Apparatus and method for die-casting metal objects in a semisolid state

Abstract

An apparatus (1) for die-casting metal objects in a semisolid state, comprising a mold which comprises an upper mold half (3) which is adapted to be coupled to a lower mold half (2) in order to define a mold cavity (4), an oven (7) being arranged below the lower mold half (2) and being provided with a supply duct (9) for liquid metal (8) which connects the oven to the mold cavity (4), the upper mold half (3) being provided with a cavity within which a forging piston (5), which accommodates a flow control plunger (6) inside it, is freely movable between the upper mold half (3) and the lower mold half (2), a vacuum channel (10) being provided circumferentially around the piece to be cast and being connected to the mold cavity (4) by means of vent channels (12), the forging piston (5) comprising a connecting channel (14) to the vacuum, in order to create the vacuum, the upper mold half (2) comprising a connecting channel (11) for connection to a vacuum pump, which connects the vacuum channel (10) to the outside, and further comprising a solenoid valve (21) for controlling the vacuum inside the channel (14) and a solenoid valve (20) for controlling the vacuum in the connecting channel (11) for connection to the vacuum pump.

Description

[0001] APPARATUS AND METHOD FOR DIE-CASTING METAL OBJECTS IN A SEMISOLID STATE

[0002] The present invention relates to an apparatus and a method for diecasting metal objects in a semisolid state.

[0003] More specifically, the invention relates to an apparatus and a method for providing objects at low pressure and forged in a semisolid state.

[0004] More specifically the metal objects can be made of brass, bronze, aluminum alloys, magnesium alloys, and light alloys and the like.

[0005] In the background art the method is known of melting and molding metal objects via what is called “low pressure”, using an apparatus that comprises a lower mold and an upper mold which are configured to define an impression or mold cavity for containing a dosed quantity of liquid metal which is introduced through a duct which is connected to an oven below.

[0006] According to the known art, the upper mold is provided with a flow control element which acts on an opening connecting to the liquid metal delivery duct, and with a compactor punch which defines an upper portion of the impression of the mold.

[0007] The use of low pressure for the molding process entails that the oven is arranged under the molding machine and that it must be pressurized. Pressurization of the oven, normally done with air, cools the metal and therefore the use of a sealed oven is required.

[0008] During the step of filling the mold cavity and pressurizing the oven, the air that is in the reascent tube and in the mold cavity must exit from the mold in order to allow the liquid metal to be introduced.

[0009] In conventional apparatuses, for the liquid metal to rise from the oven to the mold cavity, a pressure is applied on the surface of the metal in the oven. Pressurization of the oven chamber requires the use of a special type of oven.

[0010] A solution is also known from WO2021 / 070044 which makes it possible not to use a pressurized oven. That solution envisages, between the upper mold half and the lower mold half, circumferentially around the piece to be cast, a vacuum channel connected to the mold cavity by means of vent channels.

[0011] Furthermore, there is a channel for supplying the vacuum by way of a vacuum pump, and this channel is connected to the mold cavity through one or more vent channels.

[0012] A reascent channel for the metal contained in the oven connects the oven to the mold cavity.

[0013] However, the above solution presents critical issues, in that when the metal from the duct i.e. from the reascent channel rises to fill the mold cavity, inevitably it also fills the vent channels, and therefore the vacuum that was created previously is no longer present.

[0014] This means that the metal that rose in the reascent channel will go back into the oven, a situation that is utterly undesirable.

[0015] The aim of the present invention is to provide an apparatus and a method for die-casting objects in the solid state made of brass, bronze, aluminum alloys, magnesium alloys and light alloys and the like, that makes it possible to obtain metal objects without impurities (porosity), despite using a pressurized oven, therefore eliminating the drawbacks of the pressurized oven.

[0016] Within this aim, an object of the present invention is to provide an apparatus and a method for die-casting metal objects in a semisolid state in which a conventional pressurized oven can be used.

[0017] Another object of the present invention is to provide an apparatus and a method that are highly reliable, easily and practically implemented and at low cost.

[0018] This aim and these and other objects which will become better apparent hereinafter are achieved by an apparatus for die-casting metal objects in a semisolid state, comprising a mold which comprises an upper mold half which is adapted to be coupled to a lower mold half in order to define a mold cavity, an oven being arranged below said lower mold half and being provided with a supply duct for liquid metal which connects said oven to said mold cavity, said upper mold half being provided with a cavity within which a forging piston, which accommodates a flow control plunger inside it, is freely movable between the upper mold half and the lower mold half, a vacuum channel being provided circumferentially around the piece to be cast and being connected to said mold cavity by means of vent channels, said forging piston comprising a connecting channel to the vacuum, in order to create the vacuum, the upper mold half comprising a connecting channel to a vacuum pump, which connects said vacuum channel to the outside, characterized in that it comprises a solenoid valve for controlling the vacuum inside said channel and a solenoid valve for controlling the vacuum in the connecting channel to the vacuum pump.

[0019] Further characteristics and advantages of the invention will become better apparent from the description of a preferred, but not exclusive, embodiment of the apparatus and of the method according to the invention, illustrated by way of non-limiting example in the accompanying drawings wherein:

[0020] Figure 1 is a cross-sectional view of the apparatus according to the present invention, in a first operating step thereof;

[0021] Figure 2 is a cross-sectional view of the apparatus according to the invention, in a second operating step thereof;

[0022] Figure 3 is a cross-sectional view of the apparatus according to the invention, in a third operating step thereof;

[0023] Figure 4 is a cross-sectional view of the apparatus according to the invention, in a fourth operating step thereof;

[0024] Figure 5 is a cross-sectional view of the apparatus according to the invention, in a fifth operating step thereof.

[0025] With reference to the figures, in which identical reference numerals refer to identical elements, the apparatus according to the invention, generally designated by the reference numeral 1, comprises a mold which comprises a lower mold half 2 which can be mated with an upper mold half 3, so as to define an impression or mold cavity 4.

[0026] A forging piston 5 can move in a channel defined inside the upper mold half 3, and accommodates a flow control plunger 6 inside it.

[0027] An oven 7 is arranged below the lower mold half 2 which is adapted to contain liquid metal 8. The oven 7 has a reascent channel 9 for the liquid metal to rise toward the mold cavity 4.

[0028] Conveniently, a vacuum supply channel 10 is defined between the upper mold half 3 and the lower mold half 2.

[0029] The vacuum supply channel 10 is connected, through a duct 11 defined in the upper mold half 3, to a vacuum pump (not shown).

[0030] A solenoid valve 20 for controlling the vacuum is arranged in the duct 11.

[0031] The vacuum supply channel 10 is furthermore connected, by way of a plurality of vent channels 12, to the mold cavity 4.

[0032] The vent channels 12 are in contact with the surface of the piece being cast and are arranged perimetrically around that surface.

[0033] Conveniently the vent channels 12 are zigzag-shaped or in any case they are not straight.

[0034] The forging piston 5, which accommodates the flow control plunger 6, is provided with a vacuum creation channel 14 arranged at its upper end, and vent channels 13 arranged at a substantially intermediate region thereof, which can be closed by the flow control plunger 6 in its stroke inside the forging piston 5.

[0035] An additional solenoid valve 21 for controlling the vacuum is arranged in the vacuum creation channel 14 of the forging piston 5; there can be a dedicated vacuum pump, or the vacuum pump can be the same as the one that creates the vacuum in the channel 10.

[0036] Advantageously the upper mold half 3 is provided with a sensor 15 of the level of the metal in the mold cavity 4.

[0037] The method of die-casting according to the invention, using the apparatus described above, is described below.

[0038] Figure 1 illustrates the apparatus according to the invention in the condition in which the first mold part is closed with the oven 7 containing the liquid metal 8, and with the vacuum created both in the vacuum channel 10 (by way of the vacuum pump attached to the duct 11), and in the vents 13 on the forging piston 5.

[0039] In the step illustrated in Figure 1, the vacuum is created simultaneously in the vacuum connection channel 14 defined on the forging piston 5 and simultaneously also in the channel 11.

[0040] In this step the solenoid valves 20 and 21 are activated in order to control the vacuum, and the depression created must have a value such that the liquid metal 8 cannot rise up to the mold cavity 4 (see Figure 2).

[0041] After a time which can vary for example between 1 and 10 seconds, determined as a function of the type of liquid metal 8 present in the oven 7 and as a function of the volume of the mold cavity, the pressurization of the chamber of the oven 7 is commanded so that the liquid metal 8 will rise into the mold cavity.

[0042] Figure 2 then shows the step wherein, as a consequence of the pressurization of the chamber of the oven 7, the liquid metal enters the channel 9 and fills the mold cavity 4, in the absence of air in the mold cavity 4 and in the liquid metal reascent channel 9.

[0043] In this condition the vents 13 of the forging piston are still open by virtue of the position of the flow control plunger 6.

[0044] Filling of the mold cavity 4 with liquid metal 8 occurs via the pressurization of the chamber of the oven 7 and the rise of the forging piston 5, with the “syringe effect”.

[0045] The step of filling is controlled by the sensor 15 which determines when to stop the flow of liquid metal into the mold cavity 4. Figure 2 then indicates the apparatus according to the invention with the syringe effect concluded and with the oven pressurized.

[0046] Figure 3 shows the descent of the flow control plunger 6, after a programmed time, with consequent closure of the supply duct 9 of the liquid metal and with the vents 13 closed. At this point the pressurizing is stopped.

[0047] In this condition the metal 8 present in the supply duct descends to the level of the metal present in the oven 7.

[0048] Figure 4 shows the apparatus according to the invention in the step of forging, with the supply channel 9 of the metal 8 closed and with the air vents closed, and with the forging piston 5 having moved downward in the end-of-forging position.

[0049] During the method, up to the end of the step of forging, the vacuum remains active and the air vents / vacuum creation channels are closed with the metal 8 that rises from the pressurized oven 7.

[0050] At this point the mold can be opened and the cast piece extracted.

[0051] In practice it has been found that the apparatus and the method according to the invention achieve the intended aim and objects, in that they make it possible to use an oven of the pressurized type, but without incurring in the drawbacks inherent in the solution in the known art and at the same time eliminating the drawbacks of the solution without a pressurized oven, thus preventing the metal, once the mold cavity has been filled, from being able to return back down the reascent channel that connects the oven to the mold cavity.

[0052] In creating a depression in the mold for the liquid metal to rise in the first step, the air contained in the mold cavity and in the reascent channel is extracted, and therefore there is no porosity in the end product.

[0053] The method and the apparatus, thus conceived, are susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

[0054] Moreover, all the details may be substituted by other, technically equivalent elements.

[0055] In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to the requirements and to the state of the art. The disclosures in Italian Patent Application No. 102022000026292 from which this application claims priority are incorporated herein by reference.

[0056] Where the technical features mentioned in any claim are followed by reference numerals and / or signs, those reference numerals and / or signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference numerals and / or signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference numerals and / or signs.

Claims

CLAIMS1. An apparatus (1) for die-casting metal objects in a semisolid state, comprising a mold which comprises an upper mold half (3) which is adapted to be coupled to a lower mold half (2) in order to define a mold cavity (4), an oven (7) being arranged below said lower mold half (2) and being provided with a supply duct (9) for liquid metal (8) which connects said oven to said mold cavity (4), said upper mold half (3) being provided with a cavity within which a forging piston (5), which accommodates a flow control plunger (6) inside it, is freely movable between the upper mold half (3) and the lower mold half (2), a vacuum channel (10) being provided circumferentially around the piece to be cast and being connected to said mold cavity (4) by means of vent channels (12), said forging piston (5) comprising a connecting channel (14) for connection to the vacuum, in order to create the vacuum, the upper mold half (3) comprising a connecting channel (11) for connection to a vacuum pump, which connects said vacuum channel (10) to the outside, characterized in that it comprises a solenoid valve (21) for controlling the vacuum inside said channel (14) and a solenoid valve (20) for controlling the vacuum in the connecting channel (11) for connection to the vacuum pump.

2. The apparatus according to claim 1, characterized in that said forging piston (5) comprises air vent channels (13) which are adapted to be occluded by said flow control plunger (6) during its stroke within said forging piston (5).

3. The apparatus according to claim 1 or 2, characterized in that said solenoid valves (20, 21) are connected to a single vacuum pump.

4. The apparatus according to claim 1 or 2, characterized in that said solenoid valves (20, 21) are each connected to a vacuum pump.

5. A method for die-casting metal objects in a semisolid state by means of an apparatus according to one or more of the preceding claims, which comprises the following steps:- closing said upper mold half (3) onto said lower mold half (2) and defining said mold cavity (4);- by means of said oven (7), heating metal (8) contained therein;- creating the vacuum in the mold cavity (4), in said vacuum channel and in the channel (14) of the forging piston (5), by activating said two solenoid valves (20, 21), the level of vacuum being such as to prevent the metal contained in said oven from rising up to the mold cavity (4);- pressurizing the oven in order to allow the metal to rise inside the supply duct (9) in order to fill the mold cavity (4) in the absence of air;- said vacuum creation step being performed by simultaneously creating the vacuum in said vacuum channel (14) of said forging piston (5) and in said vacuum channel (10) of said upper mold half (3), with the return upwards of said forging piston (5);- closing said supply duct (9) by means of said flow control plunger(6) and interrupting the pressurization of the oven;- making said forging piston (5) descend in order to perform a step of forging the piece being cast contained in said mold cavity (4);- opening the mold (2, 3) and extracting the cast piece.

6. The method for die-casting metal objects in a semisolid state according to claim 5, characterized in that said step of pressurizing the oven(7) is commanded after a time which is variable depending on the type of metal contained in the oven and on the volume of the mold cavity (4).

7. The method for die-casting metal objects in a semisolid state according to claim 5, characterized in that during the steps of the method, up to the forging step, the vacuum stays active and said vacuum channels (10, 14) and said vent channels are closed by said metal (8) rising from said pressurized oven (7).

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