GB2132524A

GB2132524A - Casting aluminium or aluminium alloys on to other metal materials

Info

Publication number: GB2132524A
Application number: GB08331135A
Authority: GB
Inventors: Neil Anthony Graham; David Alec Parker; Dr Robert Munro
Original assignee: AE PLC
Current assignee: AE PLC
Priority date: 1982-11-24
Filing date: 1983-11-22
Publication date: 1984-07-11
Also published as: AU2265683A; WO1984002096A1; EP0126748A1; IT8323831A0; IT8323831A1; IT1167008B; GB8331135D0

Abstract

A method of connecting aluminium or aluminium alloy to another metal material in which the other metal material (13) is connected first to a porous metal material (12). This may be by brazing or welding. This assembly is then placed in a die and the aluminium or aluminium alloy (10) is fed under gravity to the die and then solidified under pressure in a squeeze casting technique. The aluminium or aluminium alloy (10) penetrates the porous metal material (12) so that, on solidification, the aluminium or aluminium alloy (10) is firmly connected to the other material (13). This can find particular application in the manufacture of pistons for internal combustion engines where the piston body is of aluminium of aluminium alloy and a wear of heat-resistant insert is of ferous material. The insert may form a crown of the piston or an expansion control insert or a piston ring groove or an entrance to a combustion bowl or a combination of these features.

Description

SPECIFICATION The connection of aluminium or aluminium alloys to other metal materials The invention relates to the connection of aluminium or aluminium alloys to other metal materials and particularly, but not exclusively, to such connections in pistons for internal combustion engines.

Because of their comparatively light weight, aluminium and aluminium alloys find wide use in many engineering appiications, for example, in the manufacture of pistons for internal combustion engines. They suffer, however, from the disadvantages that, as compared with many other metal materials, such as ferrous materials, they do not wear well and are not well able to withstand elevated temperatures. In the case of pistons for internal combustion engines, for example, aluminium and aluminium alloys are not well able to withstand the temperatures found in the combustion chambers of internal combustion engines and cannot readily resist the wear of steel piston rings commonly carried by such pistons.

Accordingly, there have been various proposals for reinforcing parts of articles of aluminium or aluminium alloy which are subjected to high temperatures or to wear with members of other metal materials. In all such cases, however, there has been the problem of connecting the material securely to the aluminium or aluminium alloy since any failure of the connection can have far reaching consequences.

One proposal for overcoming this problem has been to cast the aluminium or aluminium alloy around the material. Examples of this are shown in our British Patent Specification No. 1 292 808 in which an insert of a ferrous material is cast into a piston of aluminium or aluminium alloy. A further example is in British Patent Specification No.

548 400 in which an aluminium or aluminium alloy piston is cast around a ferrous insert which forms a wall or walls of a piston ring groove.

Such a casting technique may not, however, create a secure bond between the aluminium or aluminium alloy and the ferrous material. The bond has been sought to be improved by use of processes such as the 'Al-Fin' process but this requires further manufacturing steps.

In addition, casting is not suitable where it is not possible to surround the majority of the material with the aluminium or aluminium alloy.

For example, where a piston of aluminium or aluminium alloy is provided with a combustion bowl, it is desirable to reinforce the entrance of the combustion bowl with a heat-resistant ferrous material, but this cannot readily be done by the previously proposed casting method.

According to a first aspect of the invention, there is provided a method of connecting aluminium or aluminium alloy to another metal material and comprising locating the other metal material relatively to a porous metal material, inserting the other metal material and the porous metal material into a die, gravity filling the die with molten aluminium or aluminium alloy and then solidifying the molten aluminium or aluminium alloy under pressure so that the molten aluminium or aluminium alloy penetrates at least a portion of the porous material to connect the aluminium or aluminium alloy to the other metal material.

According to a second aspect of the invention, there is provided a piston for an internal combustion engine having a body of aluminium or aluminium alloy connected to a reinforcement of another metal material by the method of the first aspect of the invention.

According to a third aspect of the invention, there is provided a piston for an internal combustion engine and having a body of aluminium Qr aluminium alloy and including a reinforcement of another metal material, the reinforcement being connected by a braze or a weld to a porous metal material and the aluminium or aluminium alloy body penetrating the porous material, at least partially, to connect the reinforcement to the body.

The following is a more detailed description of some embodiments of the invention, by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a cross-section of a first embodiment of a piston for an internal combustion engine and including a crown reinforcement, Figure 2 is a cross-section of a second embodiment of a piston for an internal combustion engine and including a combustion bowl reinforcement, Figure 3 is a cross-section of a third embodiment of a piston for an internal combustion engine and including a combined crown and combustion bowl reinforcement, Figure 4 is a cross-section of a fourth embodiment of a piston for an internal combustion engine, and including a reinforcement around an entrance of a combustion bowl, Figure 5 is a cross-section through a crown end of a fifth embodiment of a piston for an internal combustion engine and including a reinforced crown and combustion bowl and reinforcements for forming piston ring grooves, Figure 6 is a cross-section of a sixth embodiment of a piston for an internal combustion engine and including a reinforced crown having a heat-insulating barrier, Figure 7 is a cross-section of a seventh embodiment of a piston for an internal combustion engine and including a reinforced crown having a heat-insulating barrier, Figure 8 is a cross-section of an eighth form of piston for an internal combustion engine and including a reinforced crown and combustion bowl and an insulating heat barrier, and Figure 9 is a cross-section of a ninth form of piston for an internal combustion engine and including a reinforced crown separated from the remainder of the piston by a heat-insulating barrier.

All the embodiments shown in the drawings have certain features in common. These are described generally below and are to be understood to be present in each embodiment.

All the embodiments show a piston having a body 10 of aluminium or aluminium alloy with a crown end 11. In all the embodiments, the piston body is produced by a squeeze casting process in which molten aluminium or aluminium alloy is passed under gravity (not under pressure) into a closed die where the molten metal is solidified under a high load which may be many tonnes.

Prior to the filling by molten metal, a required reinforcement is placed in the die and may take any of the forms described below with reference to the drawings. The piston may be cast 'crownup' (i.e. with the crown end uppermost) or, preferably, 'crown-down' (i.e. with the crown end lowermost). A piston body 10 produced by squeeze casting is strong because voids, gas pockets and other forms of porosity are almost non-existent so that the material is uniform and homogeneous. In addition, the piston body shrinks very little on being removed from the die so reducing the problems associated with such shrinkage.

In all the embodiments, a material is used which will be described in relation to each embodiments as 'a porous metal material'. This material may be a metallic three-dimensional mesh, or a knitted metal material or a material sold under the trade mark 'RETIMET' or any other suitable material which, while being capable of being shaped into a body of predetermined form, allows molten metal under pressure to penetrate the body and can withstand the temperatures and pressures of casting. The metal may be a ferrous metal or a copper base metal such as a copper alloy.

The individual embodiments will now be described in turn.

In Figure 1, a reinforcement is formed by brazing or welding one face of a generally circular steel plate 13 to an end face of a cylindrical body of porous metallic material 12, whose area is generally the area of the plate 13. The steel plate 13 and the porous metal material 12 are then placed in the die and the piston-forming squeeze casting step is performed as described above to produce the piston body 10.

During squeeze casting, molten aluminium or aluminium alloy is forced into the pores in the porous metal material 12 until the pores are completely filled. The fact that the casting takes place under a load of many tonnes ensures that complete filling is reliably achieved.

On solidification, a piston is produced in which the steel plate 13 covers completely the crown end 11 of the piston body 10. The aluminium or aluminium alloy within the porous metal material forms an interlocked connection between these two parts which thus joins the steel plate 1 3 firmly to the body 10. Since the crown is the portion of the piston which is subjected to the highest temperatures, when the piston is in operation in an internal combustion engine, the steel plate 13, being more heat-resistant than the aluminium or aluminium alloy, protects the aluminium or aluminium alloy of the body from the elevated temperatures.

In Figure 2, a reinforcement is formed by brazing an exterior face of a sheet metal combustion bowl 14 to a cup-shaped body of porous metal material 12. The bowl 14 and the porous metal material 12 are both inserted in a squeeze casting die and a piston body 10 is squeeze cast around them, as described above.

Since the solidification of molten aluminium or aluminium alloy takes place under load, the aluminium or aluminium alloy penetrates completely the porous metal material 12.

When the molten material has solidified and is removed from the die, a piston is formed having a combustion bowl 14 which is securely locked to the body 10 by the solidified aluminium or aluminium alloy within the body of porous metal material. Since combustion takes place, in this combustion bowl, the steel plate 13 forms a heatresistant barrier which protects the piston body 10 from the elevated temperatures encountered in the bowl.

Referring next to Figure 3, in this embodiment, a reinforcement is prepared in which a sheet steel member 15 is formed with a central bowl 1 6 and a peripheral flange 1 7. The outer surface of the bowl and the flange are brazed to a correspondingly shaped surface of a body of porous metal material 12 and the reinforcement is then inserted in a squeeze casting die and has the piston body 10 squeeze cast therearound as described above. The pressure applied to the aluminium or aluminium alloy during solidification ensures that the molten aluminium or aluminium alloy penetrates throughout the body of porous metal material 12.

After casting, a piston is produced in which the sheet steel member 1 5 forms a combustion bowl and covers the remainder of the crown between the edge of the combustion bowl and the outer periphery of the piston. This protects the whole crown end 11 of the piston body 10 from the temperatures encountered in use in a combustion chamber of an internal combustion engine. The solidified aluminium or aluminium alloy within the porous metal material 12 forms a firm interlock between the steel members and the piston body.

Referring next to Figure 4, in this embodiment, a reinforcement is formed by an annular steel member 18 which is of generally triangular section and which has one surface brazed to a correspondingly shaped surface of an annular body of porous metal material 1 9. This is then placed in a squeeze casting die with the annular member 1 8 concentric with the axis of the piston to be cast. The die is provided with a hemispherical core (not shown) around which the insert 18 extends.

The piston body 10 is then squeeze cast as described above. The molten material penetrates the porous metal material 1 2 so that, on solidification, the steel member 18 is securely locked to the piston body 10. The insert thus forms an entrance extending around a combustion bowl 20 formed by the core. In use of such a piston in an internal combustion engine, the entrance to the combustion bowl is subjected to the highest temperatures and is susceptible to heat damage because of the comparative thinness of the material at this point. The steel insert 1 8 is well able to withstand these temperatures; thus protecting the aluminium or aluminium alloy of the piston body 10.

Referring next to Figure 5, this embodiment is generally similar to the embodiment of Figure 3 and parts common to Figures 5 and 3 will not be described in detail and will be given the same reference numerals.

In this embodiment, the reinforcement is formed by a greater amount of porous metal material 12 than in the Figure 3 embodiment and this material is of substantial thickness in an axial direction. The porous metal material 12 is brazed to two annular members 21,22 which are arranged concentric with the centre of the generally circular sheet steel member 1 7. The two annular members 21, 22 are of a ferrous material and are axially spaced from one another and from the sheet steel member 1 7.

The upper surface of the sheet steel member 17 is connected to a member 23 of similar shape, also made of sheet steel, via an annular washer 24; the connections being by welding. The chamber formed between the two members 1 7, 23 may be evacuated.

This reinforcement assembly is inverted and placed in the squeeze casting die, and the piston body is squeeze cast therearound so that the molten aluminium or aluminium alloy penetrates the porous metal material to connect the assembly securely to the piston body 10. Upon removal from the die, one or more piston ring grooves are machined in the first insert 21. The second insert 22 acts as an expansion control insert for the piston and the second sheet steel member 23 provides a combustion bowl 24. The chamber between the two sheet steel members 1 7, 23 provides an insulating heat barrier gap so isolating the piston body 10 from the effects of heat in the combustion chamber.

It will be appreciated that this technique could be used just to provide piston ring grooves and an expansion control insert (without providing the reinforced and insulated crown).

Referring next to Figure 6, in this embodiment, a reinforcement is formed by a closed annular steel box welded from steel plates with upper and lower circular ends 25, 26 and an annular wall 27.

The ends 25, 26 and the wall 27 are brazed to a porous metal material 1 2a contained within the box.

The outer surface of the lower end 26 is also brazed to a cylindrical body of porous metal material 1 2b.

This assembly is placed in a squeeze casting die and the piston body 10 is squeeze cast from molten aluminium or aluminium alloy, as described above. The molten aluminium or aluminium alloy penetrates the porous metal material 1 2b and, on solidification, connects firmly the piston body 10 the steel box. Plainly, the molten material does not reach the porous metal material 12a, because it is contained within the box formed by the steel plates.

The upper end 25 of the assembly forms a heat-resistant crown surface of the piston. The annular wall 27 is subsequently formed with one or more wear-resistant piston ring grooves (not shown). The unfilled porous metal material 1 2a within the box forms an heat-insulating barrier between the crown end of the piston and the aluminium or aluminium alloy body.

In the embodiment of Figure 7, a reinforcement is formed by two generally circular steel plates 28, 29 which have sandwiched between them a layer of porous metal material 1 2a which is brazed thereto. The other surface of one of the sheet steel members 29 is brazed to a cylindrical body of porous metal material 1 2b.

it will be appreciated that the two plates 28, 29 may be formed with registering central depressions so that the upper plate 28 defines a combustion bowl in the completed piston. In addition, the upper plate 28 need not be of steel, if could be of any other suitable material.

This assembly is placed in a squeeze casting die, and the piston body 10 is squeeze cast from molten aluminium or aluminium alloy, as described above, with the molten aluminium or aluminium alloy penetrating the porous metal material 126. It will be understood that, of course, the molten aluminium or aluminium alloy cannot pass the steel plate 29 and so the porous metal material 1 2a remains unpenetrated by the molten aluminium or aluminium alloy.

On solidification, a piston is formed in which one steel plate 28 forms a heat-resistant surface to the crown of the piston while the unpenetrated porousmetal material 1 2a forms an insulating layer between the crown end of the piston and the body 10 of the piston. The porous metal material 1 2b forms a secure connection between the piston body 10 and the plates 28, 29.

Referring next to Figure 8, this embodiment is similar to the embodiment of Figure 5 and parts common to Figures 5 and 8 will not be described in detail. In this embodiment, the two annular inserts 21,22 are dispensed with and the porous metal material 12 is provided simply for attaching the two spaced steel sheets 1 7, 23 to the piston body 10.

Referring to Figure 9, this embodiment is similar to that of Figure 1 and parts common to this Figure and to Figure 9 are given the same reference numerals and will not be described in detail. In this embodiment, the porous metal material 12 has, extending partially into the material from one surface thereof, a filling of a water-soluble salt. The circular steel plate 1 3 is brazed to this surface. The aluminium or aluminium alloy piston body is then squeeze cast around this assembly with aluminium or aluminium alloy penetrating the unfilled porous metal material and the salt preventing penetration of the filled portion. The cast piston is then removed from the squeeze casting die and the salt flushed away with water.In this way, the unpenetrated porous metal material forms a heat barrier 31 between the sheet steel crown 13 and the aluminium or aluminium alloy body 10.

This technique may be used in the embodiments of Figures 2, 3 and 4.

It will be appreciated that, in the embodiments described above with reference to the drawings, the region below the crown is reinforced by the porous metal material. It may therefore be advantageous to arrange that the porous metal material extends to the piston ring band so that one or more of the piston ring grooves is formed in the porous metal material reinforced portion of the piston.

It will also be appreciated that in all the embodiments described above with reference to the drawings, an assembly of porous metal material connected to a ferrous or other suitable metal, material is placed in a squeeze casting die and the piston is then cast. Although this can, as mentioned above, be down crown-up or crowndown, there are considerable advantages to crown-down casting.

These include the fact that the molten metal can be easily fed into the die at the top of the die.

This is because the insert does not obstruct the top of the die (as it would in crown-up casting). In addition, there is a reduced likelihood of the molten metal solidifying before the squeeze casting pressure is applied. This is a danger in crown-up casting where the lower part of the die defines the piston skirt which is of much lesser thickness that the crown so affording the possibility of the molten metal of the skirt portion solidifying while the molten metal is being poured into the die (i.e. before pressure is applied). This means that the piston is not fully squeeze cast. In crown-down squeeze casting, the initial molten metal forms the crown of the piston and, because of the volume of the crown, the molten metal does not solidify before the load is applied. In this way, a fully squeeze cast piston is produced.

A further advantage of crown-down squeeze casting such assemblies is that the molten metal often contains impurities such as dross and oxides which rise to the surface of the molten metal during pouring. In crown-down casting these only affect the lower end of the skirt, which is generally of little significance. In crown-up squeeze casting with an insert assembly, the impurities can enter the assembly and this is undesirable since it could weaken the connection formed during casting.

There is also the advantage that, in general in squeeze casting, solidification commences from the lower end of the die. In crown-down squeeze casting, this means that the crown solidifies first and this reduces the possibility of differential solidification rates across the cross-section of the piston from distorting the piston, because at the lower end of the die any differences are minimal.

In crown-up casting, the crown is at the upper end of the die, where maximum differential solidification occurs, so giving the possibility of distortion of the assembly by such differential solidification.

Although the embodiments described above with reference to the drawings have been pistons, it will be appreciated that the method described above may be used where ever it is desired to connect another metal material to aluminium or aluminium alloy. Examples may be found in the automotive industry, the machine tool industry and in any other casting process.

Claims

1. A method of connecting aluminium or aluminium alloy to another metal material and comprising locating the other metal material relatively to a porous metal material, inserting the other metal material and the porous metal material into a die, gravity filling the die with molten aluminium or aluminium alloy and then solidifying the molten aluminium or aluminium alloy under pressure so that the molten aluminium or aluminium alloy penetrates at least a portion of the porous material to connect the aluminium or aluminium alloy to the other metal material.

2. A method according to claim 1, wherein the other metal material is a ferrous material.

3. A method according to claim 1 or claim 2, wherein the other metal material is located relatively to the porous metal material by the arrangement of the porous metal material around the other metal material.

4. A method according to claim 1 or claim 2, wherein the other metal material may be located relatively to the porous metal material by a weld or braze therebetween.

5. A method according to any one of claims 1 to 4, and comprising arranging the molten aluminium or aluminium alloy to penetrate only a portion of the porous metal material, to leave unpenetrated porous metal material between the aluminium or aluminium alloy and the other metal material to provide a heat-insulating barrier between the other metal material and the aluminium or aluminium alloy.

6. A method according to claim 5 and comprising, before insertion of the porous metal material into the die, placing a removable filling in that portion of the porous metal material which is to be unfilled by the aluminium or aluminium alloy, then performing the inserting, filling and pressure solidifying steps, with the molten aluminium or aluminium alloy being prevented from penetrating said filled portion by said filling, and then removing the filling from the portion.

7. A method according to claim 5, wherein the portion of the porous metal material which is to be unfilled is separated from the portion which is to be filled by a physical barrier.

8. A method according to claim 7, wherein the porous metal material may be divided into two parts by an area of metal material connected to both parts.

9. A method according to any one of claims 1 to 8, wherein the aluminium or aluminium alloy forms the body of a piston for an internal combustion engine and the other metal material is more resistant than aluminium or aluminium alloy and forms a reinforced part of the piston.

10. A method according to any one of claims 1 to 9 and comprising placing the metal material and the porous metal material at a base of the die so that the molten aluminium or aluminium alloy fills the die above the metal material and the porous metal material.

11. A method of connecting aluminium or aluminium alloy to another metal material, substantially as hereinbefore described with reference to the accompanying drawings.

12. A piston for an internal combustion engine having a body of aluminium or aluminium alloy connected to a reinforcement of another metal material by a method according to any one of claims 1 to 11.

13. A piston for an internal combustion engine and having a body of aluminium or aluminium alloy and including a reinforcement of another metal material, the reinforcement being connected by a braze or weld to a porous metal material and the aluminium or aluminium alloy body penetrating the porous material, at least partially, to connect the reinforcement to the body.

14. A piston according to claim 13, wherein the other metal material forms or includes a combustion bowl for the piston.

1 5. A piston according to claim 13 or claim 14, wherein the other material forms an expansion control insert located within the piston body.

1 6. A piston according to any one of claims 1 3 to 15, wherein the other metal material forms an annular insert extending around the piston body for the formation therein of a piston ring groove or grooves.

1 7. A piston according to any one of claims 13 to 16, wherein the other metal material forms an extrance extending around a combustion bowl formed in the aluminium or aluminium alloy of the piston body.

1 8. A piston for an internal combustion engine substantially as hereinbefore described with reference to any one of Figures 1 to 9 of the accompanying drawings.