WO1991005622A1

WO1991005622A1 - Extrusion

Info

Publication number: WO1991005622A1
Application number: PCT/GB1990/001595
Authority: WO
Inventors: Gordon Howard Goddard
Original assignee: Gordon Howard Goddard
Priority date: 1989-10-16
Filing date: 1990-10-16
Publication date: 1991-05-02
Also published as: AU6602490A

Abstract

A method and apparatus for extruding a material billet (26) has a die holder assembly (22) containing an extrusion die (20) and a chamber (21) for receiving the billet (26). A punch assembly (12) having a punch (16) and punch holder (14) is lowered to bring the punch (16) into contact with the billet (26) and force the latter through the die (20). An enlarged diameter portion of the punch assembly (62) causes a thin-walled hollow portion (80) to be formed in the extrusion at the end of the extrusion process and a suitable stop (34) which is contacted by the free end of the extrusion during or after extrusion of the thin-walled portion (80) causes the latter to crinkle, preventing withdrawal of the extrusion through the die (20). The punch assembly (16) has suitable keying surfaces (64) to retain a butt end portion (84) of the extrusion on the assembly when the latter is withdrawn, ensuring separation of the butt end portion (84) from the extrusion.

Description

Title; Extrusion

The present invention relates to extrusion.

In an extrusion process, a metal billet is heated to a required temperature and fed into a cylindrical container of an extrusion press. A ram of the press forces the billet through a die whose orifice has the desired shape to produce a cross-section extrusion. The metal is produced from the die horizontally in a continuous extrusion which is cut to required lengths. The process is suitable for the production of solid and tubular lengths of material having a fixed cross-sectional shape. In the extrusion of tubular products the ram carries a mandrel which penetrates the die orifice and during extrusion the metal flows through the space between the two.

In order to reduce the cross-section of an extruded rod to the desired size, the rod is drawn and then annealed and drawn through successively smaller dies. As a result, the process takes a considerable amount of time and is relatively expensive.

The present invention seeks to provide an improved extrusion process.

Accordingly the present invention provides a method of extruding material from a material billet comprising applying pressure to said billet to force the material through a die to form an extrusion having a butt end portion preceding and adjacent said die; extruding a thin-walled, hollow portion connected to said butt end portion and adjacent said die at the end of the extrusion operation; causing said thin-walled hollow portion to collapse after it has been extruded from said die to inhibit withdrawal of said extrusion through said die; and withdrawing said butt end portion from said die to cause separation of said butt end portion from said extrusion at said thin-walled hollow portion.

The present invention also provides an apparatus for extruding a material billet, comprising a die holder assembly for receiving and retaining an extrusion die, said die holder assembly having a chamber for receiving said billet; ram means having a punch assembly for forcing said material through said die to form an extrusion having a first end portion remote from said die and a butt end portion adjacent said die, said punch assembly having retaining means for retaining said butt end portion on said punch assembly and having means for forming a thin-walled hollow portion in said extrusion adjacent said butt end portion; and means for causing said thin-walled hollow portion to collapse after extrusion through said die for inhibiting withdrawal of said extrusion through said die and enabling separation of said butt end portion from said extrusion on withdrawal of said punch assembly.

Preferably, the punch assembly is movable into and out of said chamber for extruding said billet through said die, said punch 1 assembly comprising a punch, and mandrel means secured thereto and arranged to enter into an orifice of said die so as to produce said thin-walled hollow portion in said extrusion.

Advantageously, said punch assembly is formed with at least one keying surface for keying into said butt end portion during extrusion to secure said butt end portion to said punch assembly.

In a preferred form of the invention the die holder assembly is slidably mounted for lateral movement relative to said ram means between preset limits and said die holder assembly and said ram means have cooperating alignment means for axially aligning said die and said ram means during movement of said ram means towards said die.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of a preferred form of extrusion apparatus according to the present invention;

Figure 2 is a plan view of the apparatus of Figure 1;

Figure 3 is a plan view of a butt stripping device;

Figure 4 is a section along the line 4-4 of Figure 3. Figure 5 is a side elevation of a clamping mechanism;

Figure 6 is a plan view of the mechanism of Figure 5;

Figure 7 is a side elevation of a punch assembly of the apparatus of Figure 1;

Figure 8 is a section on the line 8-8 of Figure 7;

Figure 9 is a side elevation, similar to that of Figure 8, showing use of a punch for producing extrusions of solid cross- sectional shape; and

Figures 10 to 13 illustrate four stages in the extrusion of a length of tubing of circular cross-section.

Referring to the drawings, these show a preferred form of extrusion apparatus 10 according to the present invention. The apparatus has a preselected number (preferably six) of punch assemblies 12 each of which has a punch holder 14 to which a punch 16 is detachably secured. Each punch holder 14 is rigidly secured beneath a generally circular support plate 18, the punch holders being equi-angularly spaced about the periphery of the plate 18. The latter is rotatable about its central axis to index each of the punch holders in turn successively through an extrusion station 100 at which the associated punch 16 lies vertically above a cooperating die 20, a butt stripping station 200, a quenching station 300 and a lubricating station 400. The support plate 18 is also movable along its axis towards and away from the die 20 either mechanically or under the action of one or more hydraulic rams in order to move the punch 16 towards and away from the die.

Each die 20 is supported in a die holder assembly 22 which is one of six such assemblies equi-angularly spaced about a central point of a support 23 above a generally circular base plate 36. The die holder assemblies 22 are supported for movement about the central point above the base 36 in order to index each die holder assembly 22 in turn successively through a feeding station 500, the extrusion station 100, a cleaning station 600 and a lubrication station 700.

The support plate 18 is indexed by a motor 38 which has a drive pinion 42 which meshes with gear teeth 44 on the periphery of the support plate 18. The latter is conveniently mechanically coupled to the support 23 such that indexing of the plate 18 and support 23 is synchronised to bring each punch 16 directly above a cooperating die holder assembly 22 at the extrusion station 100. At the extrusion station 100 each die holder assembly 22 is postioned above a base 25 which is secured on the base plate 36. The base 25 has a central through-hole which is aligned with the die orifice when the die holder assembly 22 is in position, the base 25 serving to support the die holder assembly 22 during the extrusion process.

The die 20 forms the outside profile or outside diameter of the extrusion and has an insert 24 which provides the actual S extrusion profile. The material of the die insert is of a nature such that extruded material does not deposit on the die insert, which would adversely affect the extrusion.

The die holder assembly 22 has a chamber 21 which retains a billet 26 of the material to be extruded in position above the die 20. The die holder assembly 22 is heated to maintain the billet 26 at the desired temperature.

As the billet 26 is extruded through the die, the extrusion passes into a main cooling system. The latter has one or more pipes 28 which extend parallel with the extrusion and are formed with a plurality of spray nozzles 30 through which coolant such as water is sprayed onto the extrusion. The spray nozzles 30 are arranged such that the whole of the length of the extrusion passing into the cooling system is continually sprayed with coolant.

The spray nozzles extend from immediately adjacent the die holder assembly 22 so that the extrusion is immediately quenched in the cooling water in the cooling system, the rapid cooling resulting in a fine grain being formed in the extrusion material.

The water cooling immediately after extrusion also prevents oxidation of the extruded material.

The cooling system is also provided with a stop in the form of a sprung striker plate 34 on a striker plate assembly 35. This 2 is suspended below the die assembly 22 by means of a piston- cylinder unit 48 which is extendable and retractable to lower and raise the striker plate assembly 35. In its uppermost position the striker plate 34 is located at a point slightly above that to which the extrusion extends when the billet 26 is fully extruded.

The striker plate 34 carries a clamp 46 for clamping the lower end of the extrusion, as is fully described later. The clamp may be actuated by any suitable means, for example pneumatically, mechanically or electrically.

The punch holder 14 is of generally cylindrical cross-section and has an end portion 40 to which the punch 16 is coaxially secured (Fig.7). In this example the punch 16 is intended for tubular extrusions.

The punch 16 is of circular cross-section and, for the extrusion of a material such as copper, is provided with a base 50 formed by a generally frusto-conical body portion 52 which tapers from a cylindrical portion 54. A connector in the form of a locating tube 56 projects axially from the portion 54 and engages in a co¬ operating annular recess in an abutment surface 58 of the free end of the punch holder to locate the punch 16 coaxially in position on the punch holder with the abutment surface 58 in abutment with a co-operating surface of the cylindrical portion 54. £ For the extrusion of certain materials other than copper, a punch in which the frusto-conical body portion 52 is omitted may be used.

A mandrel 60 extends coaxially from the tapered end of the frusto-conical portion 52 and is formed with a shear shoulder 62 adjacent the tapered end of the frusto-conical portion. The shear shoulder 62 is cylindrical in shape and is of a greater diameter than that of the mandrel 60 such that when the shear shoulder 62 enters the die 20 at the end of the extrusion process the annular gap between the die and the shear shoulder is considerably reduced relative to that between the die and the mandrel 60, as is explained below.

The portion 50 of the punch is formed with at least two diametrically opposed (and possibly three equispaced) grooves 64 in its radially outer surface, the longitudinal axes of the grooves extending parallel with the axis of the punch.

Each groove 64 is also provided at its upper end adjacent the punch holder 14 with chamfered recesses 66. The base of each groove 64 is conveniently of semi-circular cross-section.

The preferred extrusion process is now described below with reference to the extrusion of a length of copper tubing, although it will be appreciated that any other suitable materials may be used. £ The metal billet 26, in this case copper, is heated to the required temperature and placed in the die assembly 22 above the die 20 (Figure 10) either before or when the die assembly 22 is indexed into the extrusion station 100. The billet is a cylindrical billet typically 50 mm in length and 50 mm in diameter.

As the support plate 18 is lowered to lower the associated punch 16 towards the die, the mandrel 60 hits the copper billet 26 and begins forcing the billet through the die 20. The axial length of the mandrel 60 should be such as to ensure that it is not long enough to penetrate completely through the billet 26, leaving the tube with a sealed end.

As the extrusion process continues, the copper tube is extruded from the die and enters the cooling system where it is quenched by the water sprayed from the nozzles 30. At the same time, the copper also flows upwardly from the die into the grooves 64 and recesses 66 in the base 50 of the punch 16.

As the punch continues its downward movement, the mandrel 60 moves through the die 20 until the shear shoulder 62 enters the narrowest portion of the die, reducing the width of the annular spacing between the punch and the die. This results in a final end portion 80 of the extruded tube having a much thinner wall then the previously extruded tube, and a reduced cross sectional area. As extrusion continues, the lower end of the extruded tube contacts the striker plate 34. The major portion of the tube from its lower end is relatively hard, having been quenched, whilst the thin-walled portion 80 is still quite soft. As a result of this and the difference in cross sectional area between the main extrusion and the reduced portion, the contacting of the striker plate by the extruded tube causes the thin-walled portion 80 to collapse. The resulting corrugations in the thin-walled portion 80 prevent the extruded tube being pulled back through the die as the punch 16 is retracted.

When the lower, cooled end of the tube hits the striker plate 34, suitably positioned sensors actuate the clamp 46 to clamp the tube as shown in Figure 11. The sensors may be of any suitable type. i

Once the extruded tube has been gripped by the clamp 46, the punch is withdrawn from the die 20. However, the extruded material which was forced into the grooves 64 and chamfered edges 66 serves to key the upper or butt end 84 of the extruded rod to the punch 16. As a result, the butt end 84 is withdrawn from the die with the punch 16 causing the butt end to separate from the extruded tube at the thin-walled portion 80.

On or immediately after separation of the butt end 84 from the extruded tube, the striker plate assembly 35 is lowered by the piston-cylinder unit 48 to draw the extruded tube away from the die assembly 22. il The extruded tube can be removed from the cooling system in number of ways.

Once the extruded tube has been separated from the butt end 84 and fully quenched by the cooling water, it can be pushed sideways away from the cooling system. Extruded tubes can then easily be removed by any suitable conveying system.

After extrusion, the support plate 18 is raised vertically to withdraw the punch, complete with butt end 84, from the die assembly. The punch 16 is then indexed in a counter clockwise direction as seen in Figure 1 into the butt stripping station 200. The butt stripping station 200 has a stripping device 202 shown in Figures 3 and 4. The device has a housing 204 in which a generally cylindrical, vertical through-bore 206 is formed. The bore has a diameter slightly larger than that of the cylindrical portion 54 of the punch 16 and the butt end 84 combined. The housing 204 also has two toothed ratchet wheels 208 which are rotationally supported on horizontal axes in recesses 210 such that the toothed peripheries of the ratchet wheels project into the bore 206 at preferably diametrically opposed positions. The ratchet wheels are allowed to rotate in the directions shown in Figure 4 to allow entry of the punch 16 but are prevented from rotating in their reverse directions.

At the stripping station 200 the punch 16 with the butt end 84 attached is lowered into the bore 206 in the direction of arrow A in Figure 4. The spacing of the ratchet wheels is greater than the diameter of the cylindrical portion 54 of the punch 16 but is less than the outer diameter of the butt end 84 so that the teeth on the periphery of the ratchet wheels 208 bite into the material of the butt end 84. As a result of this, when the support plate is raised to draw the punch 16 from the bore 206 the butt end 84 is stripped from the punch by the ratchet wheels. The ratchet wheels will retain the butt until it is forced to drop into a suitable receptacle below the stripping station 200, when the next butt is lowered into the bore 206 after the next extrusion operation.

Although the bore 206 is shown as being generally cylindrical it may be of any suitable shape provided that the spacing between the ratchet wheels is such as to ensure operation of the stripping device as described above.

It will be appreciated that more than two ratchet wheels may be used at equiangularly spaced intervals.

The die holder assembly 22 is slidably mounted on two parallel guide rails 106 which extend generally radially outwardly of the support 23 (Fig.l). Each guide rail 106 engages in a co¬ operating groove 108 in the die holder assembly 22 such that the latter is slidable radially of the support 23. Each punch holder assembly 22 is provided with two guide lugs 114 each of which has a respective hole or slot 116. As can be seen in Figure 1 each punch holder 14 has two guide pillars 110 whose axes lie in the same plane as and parallel with the axes of the punch holder 14. Each guide pillar 110 has a tapered end portion 112 which is conveniently in frusto-conical form. The guide lugs 114 and guide pillars 110 are positioned relative to the die holder assembly 22 and punch assembly 12 so that when the punch assembly 12 is lowered at the extrusion station to commence an extrusion operation, before the punch 16 contacts the billet 26 the tapered end 112 of each guide pillar 110 enters into the co-operating guide slot 116 to centre the die holder assembly 22 accurately beneath the punch 16. The sliding movement of the die holder assembly is limited by end stops to ensure that, regardless of the position of the die holder assembly 22, the guide slots 116 are positioned relative to the guide pillars for locating engagement of the tapered ends 112 of the guide pillars in the guide slots 116.

Once the guide pillars 110 have fully engaged the guide slots 116 to position the die holder assembly 22 the latter is clamped in position by a clamping mechanism 118. The clamping mechanism is shown in Figures 5 and 6 and is actuated conveniently by a suitable sensor 120 which senses, for example, lowering of the support plate 18 through a preselected position at which time the guide rods 110 are fully engaged in the guide slots 116.

The clamping mechanism 118 has a clamping arm 120 which is pivoted intermediate its ends, one end being connected to a double acting piston-cylinder unit 122 whilst the other end is U-shaped to engage the upper surface of the die holder assembly 22 without obscuring the die. Once the punch assembly 12 has ϋ been withdrawn from the die holder assembly 22 the clamping mechanism is released.

The preferred process and apparatus according to the present invention allow a 50 mm long billet to be extruded into a 2500 mm standard length of tubing on one operation with a cycle time of typically 2 seconds. One further calibration draw may be required, but this apart, no further drawing or extrusion operations are necessary. In addition, because of the very simple nature of the process and the fact that relatively small billets are used, the force required to effect extrusion is considerably reduced (typically 200 tons), enabling the cost and size of the extrusion apparatus to be kept to a minimum.

Whilst the preferred extrusion process according to the present invention has been described with reference to the extrusion of material of hollow cross-section, it is also applicable to the extrusion of material of solid cross-section. In this latter case, the punch 16 is replaced by an alternative punch 140 as shown in Figure 9 which is a view, similar to that of Figure 8 showing the punch 140 attached to the punch holder 14. The punch 140 operates in exactly the same way as punch 16 but as can be seen the frusto-conical portion 52 and mandrel 60 are omitted, leaving a cylindrical end portion 54' and a shear shoulder 62' . The punch is also provided with grooves 64 with chamfered edges 66. It will be appreciated that any cross sectional shape may be extruded. A major advantage of the above-described and illustrated extrusion process compared with the conventional process is that whilst the conventional process is always horizontal and produces a continuous extrusion which is cut to required lengths, the applicant's process is effected vertically and extrudes one standard length of extrusion for each stroke of the extrusion press.

Claims

1. A method of extruding material from a material billet comprising applying pressure to said billet to force the material through a die to form an extrusion having a butt end portion preceding and adjacent said die; extruding a thin-walled, hollow portion connected to said butt end portion and adjacent said die at the end of the extrusion operation; causing said thin-walled hollow portion to collapse after it has been extruded from said die to inhibit withdrawal of said extrusion through said die; and withdrawing said butt end portion from said die to cause separation of said butt end portion from said extrusion at said thin-walled hollow portion.

2. A method as claimed in claim 1 further comprising cooling said material after extrusion through said die.

3. A method as claimed in claim 2 wherein said material is quenched immediately after exiting from said die.

4. A method as claimed in any preceding claim wherein said material billet is received within a chamber adjacent said die prior to extrusion through said die and said material is extruded by means of a punch assembly movable into said chamber towards said die to cause extrusion of said material through said die.

5. A method as claimed in claim 4 wherein said punch assembly is caused to key into said butt end portion to cause said butt end portion to be retained on said punch assembly on withdrawal of said punch assembly.

6. A method as claimed in claim 4 or 5 wherein said butt end portion is stripped from said punch assembly after withdrawal of said punch assembly and said butt end portion from said chamber.

7. An apparatus for extruding a material billet, comprising a die holder assembly for receiving and retaining an extrusion die, said die holder assembly having a chamber for receiving said billet; ram means having a punch assembly for forcing said material through said die to form an extrusion having a first end portion remote from said die and a butt end portion adjacent said die, said punch assembly having retaining means for retaining said butt end portion on said punch assembly and having means for forming a thin-walled hollow portion in said extrusion adjacent said butt end portion; and means for causing said thin-walled hollow portion to collapse after extrusion through said die for inhibiting withdrawal of said extrusion through said die and enabling separation of said butt end portion from said extrusion on withdrawal of said punch assembly.

8. An apparatus as claimed in claim 7 wherein said punch assembly is movable into and out of said chamber for extruding said billet through said die, said punch assembly comprising a punch, and mandrel means secured thereto and arranged to enter into an orifice of said die so as to produce said thin-walled hollow portion in said extrusion.

9. An apparatus as claimed in claim 8 wherein said punch assembly is formed with at least one keying surface for keying into said butt end portion during extrusion to secure said butt end portion to said punch assembly.

10. An apparatus as claimed in claim 9 wherein said laying surface comprises at least two equi-angularly spaced grooves coaxial with said punch assembly and formed in a radially outer surface thereof.

11. An apparatus as claimed in claims 8, 9 or 10 wherein said mandrel means and said die orifice are shaped so as to enable said mandrel means to penetrate at least partially into said die orifice for forming said thin-walled hollow portion.

12. An apparatus as claimed in claim 11 for extruding tubular material sections wherein said mandrel means is a mandrel arranged to penetrate through said die orifice during extrusion, said mandrel having an axial portion of a cross-sectional shape increased in size for entering said die orifice to form said thin-walled hollow portion.

13. An apparatus as claimed in any of claims 7 to 12 wherein said means for causing said thin-walled hollow portion to collapse comprises stop means for limited longitudinal movement of said extrusion, said stop means being positioned a preset distance from said die.

14. An apparatus as claimed in claim 13 wherein said stop means comprises a striker plate for abutting said first end portion of said extrusion.

15. An apparatus as claimed in any of claims 7 to 14 further comprising means for gripping said extrusion and preventing movement of said extrusion towards said die to assist separation of said extrusion and said butt end portion on withdrawal of said punch assembly.

16. An apparatus as claimed in any of claims 7 to 15 further comprising cooling means for cooling said extrusion after its passage through said die orifice.

17. An apparatus as claimed in claim 16 wherein said cooling means is operable to cool said extrusion at a position at least immediately adjacent said die.

18. An apparatus as claimed in claim 16 or 17 wherein said cooling means is operable to quench said extrusion immediately on exiting from said die orifice and along its full length.

19. An apparatus as claimed in any of claims 7 to 18 wherein said die holder assembly is slidably mounted for lateral movement relative to said ram means between preset limits and said die holder assembly and said ram means have cooperating alignment means for axially aligning said die and said ram means during movement of said ram means towards said die.

20. An apparatus as claimed in claim 19 wherein said alignment means comprises at least one recess on one of said die holder assembly and said ram means and cooperating locating means on the other of said die holder assembly and ram means, said recess and said locating means being engagable during movement of said ram means towards said die to align axially said die and said ram means.

21. An apparatus as claimed in claim 20 wherein said recess means comprises a plurality of axially extending slots formed in said die holder assembly and said locating means comprises a corresponding number of axially extending projections secured to said ram means, said projections engaging in said slots to align said die holder assembly axially with said ram means prior to commencement of extrusion.

22. An apparatus as claimed in claim 20 or 21 wherein said alignment means comprises a plurality of holes formed in laterally extended flange means on said die holder assembly and a corresponding number of guide rods on said ram means, said holes and said guide rods being spaced about the axes of said punch assembly and said die holder assembly.

23 . An apparatus as claimed in any of claims 19 to 22 wherein said preset limits of lateral movement of the die holder assembly are such as to ensure positioning of said at least one recess relative to said locating means for locating engagement during movement of said ram means towards said die holder assembly.

24. An apparatus as claimed in any of claims 19 to 23 further comprising clamping means for clamping said die holder assembly in position after axial alignment of said punch assembly and said die holder assembly by engagement of said locating means in said at least one recess.

25. An apparatus as claimed in any of claims 7 to 24 further comprising means for removing said butt end portion from said punch assembly after withdrawal of said punch assembly from said die holder assembly.

26. An apparatus as claimed in claim 25 wherein said removing means comprises gripping means remote from said die holder assembly, punch assembly being movable towards said gripping means after withdrawal from said die holder assembly to enable said gripping means to grip said butt end portion and retain said butt end portion on withdrawal of said punch assembly from said removing means.

27. An apparatus as claimed in claim 21 or 22 wherein said removing means comprises at least two toothed wheels supported in spaced relationship for receiving therebetween said butt end portion on engagement of said punch assembly in said removing means, said toothed wheels having ratchet means allowing rotation of said toothed wheels in a direction to allow engagement of said butt end portion between said wheels and preventing rotation of said wheels in the reverse direction to retain said butt end portion therebetween on withdrawal of said punch assembly.

28. An apparatus as claimed in any of claims 7 to 27 wherein said ram means comprises a plurality of punch assemblies secured to and equi-angularly spaced about a selected point of a support means, said support means being rotatable about said selected point to index each of said punch assemblies in turn through a first extrusion station for extruding said material billet through said die, a second station having said removing means for removing said butt end portion, a third station having means for cooling each said punch assembly and a fourth station having means for lubricating each said punch assembly; and further comprising a plurality of die holder assemblies equi-angularly spaced about a second support means rotatable to index each said die holder assembly in turn successively through a fifth station for receiving said material billet, said first, extrusion station for extrusion of said material billet, a sixth station having means for cleaning each said die and a seventh station having means for lubricating said die, rotation of said first and second support means being synchronised so as to index each said punch assembly and said die holder assembly into substantially axial alignment at said first, extrusion station.