Apparatus and method for casting metal parts

Abstract

The present invention discloses an apparatus and method for casting metal parts. The method involves steps of: melting a metallic material in a melting chamber until a molten metal reaches a low superheat temperature of about 5-20 degrees Celsius, and applying vigorous convection to the molten metal to create a superheated slurry with numerous solid particles or nuclei using a porous material probe. The method further involves steps of: pouring a superheated slurry in a mold chamber having a non-sticking surface, and solidifying the slurry at the mold chamber while applying pressurized inert gas to ensure complete mold filling, minimize porosity, and achieve casting the sound metal part with a uniform grain structure.

Description

APPARATUS AND METHOD FOR CASTING METAL PARTSTECHNICAL FIELD

[0001] The present disclosure relates generally to an apparatus and method for casting metal parts, and more particularly, an apparatus and method for casting metal parts, while achieving near-net shape casting with uniform microstructure, and eliminating gas porosity, shrinkage porosity, hot tearing, and solute segregation without the need for die lubricants.BACKGROUND

[0002] The traditional casting method involves melting, filling and solidification. Initially, metals are melted in large furnaces using electric resistance wires or natural gas. The furnace maintains a high superheat temperature to improve the fluidity of the melt. However, maintaining the temperature significantly increases energy consumption, which leads to higher operational costs and greater carbon emissions.

[0003] Further, before the filling process, permanent dies are typically sprayed with cooling fluid with a mold release agent to prevent soldering, which contributes to air pollution. After the step of melting, the molten metal is transferred to a mold defining a filling stage. For example, in high- pressure die casting, the molten metal is forced into the mold at high velocities. However, the higher gate velocity in high-pressure casting causes turbulent flow and gas porosity, which can result in defects.

[0004] After the step of filling, the metal cools and solidifies within the mold. During solidification, shrinkage porosity can occur at hot spots in the casting. To address the defects due to shrinkage porosity, traditional methods often rely on large risers or the application of high intensification pressures, but these solutions can reduce material yield and shorten the life of the molds, leading to increased production costs. Additionally, mold surfaces in permanent die casting are typically treated with lubricants to prevent the metal from sticking, but these substances contribute to environmental pollution and further increase production costs. Further, defects such as dendritic grain structure, micro-shrinkage porosity, hot tearing on metal parts formed by the conventional method are shown in picture (100, 200) of FIG. 1 and FIG. 2.

[0005] Therefore, there is a need for an apparatus and method for casting a metal part with sound and uniform grain structure. The apparatus and method need to address one or more afore- discussed drawbacks, for example, gas porosity, shrinkage porosity, hot tearing, solute segregation, oxide film contamination, increased energy consumption and carbon emissions. The apparatus and method further need to address the disadvantages of conventional casting with respect to high superheat temperatures, mold lubricants, low material yield, and air pollution.SUMMARY OF THE INVENTION

[0006] The present invention discloses an apparatus and method for casting metal parts. The apparatus comprises a melting chamber having a crucible and at least one heating module. The melting chamber is configured to melt a metallic material in the crucible until a molten metal reaches a low superheat temperature of about 5-20 degrees Celsius. The apparatus further comprises a porous material probe mounted on the melting chamber. The porous material probe comprises a porous probe. The porous probe is configured to extend into the crucible. The porous material probe is configured to apply vigorous convection to the molten metal and create a superheated slurry with numerous solid particles or nuclei. In one embodiment, the slurry comprises maximum solid particles of about 10% by volume when the temperature of the metallic material is below the liquidus temperature. In one embodiment, the slurry comprises maximum solid particles of about 5% by volume when the temperature of the metallic material is above the liquidus temperature.

[0007] The apparatus further comprises a mold chamber made of a non-sticking die material configured to receive the superheated slurry to solidify the melt while applying pressurized inert gas to ensure complete mold filling, minimize porosity, and achieve casting the sound metal part with a uniform grain structure. Further, the casting temperature is about 5-20°C above the metal's liquidus temperature. The mold chamber is maintained at a pressure of less than 0.05 MPa and inert gas is applied at about 1 to 2 bars of pressure.

[0008] In one embodiment, the melting chamber is configured to maintain at least one of a low- oxygen atmosphere and an inert gas atmosphere. In one embodiment, melting chamber is configured to maintain an atmosphere with air. In one embodiment, the heating module comprisesan induction coil. In one embodiment, the melting chamber comprises at least one of an induction heater and an electric heater.

[0009] In one embodiment, the metallic material is selected from a group including, but not limited to, aluminum, aluminum alloy, low silicon aluminum, titanium, magnesium, ceramic materials including graphite, alumina, and silicon carbide, and titanium with non-wetting forms of oxides, carbides, or nitrides. In one embodiment, the mold chamber is made of materials selected from a group including, but not limited to, graphite, ceramics, anodized metals, metals with thin- film coatings.

[0010] The apparatus further comprises a vacuum cover configured to enclose components of the apparatus, with optional components including a solar energy module to supply power and an air filter to clean powder or dust during castings in the vacuum cover. The apparatus further comprises a vacuum pump in fluid communication with the vacuum cover. The vacuum pump is configured to maintain a low level of oxygen. The apparatus further comprises a pressure sensor configured to monitor pressure within the vacuum cover.

[0011] The method involves steps of: melting a metallic material in a melting chamber until a molten metal reaches a low superheat temperature of about 5-20 degrees Celsius. The metallic material is free from oxide films.

[0012] The method further involves step of: applying vigorous convection to the molten metal to create a superheated slurry with numerous solid particles or nuclei using a porous material probe. In one embodiment, the slurry comprises maximum solid particles of about 10% by volume when the temperature of the metallic material is below the liquidus temperature. In one embodiment, the slurry comprises maximum solid particles of about 5% by volume when the temperature of the metallic material is above the liquidus temperature. In one embodiment, the superheated slurry is created by vigorous convection using a heat extraction probe and fine inert gas bubbles.

[0013] The method further involves step of: pouring a superheated slurry in a mold chamber having a non-sticking surface. The method further involves step of: solidifying the slurry in the mold chamber while applying pressurized inert gas to ensure complete mold filling, minimize porosity, and achieve casting the sound metal part with a uniform grain structure. In oneembodiment, the casting temperature is about 5-20°C above the metal's liquidus temperature. In one embodiment, the mold chamber is at a pressure of less than 0.05 MPa and inert gas is applied at about 1 to 2 bars of pressure.

[0014] The method further involves step of: applying squeeze pins to reduce shrinkage porosity. In one embodiment, the step of melting is performed in at least one of a low-oxygen atmosphere and an inert gas atmosphere. In one embodiment, the step of melting is performed under air. In one embodiment, the step of melting is performed using at least one of an induction heater and an electric heater.

[0015] In one embodiment, the metallic material is selected from a group including, but not limited to, aluminum, aluminum alloy, low silicon aluminum, titanium, magnesium, ceramic materials including graphite, alumina, and silicon carbide, and titanium with non-wetting forms of oxides, carbides, or nitrides. In one embodiment, the mold chamber is made of materials selected from a group including, but not limited to, graphite, ceramics, anodized metals, metals with thin- film coatings.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a picture of hot tearing defect in metal parts formed using a conventional casting method.

[0017] FIG. 2 is a picture showing dendritic grain structure and micro-shrinkage porosity in a liquid sample formed during the conventional casting method.

[0018] FIG. 3 exemplarily illustrates an apparatus for casting metal parts with sound and uniform grain structure, according to an embodiment of the present invention.

[0019] FIG. 4 exemplarily illustrates a method for casting metal parts, according to an embodiment of the present invention.

[0020] FIG. 5 is a picture showing the uniform anodized quality of sample produced according to an embodiment of the present invention.

[0021] FIG. 6 is a picture showing the sound and uniform grain structure of 7075 alloy sample produced according to an embodiment of the present invention.

[0022] FIG. 7 is a picture showing the sound and uniform grain structure of 6063 alloy sample produced according to an embodiment of the present invention.DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0023] Example embodiments of the disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments are shown. The concepts discussed herein may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope to those of ordinary skill in the art. Like numbers refer to like elements but not necessarily the same or identical elements throughout.

[0024] Referring to FIG. 3, an apparatus 300 comprises a melting chamber 302 comprising a crucible and a heating module. The heating module is configured to melt a metallic material in the crucible until the melt reaches a low superheat temperature of about 5-20 degrees Celsius. In one embodiment, the heating module comprises an induction heater. In another embodiment, the heating module comprises an electric heater. The heating module enables to achieve precise and consistent melting temperatures. In one embodiment, metallic material comprises aluminum ingot.

[0025] In one embodiment, the melting chamber 302 is configured to maintain a low-oxygen atmosphere. In another embodiment, the melting chamber 302 is configured to maintain an inert gas atmosphere. In yet another embodiment, the melting chamber 302 is configured to maintain an atmosphere with air. In one embodiment, the metallic material is selected from a group, including, but not limited to, aluminum, titanium, magnesium, ceramic materials including graphite, alumina, and silicon carbide, and titanium with non-wetting forms of oxides, carbides, or nitrides. In another embodiment, the metallic material comprises aluminum alloy. In yet anotherembodiment, the metallic material comprises low silicon aluminum alloy.

[0026] The apparatus 300 further comprises a porous material probe mounted on the furnace. The porous material probe comprises a porous probe that extends into the crucible. The porous material probe is configured to apply vigorous convection to the melt and create a superheated slurry with numerous solid particles or nuclei in the melt or molten metal. In one embodiment, the porous material probe is a heat extraction probe 304. In one embodiment, the slurry comprises maximum solid particles of about 10% by volume when the temperature of the metallic material is below the liquidus temperature. In one embodiment, the slurry comprises maximum solid particles of about 5% by volume when the temperature of the metallic material is above the liquidus temperature.

[0027] The apparatus 300 further comprises a mold chamber 306. In one embodiment, the mold chamber 306 is made of a non-sticking die material. The metallic material is in a superheated slurry state before pouring into the mold chamber 306. The mold chamber 306 is configured to receive a superheated slurry.

[0028] The apparatus 300 is configured to feed pressurized inert gas to the mold chamber 306 during solidification. The application of pressurized inert gas improves feeding and reduces riser porosity and shrinkage porosity. Further, the casting temperature is about 5-20°C above the metal's liquidus temperature. The mold chamber 306 is maintained at a pressure of about 0.05 MPa and inert gas is applied at about 1 to 2 bars of pressure.

[0029] In one embodiment, the mold chamber 306 is made of materials selected from a group including, but not limited to, graphite, ceramics, anodized metals, metals with metals with thin-film coatings. In one embodiment, titanium mold has been anodized to create a ceramic coating on the surface of the mold chamber 306, which prevents the molten metal from sticking to the mold chamber 306. In one embodiment, during solidification, the feeding pressure of 1-10 bar by air or Nitrogen gas is maintained, which will help to reduce the shrinkage porosity. The metal temperature in melting chamber 302 is about 10-20°C higher than liquidus of alloy. Further, the lower superheated slurry maintains a higher proportion of solid particles within the melt, contributing to improved die life by reducing thermal stress and minimizing wear on the mold.

[0030] The apparatus 300 further comprises a vacuum cover or enclosure 308 configured to enclose components of the apparatus 300, and may optionally include a solar energy module to supply power. Additionally, the apparatus 300 may include an air filter to clean powder or dust during castings in the vacuum cover 308.

[0031] The apparatus 300 further comprises a vacuum pump in fluid communication with the vacuum enclosure 308 configured to maintain a low level of oxygen, and a pressure sensor configured to monitor pressure within the vacuum enclosure 308. The apparatus 300 comprises one or more inlet and outlet valves (314, 316) to regulate oxygen level, and pressure. The inlet and outlet valves (314, 316) are used to feed inert gas into the mold chamber 306.

[0032] Referring to FIG. 4, a method 400 for casting sound metal parts is disclosed. At step 402, raw material or ingot is melted in an induction heater in a crucible based on casting weight until the melt reaches a low superheat temperature of about 5-20 degrees Celsius. The metallic material is free from oxide films.

[0033] At step 404, a heat extraction probe 304 is used to achieve vigorous convection, which creates a superheated slurry with numerous solid particles or nuclei in the melt. In one embodiment, the slurry comprises maximum solid particles of about 10% by volume when the temperature of the metallic material is below the liquidus temperature. In one embodiment, the slurry comprises maximum solid particles of about 5% by volume when the temperature of the metallic material is above the liquidus temperature. In one embodiment, the superheated slurry is created by vigorous convection using a heat extraction probe 304 and fine inert gas bubbles. At step 406, the superheated slurry is transferred into the mold chamber 306 made of non-sticking die material.

[0034] At step 408, inert gas is fed into the mold chamber 306, while applying pressure to the solidifying metal to assist feeding, reducing riser and shrinkage porosity. The method 400 ensures complete mold filling, minimizes porosity, and achieves casting of sound metal parts with a uniform grain structure. In one embodiment, the casting temperature is about 5-20°C above the metal's liquidus temperature. In one embodiment, the mold chamber 306 is at a pressure of less than 0.05 MPa and inert gas is applied at about 1 to 2 bars of pressure. Further, a uniform anodized quality of the sample produced according to an embodiment of the present invention, is shown inpicture 500 of FIG. 5.

[0035] The method 400 further involves step of: applying squeeze pins to reduce shrinkage porosity. In one embodiment, the step 402 of melting is performed in at least one of a low-oxygen atmosphere and an inert gas atmosphere. In one embodiment, the step 402 of melting is performed under air. In one embodiment, the step 402 of melting is performed using at least one of an induction heater and an electric heater.

[0036] In one embodiment, the metallic material is selected from a group including, but not limited to, aluminum, aluminum alloy, low silicon aluminum, titanium, magnesium, ceramic materials including graphite, alumina, and silicon carbide, and titanium with non-wetting forms of oxides, carbides, or nitrides. In one embodiment, the mold chamber 306 is made of materials selected from a group including, but not limited to, graphite, ceramics, anodized metals, metals with thin-film coatings.

[0037] The following two examples illustrate two embodiments of the present invention. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein.Example 1: Gravity Die Casting of 7075 Alloy

[0038] 7075 alloy is cast into a graphite die, preheated to about 500°C. The alloy, with a liquidus temperature of about 635°C, is poured at about 640°C, with a superheat temperature of about 5°C. A heat extraction probe achieves vigorous convection by flowing fine inert gas bubbles through a porous probe. The melt is transferred and poured into the die cavity in less than 5 seconds. The process is performed in a low-oxygen chamber with a pressure of about 0.05 MPa. Nitrogen gas flows into the chamber after the melt fills the die cavity completely, with about 1 to 2 bars of pressure. Results show uniform grain structure and no hot tearing, compared to conventional casting at about 700°C. Further, a picture 600 showing the sound and uniform grain structure of 7075 alloy sample produced according to an embodiment of the present invention is shown in FIG. 6.Example 2: Gravity Die Casting of 6063 Alloy

[0039] 6063 alloy is cast into a metal mold, preheated to about 530°C. The alloy, with a liquidustemperature of about 654°C, is poured at about 660°C, with a superheat temperature of about 6°C. A heat extraction probe achieves vigorous convection by flowing fine inert gas bubbles through a porous probe. The melt is transferred and poured into the casting basin in less than 5 seconds. The process is performed in a low-oxygen chamber with a pressure of about 0.05 MPa. Nitrogen gas flows into the chamber after the melt fills the die cavity completely, with about 1 to 2 bars of pressure. Results show uniform grain structure and good anodizing surface. Further, a picture 700 showing the sound and uniform grain structure of 6063 alloy sample produced according to an embodiment of the present invention is shown in FIG. 7.

[0040] Advantageously, the present invention achieves a near-net shape casting with sound and uniform grain structure and eliminates gas porosity, shrinkage porosity, hot tearing, and solute segregation without the need for die lubricants.

[0041] The method of the present invention reduces production costs and energy consumption by using induction or electric melting and minimizes environmental impact through sustainable practices. As a result, the method yields high-quality, cosmetically anodized products with lower overall costs. In addition to casting low-silicon aluminum alloys, the method is also beneficial for casting other metals and alloys to achieve a sound structure at low production costs.

[0042] The present invention enables to achieve uniform microstructure through casting with a low or zero superheat temperature, resulting in consistent quality throughout the cast part. The method involves casting in a near vacuum or low-oxygen chamber, eliminating gas entrapment within the cast part. The present invention utilizes low or zero superheat temperature with directional solidification techniques and sufficient applied pressure to produce cast parts without shrinkage porosity or hot tearing. Further, casting at low or zero superheat temperature yields uniform grain structure and distribution of alloying elements, minimizing solute segregation. Further, using clean metal and melting in a low-oxygen atmosphere prevents the formation of detrimental oxide films. The present invention uses non-sticking die materials such as graphite, ceramic, anodized metals, or PVD / CVD thin film coatings to eliminate the need for die lubricants. Further, near-net shape casting significantly reduces machining process costs and the costs associated with melting machined metal. The present invention utilizes induction or electric melting methods to significantly improve energy efficiency in the melting process.

[0043] Although the features, functions, components, and parts have been described herein in accordance with the teachings of the present disclosure, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all embodiments of the teachings of the disclosure that fairly fall within the scope of permissible equivalents.

[0044] Many modifications and other implementations of the disclosure set forth herein will be apparent having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosure is not to be limited to the specific implementations disclosed and that modifications and other implementations are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

WHAT IS CLAIMED IS:1 . A method for casting metal parts, comprising the steps of: melting a metallic material in a melting chamber until a molten metal reaches a low superheat temperature of about 5-20 degrees Celsius, wherein the melting chamber having a crucible and at least one heating module; applying vigorous convection to the molten metal to create a superheated slurry with numerous solid particles or nuclei using a porous material probe; pouring a superheated slurry in a mold chamber having a non-sticking surface, and solidifying the slurry at the mold chamber while applying pressurized inert gas to ensure complete mold filling, minimize porosity, and achieve casting the sound metal part with a uniform grain structure.

2. The method of claim 1 , wherein the melting is performed in at least one of low-oxygen atmosphere and inert gas atmosphere, and wherein the melting is performed using at least one of an induction heater and an electric heater.

3. The method of claim 1 , wherein the melting is performed in an atmosphere with air.

4. The method of claim 1 , wherein the metallic material is selected from a group comprising aluminum, aluminum alloy, low silicon aluminum, titanium, and magnesium.

5. The method of claim 1 , wherein the ceramic materials is selected from a group comprising graphite, alumina, and silicon carbide, and titanium with non-wetting forms of oxides, carbides, or nitrides.

6. The method of claim 1 , wherein the mold chamber is made of materials selected from a group comprising graphite, ceramics, anodized metals, and metals with thin-film coatings.

7. The method of claim 1 , wherein the superheated slurry is created by vigorous convection using a heat extraction probe and fine inert gas bubbles.

8. The method of claim 1 , wherein the metallic material is free from oxide films.

9. The method of claim 1 , wherein a temperature of casting is about 5-20°C above the metal's liquidus temperature.

10. The method of claim 1 , wherein the mold chamber is at a pressure of less than 0.05 MPa and inert gas is applied at about 1 to 2 bars of pressure.

11. The method of claim 1 , wherein the slurry comprises maximum solid particles of about 10% by volume when the temperature of the metallic material is below the liquidus temperature.

12. The method of claim 1 , wherein the slurry comprises maximum solid particles of about 5% by volume when the temperature of the metallic material is above the liquidus temperature.

13. The method of claim 1 , further comprising steps of: applying squeeze pins to reduce shrinkage porosity.

14. An apparatus for casting metal parts, comprising: a melting chamber having a crucible and at least one heating module configured to melt a metallic material in the crucible until a molten metal reaches a low superheat temperature of about 5-20 degrees Celsius; a porous material probe mounted on the melting chamber comprises a porous probe, wherein the porous probe is configured to extend into the crucible, wherein the porous material probe is configured to apply vigorous convection to the molten metal and create a superheated slurry with numerous solid particles or nuclei, anda mold chamber made of a non-sticking die material configured to receive the superheated slurry to solidify the melt while applying pressurized inert gas to ensure complete mold filling, minimize porosity, and achieve casting the sound metal part with a uniform grain structure.

15. The apparatus of claim 14, wherein the melting chamber is configured to maintain at least one of a low-oxygen atmosphere and an inert gas atmosphere, and wherein the heating module comprises an induction coil.

16. The apparatus of claim 14, wherein the melting chamber is configured to maintain an atmosphere with air.

17. The apparatus of claim 14, wherein the melting chamber comprises at least one of an induction heaters and an electric heater.

18. The apparatus of claim 14, wherein the metallic material is selected from a group comprising aluminum, aluminum alloy, low silicon aluminum, titanium, and magnesium.

19. The apparatus of claim 14, wherein the ceramic materials is selected from a group comprising graphite, alumina, and silicon carbide, and titanium with non-wetting forms of oxides, carbides, or nitrides.

20. The apparatus of claim 14, wherein the mold chamber is made of materials selected from a group comprising graphite, ceramics, anodized metals, and metals with thin-film coatings.

21. The apparatus of claim 14, wherein a temperature of casting is about 5-20°C above the metal's liquidus temperature.

22. The apparatus of claim 14, wherein the mold chamber is at a pressure of less than 0.05 MPa and inert gas is applied at about 1 to 2 bars of pressure.

23. The apparatus of claim 14, wherein the slurry comprises maximum solid particles of about 10% by volume when the temperature of the metallic material is below the liquidustemperature, and wherein the slurry comprises maximum solid particles of about 5% by volume when the temperature of the metallic material is above the liquidus temperature.

24. The apparatus of claim 14, further comprises: a vacuum cover configured to enclose components of the apparatus; a vacuum pump in fluid communication with the vacuum cover configured to maintain a low level of oxygen, and a pressure sensor configured to monitor pressure within the vacuum cover.

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