WO1996024453A1

WO1996024453A1 - Forming metal matrix composite with particulate filler

Info

Publication number: WO1996024453A1
Application number: PCT/AU1996/000060
Authority: WO
Inventors: Graham Rex Withers
Original assignee: Graham Rex Withers
Priority date: 1995-02-10
Filing date: 1996-02-09
Publication date: 1996-08-15
Also published as: AUPN107195A0

Abstract

An apparatus (10) and a method are provided for moulding or die casting a metal matrix composite product with a dispertion of particulate filler material. A cartridge (16) is inserted into the inlet passage (11) to the mould or die cavity (13), the cartridge (16) having at least one outer section (18) rupturable by molten metal flow and containing particulate filler material (19). The arrangement is such that when molten metal is injected through the inlet passage (11), it ruptures the cartridge (16) and carries the particulate filler material (19) into the mould or die cavity (13) while at the same time dispersing the filler material (19) throughout the molten material.

Description

FORMING METAL MATRIX COMPOSITE WITH PARTICIPATE FILLER The present invention relates primarily to a novel method of forming and apparatus for forming metal matrix products, however, the method and apparatus may also be useful in moulding products made from any material in which it is desired to disperse a particuiate or fibre filler material. This invention will be particularly useful in producing products disclosed in Patent Nos. 83399/87 (GENI) and 61450/90 (GENII).

In the prior art there is disclosure of methods and apparatus for forming metal products using, for example aluminium or its alloys, magnesium or its alloys, tin or its alloys and zinc or its alloys, in which a particuiate filler material is dispersed such as fly ash or other ceramic particles. There are certain advantages in using such fillers in that it may provide lighter and at least as strong end products that are cheaper because the filler is not as expensive as the metal. Other advantages include the ability to adjust or improve ductility, wear resistance, hardness, thermal expansion and other similar properties. It is, however, desirable to achieve a simple and inexpensive method of producing such products such that any savings resulting from the materials used are not wasted by the manufacturing methods and the costs of the apparatus required to form the product. Several difficulties exist in relation to mixing particuiate material into a liquid matrix (such as a metal matrix) prior to being introduced in a mould or die cavity. These include that, depending on the materials involved, the particuiate material might tend to float or sink in the matrix material so that widely different dispersion levels can result in the product ultimately formed. This can occur if the particuiate material is mixed into the liquid matrix material well before introduction into the mould or die. This may be partly resolved by continually mixing the particuiate material and the matrix material, however, this adds a further cost and difficulty and moreover, stratification can still result as the material is transferred from the mixing zone to the die or mould. The additive materials may also be destroyed or damaged as a result of mechanical or other types of mixing apparatus in a melting pot. The additives may also become scorched under super heated conditions that the liquid metal is kept, thus resulting in intermetallic phases.

A still further difficulty is that it is difficult to mix particuiate material that might be reactive to some extent with the liquid matrix material as extensive mixing times provide for the possibility of deleterious reactions between the materials.

The objective therefore is to provide a relatively low cost method and apparatus for forming products by moulding techniques comprised of a particuiate material dispersed in a matrix material with the particuiate material having satisfactory dispersion levels for the product being formed.

Accordingly, the present invention provides in a first aspect, a method of forming a composite product comprising heating a metal matrix material to its liquid state, introducing said liquid metal matrix material to a mould or die cavity while still in its liquid state, and introducing a volume of particuiate filler material into said liquid matrix material either at or immediately prior to an entry point of said liquid metal matrix material into said mould or die cavity. Preferably this introduction point of the particuiate material occurs in the mould or die. in accordance with this aspect the present invention also proposes apparatus for forming a composite product comprising a mould or die including a mould or die cavity, means for receiving and introducing a molten metal matrix material into said mould or die cavity, and means for introducing a volume of particuiate material into said molten metal matrix material either at or immediately prior to said molten metal matrix material entering said mould or die cavity. It has been surprisingly found that introducing the particuiate material as aforesaid provides adequate distribution of the particuiate material in the product being formed.

In accordance with a preferred aspect of the present invention there is provided a method of forming a composite product comprising the steps of providing: a mould or die with a mould or die cavity; locating a volume of particuiate material in a path for the flow of liquid matrix material into said die or mould cavity, said particuiate material being located in an outer sheath capable of being at least partially ruptured by liquid matrix material flowing into said die or mould cavity; and heating a matrix material to its liquid state and arranging same to flow past said volume of particuiate material whereby said paniculate material is carried with and dispersed through said liquid matrix material within said die or mould cavity. In accordance with this aspect, the present invention also provides apparatus comprising a mould or die having a mould or die cavity, a liquid flow path for liquid matrix material leading into said mould or die cavity, and means located in said liquid flow path either at or immediately before an entry point into the mould or die cavity to support a volume of particuiate located in an outer sheath, said outer sheath being adapted for rupture upon said liquid matrix material passing along said liquid flow path. Conveniently the sheath material may be a metal foil. In the case of moulding a metal matrix material such as aluminium or its alloys or magnesium or its alloys, the metal foil of sheath material might appropriately be either or both an aluminium (or its alloys) or magnesium (or its alloys) foil. In such a case the foil material might be heated by the incoming liquid matrix material beyond its liquid state and the sheath material might simply form part of the liquid matrix material entering the mould or die cavity. In any event in such circumstances, the sheath material should not be made of a material that will adversely react with the liquid matrix material. In a still further aspect, the present invention also provides a cartridge for location in an inlet flow passage of a die or mould, said cartridge having an outer wall of metal configured to be positioned in said inlet flow passage and retaining particuiate filler material within an inner space thereof.

In a still further aspect, the present invention also provides a method of die casting metals with a dispersion of particuiate filler material, said metal injected as molten metal into a die cavity of a die, the injection of the molten metal into said die cavity being through an inlet runner leading into the die cavity, said method comprising: inserting into said runner a cartridge containing a predetermined volume of particuiate filler material to be dispersed in a metal casting, said cartridge being sealed by at least one section formed by a metal foil layer so as to retain the filler material within the cartridge; injecting molten metal into the cavity through said cartridge, thereby rupturing the foil layer carrying the filler material into the cavity while intermixing the paniculate filler material with said molten metal; and allowing said molten metal to solidify in the die cavity before removing same.

Throughout this specification, particuiate material is referred to. It should be understood that this includes but is not limited to, fly ash or other ceramic particles (either spherical or not) and fibres including steel or other metal fibres and glass fibres. Obviously the material of the particuiate material will depend upon the nature of the matrix material being used therewith and the product being formed. Further, when the matrix material is a metal, the sheathing material is either made from the same metal or at least a metal compatible with the matrix metal as the sheathing material is at least in part incorporated in the end product formed.

One preferred arrangement will hereinafter be described with reference to the accompanying drawings, in which :-

Figure 1 is a partial cross-sectional view of the die chamber of a hot chamber die casting device according to the present invention;

Figure 2 is a partial cross-sectional view similar to Figure 1 showing an alternative preferred embodiment; Figure 3 is a partial cross-sectional view similar to Figure 1 showing a still further preferred embodiment.

Figures 4, 5 and 6 are respective cross-sectional views taken on line I-I of Figures 1 to 3 showing different possible arrangements within the inlet molten metal delivery path of the hot chamber die casting device. The annexed drawings illustrate various features of a hot chamber casting device 10. Molten metal can be delivered by any known method or apparatus to the inlet path 11 of the casting device 10 which is formed in a fixed die part 12. A die cavity 13 is formed between the fixed die part 12 and a movable die part 14 with the inlet path 11 leading into the die cavity 13. In the drawings, the die cavity 13 is shaped so as to enable a power steering pump pulley for a motor vehicle to be die cast but it will be apparent that many other shapes can be die cast according to the principles of the present invention. The fixed part die part 12 includes a sprue bushing 15 through which the inlet passage or runner 11 is formed. Prior to a casting operation, a cartridge 16 is positioned within the inlet runner 11 as illustrated in Figures 1 , 2 and 3 with the structure of the cartridge 16 being as described hereinafter. Conveniently, the cartridge 16 may be mounted at least partially on a sprue post 17 or any other means might be utilised to locate the cartridge 16 as desired in the inlet runner 11. The cartridge 16 comprises an outer structural sheath 18 and a predetermined quantity of filler material particles 19 depending on the desired quantity of such material in the finished product. The filler material particles are conveniently microspheres such as fly-ash but many other forms of filler material could also be utilised.

During a die casting operation, the cartridge 16 is first positioned as desired in the inlet runner 11 and the die parts 12 and 14 are closed and pressed against one another. Thereafter, molten metal (conveniently magnesium, aluminium or alloys of magnesium and aluminium) is introduced into the die cavity 13 under high pressure through the inlet runner 11. At least part of the sheath material 18 is ruptured and the filler material is carried into the die cavity 13 with the molten metal while being dispersed throughout the molten metal. The introduction of the molten metal into the die cavity 13 occurs very rapidly (often in less than a second) which enables the filler material particles to disperse well throughout the molten metal. Further, it will be apparent that in the illustrated embodiments, the cartridge 16 is located right at the introduction point to the mould cavity such that there is insufficient time for the filler material particles 19 to adversely react with the molten metal. Conveniently, the sheath material 18 may be a metal foil such as aluminium foil, magnesium foil or a combination of both as illustrated in Figure 1 with the whole outer wall of the cartridge being formed by the foil. In other preferred arrangements as shown in Figures 2 and 3, the sheath may be preformed as a thin metal conical container 20 with the metal being either aluminium or magnesium or alloys of these metals. The container 20 is then capped off at either end 21 or 22 by a thin metal foil (either aluminium, magnesium or alloys of same). The sheath 18 is preferably filled with the desired paniculate material prior to being positioned in the inlet runner 11. The cartridge 16 thus formed by either of the above described methods may contact the wall of the inlet runner 11 or may have a clearance fit within the runner as shown in the drawings. The configuration of the cartridge 16 of particuiate material may vary depending on the nature of the product being produced and the desired dispersion of the particuiate material. In the case of producing a pulley wheel as illustrated, it may be desired to achieve a reasonably high level of filler material 19 (fly-ash or microspheres) in the region of the outer peripheral pulley grooves. In this situation the package of paniculate material may have a relatively small distance or no distance between it and the wall 23 of the inlet runner 11 so that a reasonably high proportion of the filler material 19 is pushed in front of the molten metal towards the extremity of the mould cavity. If this is not a requirement and a more even distribution of paniculate material is required, then a greater distance between the sheath and the sprue wall might be provided. Further, in some situations, it may be desirable to give the sheath a non-circular cross-section (eg. polygonal or wave as shown, for example in Fig. 6) so that the space between the wall 23 of the inlet runner 11 and the sheath 16 is greater at different circumferential locations. It may also be desirable, in some situations, to vary the thickness of the sheath material 19, eg. thicker near the entry to the die or mould cavity and thinner at its free end to assist with rupture of the sheath 18 and achieving a desired dispersion of the particuiate material 19.

In a further embodiment, it is proposed to automate introduction of cartridges 16 of the above described format into the inlet runner 11 of the die casting apparatus. This might be achieved by placing the cartridges 16 in a feed magazine (not shown) so that they are positioned sequentially, as illustrated in the drawings, each time the die is opened to allow removal of the cast end product. Thus, when the die is closed, it will immediately be ready for a new die casting operation. In a still further arrangement, it is possible to locate the particuiate filler material (fly-ash or the like) in individual cartridges or pockets formed on an elongated chain of such cartridges or pockets. Such a chain could be formed by metallic foil (typically magnesium, aluminium or their alloys) utilising the foil as the carrier for the chain. Alternatively, the foil cartridges or pockets containing the fly-ash or other particuiate filler material could be sequentially mounted on a web of some other material to deliver the cartridges to the die casting machine. In such a configuration, a single or possibly multiple cartridges or pockets could be separated from the carrier as the die closes so as to leave the or a selected number of such cartridges or pockets in the inlet runner 11 prior to injection of molten metal.

Arrangements as described above have been found to work satisfactorily in practice. It should however be appreciated that high pressure die casting techniques are not the only possible techniques that could be used. It is believed the methods described above might be used in hot or cold chamber die casting, squeeze casting, injection moulding, semi-solid forming, gravity/sand/centrifugal casting and continuous casting. When high injection pressures are not used in the moulding process, it is possible to simply inject through a nozzle the desired particuiate material into the liquid matrix introduction path. If turbulent conditions are not created by the liquid matrix introduction path itself then it might be desirable to provide specific turbulence enhancing devices in the introduction path to promote mixing of the particuiate material with the matrix material.

Claims

THE CLAIMS DEFINING THF INVENTION ARE AS FOLLOWS:

1. A method of forming a product comprising heating a metal matrix material to its liquid state, introducing said liquid metal matrix material to a mould or die cavity while still in its liquid state, and introducing a volume of particuiate filler material into said liquid matrix material either at or immediately prior to an entry point of said liquid metal matrix material into said mould or die cavity.

2. A method of forming a composite product comprising the steps of providing: a mould or die with a mould or die cavity; locating a volume of particuiate material in a path for the flow of liquid matrix material into said die or mould cavity, said particuiate material being located in an outer sheath capable of being at least partially ruptured by liquid matrix material flowing into said die or mould cavity; and heating a matrix material to its liquid state and arranging same to flow past said volume of particuiate material whereby said particuiate material is carried with and dispersed through said liquid matrix material within said die or mould cavity.

3. A method according to Claim 2, wherein said matrix material is a metal.

4. A method according to Claim 3, wherein said metal is aluminium, magnesium, zinc, tin or alloys of aluminium, magnesium, zinc or tin.

5. A method according to Claim 3 or Claim 4, wherein said particuiate materials are microspheres.

6. A method according to Claim 5, wherein the microspheres are ceramic microspheres.

7. A method according to Claim 5, wherein the microspheres are fly-ash.

8. A method according to any one of Claims 3 to 7, wherein the sheath material is a metal.

9. A method according to Claim 8, wherein the metal is a metal foil.

10. A method according to Claim 8, wherein the sheath material is formed as a container with container walls and an open mouth region closed by a metal foil layer.

11. A method according to Claim 10, wherein the container has opposed open ends each of which is closed by a metal foil layer.

12. A method according to any one of Claims 8 to 11, wherein the metal of the sheath material is compatible with the metal forming the matrix material.

13. A method according to Claim 12, wherein the metal of the sheath material is aluminium, magnesium, tin, zinc or alloys of aluminium, magnesium, tin or zinc.

14. Apparatus for forming a composite product comprising a mould or die including a mould or die cavity, means for receiving and introducing a molten metal matrix material into said mould or die cavity, and means for introducing a volume of particuiate material into said molten metal matrix material either at or immediately prior to said molten metal matrix material entering said mould or die cavity.

15. Apparatus comprising a mould or die cavity, a liquid flow path for liquid matrix material leading into said mould or die cavity, and means located in said liquid flow path either at or immediately before an entry point into the mould or die cavity to support a volume of particuiate located in an outer sheath, said outer sheath being adapted for rupture upon said liquid matrix material passing along said liquid flow path.

16. Apparatus according to Claim 15, wherein said sheath material is a metal.

17. Apparatus according to Claim 16, wherein the metal is a metal foil.

18. Apparatus according to Claim 16, wherein the sheath material is formed as a container with container walls and an open mouth region closed by a metal foil layer.

19. Apparatus according to Claim 18, wherein the container has opposed open ends each of which is closed by a metal foil layer.

20. A cartridge for location in an inlet flow passage of a die or mould, said cartridge having an outer wall of metal configured to be positioned in said inlet flow passage and retaining particuiate filler material within an inner space thereof.

21. A cartridge according to Claim 20, wherein the outer wall includes at least one section which is capable of rupture by molten metal flowing through said inlet passage.

22. A cartridge according to Claim 21 , wherein the or each said section is formed by a metal foil.

23. A cartridge according to any one of Claims 20 to 22, wherein the outer wall is formed by a metal foil.

24. A cartridge according to any one of Claims 20 to 23, wherein the filler material is fly-ash.

25. A cartridge according to any one of Claims 20 to 24, wherein the metal of said outer wall is magnesium, aluminium, zinc, tin or alloys of magnesium, aluminium, zinc or tin.

26. A method of die-casting metals with a dispersion of particuiate filler material, said metal injected as molten metal into a die cavity of a die, the injection of the molten metal into said die cavity being through an inlet runner leading into the die cavity, said method comprising: inserting into said runner a cartridge containing a predetermined volume of particuiate filler material to be dispersed in a metal casting, said cartridge being sealed by at least one section formed by a metal foil layer so as to retain the filler material within the cartridge; injecting molten metal into the cavity through said cartridge, thereby rupturing the foil layer carrying the filler material into the cavity while intermixing the particuiate filler material with said molten metal; and allowing said molten metal to solidify in the die cavity before removing same.

27. A method according to Claim 26, wherein the cartridge is made of a metal compatible with the molten metal injected into the die cavity.

28. A method according to Claim 27, wherein the cartridge is made of the same metal as the molten metal injected into the die cavity.

29. A method according to any one of Claims 26 to 28, wherein the molten metal is an aluminium or magnesium alloy.

30. A method according to any one of Claims 26 to 29, wherein the filler material is fly-ash.