Casting hot crack inhibition method and combined die using inhibition method

Abstract

The invention belongs to the technical field of material processing, and particularly relates to a casting hot crack restraining method and a combined mold using the restraining method. The restraining method comprises the following steps that the shape of a mold is designed based on the shape of a needed casting; carrying out casting process numerical simulation based on the mold shape; analyzing a melt cooling process temperature field based on a numerical simulation result, and determining an area with a relatively small temperature gradient; the mold corresponding to the area with the small temperature gradient is replaced with a thermal control insert, and the common mold in the other areas is kept unchanged; and forming the melt by using a combined die consisting of a common die and a thermal control insert. A traditional homogeneous solidification mold is upgraded into an insert type combined mold, and the insert type combined mold comprises a common mold and a thermal control insert. Through the high-heat-conductivity and high-hardness heterogeneous thermal control insert or the built-in cooling runner homogeneous thermal control insert, the heat dissipation efficiency is improved, the melt supercooling degree is regulated and controlled, grains are refined, isolated liquid phases are avoided, the tensile stress is reduced, hot cracks are restrained, and efficient, economical and easy-to-operate casting is achieved.

Description

Technical Field

[0001] The present application belongs to the technical field of material processing, and specifically relates to a method for suppressing casting thermal cracks and a combined mold using the method. Background Art

[0002] The formation of hot cracks is a long-standing technical problem in the casting process. Hot cracks usually occur with incomplete shrinkage during solidification and tensile stresses generated in the mushy area. The complexity of the casting cavity has a significant impact on the solidification process of the melt, which is closely related to the local temperature gradient.

[0003] Specifically, when the melt in the casting cavity solidifies, the area with a large temperature gradient has a higher nucleation rate, which helps to form an equiaxed grain structure. In this structure, the liquid phases are interconnected, which facilitates shrinkage compensation and reduces the possibility of hot cracking defects. However, in areas with a smaller temperature gradient, the melt tends to form coarse dendrites because the conditions are not sufficient to form an equiaxed structure. This dendritic structure will lead to isolated liquid phases between the dendrites, which cannot be effectively compensated during solidification, resulting in large shrinkage tensile stress. When this tensile stress exceeds the tensile strength of the material, hot cracks will form.

[0004] In particular, for some alloys with a high tendency to hot cracking, such as 7 series aluminum alloys, the problem of hot cracking defects during the casting process is more obvious. These alloys are more likely to form coarse dendrite structures during the solidification process, thereby increasing the risk of hot cracking. The appearance of hot cracks will not only affect the appearance quality of the casting, but more importantly, it will significantly reduce the mechanical properties and service life of the casting.

[0005] Therefore, how to effectively control the hot cracking problem in the casting process has become a key technical problem that needs to be solved in the casting field. Although there are some measures for hot cracking control in the prior art, they often have problems such as limited effect, complex operation or high cost, and cannot meet the growing demand for casting quality. Therefore, developing an efficient, economical and easy-to-operate casting hot cracking suppression method has important practical significance and application value. Summary of the invention

[0006] The purpose of the present application is to provide an efficient, economical and easy-to-operate casting hot crack suppression method and a combined mold using the suppression method.

[0007] The embodiments of the present application can be implemented through the following technical solutions:

[0008] A casting hot crack suppression method comprises the following steps:

[0009] S0: Design the mold shape based on the shape of the required casting;

[0010] S1: performing numerical simulation of the casting process based on the mold shape;

[0011] S2: Analyze the temperature field of the melt cooling process based on the results of the numerical simulation, and determine the area with a smaller temperature gradient;

[0012] S3: Replace the mold corresponding to the area with smaller temperature gradient with a thermal control insert, and keep the ordinary mold in the other areas unchanged;

[0013] S4: forming the melt using a combined mold consisting of the common mold and the thermal control insert.

[0014] Preferably, the following steps are included between step S3 and step S4:

[0015] Step S34: performing multiple numerical simulation optimizations on the combined mold consisting of the common mold and the thermal control insert to optimize the design of the combined mold.

[0016] Optionally, the thermal control insert is made of a metal or non-metal material with high thermal conductivity and high hardness.

[0017] Preferably, the thermal control insert is made of silicon carbide ceramic material or tungsten alloy material, and the common mold is made of steel material.

[0018] Optionally, the thermal control insert is an insert with a built-in cooling medium flow channel.

[0019] Furthermore, a water inlet and a water outlet are provided on the thermal control insert, and are respectively connected to an external water inlet pipeline and a water outlet pipeline.

[0020] Preferably, the thermal control insert is further provided with a plurality of machining holes, and the machining holes are communicated with the flow channel.

[0021] A combined mold comprises a common mold and a thermal control insert.

[0022] The embodiment of the present application provides a casting hot crack suppression method and a combined mold using the suppression method, which has at least the following features:

[0023] Beneficial effects:

[0024] The present application upgrades the traditional homogeneous solidification forming mold to an insert-type combined mold, which includes an ordinary mold and a thermal control insert. For areas where the temperature gradient is low and coarse dendrites are easily formed during the solidification process, resulting in thermal cracks, a heterogeneous thermal control insert with high thermal conductivity and high hardness or a homogeneous thermal control insert with a built-in cooling medium flow channel is used to improve the heat dissipation efficiency. While ensuring the reliability of the mold, the thermal conductivity effect is adjusted to achieve active regulation of the supercooling of each part of the melt, increase the nucleation rate of the solidification process in the local area, thereby obtaining a refined equiaxed grain structure, avoiding the occurrence of isolated liquid phases during solidification, achieving connected liquid phase flow compensation, reducing local tensile stress, and inhibiting the occurrence of thermal cracks. It has the advantages of high efficiency, economy, and easy operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the overall structure diagram of a typical inhomogeneous alloy part;

[0026] Figure 2 This is a technical principle diagram of the casting hot crack suppression method of the present application;

[0027] Figure 3 is a flow chart of the inhibition method in this application;

[0028] Figure 4 The overall structure diagram of the extrusion casting machine to which the combined mold in the present application is applied;

[0029] Figure 5 is a cross-sectional view of an extrusion casting machine to which the combined die in the present application is applied;

[0030] Figure 6 It is a schematic diagram of the principle of the built-in cooling medium flow channel insert;

[0031] Figure 7 This is the overall structural diagram of the built-in cooling medium flow channel insert.

[0032] Figure numerals: S, flow channel, 1, frame, 11, shell, 12, base, 2, vertical extrusion mechanism, 3, combined mold, 31, ordinary mold, 32, thermal control insert, 321, water inlet, 322, water outlet, 323, processing hole, 324, water plug, 4, core rod. DETAILED DESCRIPTION

[0033] Hereinafter, the present application will be further described based on preferred embodiments with reference to the accompanying drawings.

[0034] The vocabulary in this specification is used to illustrate the embodiments of the present application, but is not intended to limit the present application. Unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, an indirect connection through an intermediate medium, or a communication between the two components. For those skilled in the art, the specific meanings of the above terms in this application can be specifically understood.

[0035] In addition, in the description of the embodiments of the present application, various components on the drawings are enlarged or reduced in size for ease of understanding, but this practice is not intended to limit the scope of protection of the present application.

[0036] In the metal casting process, the application of traditional homogeneous solidification forming molds plays a vital role. From the melting of the metal to the forming of the final product, each step is inseparable from the precise design and production of the mold.

[0037] Before casting begins, mold preparation is crucial. This includes mold design, which requires precise calculation and drawing based on the specific shape, size and performance requirements of the required casting to ensure that the mold has a reasonable structure and sufficient strength, and can meet the shrinkage and deformation requirements of the casting during solidification.

[0038] The selection of mold materials is also critical. It is necessary to select materials that can withstand high temperature, high pressure and molten metal erosion, such as steel, alloys, etc., to ensure that the mold will not affect the quality of the casting due to deformation or damage during use.

[0039] Once the mold is ready, the metal can be melted and poured. During the pouring process, the temperature and pouring speed of the molten metal need to be strictly controlled to ensure that the metal can evenly and fully fill the mold and form a good solidification structure.

[0040] Through this series of sophisticated operations and controls, traditional homogeneous solidification forming molds can help cast metal products with stable quality and excellent performance.

[0041] In order to facilitate the description of the problems existing in the homogeneous solidification forming mold, this application is based on Figure 1 The typical inhomogeneous alloy part shown is used as an example.

[0042] During the solidification process of metal casting, the significant temperature difference between the mold and the melt has a decisive influence on the microstructure and properties of the casting. The mold, as a cooling medium, has a temperature much lower than that of the liquid metal, which causes the melt in contact with the mold surface to cool rapidly, thereby obtaining a large degree of undercooling. The increase in undercooling reduces the critical nucleus radius and the work required for nucleation, allowing small and uniform equiaxed grains to form in the area close to the mold. The formation of these equiaxed grains helps to improve the strength and toughness of the casting, and is one of the important characteristics of high-quality castings.

[0043] However, if Figure 2 As shown in the upper part of the figure, the solidification process of liquid metal presents different characteristics in the area far away from the mold, with lower temperature gradient and less supercooling. As the temperature gradually decreases, the metal begins to solidify in the form of dendrites. The growth of dendrites is due to the supercooling of the components caused by the redistribution of solutes at the solid-liquid interface, which in turn promotes the preferential growth of crystals. Although the formation of this dendritic structure increases the hardness of the casting to a certain extent, it also brings potential problems. In particular, when the dendrites are too developed, they will block the shrinkage feeding channel of the liquid phase, resulting in defects such as shrinkage cavities and shrinkage porosity inside the casting in the later stage of solidification.

[0044] More seriously, the formation of dendrites also increases the risk of hot crack initiation and propagation in the alloy. During the solidification process of the alloy, the shrinkage feeding effect of the liquid phase is crucial to prevent the formation of cracks. However, when the dendrites are densely arranged, they hinder the free flow of the liquid phase, making shrinkage feeding difficult. As the material continues to cool and the volume decreases, local tensile stresses are generated inside the casting. When these tensile stresses exceed the strength limit of the material, they will cause hot cracks. These cracks not only damage the integrity of the casting, but also seriously affect its performance and life.

[0045] For areas where the temperature gradient is low during solidification and coarse dendrites are easily formed, resulting in thermal cracks, the present application uses a thermal control insert 32 to improve the heat dissipation efficiency.

[0046] This application proposes a breakthrough upgrade plan for the traditional homogeneous solidification forming mold, which is innovatively designed as an insert-type combined structure (combination mold 3). This innovative design not only retains the basic functions of the traditional mold, but also achieves precise control of the melt solidification process by introducing a thermal control insert 32.

[0047] Specifically, the combined mold 3 includes a common mold 31 and a thermal control insert 32. The common mold 31, as the main structure, is responsible for providing basic forming functions and supporting functions. The thermal control insert 32, as a key innovation, is designed to replace the area with a smaller temperature gradient in the traditional mold by flexibly adjusting its parameters such as material, structure and size, and its shape precisely corresponds to the area. This design enables the mold to optimize the heat conduction effect by adjusting the parameters of the thermal control insert 32 according to different casting conditions and alloy properties during use, thereby realizing active regulation of the supercooling of each part of the melt.

[0048] In actual operation, by precisely controlling the thermal conductivity of the thermal control insert 32, the solidification nucleation rate of the local area of ​​the melt can be significantly improved. This not only helps to obtain a more refined equiaxed grain structure, improve the strength and toughness of the casting, but also effectively avoids the occurrence of isolated liquid phases during the solidification process of the melt. At the same time, due to the introduction of the thermal control insert 32, a more reasonable temperature gradient distribution is formed inside the mold, which promotes the flow compensation of the connected liquid phase and further reduces the local tensile stress inside the casting.

[0049] like Figure 2 As shown in the lower part of the figure, by adopting this block-type combined structure mold, the generation of thermal cracks can be significantly suppressed, and the overall quality and reliability of the casting can be improved. This innovative design not only brings new technological breakthroughs to the metal casting industry, but also provides strong technical support for the mass production of high-quality castings, with the advantages of high efficiency, economy and easy operation.

[0050] Based on the innovative design of the block-type combined structure, the following casting hot crack suppression methods are formed, such as Figure 3 As shown, the inhibition method comprises the following steps:

[0051] S0: Design the mold shape based on the shape of the required casting;

[0052] S1: performing numerical simulation of the casting process based on the mold shape;

[0053] S2: Analyze the temperature field of the melt cooling process based on the results of the numerical simulation, and determine the area with a smaller temperature gradient;

[0054] S3: The mold corresponding to the area with smaller temperature gradient is replaced with the thermal control insert 32, and the ordinary mold 31 of the other areas remains unchanged;

[0055] S4: Using the combined mold 3 consisting of the common mold 31 and the thermal control insert 32 to shape the melt.

[0056] In some preferred embodiments of the present application, in order to ensure the forming effect of the combined mold 3, step S34 is also included between step S3 and step S4: multiple numerical simulation optimizations are performed on the combined mold 3 composed of the common mold 31 and the thermal control insert 32 to optimize the design of the combined mold 32, that is, the respective shapes and proportions of the common mold 31 and the thermal control insert 32.

[0057] In some specific embodiments of the present application, the inhibition method is applicable to various alloys, especially alloy materials with high hot cracking tendency.

[0058] Furthermore, the design of the thermal control insert 32 needs to take into account both efficient heat dissipation and high-strength support, so its thermal conductivity is required to be higher than that of the ordinary mold 31 to ensure the heat dissipation effect, and the hardness is high enough to meet the forming function and provide the necessary support. In addition, the selection of the material of the thermal control insert 32 must also ensure that it does not react with the melt to avoid adverse effects on the performance of the cast alloy parts.

[0059] In some specific embodiments of the present application, the thermal control insert 32 is made of a metal or non-metal material with high thermal conductivity and high hardness.

[0060] In some preferred embodiments of the present application, the thermal control insert 32 is made of silicon carbide ceramic material or tungsten alloy material, and the common mold 31 is made of steel material. Among them, silicon carbide material has high wear resistance, high strength, high temperature resistance and excellent oxidation resistance, so that the thermal control insert 32 can still maintain stable performance in a high temperature environment, thereby ensuring the quality and precision of the casting; tungsten alloy material has high tensile strength, good thermal conductivity and low linear expansion coefficient, good corrosion resistance and oxidation resistance, good weldability and machining characteristics, so that the thermal control insert 32 has high stability and also provides the possibility for complex part mold manufacturing.

[0061] In some other specific embodiments of the present application, the thermal control insert 32 is an insert with a built-in cooling medium flow channel.

[0062] Furthermore, if Figure 5 and Figure 6 As shown, a water inlet 321 and a water outlet 322 are specially provided on the thermal control insert 32, and these two ports are respectively connected to the external water inlet pipeline and the water outlet pipeline to form a complete cooling medium circulation system. Through such a design, the cooling medium can flow in the flow channel S inside the thermal control insert 32, thereby effectively adjusting and controlling the temperature of the insert, and ensuring the stability and precision of the mold during the processing.

[0063] In some preferred embodiments of the present application, an efficient and simple processing method is adopted to process the complex cooling medium flow channel S with corners inside the thermal control insert 32. Specifically, a plurality of processing holes 323 are specially opened on the thermal control insert 32, and the processing holes 323 are connected to the flow channel, such as Figure 6 As shown. These processing holes 323 are opened to be able to process straight channels first. Since the cooling medium flow channel S inside the thermal control insert 32 is often not a straight line, but contains a corner position, the coordination of multiple processing holes 323 can flexibly process a curved flow channel S with a corner. After all the flow channels S are processed, these processing holes 323 are blocked with a blocking device such as a water plug 324 to ensure a closed circulation of the cooling medium. This method not only simplifies the processing process, but also improves the processing efficiency.

[0064] The density of the cooling medium flow channel S in the thermal control insert 32 can be set according to actual needs. It is conceivable that the cooling medium flow channel S can be set only in the thermal control insert 32, or in both the common mold 31 and the thermal control insert 32.

[0065] In summary, if Figure 5 As shown, when the thermal control insert 32 is made of heterogeneous materials, that is, the material of the thermal control insert 32 is different from that of the ordinary mold 31. Specifically, based on the results of numerical simulation, the area with a smaller temperature gradient is determined and the mold corresponding to the area is replaced with a thermal control insert 32 made of high thermal conductivity and high hardness material.

[0066] like Figure 6 and Figure 7 As shown, when the thermal control insert 32 is a built-in cooling medium flow channel insert, the thermal control insert 32 is the same as the ordinary mold 31 in terms of manufacturing materials, but its uniqueness lies in the internal design of the cooling medium flow channel S. This design enables the thermal control insert 32 to not only perform the basic functions of the mold, but also have the ability to control temperature.

[0067] It is conceivable that the thermal control insert 32 may also be a combination of a heterogeneous material and a built-in cooling medium flow channel S.

[0068] The structure of the extrusion casting machine to which the combined die 3 is applied will be described below.

[0069] Figure 4 Figure 5 The overall structure diagram and cross-sectional diagram of the extrusion casting machine to which the combined die in the present application is applied are shown respectively. Figure 4 Figure 5As shown, the extrusion casting machine includes a frame 1, a vertical extrusion mechanism 2 and a combined mold 3. The frame 1 includes a shell 11 and a base 12 connected to the bottom of the shell 11. The shell 11 is a shell with a hollow chamber, and a through hole is opened on the top surface to accommodate and allow the vertical extrusion mechanism 2 to move vertically and pour the melt. The combined mold 3 is installed and accommodated in the interior of the shell 11, and the melt is poured into the cavity of the combined mold 3, and then the part is formed by cooling, extrusion, etc.

[0070] In some specific embodiments of the present application, the extrusion casting machine further includes a core rod 4, which is connected to the inner wall of the housing 11. Figure 1 For the alloy parts in the casting, the core rod 4 is used to perforate the solid ingot to ensure that the required channel or cavity structure is formed inside the casting.

[0071] In some preferred embodiments of the present application, the extrusion casting machine further includes a locking ring, which is tightly fitted to the periphery of the combined mold 3. Driven by the hydraulic or mechanical system of the extrusion casting machine, the locking ring can generate sufficient locking force to firmly clamp the mold. In this way, when the melt is injected into the cavity of the combined mold 3 under high pressure, the combined mold 3 can maintain a stable closed state, thereby ensuring the smooth molding of the casting.

[0072] Squeeze casting machine, as a mature technology in the field of casting equipment, has been widely recognized and applied in this field in terms of its basic structure and working principle. In view of this, the drawings and descriptions in this application will focus on the transformation and innovation of the mold part, and will not go into detail about the other conventional design parts. Our goal is to clearly show the details of the mold transformation so that we can better understand and implement the technical solution of this application.

[0073] It is conceivable that the combined mold 3 can also be applied to a gravity casting machine.

[0074] The above is a detailed introduction to the specific implementation methods of the present application. For those skilled in the art, several improvements and modifications may be made to the present application without departing from the principles of the present application. These improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A casting hot crack suppression method, characterized in that: The following steps are involved: S0: Design the mold shape based on the shape of the required casting; S1: performing numerical simulation of the casting process based on the mold shape; S2: Analyze the temperature field of the melt cooling process based on the results of the numerical simulation, and determine the area with a smaller temperature gradient; S3: Replace the mold corresponding to the area with smaller temperature gradient with a thermal control insert, and keep the ordinary mold in the other areas unchanged; S4: forming the melt using a combined mold consisting of the common mold and the thermal control insert.

2. A casting hot crack suppression method according to claim 1, characterized in that: The steps between step S3 and step S4 also include: Step S34: performing multiple numerical simulation optimizations on the combined mold consisting of the common mold and the thermal control insert to optimize the design of the combined mold.

3. A casting hot crack suppression method according to claim 1, characterized in that: The thermal control insert is made of metal or non-metal material with high thermal conductivity and high hardness.

4. A casting hot crack suppression method according to claim 3, characterized in that: The thermal control insert is made of silicon carbide ceramic material or tungsten alloy material, and the common mold is made of steel material.

5. A casting hot crack suppression method according to claim 1, characterized in that: The thermal control insert is an insert with a built-in cooling medium flow channel.

6. A casting hot crack suppression method according to claim 5, characterized in that: The thermal control insert is provided with a water inlet and a water outlet, which are respectively connected to an external water inlet pipeline and a water outlet pipeline.

7. A casting hot crack suppression method according to claim 6, characterized in that: The thermal control insert is also provided with a plurality of processing holes, and the processing holes are communicated with the flow channel.

8. A combined mold, comprising the common mold according to any one of claims 1 to 7 and a thermal control insert.

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