Extrusion method and apparatus

Abstract

An extrusion method for forming a length of multimaterial extrudate includes providing a die; providing a container comprising a multimaterial feed material supply; effecting relative movement of the container towards the die so as to bring an axial surface of the die into contact with a rotating engagement surface of the supply of feed material; generating heat at the interface between the axial surface of the die and the rotating engagement surface of the multimaterial feed material supply so as to heat the at least two materials of the multimaterial feed material supply by the application of a contact pressure between the axial surface of the die and the rotating engagement surface of the feed material supply; pressing the heated multimaterial feed material supply through an orifice in the axial surface of the die so as to form a length of multimaterial extrudate in the extrusion channel.

Claims

1. An extrusion method for forming a length of multimaterial extrudate, the method comprising: providing a die comprising a longitudinal axis; providing a container comprising a multimaterial feed material supply comprising at least two materials, the die and the container being configured such that the container is rotatable relative to the die about a rotation axis; aligning the longitudinal axis of the die so as to be coincident with the rotation axis; rotating the container relative to the die about the rotation axis; effecting relative movement of the container towards the die so as to bring an axial surface of the die into contact with a rotating engagement surface of the supply of feed material; generating heat at the interface between the axial surface of the die and the rotating engagement surface of the multimaterial feed material supply so as to heat the at least two materials of the multimaterial feed material supply by the application of a contact pressure between the axial surface of the die and the rotating engagement surface of the feed material supply so as to generate friction therebetween; pressing the heated multimaterial feed material supply through an orifice in the axial surface of the die and into an extrusion channel in the die so as to form a length of multimaterial extrudate in the extrusion channel.

2. The extrusion method according to claim 1, comprising providing further relative movement of the container in the direction towards the die so as to force the heated multimaterial feed material supply through the extrusion channel.

3. The extrusion method according to claim 1, wherein the extrusion channel comprises an orifice arranged in axial surface of the die and wherein at least the orifice is located on the longitudinal axis of the die and preferably the extrusion channel extends at least partially along the longitudinal axis.

4. The extrusion method according to claim 1, comprising providing the multimaterial feed material supply in the container, and aligning the multimaterial feed material supply with the rotation axis such that the arrangement of at least two materials in the multimaterial feed material supply is rotationally symmetrical about the rotation axis.

5. The extrusion method according to claim 1, comprising providing a container comprising a multimaterial feed material supply comprising at least two metals and/or metal alloys.

6. The extrusion method according to claim 1, comprising providing a container comprising a multimaterial feed material supply comprising copper as a first material and aluminium as a second material.

7. The extrusion method according to claim 1, comprising rotating the container relative to the die about the rotation axis at a rotational speed of at least 90 rpm, in particular, when the cylindrical cavity 106 in the container has a cross section of 0.002 m.sup.2.

8. The extrusion method according to claim 1, wherein the contact force for the generation of heat is at least 100 kN, preferably at least 150 kN, in particular, when the cylindrical cavity in the container has a cross section of 0.002 m.sup.2.

9. The extrusion method according to claim 1, comprising plasticising a portion of the feed material supply at the engagement surface thereof by the generation of heat at the interface between the axial surface of the die and the rotating engagement surface, and flowing the plasticised portion of the feed material supply through the extrusion channel to form a length of multimaterial extrudate.

10. The extrusion method according to claim 1, wherein the arrangement of the at least two materials in the cross-section of the formed length of multimaterial extrudate is the same as the arrangement of the at least two materials in the transverse cross-section of the multimaterial feed material supply in the container, preferably wherein the ratio between the radial thickness of the two materials in the multimaterial feed material supply and in the multimaterial extrudate is essentially equal.

11. The extrusion method according to claim 1, comprising providing a cylindrical container comprising a multimaterial feed material supply located in a cylindrical cavity, and moving the container relatively towards the die such that the die is positioned at least partially inside the cylindrical cavity.

12. The extrusion method according to claim 11, wherein the engagement surface of the die is substantially circular in cross-section and the diameter of the cylindrical cavity is the same as the diameter of the outer surface of the die adjacent to the engagement surface.

13. An apparatus for providing a length of multimaterial extrudate, comprising: a die comprising a longitudinal axis and an axial surface comprising an orifice to an extrusion channel therein; a container comprising a multimaterial feed material supply comprising at least two materials, the container being rotatable rotating relative to the die about a rotation axis; the longitudinal axis of the die and the rotation axis of the container being aligned so as to be coincident; wherein the container and the die are configured such that during relative rotation of the container and the die about the rotation axis, and at least one of the die and the container are movable along the respective longitudinal axis and rotation axis so as to permit the axial surface of the die to be brought into contact with an engagement surface of the feed material supply; wherein relative rotation of the container causes rotation of the engagement surface, such that contact with the axial surface of the die causes heating of the engagement surface, and the orifice in the axial surface of the die is configured to permit flow of heated multimaterial feed material supply therethrough and into the extrusion channel.

14. The apparatus of claim 13, wherein the extrusion channel is parallel and coincident with the longitudinal axis of the stationary die.

15. The apparatus of claim 13 or 14, wherein the multimaterial feed material supply is cylindrical in shape and comprises a first material in the shape of a cylinder, and a second material in the shape of a sleeve that is arranged around the cylindrical first material.

16. The extrusion method according to claim 1, further comprising the implementation of a multimaterial extrudate as an electrical conductor or as a medical implant.

Description

DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is an illustration of a known friction extrusion method for providing a single material extrudate;

[0033] FIG. 2 is an illustration of a first arrangement of material in a multimaterial extrudate;

[0034] FIG. 3 is an illustration of a second arrangement of material in a multimaterial extrudate.

[0035] FIG. 4 is an illustration of a non-homogeneous microstructure of extruded material.

DETAILED DESCRIPTION

[0036] A known method of friction extrusion is illustrated in FIG. 1, for the extrusion of a single-material extrudate.

[0037] Here, a container 2 comprises a supply of feed material 4 which comprises a volume of feed material. The container comprises a cavity 6 in which the supply of feed material 4 is located.

[0038] The container 2 comprises a rotation axis 8 about which it is rotated while being brought into contact with a die 10. The die 10 is stationary, and comprises longitudinal axis 12 extending along the length thereof.

[0039] As illustrated in each of the three steps of FIG. 1, the longitudinal axis 12 of the die 10 is aligned with the rotation axis 8 of the container 2. The container 2 is then rotated about the rotation axis as is illustrated by arrow 14 such that the rotating supply of feed material 4 may be brought into contact with the die 10.

[0040] In order to enable the feed material supply 4 to be brought into contact with the die 10, the container 2 comprises an opening 16 that permits access to the cavity 6. The container 2 is a cylinder in this example, and the opening 16 is positioned on an axial face of the cylinder, and has a circular shape that is perpendicular and aligned with the rotation axis 8 such that rotation of the container 2 does not result in a change in shape of the opening 16 relative to the stationary die 10.

[0041] With the container 2 rotating either the stationary die 10 or the container, or both, are moved in the direction of the respective rotation axis and longitudinal axis 8, 12 until the rotational die 10 is brought into contact with the feed material 4. As illustrated in FIG. 1, it is an axial surface 18 of the die 10 that is brought into contact with an engagement surface 20 of the feed material 4. The engagement surface 20 of the feed material 4 may be oriented perpendicular to the rotation axis 8 of the container 2 and may be flat.

[0042] Upon contact with the die 10, the engagement surface 20 heats up as a result of friction between the two, as is illustrated in the central illustration of FIG. 1. The heating of the engagement surface 20 causes a top portion of the engagement surface to become plasticised. A force is applied between the die 10 and the feed material 4 in the container 2 such that the plasticised material is able to flow through an orifice 22 in the axial surface 18 of the die 10 and into an extrusion channel 24. As the plasticised material moves from being in the cavity 6 and into the channel 24, the die is able to move further into the cavity 6, where a further portion of the feed material 4 is exposed to the heat generated by the contact with the die 10. Once in the extrusion channel, the plasticised material may be permitted to cool so as to form an extrudate. By a further continuous relative movement of the container 2 towards the die 10 further plasticised material is pressed into the extrusion channel 24 so that a continuous process of forming the extrudate takes place.

[0043] With reference to FIGS. 2 and 3, an embodiment of the method according to the present disclosure will be described. Here, some of the steps as illustrated in FIG. 1, or are similar to as illustrated in FIG. 1. For example, as can be seen in FIG. 2, a container 102 is provided that comprises a cavity 106 in which a supply of feed material 104 is located. The container 102 comprises a rotation axis 108 about which it is configurable to rotate, while a die 110 is provided having a longitudinal axis 112 and an axial end face 116 (which may be known as the die face) which is configured to contact the feed material 104. The die face 116 may be a flat surface, and/or may be a roughened surface. The die face 116 may be perpendicular to the axis 108 and/or the axis 112 The die face 116 may be flat, for example located in a single plane, so as not to comprise any grooves, ribs, protrusions or the like, and the entire die face 116 may be configured to engage the feed material 104 simultaneously, for example, in the absence of protrusions, grooves, ribs, or the like, the entire surface may be flat/planar and engage the feed material 104 substantially simultaneously. When carrying the method of the present disclosure these axes 108, 112 coincide. In this embodiment of the method of the disclosure the die 110 is a stationary die, in that it is rotationally stationary. However, it should be noted that translational movement of the die along the longitudinal axis 112 may be possible, and it is also conceivable that the container 102 remains rotationally stationary and the die 110 is rotated or that both are rotated.

[0044] Here, the feed material 104 is a multimaterial feed material comprising a first material 104a and a second material 104b. The first material 104a is dissimilar to the second material 104b. The first and second material 104a, 104b may be polymers (e.g. plastics) or may be metallic materials, such as a metal alloy, or a metal. In some examples, the first material may be copper, while the second material may be aluminium. In another example, each of the first and second materials may be dissimilar alloys of aluminium.

[0045] A cross-section of the feed material 104 is illustrated on the right-hand side of FIG. 2. Here, it can be seen that the feed material 104 has a circular cross-section (and is cylindrical in shape). The first material 104a has a cylindrical shape, while the second material 104b is in the shape of a sleeve that is arranged around the cylindrical first material 104a. The longitudinal axis of the container 108 is aligned with the centre (e.g. the longitudinal axis) of the cylindrical feed material 104 such that rotation of the container 102 about the longitudinal axis does not result in a changing cross-sectional shape of the feed material 104 as a result of rotation of the feed material 104 in the container relative to the die 110. Similarly, the arrangement of the first material 104a and the second material 104b is rotationally symmetrical about the rotation axis 108 of the container 102, and also about the longitudinal axis of the cylindrical feed material 104. This has the effect of meaning that when the feed material 104 is rotated, the arrangement of the first material 104a relative to the second material 104b does not change relative to the stationary die 110.

[0046] Regarding the geometry of the container 102 and the die 110, it should be noted that the container 102 may be or comprise any prismatic shape, such as a cylinder, but also a triangular, rectangular or polygonal prism may also suffice. Although not illustrated, a rotational device, such as a motor and spindle, may be present in order to rotate the container 102 around the rotation axis 108. The shape of the container 102 may therefore be selected based on the most preferable shape for such a rotational device. The die 110 may be held stationary by, for example, a vice, and may not rotate, although axial movement of the die towards the container 102 may be permitted (e.g. the die is moved axially while the container is axially fixed). Alternatively or additionally, axial movement of the container 102 towards the die 110 may be permitted (e.g. the container is moved axially while the die is axially fixed).

[0047] The cavity 106 in this case has a circular cross-section taken perpendicular to the rotation axis 108, and is generally cylindrical in shape. As previously described in relation to FIG. 1, the container 102 comprises an opening 118 for accessing the cavity 106, and into which a feed material may be placed, as is illustrated in FIG. 2. The feed material may be in the form of a solid block or blocks of feed material, in the form of chips or in the form of powdered material.

[0048] FIG. 3 illustrates a feed material comprising a first and second material (which may be, for example, dissimilar aluminium alloys, copper and aluminium, or the like). As is illustrated in in the rightmost illustration of FIG. 3, here the feed material 104 comprises a cylinder of a first material 104a that is surrounded by a sleeve of a second material 104b, which is then surrounded by a sleeve of the first material 104a and so on, in an alternating pattern. As such, it can be seen that the multimaterial feed material 104 may be or comprise two materials that are separated into a plurality of distinct volumes, for example with each volume comprising one material, or substantially one material, for example in contrast to a composite material volume comprising multiple material types. Equally, it may be possible to have a multimaterial feed material 104 comprising more than two (e.g. three, four or more) materials. Where a multimaterial feed material 104 is present, each material may comprise at least one distinct volume.

[0049] In the examples illustrated in FIGS. 2 and 3, each of the volumes has a substantially circular (or, where appropriate, ring-shaped, as can be seen in FIGS. 2 and 3) cross-section, and each of the volumes is concentrically arranged. In the example of FIG. 2, the feed material comprises an innermost volume having a circular cross-section and an outermost volume having a ring-shaped cross-section. The outer diameter of the cross-section of the innermost volume may be equal to, or smaller than, the inner diameter of the cross-section of the outermost volume. In FIG. 3, the feed material comprises an innermost volume, and outermost volume and a plurality (e.g. one, two, three, four, or the like) of intermediate volumes, with the cross-section of the innermost volume being circular in shape, and the cross-sections of the outermost and intermediate volumes being ring-shaped. The outer diameter of the cross-section of the innermost volume may be the same, or smaller than, the inner diameter of the immediately adjacent intermediate volume, which may have a cross-section having an outer diameter that is the same, or slightly smaller than, the inner diameter of the immediately outwardly adjacent intermediate volume, and so forth, until the outermost volume. Each volume may be a different material, or two or more of the volumes may be of the same material.

[0050] The volumes in the feed material 104, although distinct, may be integrally formed or joined to one another, such that it is not possible to separate the volumes from one another without, for example, performing a work process on the feed material 104 to physically separate the volumes.

[0051] The volumes in the feed material 104 may be constant along the length of the feed material 104. For example, where the feed material 104 is in the form of a cylinder, there may be no variation of the feed material along the axial direction of the feed material 104.

[0052] As is illustrated in FIG. 2, the die 110 may be moved along its longitudinal axis 112 through the opening 118 in the container 102 to be brought into contact with the feed material 104 in the rotating container 102. As described in relation to FIG. 1, relative rotational movement between the die 110 (e.g. the die face 116 of the die) and an engagement surface 120 (which may alternatively be known as the contact plane, or contact surface) of the feed material 104 causes the engagement surface 120 and a portion of the feed material that is adjacent the engagement surface 120 to heat and become plasticised. A contact pressure is applied between the die 110 (in this case, between an axial end surface 116 of the die) and the feed material 104 such that the plasticised feed material is caused to flow through an orifice 122 in the die 110 and into an extrusion channel 124. When the feed material is plasticised, a portion of all volumes of the feed material may be plasticised (e.g. the portion in the vicinity of the die, such as at the contact surface with the die and such as in the extrusion channel) and therefore may be deformable. The flowing of the plasticised material towards and into the channel 124 may cause the engagement surface 120 between the supply material 104 and the die 110 to be a dynamic surface that is being replaced by non-plasticised material as the plasticised material flows away, and allows the die 110 to move further into the cavity 106.

[0053] Once in the extrusion channel 124, all of the volumes of the feed material may be deformed or reshaped as compared to their original form as part of the original feed material, and the material may be allowed to cool such that an extrudate is formed. Although the orifice 122 and/or the extrusion channel 124 may traditionally be cylindrical in shape, it should be noted that (for example as a result of the die 110 being rotationally stationary) any cross-sectional shape of extrusion channel 124 may be acceptable. For example, the orifice 122 and/or the extrusion channel 124 may have a triangular, square, rectangular, pentagonal or any other polygonal shape that may be chosen by the user. In the examples illustrated, a solid extrudate may be provided, for example, a non-hollow cylindrical extrudate, that may not comprise any cavities therein.

[0054] As is illustrated in both FIGS. 2 and 3, the arrangement of the first and second materials 104a, 104b in the cross-section of the cavity 106 is the same as that in the cross-section of the extrudate, although with the dimensions reduced in the cross-section of the extrudate, so as to maintain the same or similar ratio of e.g. diameter of the first material relative to the diameter of the second material. The cross-section of the feed material 104 may therefore be a similar shape as compared to the cross-section of the extrudate. In particular, the ratio between the radial thickness of the two materials in the multimaterial feed material supply and in the extrudate is essentially equal. In the case of FIG. 2 and FIG. 3, the feed material 104 may be considered to form a cladded extrudate, since a sleeve of outer material encapsulates an inner material, or group of materials. For example, a first metal may form an outer sleeve on the extrudate, while a second metal (or a plurality of second metals, which may include a volume of metal of the same material type as the outer sheath or sleeve) may be contained within the extrudate.

[0055] According to the present disclosure, the geometry of the die 110 and the container 102 may be selected and combined with specific FE parameters, so as to minimise or prevent deformation of the arrangement of the materials in the multimaterial feed material 104 during the extrusion process. For example, it is known that a specific rotational speed and contact pressure between the die 110 and the feed material 104 provides reduced deformation (e.g. radial deformation) of the materials during the extrusion process, thereby resulting in a more consistent and predictable cross-section of the extrudate.

[0056] The effects of the parameters of friction extrusion can be seen in FIG. 4. Here, the grain structure of the extrudate is shown, and it can be seen that a non-homogenous structure is present. In particular, the extrudate has a fine grain structure towards its edges and an elongated grain structure towards its centre. It has been discovered that maintaining a non-homogeneous grain structure, for example where the grain structure is fine towards the edges 126 and coarse/elongated toward the centre 128, strongly reduces the deformation in the radial direction of the feed material as a result of the extrusion process. With this being known, parameters may be selected so as to ensure such a distribution of grain structure.

[0057] In particular, with the method of the present disclosure control of the microstructure of the resulting multimaterial extrudate is obtained by varying the parameters of the process. The rotational speed of the relative rotation between the container 102 and the die 110, the speed of the relative movement of the container 102 towards the die 110, the axial pressure applied between the die 110 and the container 102, the thickness or diameter of the extrudate produced and the applied extrusion ratio may be adjusted such that tailored extrudates can be produced.