of the punch assembly is controlled by means of a temperature control unit which is able to control the temperature of the punch by adapting the speed of production of can bodies and/or by adapting the flow rate of the cooling fluid entering the internal annular cavity and/or by adapting the temperature of the cooling fluid entering the internal annular cavity.

14. A can body produced by the method according to claim 1.

15. The method according to claim 1, wherein the punch is removably, attached to the ram, wherein the discontinuous obstacles are selected from chevrons, cylinders, discontinuous walls or discontinuous zigzag walls, wherein the cooling fluid inlets arranged nearer the distal end of the punch, and the cooling fluid outlets arranged nearer the proximal end of the punch, are arranged in a regular pattern around the circumference of the punch, or wherein the cooling fluid inlets arranged nearer the proximal end of the punch, and the cooling fluid outlets arranged nearer the distal end of the punch, are arranged in a regular pattern around the circumference of the punch, or wherein the cooling fluid inlets of part of the helical cooling channels arranged nearer the distal end of the punch and the corresponding cooling fluid outlets are arranged nearer the proximal end of the punch, and the cooling fluid inlets of the other helical cooling channels are arranged nearer the proximal end of the punch and the corresponding cooling fluid outlets are arranged nearer the distal end of the punch, so that some of the helical cooling channels conduct cooling fluid from the distal end to the proximal end of the punch and the other cooling channels conduct cooling fluid from the proximal end to the distal end of the punch, wherein the direction of the cooling fluid alternates from one helical cooling channel to its adjacent helical cooling channel, wherein the inlets and outlets are arranged in a regular pattern around the circumference of the punch.

16. The method according to claim 2, wherein the punch comprises at least six adjacent helical cooling channels.

17. The punch according to claim 6, wherein the punch is removably, attached to the ram, wherein the discontinuous obstacles are selected from chevrons, cylinders, discontinuous walls or discontinuous zigzag walls, wherein the cooling fluid inlets arranged nearer the distal end of the punch, and the cooling fluid outlets arranged nearer the proximal end of the punch, are arranged in a regular pattern around the circumference of the punch, or wherein the cooling fluid inlets arranged nearer the proximal end of the punch, and the cooling fluid outlets arranged nearer the distal end of the punch, are arranged in a regular pattern around the circumference of the punch, or wherein the cooling fluid inlets of part of the helical cooling channels arranged nearer the distal end of the punch and the corresponding cooling fluid outlets are arranged nearer the proximal end of the punch, and the cooling fluid inlets of the other helical cooling channels are arranged nearer the proximal end of the punch and the corresponding cooling fluid outlets are arranged nearer the distal end of the punch, so that some of the helical cooling channels conduct cooling fluid from the distal end to the proximal end of the punch and the other cooling channels conduct cooling fluid from the proximal end to the distal end of the punch, wherein the direction of the cooling fluid alternates from one helical cooling channel to its adjacent helical cooling channel, wherein the inlets and outlets are arranged in a regular pattern around the circumference of the punch.

18. The punch assembly according to claim 8, wherein the insert with the obstacles is a product of additive manufacturing wherein the insert also comprises the cooling fluid inlets and the cooling fluid outlets.

19. The punch assembly according to claim 9, wherein the material of the insert is a machined tool steel, wherein the obstacles are machined in the insert, and wherein the insert also comprises the cooling fluid inlets and the cooling fluid outlets.

20. The punch assembly according to claim 6, wherein the plurality of continuous obstacles forming the helical cooling channels runs between a position near the distal end of the punch to a position near the proximal end of punch and wherein the helical cooling channels run below the surface of the punch, wherein each helical cooling channel is provided with its own cooling fluid inlet and its own cooling fluid outlet and wherein the punch comprises at least six adjacent helical cooling channels.

21. The punch assembly according to claim 6, wherein the plurality of continuous obstacles forming the helical cooling channels runs between a position near the proximal end of the punch to a position near the distal end of punch and wherein the helical cooling channels run below the surface of the punch, wherein each helical cooling channel is provided with its own cooling fluid inlet and its own cooling fluid outlet and wherein the punch comprises at least six adjacent helical cooling channels.

Description

DRAWINGS AND FIGURES

[0053] The invention is further described by means of the following, non-limiting drawings and figures.

[0054] FIG. 1 illustrates how a preformed deep-drawn cup 3 is formed into a finished wall-ironed can body 9. The cup 3 is placed between a redraw sleeve 2 and a redraw die 4. When punch 1 moves to the right, the cup 3 is brought to an internal diameter of the final finished can 9 by the redrawing step. Then, the punch 1 successively forces the product through (in this example) two wall-ironing rings 6 and 7. Ring 8 is an optional stripper ring. Wall ironing provides the can body 9 to be formed with its ultimate wall thickness and wall length. Finally, the base of can body 9 is formed by moving punch 1 towards an optional base tool 10. Retracting punch 1 allows to detach can 9 from the punch 1 so that it can be discharged in the transverse direction. The optional stripper ring may assist in this. The can 9 is then subsequently trimmed, optionally necked, flanged and provided with a lid after filling.

[0055] FIG. 2 provides a detailed illustration of the passage of a part of the can wall to be formed through, for example, wall-ironing ring 6. Punch 1 is indicated diagrammatically. The entry plane for wall-ironing ring 6 runs at an entry angle α to the direction of the axis of the wall-ironing ring. The thickness of the material of the wall to be formed is reduced between punch 1 and wall-ironing ring 6. This material comprises the actual metal can body wall 11 with laminate layers 12 and 13 on either side. The laminate layer 12 becomes the outside of the can body, and the laminate layer 13 becomes the inside of the can body, eventually coming into contact with the contents of the can. The figure illustrates how the thickness of all three layers 11, 12 and 13 is reduced.

[0056] FIG. 3 shows the punch 1 which typically is removably secured on the leading end of a reciprocating ram 14 in a drawing and ironing machine. FIG. 3 shows the punch on top of the ram in one of the embodiments of the invention in detail. The internal annular cavity runs between 15a and 15b and is more prominently outlined in FIG. 4 with the dashed boxes in the cross section of the punch.

[0057] FIG. 4 shows a cross-section of the punch with the continuous obstacles forming the adjacent helical cooling channels. In this figure the punch consists of a punch sleeve 19 and an insert 20. The internal annular cavity formed by the joined punch sleeve and insert is filled with the continuous obstacles.

[0058] FIG. 5a shows the outside surface of the insert 20 with the helical continuous obstacles 18. It shows six adjacent helical cooling channels (channel a-f), each with their own individual inlet and outlet for cooling fluid. FIG. 5b shows a cross section of the same insert as used in FIG. 4.

[0059] FIG. 6 shows six different examples of the internal annular cavity: without obstacles (A: prior art); with discontinuous obstacles (B: short walls perpendicular to the flow of the cooling fluid; C: circular pillars; D: chevrons; E: zig zag channels); and with continuous obstacles (F: six adjacent helical cooling channels formed by the continuous obstacles forming the walls of the channels). The distance between the cooling fluid and the work surface of the punch is the same for all embodiments.

[0060] FIG. 7 shows the surface temperature of the various examples. It is clear that all the examples according to the invention provide a very homogeneous temperature profile along the length of the punch (running from about 40 to about 110 mm). The prior art shows a significantly higher surface temperature of the punch, showing the improvement that the invention is able to provide with regard to the surface temperature of the punch. The lowest surface temperature is achieved with the continuous obstacles forming the helical channels, irrespective of the flow direction of the cooling fluid in the channels (distal to proximal, proximal to distal or mixed). All embodiments of the invention show a significant improvement over the prior art.

[0061] FIG. 8 shows the effect of this lower surface temperature. The closed circles show the temperature during the production of can bodies at 165 cans/minute using the prior art annular internal cavity without obstacles. The triangles show the punch temperature at the same production rate and identical boundary conditions for the embodiment with the six adjacent helical cooling channels, and a steady state temperature of about 65° C. is reached compared to 95° C. for the prior art punch. This means that the production rate can be increased. In the example the production rate is increased 70% to 280 cans/minute and this leads to a maximum temperature of the punch of just below 90° C., which still is below the prior art situation at a much lower production rate. The cans made at an increased production rate according to the method of the invention were free of scuffing and no abrasion damage was observed.

[0062] The results of the discontinuous obstacles are only marginally less favourable compared to the continuous obstacles and also allow a significant improvement in surface temperature control and associated production rate improvement of about 60-65%.