GB2286354A

GB2286354A - Extrusion dies

Info

Publication number: GB2286354A
Application number: GB9501660A
Authority: GB
Inventors: Frank Wilson; Roger Fielding; Yukei Takasaki; Terhiko Hanaoko
Original assignee: Alcan International Ltd Canada
Current assignee: Rio Tinto Alcan International Ltd
Priority date: 1994-01-28
Filing date: 1995-01-27
Publication date: 1995-08-16
Anticipated expiration: 2015-01-27
Also published as: GB9501660D0; GB9401619D0; GB2286354B

Abstract

An extrusion die for extruding small sections having internal flow passages. The die comprises a first body part (10) and a second body part (12). Metal to be extruded enters at the left, and is divided into two passages (16) by a bridge (14) forming part of the body part (10). Mounted by means of a shrink fit in a through-hole in the bridge (14) is a mandrel (11) which has, at its downstream end, projections (22) which define the internal shape of the extruded product The projections are positioned within a die slot in a die plate (13) which is secured within a recess (27) in the second body part (12). A plurality of set-screws (30) are used to laterally adjust the position of the die plate (13), and hence the die slot, with respect to the projections (22). <IMAGE>

Description

"EXTRUSION DIES" This invention relates to extrusion dies and is more particularly concerned with dies for extruding sections having at least one internal passage. Such sections, made from aluminium, copper, brass or certain other metals are extensively used in heat exchangers and the preferred use for the present invention is in the manufacture of multi-hole heat exchanger extrusions.

European patent application No. 0558288 describes an extrusion die assembly of the general type with which the present invention is concerned.

The die assembly comprises a die body having a bridging member which defines two or more passages along which the metal to be extruded passes. Mounted in an aperture in the bridging member is a mandrel whose downstream end is shaped to provide the desired interior profile for the extruded product. The downstream end of the mandrel projects into an aperture whose shape defines the desired exterior profile of the extruded product. This aperture is formed in a die body which is fixedly secured in a recess in the die body.

There is a demand for ever smaller sections, and the parts of the die which shape the internal passages are consequently small and fragile and in use become worn or fractured relatively quickly to a point where the required tolerances in the finished extrusion cannot be met. It has been recognised that there is a need to provide dies in which the parts which define the finished shape of the extrusion are replaceable.

According to a first aspect of this invention there is provided an extrusion die comprising a die body having passage means therethrough for a substance to be extruded and having within the passage means a part which is formed with a through-hole extending in the direction of extrusion, a mandrel, a support part of which has external dimensions corresponding to those of the through-hole so as to be a tight fit in the through-hole, the forward end part of the mandrel protruding beyond the through-hole into the passage means and defining the internal form of the extrusion, a die member providing a die aperture disposed about said forward end part of the mandrel and defining the external form of the extrusion, and wherein the die body has means for adjusting the position of said member with respect to the forward end part of the mandrel in a plane normal to the direction of extrusion.

Various means may be used for retaining the mandrel accurately and securely within its throughhole; however, it is preferred that the mandrel be thus secured by means of a shrink fit, effected either by cooling the mandrel or heating the die body, or both.

According to a second aspect of this invention there is provided an extrusion die comprising a die body having passage means therethrough for a substance to be extruded and having within the passage means a part which is formed with a through-hole extending in the direction of extrusion, a replaceable mandrel, a support part of which has external dimensions corresponding to those of the through-hole so as to be a tight fit in the through-hole, the forward end part of the mandrel protruding beyond the through-hole into the passage means and defining the internal form of the extrusion, a die member providing a die aperture disposed about said forward end part of the mandrel and defining the external form of the extrusion, and wherein said support part of said mandrel is a shrink fit in said through-hole in the die body.

Preferably the die body is formed in two parts which are bolted or otherwise fixed together for use.

The support part of the mandrel may have a uniform cross-section in the direction of extrusion.

Preferably, however, the support part has a profile which tapers towards the forward (downstream) end.

In the preferred embodiment, the support part of the mandrel has four flat sides and is of elongate crosssection providing two major faces which are parallel to each other and two minor faces which are inclined towards each other in a direction towards said one end to form said taper.

In one construction of mandrel for producing an extrusion which is wide in relation to its thickness the support portion of the mandrel has wide parallel planar sides and planar ends which are inclined towards each other. All four sides may however be inclined if desired. In another construction the body portion of the mandrel is conical matched to the conicity of the through-hole.

The invention will now be described in more detail with reference by way of example to the accompanying diagrammatic drawings in which: Figure 1 is an elevation of the entry side of an extrusion die according to the invention; Figure 2 is a sectional view on the lines II II of Figure 1; Figure 3 is a sectional elevation of a modified embodiment of the extrusion die of Figures 1 and 2; Figure 4 is a sectional view of one of the body parts of the extrusion die of Figures 1 to 3 shown positioned over a jig used during fitting of a mandrel; Figures 5, 6 and 7 are respectively an elevation, end elevation and perspective view of the mandrel of the die of Figure 1; and Figures 8 and 9 show respectively an end view and sectional elevation of a multiple cavity extrusion die embodying the invention.

Referring to Figures 1 to 3, the extrusion die comprises a first body part 10 supporting a mandrel 11 and a second body part 12 supporting a die member in the form of a die plate 13. The longitudinal axis of the die, along which the extruded metal moves in a direction from left to right in Figures 2 and 3, is indicated by reference 46. The body part 10 has an axially extending bore which is split into two separate passages 16 by a bridge 14 which is integral with the body part 10 and extends diametrically across the bore. The two axially extending passages 16 merge where the bridge terminates at its downstream edge 17. A wedge-shaped through slot is machined in the bridge 14 for receiving the support portion 18 of the mandrel 11 shown in Figures 5, 6 and 7 in a sealing fit.The support portion 18 of the mandrel has wide planar sides 19 which are parallel to each other and planar end faces 20 which may also be parallel, but are preferably inclined towards each other, as shown, at an included angle which may be in the range 10 to 100, for example 30 to 5 with respect to the longitudinal axis 46. The corners of the support portion are radiussed. At its forward (smaller) end the mandrel 11 is reduced in size and is formed with a series of peg-like projections 22, and this reduced forward end part 21 protrudes beyond the downstream end of the through-slot in the bridge and into the merged extrusion passages 16. The projections 22 define apertures in the section which is to be extruded.The profile of the through-slot in the bridge 14 corresponds to that of the support portion 18 at each position along the axial length of the latter, and the larger ends of the through-slot and support portion 18 are substantially flush. The mandrel may be made from a hard-wearing material such as sintered carbide, or may be made from tougher but softer, and therefore less hard-wearing, material such as a hot working steel, e.g. H13 steel, high speed steel or QR090 steel from Uddeholm AB. A Nimonic alloy might also be used.

The second body part 12 has a peripheral axially projecting flange 25 at its upstream end in which a short spigot projection 26 on the downstream end of the first body part registers. In the downstream face of the body part 12 is formed a recess in the form of an axial cylindrical bore 27 in which is fixedly secured the die plate 13. In the embodiment illustrated, the die plate 13 is fitted within an annular holder 29 to form a composite die member. The holder 29 is a loose radial fit in the bore 27, and its radial position in the bore is adjustable by means of a plurality of angularly spaced set screws 30. In an alternative embodiment (not shown), the holder 29 is dispensed with, and the die member takes the form of a single unit, namely a die plate, which has an exterior size which is a loose radial fit in the bore 27 so that its radial position can be adjusted by the set screws 30. When assembled, the die body 10 bears onto the die plate 13 clamping it in place.

The die shown in Figures 1 and 2 has fine set screws 30, the positions of which are clearly illustrated in Figure 1. The embodiment of Figure 3 differs from that of Figures 1 and 2 only in that four such set screws 30 are provided, as two pairs of two.

The two set-screws 30 of each pair are diametrally aligned with each other and the common axes of the two pairs intersect at right angles. Each set-screw is engaged in the screw-threaded outer part 32 of a radial hole. The radially inner part 33 of the hole is plain but is intersected by an axial screw-threaded hole in which is engaged a locking screw 34, the axially inner end part 35 of which is of reduced diameter and is plain. A setting pin 36 is slidably engaged in the plain inner part 33 of the hole and has a lengthwise slot 37 which is engaged by the plain axial end part 35 of the locking screw 34 so that the setting pin cannot rotate about its axis. The radially inner end of the setting pin 36 is cylindrically concavely curved to fit snugly against the radially outer surface of the holder 29.The die plate 13 is formed at its inner end with a die aperture in the form of a die slot 47 which is elongate and accommodates the set of projections 22 on the mandrel 11 to thereby define the external shape of the resultant extrusion. Downstream of the die slot 47 the internal surfaces 39 of the die plate are inclined outward, and continuations 40 of these surfaces are formed in the second body part 12 to permit passage of the extruded section.

In operation, aluminium or other metal is divided into two flows by the bridge 14 and forced along the two passages 16 in the first body part 10 by the extrusion press (not shown). The two flows recombine at the downstream end 17 of the bridge 14 and are forced into the interstices between the projections 22 and between the projections and the edge of the slot 47 in the die plate 13 to form a wide flat extrusion with passages extending along its length.

The assembly of the die is carried out as follows. The body part 10 is made from a metal such as H13 steel. The mandrel may be made of the same or similar steel to that of the body part 10, or of a sintered carbide. A shrink fit can be achieved by heating the body part 10 and then dropping the relatively cooler mandrel into the wedge-shaped through-slot. After cooling the body part 10, the mandrel will be a tight fit within the through slot.

A jig intended for correctly setting the longitudinal position of the mandrel 11 during this operation will be described below.

In the embodiment illustrated, the die plate 13 may be made from carbide and may be similarly shrink-fitted into the holder 29, which latter is made from H13 steel, to form the composite die member.

This member is cooled, and the two axial ends of this composite die member are then machined flush. Alternatively, as mentioned above, the holder 29 and the die plate 13 may be made integrally with each other from steel, in which case this step is unnecessary.

One end of a slip gauge which is geometrically similar to the section to be extruded is then placed about the projections 22 on the mandrel and the die plate in its holder 29 (if fitted) is next passed along the gauge into its position abutting the downstream face of the body part 10. The second body part 12 is then placed in position about the holder 29 and is bolted axially to the body part 10 by means of bolts through axial apertures 48. With the gauge still in position, the set-screws 30 are then carefully adjusted to move the setting pins 36 into abutment with the outer surface of the holder 29, so that the setting pins are tightly against the holder but the slip gauge remains free. The locking screws 34 are then tightened to lock the setting pins 36 in position and the gauge is removed. The assembly is now complete and set.

When the projections 22 on the mandrel 11 become unacceptably worn or broken, the mandrel is discarded. For this purpose, it may be possible simply to knock the mandrel out with a hammer. If necessary, the outer part of the body part 10 may be heated to allow the worn mandrel to be removed and replaced by a new mandrel. The method of locating the new mandrel is described in more detail below.

The die plate (and holder if fitted) may also be replaced at this time. Re-setting of this member by means of the set-screws 30 would probably be required whenever a new mandrel or die plate is fitted. It will be understood however that the die assembly can accommodate mandrels and die plates to form different extrusion sections so that numerous sections can be extruded using the same body parts 10 and 12.

Since, in the preferred embodiment, the through-slot and the mandrel 11 taper in a downstream direction, the resultant of the pressures exerted on the two ends of the mandrel by the metal presses the mandrel into a tight sealing engagement in the through-slot in the bridge 14.

It will be understood that the materials of the die plate holder 29 and the second body part 12 should have substantially the same coefficient of expansion, since differential radial expansion of the two components will upset the settings of the setting pins 36. This likewise applies in the event that the die member is formed as an integral unit of die member 13 and holder 29: in this case the material of the unitary die member should have substantially the same coefficient of expansion as the second body part 12.

An advantageous method of locating the mandrel will now be described, reference being made to Figure 4. After removal of the old mandrel, or on assembly of a new die as discussed above, the body part 10 is heated in order to cause expansion of the through-hole in bridge 14. To fit the new mandrel, the body part 12 is located in a jig 49, for example made of H13 steel, which defines a surface 50 which is a predetermined distance below the downstream surface of the body part 10. The through-hole in the bridge 14 of the body part 10 is made of sufficient size to allow the relatively cool mandrel to be dropped down into place in the through-hole such that it abuts the surface 50. This thus precisely defines the position of the mandrel with respect to the longitudinal axis of the die.The body part 10 is now cooled and the shape and dimensions of the through-hole are such as to securely grip the mandrel 11 as it contracts and to provide an effective all-round sealing fit between the mandrel and the through-hole.

It will be seen therefore that accurate longitudinal and lateral positioning of the mandrel with respect to the die member is catered for: the longitudinal positioning by means of the jig arrangement such as shown in Figure 4, and the lateral positioning by means of the set-screw arrangement.

This ensures that the projections 22 extend into the die slot 47 to precisely the right extent, and are positioned correctly with respect to the edges of the die slot to give an extruded product of uniform wall thickness.

In the multiple extrusion die assembly shown in Figures 8 and 9, four die plate assemblies 44 similar to those shown in Figure 3 are independently secured to a first die body part 10 and are independently set up and adjusted. The assemblies 44 are spaced apart so that adjusting keys can be inserted in the gaps 45 between them to adjust the set-screws 30 and setting pins 36. The locking pins 34 are accessible from the exposed end faces of the body parts 12. If desired, the body parts 12 of the assemblies 44 may be formed integrally with each other, with the slots 45 sufficiently long to allow access to the set-screws 30. Body part 10 has an arrangement of bridges and through holes to accommodate mandrels corresponding to the die slots 47.

Claims

1. An extrusion die comprising a die body (10,12) having passage means (16) therethrough for a substance to be extruded and having within the passage means (16) a part (14) which is formed with a through-hole extending in the direction of extrusion, a mandrel (11), a support part (18) of which has external dimensions corresponding to those of the through-hole so as to be a tight fit in the through-hole, the forward end part of the mandrel (11) protruding beyond the through-hole into the passage means and defining the internal form of the extrusion, a die member (13) providing a die aperture disposed about said forward end part of the mandrel (11) and defining the external form of the extrusion, and wherein the die body has means (30,36) for adjusting the position of said member (13) with respect to the forward end part of the mandrel (11) in a plane normal to the direction of extrusion.

2. An extrusion die as claimed in claim 1 wherein the die body is formed with a recess (27) in which is located said die member (13), the recess (27) being of sufficient size to allow a degree of lateral movement of said die member (13) during adjustment by said adjusting means (30,36).

3. An extrusion die as claimed in either one of claims 1 or 2 wherein the die body is made up of a first body part (10) and a second body part (12) which are fixedly attached together, and wherein: (i) said part (14) and said passage means (16) are formed on said first body part (10); and (ii) said adjusting means (30,36) is formed on said second body part (12).

4. An extrusion die as claimed in claims 2 and 3 wherein that face of the second body part (12) which faces the first body part (10) is formed with a bore which constitutes said recess (27) in which the die member (13) is located.

5. An extrusion die as claimed in any one of claims 2, 3 or 4 wherein said adjusting means comprises a plurality of angularly spaced radially extending bores (32,33) which extend through the die body into said recess (27), said bore being at least partially threaded to receive a respective set screw assembly which, at its inner end, engages said die member (13) to allow lateral adjustment thereof within the recess (27).

6. An extrusion die as claimed in claim 5 wherein each said set screw assembly comprises a set screw 30 which is threadedly engaged in an outer part (32) of the respective radially extending bore and a setting pin (36) which is radially movable within an inner part (33) of the respective radially extending bore.

7. An extrusion die as claimed in claim 6 further including means for preventing rotation of said setting pin (36) within its respective bore part (33).

8. An extrusion die as claimed in claim 7 wherein said means for preventing rotation comprises a slot 37 formed longitudinally in said setting pin (36) and a locking screw (34) which is engageable in a threaded bore in the die body and has an inner end which enters said slot to prevent rotation of the setting pin (36) and also to lock the setting pin in position once the correct setting has been reached.

9. An extrusion die as claimed in any one of the preceding claims wherein the die member (13) is made from a material having substantially the same coefficient of expansion as the die body.

10. An extrusion die as claimed in any one of the preceding claims wherein the support part (18) of said mandrel (11) is a shrink fit in said through-hole in the die body.

11. An extrusion die as claimed in claim 10, wherein the mandrel (11) is made from a material having a smaller coefficient of expansion than the material of the die body.

12. An extrusion die as claimed in claim 10, wherein the mandrel (11) is made from the same material as the die body.

13. An extrusion die as claimed in any one of the preceding claims wherein said die member comprises a holder (29), and a die element (13) which latter provides the die aperture and is a shrink fit in the holder.

14. An extrusion die as claimed in any one of claims 1 to 12 wherein said die member is of unitary construction.

15. An extrusion die comprising a die body (10,12) having passage means (16) therethrough for a substance to be extruded and having within the passage means (16) a part (14) which is formed with a through-hole extending in the direction of extrusion, a replaceable mandrel (11), a support part (18) of which has external dimensions corresponding to those of the through-hole so as to be a tight fit in the throughhole, the forward end part of the mandrel (11) protruding beyond the through-hole into the passage means and defining the internal form of the extrusion, a die member (13) providing a die aperture disposed about said forward end part of the mandrel (11) and defining the external form of the extrusion, and wherein said support part (18) of said mandrel (11) is a shrink fit in said through-hole in the die body.

16. An extrusion die as claimed in claim 15 wherein the die body is made up of a first body-part (10) and a second body part (12) which are fixedly attached together, and wherein said part (14) and said passage means (16) are formed on said first body part (10) and wherein said die member (13) is located in a recess (27) in said second body part (12).

17. An extrusion die as claimed in either one of claims 15 or 16 wherein the support part (18) of said mandrel has a cross section which tapers in a direction towards its forward end part.

18. A mandrel as claimed in claim 17, wherein the support part (18) of the mandrel (11) has four flat sides and is of elongate cross-section providing two major faces (19) which are parallel to each other and two minor faces (20) which are inclined towards each other in a direction towards said one end to form said taper.

19. An extrusion die as claimed in any one of claims 15 to 18 further comprising means (30,36) for adjusting the position of said member (13) with respect to the forward end part of the mandrel (11) in a plane normal to the direction of extrusion.

20. An extrusion die as claimed in any one of claims 15 to 19 wherein the support part (18) of said mandrel is of such size with respect to said throughhole that it is able, during fitting, and after the die body has been heated to expand same: (i) to be inserted into the through-hole to a predetermined reference position in the direction of extrusion; and (ii) once in the reference position, to be gripped by the die body when the latter is subsequently cooled.