WO2017115259A1

WO2017115259A1 - Liquid forging apparatus and method therefor

Info

Publication number: WO2017115259A1
Application number: PCT/IB2016/057987
Authority: WO
Inventors: Stefano Beretta
Original assignee: Stefano Beretta
Priority date: 2015-12-28
Filing date: 2016-12-23
Publication date: 2017-07-06
Also published as: ITUB20159255A1

Abstract

A liquid forging apparatus for forming metal objects is described, comprising at least one mould, an injection channel to inject in the mould a material coming in the liquid state from a furnace and a blocking plunger for plugging the injection channel. The apparatus further comprises a distribution chamber of the molten material, in fluidic connection with the injection channel and with each impression/figure, and a forging plunger coaxially mounted outside of the blocking plunger and sliding with respect to the latter between a rearward position, at which it does not occupy the distribution chamber, and a forward position, at which it occupies at least partially the distribution chamber so that to press the liquid material being in the distribution chamber and the mould, or moulds.

Description

LIQUID FORGING APPARATUS AND METHOD THEREFOR

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DESCRIPTION

Field of the Invention

The present invention relates in general to the field of forming objects made of metal and/or metal alloys and, in particular, to an apparatus and the respective method to carry out said forming.

State of the art

The technology mainly used for forming several typologies of items made of metal, such as aluminium or aluminum alloys, and specifically bronze alloys, brass alloys, or a light alloy in general, is the gravity casting .

This technique provides the presence of a furnace with open crucible of the gas combustion type, a gravity-casting machine manually or automatically controlled and an operator or anthropomorphous robot to carry out the pouring of the liquid metal into the forming chill.

The presence of this furnace has negative consequences, such as the formation of surface oxide in the metal bath, the emission of combustion gases and the risk of leakages of liquid metal with possible risks for operators assigned to pour the metal, or supervisors of the casting island.

It has to be noticed that the use of an anthropomorphous robot has been developed for the pouring step of metal in case of products such as crown wheels for gear units of middle and great size, whereas for crown wheels of outer diameter smaller than 100 mm the operator's skill is still preferred: consequently, the latter undergoes to possible injury risk and repetitive movement stress (up to 500 movements per shift) . Moreover, the plant productivity directly depends on operator performances.

Forming with gravity technology needs, in order to obtain a complete cast free of defects due to material shrinkage in solidification and cooling steps, the feeding riser to be abundantly dimensioned, frequently up to 1.5 times the figure weight of the finished cast. With the term "cast" the final product of melting and casting processes is meant.

This material surplus causes higher needs of alloy to obtain the finished cast and, consequently, the use of high energy amount to lead the metal to liquid state. This translates into high transformation costs and remarkable combustion gas emissions. In addition, the gravity process does not allow the possibility of obtaining pieces with homogeneous structure and increased mechanical properties, unless subsequent thermal treatments are employed.

Specifically, for items such as crown wheels made of bronze alloys, due to high costs of raw material than can affect more than 80% of finished product costs, manufacturers are continuously looking for a solution aiding the reduction of this cost that, since weighting significantly on the final product cost, limits the competitiveness thereof on the market.

Particularly relevant is the manufacturing of items made of brass alloys such as taps, handle components and valves. Especially in the first two cases, in addition to cast complexity also due to design requirements, aesthetic and touch features are basic aspects for the market success .

For forming these item types made of brass alloy a low-pressure casting technology is used, which however does not allow achieving the surface finishing degree the market requests .

In addition to have flow marks involving the need of a first grinding operation lasting even several minutes, there is a series of little point-like defects on the surface, which oblige the manufacturers to perform 3 to 4 galvanic operations (for example copper coating and/or nickel plating) staggered by as many taping steps, so that chrome plating treatment defining the final surface state can be carried out. This series of intermediate operations can affect costs of the finished product up to 60-70%; furthermore, the possibility of eliminating galvanic baths would add up to limit emissions, decrease the pollution and obtain energy savings, with great repercussion on environmental protection.

Regarding articles such as valves, which are subjected to high working pressures and must guarantee seal safety and resistance, nowadays hot melt molding is employed but, since this technology does not allow producing pieces with inner cavities, successive important machining operations are necessary, which often highlight inner defects; for this reason, finished products must undergo seal tests to guarantee the proper functionality.

Lastly, in case of specific aluminium alloys, attention is made particularly on those products that must be substantially free of inner defects or guarantee the seal against fluid pressures.

The technique of the so-called liquid forging proposes reducing these drawbacks to minimum. With the term "liquid forging" a technique of metal alloy casting is meant, which provides the application of high pressures on the material in the liquid state during the solidification step inside a mould. In particular, the employed material can be a bronze alloy, a brass alloy or a light alloy in general.

The Italian Patent IT 1349439 proposes equipment for molding objects by such a technique. Pressure is applied on the material in the liquid state being in a mould formed by an upper impression and a lower impression, by means of a packing plunger defining at the same time a portion of the upper impression.

However, this solution is difficult to be implemented and used since the amount of material in the liquid state to be inserted in the mould must be calculated and weighted with very high precisions impossible to be obtained in an industrial plant; in fact, an wrong material dosage would entail the impossibility of completely closing the upper impression in case of material in excess, with consequent imperfections on the object surface, or else the cavity presence in case of insufficient material amount.

In addition, according to this solution, the packing plunger has a surface contacting the liquid material determined by the final object shape; therefore, this surface is uneven and has complex geometry and then is not very appropriate in applying unidirectional pressure on the whole material. This could entail unevenness on the finished product. Furthermore, the packing plunger is bound univocally to the cast geometry and therefore cannot be employed in a cast with different shape.

Moreover, every time the moulded object is ejected, as the geometry complexity becomes higher, the packing plunger would be desirably treated with a releasing agent per each working cycle, in order to be sure that all the material is removed by the plunger itself before a new object is formed, with evident additional times and productivity losses .

Disadvantageously, this equipment allows forming only one object per every working cycle, allows making only objects with revolution solid geometry and is not suitable for manufacturing pieces of little size.

Moreover, this equipment needs to arrange a different forming plunger per each different mould or each typology of cast to be formed, with consequent costs and longer machine tooling times.

Also documents JP3417988, JP3418027, KR100669603 and EP0361837 relate to moulding apparatuses having a rod shaped to complete the mould impression, with the above referred advantages. In particular, with these solutions the plunger has to be changed depending on the mould shape and the object to be formed, the material is difficult to be correctly dosed and is almost impossible to apply unidirectional pressures on the injected material.

In addition, in the apparatuses above the material is injected directly in a mould cavity contributing to the cast forming once the injected material solidifies; consequently, with these apparatuses only one manufactured product per every cycle can be formed, having revolution solid geometry only.

Objects and Summary of the invention

Object of the present invention is to provide an apparatus and method therefor which overcome the drawbacks of the known art, allowing objects also with little size and complex shape to be formed, with high mechanical characteristics and good surface finishes.

Another object is to provide an apparatus allowing productivity increase and transformation cost decrease and having high reliability and little tooling time.

Still another object is to propose a solution minimizing the material amount necessary to obtain the finished object and allowing to minimize defects of objects obtained with conventional technologies, particularly shrinkage cavities, surface and inner porosities, lack of pressure seal.

Therefore, the present invention concerns an apparatus of liquid forging according to claim 1.

In particular, the apparatus comprises at least one mould formed by a lower half-mould and an upper half-mould and adapted to define one or more impressions; an injection channel to inject in each mould or impression a material, specifically a metal, coming in the liquid state from a furnace; a blocking plunger for plugging the opening of the injection channel; a distribution chamber, in which the liquid material coming from the injection channel flows and stores up, in fluidic connection with each mould or impression; a forging plunger coaxially mounted outside of the blocking plunger and sliding between a rearward position and a forward position and vice versa; so that the forging plunger can be translated from a position in which it remains outside of the distribution chamber to a position in which it occupies at least part of the chamber, thus compressing the liquid material due to the pressurization effect in each impression of the mould or moulds .

Advantageously, the forging plunger therefore does not constitute part of the mould but operates outside of it by forcing into the mould the material so that the shrinkage thereof is compensated during solidification, thus avoiding cavities to be created, and so that the pressure in the liquid material is increased to force its instantaneous solidification, thereby obtaining very fine and uniform metallurgic structure of the finished product. The stroke of the forging plunger, varying depending on the shrinkage of the solidifying metal, allows to maintain a continuous pressure applied onto the material until the solidification expires. In other words, the forging plunger does not concur in forming any of the impressions, or the only one impression, i.e. it does not comprise any shaped portion completing the mould, thus defining a portion of the only one impression or the impressions.

In addition, thanks to this configuration, a unique forging plunger can be used for different moulds, its shape being independent of the shape of the object to be obtained .

Advantageously, also the distribution chamber does not concur in forming the mould impression/s ; in other words, the distribution chamber is not obtained at the level of part of the impressions themselves, but is a separate element usable for a lot of casts. This solution allows to forge several manufactured articles contemporaneously and to make casts of whatever geometry.

Advantageously, the injection channel is vertically oriented and the liquid material is introduced from below, the distribution chamber being placed above the injection channel. The blocking plunger and the forging plunger are above the distribution chamber and vertically oriented. The introduction channel has a top seat on which the blocking plunger is rested, the latter being movable from top to bottom, to plug the channel itself.

The blocking plunger and the forging plunger are both susceptible to movements from top to bottom and vice versa in the vertical direction and can be moved separately, the first to plug the injection channel and the second to move in the distribution chamber.

Advantageously, only one mould can be provided, defining the impression of only one object to be made, or more advantageously a unique mould defining a plurality of impressions. In this case, the resulting cast comprises several objects that shall be separated once the cast is removed from the mould. Alternatively, several moulds can be provided as radially arranged around a distribution chamber .

Advantageously only one mould is provided which is equipped with one or more impressions, the distribution chamber being obtained in this mould; each impression is arranged around the distribution chamber.

To avoid the solidification of the material inside thereof, the injection channel is provided with heating means, such as electric resistances.

Advantageously, to facilitate the positioning and the removing of the mould from the apparatus, the blocking plunger and the forging plunger are assembled on a vertically movable translating head. In this way, they can be moved away from the mould and taken to a raised position and moved closer to it in a lowered position in which the translating head is rested on the upper half-mould, so that to apply pressure and assure the mould is closed during the injecting and forging steps of the material.

Advantageously, the liquid forging apparatus allows to obtain a product having very fine and uniform metallurgic structure and is substantially free of oxidations and surface defects.

The invention also concerns a method for making objects by liquid forging according to claim 8.

Advantageously, this method provides for forcing in the mould, or moulds, the liquid material coming from the injection channel and present also in the distribution chamber after the injection channel has been plugged by the blocking plunger, by taking part of the forging plunger inside the distribution chamber until a given pressure in the liquid material is reached.

In order to position the half-moulds, the translating head is moved to raised position and then lowered once this position has been reached, to keep each mould closed.

Advantageously, once the material has solidified, the blocking plunger is moved away from the injection channel by moving it upwards, the forging plunger is moved back and the translating head is moved away to allow the mould to be removed for the successive ejection of the cast from the mould .

Furthermore, the invention concerns a liquid forging plant according to claim 11.

Substantially, this plant comprises a furnace provided with its pressurizing means, a rotary table having means for hooking at least one lower half-mould and movable in different position corresponding to as many working stations, and at least one supporting arm combined with the rotary table and provided with means for holding at least one corresponding upper half-mould and means for moving closer/away each couple of upper and lower half-moulds to carry out the closing and the opening of each mould. Advantageously, the supporting arm is each time positioned, integrally with the rotary table, at one of the stations and in particular:

in a loading station, in which during the tooling step the half-moulds are fastened to the supporting arm and the rotary table;

- in a forging station, in which each mould is positioned and held in the forging apparatus;

in an unloading station, in which the cast is unloaded from the one respective mould;

in a cooling and washing station, in which the mould is cooled and washed, preferably by spraying a releasing agent.

Preferably, four supporting arms are combined to the rotary table and positioned so that to be each at one of the working stations and to be moved every time the rotary table, and supporting arms therewith, is moved to the station subsequent the previously occupied one. This allows to carry out four operations contemporaneously and automatically on different moulds, thus optimizing production times. As a matter of fact, for proceeding to forge new moulds it is not necessary to wait for the unloading and washing of a mould, because the operations occur in parallel in the single stations.

Advantageously, the plant comprises also a control panel to set the furnace pressurization, the temperature of the liquid material, the filling time of the mould and distribution chamber, the movements of the blocking plunger and forging plunger, the movement of the rotary table, translating head and mould closing/opening means.

List of figures

Further characteristics and advantages of the invention will be more evident by the review of the following specification of a preferred, but not exclusive, embodiment, which is depicted for illustration purposes only and without limitation, with the aid of the attached drawings, in which:

- figure 1 is a perspective view of a liquid forging plant according to the present invention;

- figure 2 shows the section of the liquid forging plant of figure 1 ;

- figures 3a, 3b, 3c, 3d, 3e and 3f show the section of the forging apparatus according to the present invention, circled in figure 2 and in different operative steps ;

figure 4 shows a top view of a lower half-mould defining four figures for making four different objects. Detailed description of the invention

Figure 1 and figure 2 respectively show perspective and sectional views of a liquid forging plant 1 comprising a forging apparatus 2 according to the present invention.

Figures 3a to 3f show a magnified sectional view of the only forging apparatus 2 of figure 2 in different operative steps.

The liquid forging apparatus 2 comprises a reaction plate 3 on which at least one mould 4 is each time positioned. Each mould is formed by a lower half-mould 5 in which at least one lower impression is made, completely or partially, of a manufactured article to be made, and by a respective upper half-mould 6, in which part is made of at least one upper impression of a manufactured article to be made .

Each lower half-mould and the respective upper half- mould can also have one or more housings for positioning possible cores and metal components (for example cast iron hubs in case of crown wheel production for gear units) in the mould. The two half-moulds, once joined, form at least one impression defining an object to be made; advantageously and preferably, only one mould having one or more impressions is provided, for example four impressions 7, 8, 9 and 10, as shown in the example depicted in figure 4; alternatively, two or more distinct moulds can be provided. Each couple of half-moulds defines a cast 11, i.e. a semifinished product that undergoes to a finishing process to give one or more objects.

The apparatus further comprises an injection channel 12 connected to a holding furnace 13 to convey an amount of material 14 in the liquid state, specifically of molten material, from the furnace into each mould; for example the material can be aluminium, or bronze alloys, brass alloys, or else light alloys in general. Preferably, the injection channel is vertically oriented and the material is injected from below to the moulds. The reaction plate 3 is arranged outside of a part of the injection channel. The injection channel ends with a top opening 15 from which the liquid material comes out.

The furnace 13 is an electric furnace of crucible type and is completely closed and insulated. Moreover, the furnace can be pressurized in accordance with a pre- configurable ramp to carry out the injection of liquid material in each mould 4 through the injection channel 12.

The apparatus is provided with a distribution chamber

16 of the liquid material coming from the furnace in communication with the top opening 15. Preferably, the distribution chamber is placed above the injection channel. The distribution chamber 16 is in turn in communication with each mould if more than one, or with each impression of the mould, when there is only one mould through apposite openings and/or runners 17.

Advantageously, the mould is configured so that it defines the impression/s as arranged around the distribution chamber; preferably, the distribution chamber 16 and the runners 17 are integrated in the mould itself. In case of a plurality of moulds, each of them is radially arranged around the distribution chamber.

In its upper portion, the apparatus comprises a vertically arranged blocking plunger 18, above and next to the injection channel 12. The blocking plunger vertically slides between a starting rest position, in which it is away from the top opening of the injection channel - as shown in figures 3b and 3c -, and a closed position in which an ending portion thereof is rested in a seat 19, preferably with conical shape, at the level of the top opening so that the injection channel is plugged, as shown in figures 3d and 3e.

A forging plunger 20 is assembled outside of the blocking plunger 18. The forging plunger is coaxial to the blocking plunger and sliding with respect to it between a rearward position, at which it does not occupy the distribution chamber - as shown in figures 3b-3d -, and a forward position, at which it occupies at least partially the distribution chamber - as shown in figure 3e. The blocking plunger and the forging plunger are movable vertically and independently from one another. Since the blocking plunger keeps plugged the injection channel, the liquid material contained in the volume of the distribution chamber is forced into the mould, or moulds. This volume of additional material is for the shrinkage compensation, during the solidification step, of the material which is initially in each mould, and for increasing the pressure of the material in each mould in order to force the solidification thereof and to obtain a cast 11 substantially free of imperfections and having very fine and uniform metallurgic structure.

The injection channel is provided with heating means - not shown - to avoid the solidification of the liquid material 14 during the injection step. To facilitate the positioning of each mould 4 in the liquid forging apparatus 2, the blocking plunger 18 and the forging plunger 20 can be advantageously assembled on a translating head 21. The translating head is vertically movable downwards - as depicted by the arrow in figure 3a - between a raised position and a lowered position; in the raised position, the translating head is moved away from each mould, the blocking plunger and the forging plunger are far away from the distribution chamber and then each mould can be positioned on the reaction plate; in the lowered position, the translating head rests on the upper half-mould of each mould, so that the closing thereof during the forging step is guaranteed.

During the forging step, each mould transfers the force applied by the translating head and the liquid material on the reaction plate.

At the end of the forging step, the translating head is vertically movable upwards - as shown by the arrow in figure 3f - from the lowered position to the raised position, to allow each mould to be removed.

The translating head can slide on guides 22 and can be hydraulically moved.

The forging plunger 20 is integral with the translating head 21 and can translate relatively thereto in the vertical direction so that pressure is applied on the liquid metal being in the distribution chamber.

Also the blocking plunger 18 is integral with the translating head 21, can translate relatively thereto, is concentric with respect to the forging plunger 20 and can slide inside thereof in order to plug the injection channel after the mould has been filled with liquid metal.

Advantageously, the liquid forging plant 1 can also comprise a rotary table 23 adapted to house at least one lower half-mould, movement means - not shown - for its rotation in different positions corresponding to as many working stations 24, 25, 26, 27, and at least one supporting arm 28, preferably a supporting arm per each working station, as shown in figure 1. In order to house each lower half-mould, the rotary table can be provided with one or more seats, not shown in the figures.

Each supporting arm 28 is integral with the rotary table and can be positioned next to each of the working stations 24, 25, 26, 27. Each supporting arm is provided with means - not shown - to hold at least one upper half- mould 6 and with possible closing/opening means 29 to move each upper half-mould 6, so that the half-moulds are moved closer/away to/from one another to respectively close and open the corresponding mould 4; the closing/opening means 29 comprise movement means 30 to raise or lower each supporting arm 28, as required.

Each supporting arm is movable between the following working stations:

- a loading station 24 in which, at the production start, the half-moulds of each mould are fastened to the supporting arm 28 and on the rotary table; such operation is carried out by keeping open the mould, manually or automatically; in this station, the positioning in the mould of cores and possible metal components, if present, can also be provided;

- a forging station 25, in which each mould is positioned and kept closed inside the forging apparatus on the reaction plate during the liquid forging;

- a loading station 26, in which the cast is removed from the respective mould; such unloading operation of means after their forming is carried out with the mould open, manually or automatically;

a cooling and washing station 27, in which each mould is cooled and washed by spraying a releasing mixture; the washing and cooling are carried out with the mould open.

In order to carry out the mould cooling and washing, the plant comprises a storage tank 31 and a washing apparatus 32 which is provided with nozzles 33 for diffusing the washing liquid on all of the mould surfaces. The washing liquid can be constituted by a mixture of water and releasing liquid; the storage tank acts as reservoir for storing and salvaging the excess washing liquid after the moulds have been sprayed.

In addition the plant, for its correct operation, comprises a pressurization system 34 to pressurize the holding furnace, which determines the thrust of the liquid metal for the injection into the mould and the cast forming; a control panel 35 to set the furnace pressurization, the temperature of the liquid material, the filling of the mould and distribution chamber, the movements of the blocking plunger and forging plunger, to set the movement of the rotary table, translating head, mechanism for opening/closing the moulds and means for raising and lowering each mechanic arm, and to manage the washing apparatus; an oleodynamic control unit 36 managed by the control panel, to move the hydraulic actuators 37 to move the holding furnace 13, the rotary table 23, the translating head 21 and the blocking 18 and forging 20 plungers; and a managing system 38 for pressurizing and maintaining the temperature of the cooling liquid of the blocking and forging plungers .

The productivity of such a liquid forging plant is 3-4 washing cycles per minute, depending on cast size; this productivity is twice the existing technologies.

Advantageously, the liquid forging plant can have a portal-like structure 39 - as shown in figures 1 and 2, to best integrate the various components.

The above described liquid forging apparatus allows to form objects from a material in the liquid state. The material is a metal or metal alloy and can be led and maintained in the liquid state by the furnace 13.

Substantially, the method comprises of:

- through the injection channel, injecting a volume of material into the mould, or moulds, and into the distribution chamber;

- lowering the blocking plunger so that to plug the injection channel;

- lowering the forging plunger until at least part of the distribution chamber is occupied, in order to force at least part of the liquid material initially in the distribution chamber into the mould, or the moulds, until a given pressure in the liquid material is reached;

- solidifying the material in the mould, or moulds, to achieve at least one cast corresponding to one or more objects. A translating head carrying the blocking plunger and the forging plunger can be arranged, as described above, and kept in the raised position during the mould positioning, then successively lowered so that each mould is kept closed during the injecting and forging steps, in order to position more easily the mould/s into the liquid forging apparatus .

Once the cast/s has/have been obtained, the blocking plunger is returned to its starting position, moved away from the injection channel; the forging plunger is returned to its rearward position; and the translating head is moved away from the upper half-mould to move again the mould from the apparatus and unload the mould.

Then the following steps are provided:

STEP 1: each lower half-mould is in the working position, aligned with the translating head and the forging and blocking plungers; the upper half-mould is coupled to the lower half-mould and the translating head is in the raised position, then detached from the upper half-mould (see figure 3a) .

STEP 2: the half-moulds are coupled to one another, the translating head is lowered until rested on the upper half-mould; the forging plunger, together with the blocking plunger, goes down with the translating head and couples with the upper half-mould, thus causing the closing of the injection chamber (see figure 3b) .

STEP 3: the furnace is pressurized and the liquid metal goes up through the injection channel and fills the cavities of the mould/s and the distribution chamber, so that a cast is formed; the translating head presses the upper half-mould so that the mould is absolutely closed and the metal is prevented from leaking out (see figure 3c) .

STEP 4: when the filling of the mould is ended, the blocking plunger lowers so that to close the injection channel and stop the entry of liquid material; contemporaneously, the furnace is depressurized so that the return of excess metal in its inside is guaranteed; the translating head presses on the upper half-mould to guarantee the closing of the mould and prevent the metal from leaking out (see figure 3d) .

STEP 5: once the descent of the blocking plunger is ended, the forging plunger is activated and in turn lowers and sinks into the liquid material present in the distribution chamber, thus forcing the displacement of the liquid metal in the impression or impressions of each mould through the runners; the pressure applied on the metal during solidification speeds up the solidification of the metal and balances the shrinkage thereof; the translating head goes on pressing on the upper half-mould to guarantee the closing of the mould during the forging action (see figure 3e) .

STEP 6: once the casts have solidified, the forging plunger and the blocking plunger take off from the distribution chamber and, subsequently, the translating head is moved upwards and the upper half-mould is unconstrained (see figure 3f) .

Therefore the sequence of liquid forging steps is ended; at this point, the rotary table can be activated to move the half-moulds to the subsequent station for unloading the casts and subsequently to other stations to complete the working cycle and take a new mould to the liquid forging apparatus.

Each cast is then subjected to a mechanical cutting operation to obtain the final product.

Such a plant allows to drastically reduce also labor costs and risks for the operators: in fact, the operator role decreases to supervise the casting island and control the product obtained.

The product obtained by the above described liquid forging apparatus is substantially free of oxidations and surface defects.

The finished product, as a matter of fact, thanks to the high pressure applied on the liquid material during solidification, has very fine and uniform metallurgic structure and, consequently, mechanical properties greater than products obtainable with known to date technologies. This allows to reduce the need of raw material to minimum, because thicknesses can be reduced; for example, in case of crown wheels, their thickness can be reduced, the transmitted torque and power being the same, at the same time guaranteeing a better wear resistance; this allows to significantly reduce crown wheel and finished product costs, up to 30%.

Obtained casts have surface finishing that depends only from the finishing degree of the mould: in fact, the forging pressure forces the material to flow on the mould walls and reduces to minimum the interaction between liquid material and mould surface, which is the greatest cause of surface defects.

With the liquid forging technology, products with complex shapes and inner cavities, free of inner and surface defects and with high mechanical properties and sealing features of their surfaces, can be obtained.

In particular, the advantages of the liquid forging apparatus according to the present invention can be summarized as:

1) Possibility of making every type of items: monocomponents , bicomponents , with inner cavities and complex shapes;

2) Obtaining products with mechanical properties higher than those obtained by gravity and low-pressure forming;

3) Having process cycle times shorter than gravity and low-pressure processes, with consequent increase of productivity and reduction of transformation costs;

4) Using the minimum amount of metal for the cast forming, because with the liquid forging only the material strictly necessary for obtaining the cast is injected;

5) Obtaining items with surface finishes depending only on mould finishing and without the formation of surface oxides;

6) Reducing to minimum cast defects arising with conventional technologies, in particular shrinkage cavities, surface and inner porosities, lack of pressure seal;

7) Drastically reducing the emission level into the atmosphere: all the process steps (melting of metal, injecting, forging, cooling and spraying the releasing agent) are carried out in a closed environment to reduce to minimum emissions and the need of installation of captation and abatement plants.

The following table compares the features of the process according to the present invention with the state of the art.

Technical Gravity Low-pressure Liquid forging features casting forming

Surface Galvanic and Galvanic and Reduction of 60- finishing mechanical mechanical 70% in the degree operations operations are working cycle, are necessary to i.e. in necessary to eliminate transformation eliminate surface defects costs

surface

defects

Mechanical Not Can be increased 30% of expected features of modifiable by 10-20% after increase and the cast inj ection above

parameters have

been set up

Combustion Not present Not present Not present emissions because of because of because of gas holding holding furnace holding furnace furnace use pressurization pressurization and induction and resistance technology technology

Powder Use of Use of graphite Possibility of emissions graphite powder as using not- powder as releasing agent powdered

releasing releasing agents agent without powder emissions

Safety Accident No risks for the No risks for the risks for operators operators the

operators

Claims

1 . A liquid forging apparatus (2) for forming objects, with at least one material in the liquid state (14), said material being a metal, or a metal alloy, comprising:

- at least one mould (4) defined by a lower half-mould (5) and an upper half-mould (6) together defining a cast (11), comprising one or more impressions (7, 8, 9, 10);

- an injection channel (12) in the at least one mould of material coming in the liquid state from a furnace (13);

- a blocking plunger (18) for plugging said injection channel ( 12 ) ;

characterized in that it comprises:

a distribution chamber (16) of the molten material (14), in fluidic connection with the injection channel (12) for the material and with each impression (7,

8, 9, 10) of said at least one mould (4);

a forging plunger (20) coaxially mounted outside of the blocking plunger (18) and sliding with respect to the latter between a rearward position, at which it does not occupy the distribution chamber, and a forward position, at which it occupies at least partially the distribution chamber to push the liquid material in each impression (7, 8, 9, 10) of the mould (4), or moulds if more than one, and maintain under pressure the liquid material therein, wherein said forging plunger does not concur in forming any of the one or more impressions (7, 8,

9, 10), i.e. it does not comprise any shaped portion to define at least partially said one or more impressions (7, 8, 9, 10) .

2 . Forging apparatus according to claim 1, wherein the injection channel (12) is vertically oriented so that the liquid metal is introduced from below into the distribution chamber and into each mould.

3 . Forging apparatus according to claim 1 or 2, wherein the blocking plunger (18) and the forging plunger (20) are vertically oriented and are arranged at the opposite side of the injection channel (12) with respect to the distribution chamber (16); and wherein the blocking plunger and the forging plunger are movable in the vertical direction, together or separately.

4. Forging apparatus according to one of the preceding claims, comprising only one mould (4) provided with one or more impressions (7, 8, 9, 10), or else a plurality of moulds radially arranged around the distribution chamber.

5. Forging apparatus according to claim 4, wherein there is only one mould provided with one or more impressions, in which the distribution chamber is obtained, said one or more impressions being arranged around said distribution chamber and connected therewith through respective runners (17) .

6. Forging apparatus according to one of the preceding claims, wherein the injection channel (12) is connected to a pressurized furnace (13) and is provided with heating means so that the material is maintained liquid during injection.

7. Forging apparatus according to one of the preceding claims, wherein the blocking plunger (18) and the forging plunger (20) are assembled on a translating head (21) vertically movable between a raised position, in which it is moved away from the at least one mould, in order to position the at least one mould, and a lowered position, in which it rests on the upper half-mould of said at least one mould, so that the closing of said at least one mould is guaranteed .

8. A method for making objects by liquid forging starting from a material in the liquid state, said material being a metal or a metal alloy, comprising the steps of: a) prearranging an apparatus according to any one of claims 1-6;

b) through the injection channel, injecting a volume of material in the liquid state into the mould, or moulds if more than one, and into the distribution chamber;

c) plugging the injection channel by the blocking plunger;

d) forcing at least part of the liquid material initially in the distribution chamber to enter the mould, or moulds if more than one, by moving the forging plunger in order to occupy at least part of the distribution chamber, until a predetermined pressure in the liquid material is reached;

e) by the pressurization of the liquid material, forcing the rapid solidification of the material in the mould, or moulds, to obtain said objects.

9. Method according to claim 8, wherein before the step b) , the steps are provided of:

a') keeping the translating head in a raised position; a'') positioning the at least one mould;

a''') lowering the translating head to the lowered position to keep closed each mould during the steps b) -e) .

10. Method according to claim 8 or 9, wherein after the step e) , the steps are provided of:

f) moving the blocking plunger to its initial position, in which it is moved away from the injection channel ;

g) moving the forging plunger to its rearward position;

h) moving the translating head to its raised position; i) removing the mould to unload the cast.

11. Liquid forging plant comprising an apparatus according to any one of claims 1-7 and further comprising:

a closed furnace (13) provided with pressurizing means to inject the liquid material through the injection channel;

a rotary table (23) carrying at least one lower half-mould and provided with handling means at different positions corresponding to as many working stations (24, 25, 26, 27) ;

- at least one supporting arm (28), integral with the rotary table to be moved in succession to each working station, and provided with restraining means to restrain at least one upper half-mould and with closing/opening means (29) to close/open each mould.

12. Liquid forging plant according to claim 11, wherein said at least one supporting arm (28) is movable, together with the rotary table (23), between a loading station (24) to load the half-moulds on the supporting arm and the rotary table; a forging station (25) to position said at least one mould in the forging apparatus; an unload station (26) to unload the cast from said at least one mould; and a cooling and washing station (27) to cool and wash said at least one mould.

13 . Liquid forging plant according to claim 11 or 12, wherein several supporting arms (28) are combined with the rotary table and can be each positioned, together with the rotary table, at a different working station and can be moved, on case-by-case basis, to the following station in order to contemporaneously carry out the operations each station provides.