WO2002090020A1

WO2002090020A1 - Method and device for quickly and economically forming at least one die casting without casting material wastage

Info

Publication number: WO2002090020A1
Application number: PCT/IB2002/001397
Authority: WO
Inventors: Pietro Maurizio Perucchi
Original assignee: Alcast S.R.L.
Priority date: 2001-05-04
Filing date: 2002-04-24
Publication date: 2002-11-14

Abstract

A method for forming at least one die casting, in particular the rotor cage surrounding a lamination pack (7) of an electric motor, said method comprising the use of a mould (1) in which a cavity (6) is provided into which a molten material is injected and which has the shape of said die casting, an injection piston (13) being provided to compress said material in said cavity (6) until said die casting is formed; the molten material is fed into a chamber (12) within which the piston (13) moves, this latter then being moved in order to push the molten material into the said cavity (6), said movement terminating in correspondence with the cavity (6) to enable the die casting to be formed in it without feedhead. The device for implementing the aforesaid method is also claimed.

Description

METHOD AND DEVICE FOR QUICKLY AND ECONOMICALLY FORMING AT LEAST ONE DIE CASTING WITHOUT CASTING MATERIAL WASTAGE

The present invention relates to a method for forming at least one die casting, in accordance with the introduction to the main claim. The invention also relates to a device for implementing the afβresaid method.

The present invention is applicable within a mould for obtaining a die casting from any metal material and for any use; for example, the invention is usable within a mould for obtaining an electric component (for example an electric motor rotor cage), a mechanical component (for example a connecting rod or a gearwheel), or articles of common use (for example for cooking) or toys. A known method for obtaining a die casting comprises creating within a mould, defined by two dies or half-moulds movable relative to each other, a cavity into which the molten material (for example a metal such as aluminium) is fed and then subjected to compression by a piston or equivalent pressing member. As a result of the action of this latter, the molten material completely occupies the aforesaid cavity and cools within it to form the die casting. Said die casting can be extracted by opening the mould.

With particular but non-limiting reference to the field of electric rotors, these present a rotor cage obtained by die casting aluminium within an appropriate mould in which the aforesaid method is conceptually implemented. In this specific case, a single mould can also enable a plurality of rotor cages (and hence rotors) to be obtained. In such a case, a previously assembled lamination pack is placed in each mould cavity. After mould closure, this pack is exposed to the molten material injected into the piston cavity, said material suitably wrapping the lamination pack so as to incorporate it after its cooling. However, on opening the mould, the rotor obtained presents a considerable excess of casting material (feedhead) which is separated from it. If the mould enables a plurality of rotors (or rotor cages about corresponding lamination packs) to be simultaneously obtained, these are all connected together by the feedhead which only in some cases becomes removed from the produced castings on opening the mould. The feedhead is then remelted and reused. However this reuse involves costs and is incomplete as part of the recovered aluminium oxidizes and is successively scrapped or, if the remelting operation is repeated several times, "contaminates" the pure aluminium fed into the mould, with obvious drawbacks.

In addition, the aforesaid method is implemented within a mould in which the aluminium passage rate and pressure are high because of the presence of a single presser piston for feeding the molten material into several cavities via small cross-section passages. This results in adhesion of the aluminium to the iron of the lamination pack and the possible presence of weakened regions within the rotor cages deriving from porosity or bubbles caused by aluminium shrinkage or by gas (for example deriving from mould lubricants or present in the process) after its compression and subsequent cooling. An object of the present invention is to provide a method, and a corresponding device for its implementation, which is improved compared with known methods, and the corresponding moulds.

A particular object of the invention is to provide a method and device of the aforesaid types which enable at least one die casting, for example a rotor cage of an electric rotor, to be obtained which is substantially free of feedhead material and which therefore enable the die casting to be obtained by the substantial melting of just that quantity of material, for example aluminium, necessary for its formation.

Another object is to provide a method which enables the aforesaid die casting, for example of aluminium, to be obtained presenting a material density which makes it superior to that obtainable with traditional methods.

A further object is to provide a method and a corresponding device which enable the molten material to be fed into the mould and into a component possibly present therein at a rate and pressure which are lower than those obtainable with traditional methods and moulds, so obtaining a casting with substantially non-existent deformations; in the specific case of an aluminium rotor of an electric motor, the method and device enable a rotor cage to be obtained with substantially non-existent adhesion to the lamination pack, with excellent molten material (aluminium) balance.

Another object is to provide a die casting device of the stated type which is extremely simple compared with known devices, which is of extremely small bulk compared with these latter, and which presents a high duty cycle rate and a lower mould cost.

A further object of the present invention is to provide a device which makes it unnecessary to correctly meter the quantity of molten material to be fed into the device cavity within a die casting mould in which the aforesaid method is implemented, while still obtaining correctly shaped products which are integral both at the macroscopic and microscopic level.

These and further objects which will be apparent to an expert of the art are attained by a die casting method and device in accordance with the accompanying claims. The present invention will be better understood from the accompanying drawing, which is provided by way of non-limiting example and in which:

Figure 1 is a lateral cross-section through a first embodiment of a mould according to the invention;

Figure 2 is a view similar to that of Figure 1 , showing a second embodiment of a mould according to the invention;

Figure 3 is a view similar to that of Figure 1 , showing a third embodiment of a mould according to the invention;

Figure 4 is a cross-section through a fourth embodiment of a mould according to the invention;

Figure 5 is a section on the line 5-5 of Figure 4;

Figure 6 is a schematic cross-section through a member for carrying a metered quantity of molten material into a mould according to the invention;

Figure 7 is a lateral cross-section through a further embodiment of a device according to the invention applied to a die casting mould;

Figure 8 is a section on the line 2-2 of Figure 7;

Figure 9 is a view similar to that of Figure 7, but showing a different embodiment of a device according to the invention in a first operative stage;

Figure 10 is a view similar to that of Figure 9, but with the device represented therein shown in a second operative stage; and

Figure 11 is a view similar to that of Figure 7, but showing a further embodiment of a device according to the invention.

With reference to Figure 1, this shows a mould 1 comprising a portion or container 2 in which a first and a second half-mould (or dies) 3 and 4 are movable relative to each other. The relative movement between these dies or half-moulds is obtained in known manner and is therefore not described. Between the half-moulds or dies 3 and 4 there is defined a die casting cavity 6 in which, in the example, a lamination pack 7 is placed to define, with the obtained casting, a rotor for an electric motor. Said die casting has the shape of the cavity 6. The pack 7 is mounted on a pin 8 which is inserted into the cavities 9 and 10 of the respective half-moulds or dies 3 and 4.

Between a central part 11 (or half-die) of the second die 4 and the container 2 an annular chamber 12 is present in which an injection piston 13 of corresponding shape (annular) moves, driven in known manner (for example hydraulically) and not shown. The chamber 12 communicates with a port 14 provided in the container for feeding the molten material (for example aluminium); the communication is closed by the piston when it moves towards the cavity 6.

This latter, in the examined example, presents annular recesses 15 and 16 provided in two dies 3 and 4, the recess 16 provided in the die 4 communicating with the annular chamber 12. Between this latter and said recess 16 a boundary region or surface 17 is present.

The implementation of the method of the invention commences with the feed of the molten material, for example aluminium, aluminium alloy or other metal, into the port 14 and from there to the chamber 12. In the implementation example, the molten material is in a metered quantity (obtained by the method described hereinafter) such as to fill the cavity 6 and the interstices present within the lamination pack 7 (known and not shown) in order to obtain the desired rotor cage.

The molten material (aluminium) falls from the mouth 14 into the chamber 12 and partially fills it; the piston 13 is then driven towards the cavity 6 in order to feed the entire said aluminium thereinto. In particular, the pressure of the piston (sufficiently low, for example less than 100 kg/cm²) causes all the aluminium to fill the cavity 6 at all its points and to fill the interstices present in the pack 7. By virtue of the fact that the quantity of molten aluminium is metered, the cavity 6 and said interstices become filled when the piston 13 is in proximity to the boundary region 17. Any further movement of the piston is prevented by the presence of the aluminium in front of it.

The piston is maintained in a thrust state in the attained position for the time necessary for the aluminium to cool and solidify without it producing voids in its interior during its shrinkage (shrinkage porosity); the first die 3 is then moved so that it detaches itself from the pack 7 (and from the die casting), and the piston 13 is then again moved towards the cavity 6 with the result that it exerts a thrust on the rotor present in it, to cause it to fall out of the mould. The die casting operation does not result in any feedhead formation in that, during the described pressing operation on the aluminium, the piston 13 is moved exactly as far as the region 17 in which the outer portion of the rotor cage is formed by transferring into the cavity 6 all the molten aluminium fed into the mould. In addition, the speed of movement of the piston is chosen at a low value (for example less than 1 m/s) just sufficient for the flow of aluminium into the cavity 6 to take place sufficiently slowly to fill this cavity without turbulence arising therein; this is to prevent possible turbulence being able to result in a deformed or internally weakened rotor cage. Because of the low flow rate (and pressure) of the aluminium in the cavity 6 (under the thrust of the piston 13), adhesion of the aluminium to the pack 7 is prevented.

In Figure 1, the die 4 is therefore substantially defined by a fixed part (half-die 11) and a movable part (the piston 13)); with reference to Figure 2, in which parts corresponding to those already described in Figure 1 are indicated by the same reference numerals, the die 4 also comprises a further movable part 20. This is internal to the half-die 11 and acts to expel the rotor from the cavity 6 after the die cast cage has been obtained. The movement of this part or expulsion element 20 is obtained in known manner and is therefore not described. The method implemented by the mould of Figure 2 is therefore identical in its steps as that implemented by the mould of Figure 1 , except for the fact that after the die casting operation, the piston 13 remains at rest and the rotor expulsion is obtained by moving the expulsion element 20. It should also be noted that the piston 13 can present within that end surface 22 facing the cavity 6 a plurality of recesses 23 (of equal or different volume and dimensions) to enable usual pins and/or fins to be formed on the rotor cage. Similar recesses 24 can also be provided in the end surface 25 of the first die 3 present at the recess 15.

The first die 3 can also be provided with an expulsion element 27 within an annular portion 28 thereof. The purpose of this is to achieve separation of the die 3 from the die casting by retracting the portion 28 and maintaining the expulsion element 27 at rest.

Embodiments have been described in which a mould 1 provided with a single die casting cavity 6 is represented. However, if the mould 1 possesses a plurality of cavities 6 to enable several die castings to be simultaneously obtained, a chamber 12 and a respective piston 13 will be present at each cavity, said chambers receiving a metered quantity of molten material via suitable channels provided within the mould and connected to one or more feed ports 14. After feeding the molten material into the mould, the entire material reaches the chambers 12 without in any way remaining in the mould channels. Figures from 3 to 5 show a further two moulds in which the axis is inclined to a horizontal plane K in which the moulds lie by an angle a less than 90° (Figure 3) or equal to 90° (Figures 4 and 5). In both the figures, in which parts corresponding to those of the already described figures are indicated by the same reference numerals, the mould 1 comprises a feed port 14 which can be closed by a closure member of side valve type 30 (Figure 3) or 40 (Figures 4 and 5). In Figure 3, the closure member 30 moves within a seat provided in the container 2 parallel to this latter; in Figures 4 and 5 the closure member 40 moves in a direction perpendicular to the container 2.

The function of the members 30 and 40 is to close the port 14 after feeding the molten material into the chamber 12, to prevent it from escaping following movement of the piston 13 towards the cavity 6 (because of the inclined arrangement of the mould to the horizontal).

The movement of the closure member 30 and 40 is obtained in known manner (for example by a hydraulic actuator) and is therefore not described. The use of the moulds. , shown in Figures 3, 4 and 5 is identical to that of the mould shown in Figure 1; consequently this use and the method defined by it will not be further described.

To feed a metered quantity of molten material into the port 14 of the mould 1 the dispenser shown in Figure 6 is used. In this, the dispenser is indicated by 60 and is associated with a cup withdrawal element 61 carried by a support 62 movable along perpendicular axes X-Y and rotatable about an axis Z perpendicular to the first two. Between the support 62 and the cup element (or simply cup) 61 an aperture 63 is present. This element is arranged to carry the molten material to the mould 1 , as described hereinafter. A regulator element 64 is inserted into the cup 61 to regulate the quantity of molten material withdrawn from a crucible 65. The regulator element 64 has the double function of enabling a metered quantity of molten material to be fed into the cup and of enabling this material to be safely transported without it reducing in quantity. More specifically, the reg > ulator element 64 comprises an end or dip piece 68 to be inserted into the cup 61. The dip piece is rigid with an at least partly threaded shaft 69 frontally associated with the support 62 and cooperating with female threaded members 70 which when rotated about the shaft 69 causes the shaft 69 to move along the Y axis and with it the dip piece 68, which penetrates into or withdraws from the cup 61. The members 70 are carried by an arm 72 rigid with a shaft 73 subjected to an actuator which moves the arm 72 along a direction parallel to said Y axis (i.e. perpendicular to the cup 61 or to the plane K) to hence raise the element 64 and in particular to extract the dip piece 68 from the cup 61 during its transport from the crucible 65 to the mould 1. In order to feed into this latter a metered quantity of molten material, the relative position of the dip piece 68 within the cup 61 is micrometrically adjusted such that when it (together with the dip piece 68) is immersed into the molten material present in the crucible and then extracted from it, the cup is filled as far as its free edge 78. Said position of the dip piece 68 in the cup defines a first end-of- travel position of the dip piece.

After extracting the cup from the crucible, the actuator is operated to act on the shaft 73 in order to raise it (arrow N of Figure 6) as far as a second end-of-travel position in which the dip piece 68 is at least partly extracted from the cup. As a result of the at least partial emergence of the dip piece 68 from the cup 61 , the free surface 80 of the molten material in the cup is lowered and withdraws from the edge by a distance L such as to enable the cup to be moved (slowly) towards the mould and then rotated (arrow W of Figure 6) about the Z axis to pour the molten material into the port 14 of the mould.

As the material is spaced from the edge 78 of the cup 61 , nothing is lost from this latter during said movement and the desired metered quantity of molten material (such as to fill every point of the cavity 6 of the mould 1 during die casting) can be fed into the mould.

After feeding the molten material into the mould port 14, the cup 61 is returned above the crucible 65, the dip piece is again inserted into it (by moving the shaft

73) and the combination is again immersed into the crucible.

The mould 1 and the aforedescribed dispenser 60 define a die casting device of simple construction and extremely small size, which achieves a high cycle rate at low cost.

Although the described method and device enable products to be obtained without creating feedhead during their production, they have the drawback of requiring correct metering of the molten material to be fed into the die casting cavity to achieve correct movement and positioning of the injection piston relative to the cavity.

The purpose of the embodiment described in terms of various variants in Figures

7-11 is to overcome the drawback of the aforesaid metering of the molten material.

With reference to Figure 7, the annular recess 15 of the die casting cavity comprises, at its end 200, at least two slots 210, 220 communicating with at least one variable volume chamber 230. The chamber 230 is a single chamber if annular; otherwise, each slot communicates with a corresponding variable volume chamber 230 formed within the die 3. In each chamber 230 there moves a piston 240 having a piston rod 250 passing through a shoulder 260 and terminating with a head 270 on which there acts a thrust member 280 interposed, within a cavity 290, between the head and a closed end 300 of said cavity; in the example the member 280 is a compression spring. In the case of an annular chamber 230, the piston 240 is also annular, as is its rod, the head and said member or spring 280.

Heating elements 310, such as electrical resistance elements, are present in the die 3, in correspondence with the slots 210, 220.

During the use of the mould to produce, for example a rotor cage of an electric motor, the molten material (for example aluminium or copper) falls from the feed port 14 and into the chamber 12 to partially fill it; the piston 13 is then moved towards the cavity 6 to feed all of said aluminium into this latter. The pressure of the piston (low, for example less than 100 kg/cm²) causes all the molten material to fill the cavity 6 at all its points and to fill the interstices present in the pack 7.

Any excess molten material, thrust by the piston 13, passes through the slots

210, 220 and into each chamber 230, pressing against the corresponding piston

240 and withdrawing it from the slots. The latter piston moves in accordance with the arrows G of Figure 7 against the corresponding spring 280 which compresses it.

When the piston 13 reaches the region 17, it halts by being opposed in its movement by the molten material (aluminium in the example, or copper) present in the cavity 6.

The piston is maintained in the thrust state in its attained position for the time necessary for the molten material to cool and solidify.

During its cooling, this material undergoes inevitable shrinkage. In the cavity 6, microcavities (of larger or smaller extent depending on the quantity of material contained in the mould) can hence form and be filled by the molten material which has passed through the slots 210 and 220 into each chamber 230. In this respect, from these latter this material (maintained heated and hence molten by the heating elements 310) is pushed towards the cavity 6 by the piston 240. As stated, said material is maintained molten for a longer time than that in said cavity 6 by virtue of the electrical resistance or other heating elements 310 provided about said slots. Specifically, the material in each chamber 230 is maintained molten for the time necessary for the piston 240 to compensate the shrinkage of the molten material within the cavity 6.

After said passage through the slots 210 and 220 and into the cavity 6 has terminated and the time required for solidification of the said material has passed, the first die 3 is moved so that it separates from the pack 7 (and from the die casting) and detaches the excess part of the material, then the piston 13 is further moved towards the cavity 6 with the result that a thrust is exerted on the product present in the cavity 6, causing it to fall out of the mould. The aluminium residues present in each chamber 230 are then removed from the die 3 and the mm is again ready for use.

Hence by virtue of the slots 210, 220, the solidified material which has escaped from the cavity 6 simply breaks off automatically when the mould is opened. The die casting operation does not result in any feedhead formation because, as already described, the piston 13 is moved during aluminium pressing exactly as far as the region 17 in which the outer portion of the rotor cage forms, to transfer all the fed molten aluminium into the mould cavity 6. Likewise, any excess molten material which has passed through the slots 210, 220 and has remained in each chamber 230 does not constitute a true feedhead as it is in minimum quantity because of the small aperture of the slots 210, 220. This small aperture also enables the material to break off on opening the mould, as already stated. Figures 9 and 10 show another embodiment of the invention. In these figures, parts corresponding to those of the already described figures are indicated by the same reference numerals.

This further embodiment comprises a half-mould 3 having at least one variable volume chamber 230 defined between a plurality of relatively movable (see arrows T, P of Figure 9), telescopically coupled concentric parts 3A, 3B, 3C of said half-mould. Specifically, the part 3A is the most inner, the part 3B acts as a jacket for the part 3A, and the part 3C is external and comprises an element 400 coupled to a shaft 410 slidable (arrow J) in a seat 420 of a block 430 associated with the container 2 and acting as a support and guide for the movement of the half-mould 3. The chamber 230 is formed between said parts at the recess 15. The parts 3A and 3B are associated with known mover means (for example hydraulic actuators, not shown) which provide for their independent movement. The embodiment of the invention illustrated in Figures 9 and 10 is used in the following manner, after the molten material has been fed into the cavity 6 and passed into the chamber 230 with at least a part of the material present in the chamber 230 returning to the cavity 6, followed by solidification in said cavity, the part or jacket 3B is moved along the inner part 3A so that the molten material present in the chamber 230 is thrust into the cavity 6 to fill any spaces created within the molten material during its cooling and shrinkage. When expulsion of the material from the chamber 230 has terminated, the part 3C is slightly detached from the cavity 6, to hence separate its contents from that remaining in the chamber 230. The part or jacket 3B is then moved towards the half-mould 4 (arrow D of Figure 10) to thrust what remains in the chamber 230 beyond the free end 480 of the part 3A and detach it from the half-mould 4. The part 3C is finally moved away from the half-mould 4, to hence enable the die casting present in the cavity 6 to be recovered.

Figure 11 shows a further embodiment of the invention. In this figure, parts corresponding to those already described in the preceding figures carry identical reference numerals.

The embodiment of Figure 11 shows the half-mould 3 comprising an internally hollow first (external) element 500 containing a second element 510. In this latter, chambers 230 are present within which pusher elements 540 and 550 move respectively (arrows A and B). The chambers 230 communicate with the slots 210 and 220 during the die casting operation.

Each presser element presents a head 600 associated with a body 610 rigid with a shaft 620 fixed to a head 630 rigid with a piston 640 of a hydraulic actuator 650, the cylinder 660 of which is external (and connected) to a body 670 hollow at 680, the head 630 being located in the cavity 680. Each shaft 620 penetrates into the cavity 680 through an aperture 700 provided in a part 710 of the body 670.

Cylinders 720 of hydraulic actuators 730 not connected to the body (but supported by another part of the mould as is the actuator 650) are present outside the body 670 and are operated simultaneously (by a mould control unit, not shown), the piston 740 of which is rigid with a plate 750 fixed to the first external element 500 of the half-mould 3 by fixing elements (for example screws) 760. The part 710 is instead fixed by mechanical fixing elements (for example screws) 770 to the second (internal) element 510 of the half-mould 3. Finally, the first element 500 presents an aperture 800 in a lower portion 810 in correspondence with the second element 510. Any material portion remaining in any chamber 230 after the die casting operation is expelled from this aperture. This operation takes place in the already described manner. After the material has been fed into the cavity 6 and has passed into the chambers 230, while the material is cooling in said cavity the pusher elements 540 and 550 are moved by the hydraulic actuator 650 towards the cavity 6 via the head 630 and the shafts 620 so as to urge at least part of the material present in the chambers 230 into this cavity. After this step, the actuator 650 operates the pusher elements 540 and 550 to move them away from the cavity 6. Then when the head 630 comes into contact with a plate 820 (opposite the plate 750) of the body 670, it drags this body into movement to withdraw the second element 510 of the half-mould 3 from the first element 500.

It, should be noted that this movement is allowed by the position attained by the bodies 610, having been brought into the vicinity of the plate 750. The actuator 650 is then again operated to move the pusher elements 540, 550 towards the cavity 6 and expel every residue of solidified molten material from the chamber 230, this material escaping from the first element 500 through the aperture 800.

The entire half-mould 3 is then moved away from the cavity 6 by the effect of the actuators 730 acting on the plate 750 rigid with the first element (obviously, the actuator 650 is "under discharge" to enable the piston 640 to move freely, dragged by the action of the first element 500 on the second 510). By virtue of the device of the invention described in Figures 7-11 it is not necessary to exactly meter the quantity of molten material fed into the cavity 6 by the piston 13 as it is in the case of Figures 1-6. Any excess material is recovered in each variable volume chamber 230 and serves to make up any voids created in the die casting after the shrinkage of said material. Moreover, by virtue of the fact that the piston 13 operates at low pressure, copper die castings can be made using ceramic materials for the moulds. This is not possible with traditional moulds as copper has a melting point close to that of steel, the material with which the moulds are made; if high die casting pressures and rates are used, the moulds quickly deteriorate. In the case of ceramic material (of high melting point), the high pressures acting in traditional moulds make its use unsuitable for the construction of such moulds as they would be unable to withstand the thrust stresses generated within them during die casting. With the invention such materials as copper and others can now be die cast in steel or ceramic moulds as the die casting operation is carried out at low pressure.

Finally, by virtue of the invention, a fixed prechosen travel stroke is determined for the injection piston, so precisely determining the position of the mould region 17 in which the piston terminates its travel during the molten material feed into the die casting cavity.

Claims

1. A method for forming at least one die casting, said method comprising the use of a mould (1) in which a die casting cavity (6) is provided into which a molten material is injected and which has the shape of said die casting, an injection piston (13) being provided to compress said material in said cavity (6) until said die casting is formed, characterised by feeding the molten material into a chamber (12) within which the piston (13) moves and which is connected to said cavity, then moving the injection piston (13) in order to push all the molten material into the said cavity (6), said movement terminating at the end of said chamber (12) in correspondence with the cavity (6) to enable the die casting to be formed in it without feedhead.

2. A method as claimed in claim 1 , characterised in that the molten material is fed in a metered quantity into the chamber within which the piston (13) moves, said metering enabling a quantity of material to be fed into said chamber (12) which is exactly equal to the quantity required to obtain the die casting.

3. A method as claimed in claim 1 , characterised in that after the injection piston (13) has been moved towards the die casting cavity (6) it is maintained locked in correspondence with a region or surface of separation (17) between said cavity (6) and the chamber (12) into which the molten material is fed, for the entire time necessary for solidification of the die casting obtained, the mould (1) being opened after said solidification, and the die casting extracted.

4. A method as claimed in claim 3, characterised in that the die casting is extracted by thrusting by the injection piston (13).

5. A method as claimed in claim 3, characterised in that the die casting is extracted by a thrust exerted on it by an expulsion element (20) different from the injection piston (13) but contained in it.

6. A method as claimed in claim 1 , characterised by closing a feed port (14) for the molten material after this latter has been fed into the mould (1) but before moving the injection piston (13), said feed enabling said material to enter the chamber (12), which is occupied totally by the piston on termination of injection.

7. A method as claimed in claim 1 , characterised in that the molten material is metered during its withdrawal from a containing crucible (65), such that a quantity of material is withdrawn from the crucible (65) which enables the die casting to be formed without feedhead.

8. A method as claimed in claim 7, characterised in that the molten material is withdrawn from the crucible (65) by immersing into this latter a concave withdrawal element (61), into said element (61) there having previously been at least partly inserted a metering member (68) arranged to reduce the useful volume of the withdrawal element (61) such that it contains the required quantity of molten material, said metering member (68) being at least partly extracted from said withdrawal element after this has been extracted from the crucible (65) in order to distance the free surface (80) of the molten material from the edge (78) of said element in order to enable it to be moved with safety, the withdrawal element then being brought to the mould (1), into which the molten material present therein is then fed, said element (61) then being returned above the crucible (65) where the metering member (68) is reinserted into said element (61) before this is inserted into the molten material of the crucible (65).

9. A method as claimed in claim 8, characterised by regulating the position of the metering member (68) within the withdrawal element (61).

10. A device for implementing the method claimed in claim 1 , and in particular for forming at least one die casting, said die casting being obtained in a die casting cavity (6) of corresponding shape within a mould (1) comprising at least two half-moulds or dies (3, 4) movable relative to each other and defining said cavity (6) when closed one on the other, a feed mouth (14) being provided through which a molten material is fed into the mould (1), said material being prepared in a crucible (65) and being transported to the mould by feed and transporter means (61), the mould comprising presser means in the form of at least one injection piston (13) arranged to urge the molten material into the cavity (6) and to maintain it under pressure for its solidification, characterised by comprising a chamber (12) into which the feed port (14) opens and which receives the molten material before it reaches the die casting cavity (6), said chamber being located to the front of the injection piston (13), this latter moving within the chamber (12) in order to urge the molten material into said cavity (6), this movement halting in correspondence with the boundary region (17) between said chamber (12) and said cavity (6), said movement carrying all the molten material into the die casting cavity to enable the die casting to be obtained without any feedhead.

11. A device as claimed in claim 10, characterised in that the chamber (12) reached by the molten material is annular, the injection piston (13) being of corresponding shape.

12. A device as claimed in claim 11 , characterised in that at least the chamber (12) reached by the molten material is disposed with its axis parallel to a plane (K) in which the mould (1) lies.

13. A device as claimed in claim 12, characterised in that at least the chamber (12) reached by the molten material is disposed with its axis inclined by an angle (a) to the plane (l<) in which the mould lies.

1 4. A device as claimed in claim 1 3, characterised in that the angle (a) to the plane (K) in which the mould lies is greater than 0° and less than or equal to 90°.

15. A device as claimed in claim 10, characterised in that the feed port (14) is closable by a closure member (30, 40).

16. A device as claimed in claim 10, characterised in that the mould (1) comprises at least one element (13, 20, 27) for expelling the die casting from the die casting cavity (6).

17. A device as claimed in claim 16, characterised in that the expulsion element is the injection piston (13).

18. A device as claimed in claim 16, characterised in that the expulsion element (20) is an element inserted into the injection piston (13).

19. A device as claimed in claim 16, characterised in that each half-mould or die (3, 4) comprises its own expulsion element (13, 20; 27), these expulsion elements being movable independently of each other.

20. A device as claimed in claim 10, characterised in that the expulsion piston (13) comprises, on that end surface (22) facing the die casting cavity (6), at least one recess (23) arranged to define a portion of the die casting.

21. A device as claimed in claim 10, characterised in that the mould (1) comprises a plurality of die casting cavities (6), each communicating with a corresponding chamber (12) reached by the molten material and within which a corresponding injection piston moves.

22. A device as claimed in claim 10, characterised in that the means for feeding and transporting the molten material from the crucible (65) to the mould (1) are a withdrawal element (61) associated with a support (62) movable in accordance with the three spatial axes.

23. A device as claimed in claim 10, characterised by comprising metering means (60) for metering the quantity of material withdrawn from the crucible (65) by the feed and transporting means (61), said metered material being inserted into the chamber (12) to the front of the injection piston (13) before reaching the die casting cavity (6).

24. A device as claimed in claim 23, characterised in that the metering means (60, 64) are positioned in correspondence with the support (62) for the withdrawal element (61).

25. A device as claimed in claim 23, characterised in that the metering means

(60) comprise a regulator element (64) insertable into the withdrawal element

(61) in an adjustable manner, said regulator element (64) being carried by an arm (72) associated with a support member (73) movable at least along an axis perpendicular to the withdrawal element or to the plane (K) in which the mould (1) lies.

26. A device as claimed in claim 25, characterised in that the regulator element (64) comprises an end or dip piece (68) to be inserted into the withdrawal element (61), said dip piece being rigid with adjustment means (69, 70) enabling the depth reached by the dip piece (68) in the withdrawal element (61) to be adjusted.

27. A device as claimed in claim 26, characterised in that the adjustment means are an at least partly threaded shaft (69) cooperating with female threaded members (70) carried by the arm (72) rigid with the movable support member (73).

28. A device as claimed in claim 10, characterised in that the speed of the injection piston (13) within the chamber (12) connected to the die casting cavity (6) is less than 1 m/s, the pressure exerted on the molten material being less than 100 kg/cm².

29. A device as claimed in claim 10, characterised in that the die casting cavity (6) is connected to at least one variable volume chamber (230) provided in a half-mould (3) at the opposite end thereof to that reached by the presser means (13), said chamber (230) receiving that part of the molten material thrust into the die casting cavity (6) which exceeds the volume of molten material insertable into said cavity (6), pusher means (240, 3B, 540, 550) being provided to return at least part of said material into said cavity (6) after the presser means (13) have halted and after at least the commencement of cooling of the material present in said cavity (6), the opening of the mould by separating its dies (3, 4) leading to automatic separation of the material contained in the die casting cavity (6) from any material remaining in the variable volume chamber (23).

30. A device as claimed in claim 29, characterised in that the die casting cavity (6) presents a slot (210, 220) in that end facing the variable volume chamber (230) in order to connect it to this latter.

31. A device as claimed in claim 29, characterised in that the variable volume chamber (230) is annular.

32. A device as claimed in claim 29, characterised in that the pusher means (240, 3B, 540, 550) are part of the half-mould (3) in which the variable volume chamber (230) is provided.

33. A device as claimed in claim 32, characterised in that the pusher means are a member (240) movable within the variable volume chamber (230) and subjected to a pressing element (280) which urges it towards the slot (210, 220) connecting said chamber (230) to said cavity (6), the variable volume chamber (230) being defined between said slot (210, 220) and said movable member (240).

34. A device as claimed in claim 33, characterised in that the pressing element is a spring (280).

35. A device as claimed in claim 32, characterised in that the pusher means (3B) are a first part of the half-mould (3) telescopically movable between two other movable parts (3A, 3C) of said half-mould (3), said first part (3B) moving in front of the slot (210, 220) connecting the variable volume chamber (230) to the die casting cavity (6).

36. A device as claimed in claim 35, characterised in that the first part (3B) is movable telescopically along an inner part (3A) of the half-mould (3), said parts being independently movable relative to the third part (3C) of said half-mould.

37. A device as claimed in claim 32, characterised in that the pusher means comprise means (800) for expelling any die casting material remaining in the variable volume chamber (230) on termination of casting.

38. Use of the device claimed in claim 10 within a mould of ceramic material.

39. Use of the device claimed in claim 10 for casting products of high melting point material such as copper and the like.