Intelligent low-stress sand mold casting method for high-end numerical control machine tool basic large part

Abstract

The invention discloses an intelligent low-stress sand casting method for a high-end numerical control machine tool basic large part, and belongs to the crossing field of mechanical manufacturing automation and a sand casting technology. According to the intelligent low-stress sand mold casting method for the basic large part of the high-end numerical control machine tool, different sand mold structures are selected for manufacturing parts with different moduli based on the obtained machine tool structural part model. A multi-material hollowed-out intelligent sand mold is selected for forming a high-modulus part, and the part of the sand mold comprises three main parts, namely a surface contact area, a hollowed-out sand mold area and an intelligent control unit. The part with the low modulus is formed by an intelligent compact sand mold, the sand mold of the part is based on a traditional compact sand mold, and a heating material and a control system are arranged in the sand mold. According to the method, the solidification process of each part of the machine tool casting can be intelligently regulated and controlled, so that low-stress casting of the casting is realized, the time required by subsequent aging is shortened, the production responsivity of the machine tool casting is improved, and production and development of a high-precision and high-stability machine tool are promoted.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of equipment manufacturing and sand casting technology, specifically involving an intelligent low-stress sand casting method for large basic components of high-end CNC machine tools. Background Technology

[0002] The manufacturing industry has an increasing demand for large, high-precision machine tools and machining centers, which requires these machine tools to have high stability. The fundamental factor determining the high precision and high stability of a large machine tool is the working state of its structural components, such as their installation state, fit state, and stress state. Among these, the stress state of the machine tool's structural components is the most easily overlooked.

[0003] The stress state of a machine tool structure can be preliminarily divided into three stages. The first stage involves phase transformation stress generated during the solidification of the molten metal in the casting process. This stress is continuously generated and released during solidification, manifesting as deformation at different stress levels. Mild deformation can lead to casting warping, while severe deformation can cause thermal cracking. The second stage involves thermal stress generated after the casting has solidified, due to the resistance of the sand mold to cooling and shrinking. This stress can cause deformation, and excessive stress can lead to cold cracking. The third stage is the residual stress remaining after the casting has completely cooled. This stress is largely generated from the first two stages during the cooling process. This residual stress is continuously released during the actual use of the machine tool as the load increases, severely compromising the machine tool's accuracy and stability.

[0004] Traditionally, machine tool structural parts rely on natural aging to remove residual stress. However, with the increasing demand for large machine tools and the growing size of machine tool structural parts, the natural aging time for castings is also increasing, sometimes taking several years. This significantly hinders the manufacturing response of large, high-precision machine tools. Therefore, reducing stress accumulation during the casting process is crucial for obtaining high-quality machine tool structural castings. The foundation for eliminating stress accumulation lies in controlling the solidification process of different parts of the casting, reducing the difference in cooling rates between different parts, achieving simultaneous solidification, and obtaining low-stress castings. Summary of the Invention

[0005] To address the aforementioned issues, this invention discloses an intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools. By employing a multi-material hollow structure design, the solidification process of machine tool structural parts is unified, reducing stress generation and accumulation in large machine tool structural parts, shortening subsequent natural aging time, solving the problem of difficult design and manufacturing response for large machine tool castings, opening up new avenues for low-stress sand casting, and promoting the development of the high-precision machine tool industry.

[0006] This invention discloses an intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools. Based on the obtained machine tool structural component model, the wall thickness of each part of the machine tool structural component is analyzed, and the equivalent modulus of each part of the machine tool structural casting is calculated to obtain the wall thickness modulus analysis results of the machine tool structural component. Subsequently, sand mold structure design is carried out. Based on the structural analysis results of the machine tool structural component, sand molds with large modulus differences and more complex structures are divided into blocks, and different sand mold structures are selected for manufacturing parts with different moduli.

[0007] For the thick-walled, high-modulus sections of machine tool structural parts, multi-material hollow intelligent sand molding is used. This sand mold consists of three main parts: a surface contact area, a hollow sand mold area, and an intelligent control unit. The surface contact area is the part in direct contact with the molten metal; a dense structure is selected here, and the material can be abrasive sand, silica sand, zircon sand, chromite sand, etc., depending on the alloy. The hollow sand mold area provides support and heat dissipation; by adjusting the hollow structure, a balance between support and heat dissipation is achieved, while also reducing the weight of the sand mold. The intelligent control area consists of a fan and an intelligent control unit, which intelligently regulates the solidification process during the molten metal solidification. For the lower-modulus sections, intelligent dense sand molding is used. This sand mold is based on traditional dense sand molds, but incorporates heating materials and a control system, which intelligently controls the heat release of the heating materials, providing insulation for the low-modulus sections.

[0008] The designed sand mold is manufactured in sections. The hollow sand mold is formed by additive manufacturing, while the other sand molds are cut and shaped. Thermocouples are installed in each sand mold section to monitor the subsequent solidification process. The manufactured sand mold sections are then assembled into a complete sand mold system.

[0009] The molten metal is poured into the sand mold system. As the molten metal solidifies, thermocouples at different locations monitor the solidification process of the molten metal at each location in real time. The solidification information of each location is imported into the control system. The control system actively activates the fan in the hollow sand mold and the heating material in the dense sand mold to balance the solidification process of each location. First, all parts of the casting solidify simultaneously, reducing the stress caused by the uneven solidification process of each part.

[0010] To achieve the above objectives, the intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools of the present invention is carried out according to the following steps: Step 1: Based on the actual machine tool casting model, analyze the wall thickness characteristics of each part, and use the formula M = (casting volume / casting heat dissipation surface area) to calculate the equivalent modulus of each part and the average equivalent modulus of the entire casting. Step 2: Based on the wall thickness, modulus calculation and analysis results and the structural characteristics of the casting, the area in the casting that is more than 50% higher than the average equivalent modulus is called the thick-walled large modulus area, and the area that is less than 50% of the average equivalent modulus is called the thin-walled small modulus area. Based on this, multiple sand mold modules for the thick-walled large modulus area, sand mold modules for the thin-walled small modulus area, and other sand mold modules that need to be processed are divided. Step 3: Design the intelligent hollow sand mold structure for the thick-walled, large-modulus area. Select the molding sand material for the surface contact area according to the actual alloy type. For alloys with higher pouring temperatures, use high-cooling-rate molding sand such as zircon sand and chromite sand. For alloys with lower pouring temperatures, use low-cooling-rate molding sand such as sand sand and pearl sand. Step 4: Design the hollow structure features based on the specific dimensions of a certain intelligent hollow module. The hollow structure can be selected as a grid, face-centered cubic, body-centered cubic lattice, etc. Step 5: Combine the above-mentioned hollow structure design with the active heat dissipation air duct and fan installation position, and set up thermocouples to monitor the solidification process of molten metal; Step 6: Design a smart dense sand mold structure for the thin-walled, small-modulus area, select a profile material with a large heat storage coefficient to manufacture this part of the sand mold, and set heating materials and monitoring thermocouples in the sand mold.

[0011] Step 7: Process and manufacture each sand mold module, use sand mold additive manufacturing equipment to manufacture intelligent hollow sand molds, and use sand mold cutting equipment to prepare other modules; Step 8: Assemble the sand mold modules, install the active cooling fan, heating material, and temperature monitoring thermocouple to form an intelligent low-stress sand casting system; Step 9: Spray paint inside the entire sand mold and dry it to complete the preparation of the sand mold before pouring; Step 10: Pour molten metal into the intelligent low-stress sand casting system; Step 11: The monitoring thermocouples set up in each area collect the temperature of the sand mold and the temperature of the molten metal in that part, and input them into the control computer. The computer uses the Newton baseline method to quickly process and calculate the solidification fraction of the molten metal in that part. Step 12: By comparing the differences in the solidification fraction of the molten metal in each part, the computer automatically controls the start and speed of the active cooling fan to achieve precise control of the cooling rate of the area and control the heating of the insulation material to achieve forced heat dissipation in the thick-walled area and heat preservation in the thin-walled area, balance the solidification rate of the molten metal in each part, achieve simultaneous solidification of all parts of the casting, and reduce the generation and accumulation of stress during the solidification process. Step 13: Monitor the solidification process of the casting until it is completely solidified; Step 14: When the casting temperature cools down to below 400~500℃, promptly carry out sand removal and cleaning. Step 15: The casting is further cooled and then polished to obtain a low-stress machine tool structure casting.

[0012] Step 16: Save the temperature curves of each part of the casting and the time curve of the intelligent sand mold process, and establish a database for this type of product; Step 17: When this type of product is produced again, repeat steps 1-8 and directly call the existing data to control the operation of the intelligent low-stress sand casting system to ensure the stability of different batches of products; Furthermore, this system is not limited to machine tool castings, which are designed for large machine tool structural parts with significant differences in module thickness among their various components.

[0013] Furthermore, the method manufactures an intelligent low-stress sand casting system using resin sand molds, including but not limited to clay sand molds, frozen sand molds, ceramic sand molds, and ceramic cores.

[0014] Furthermore, the method is applicable to metal materials suitable for sand casting, including but not limited to high-pouring-temperature materials such as ferrous metals and low-pouring-temperature materials such as non-ferrous metals.

[0015] The beneficial effects of this invention are: 1. This invention analyzes the structure of machine tool castings and designs sand molds in sections. For areas with significant thickness and modulus differences, intelligent hollow sand molds are used; for thin-walled areas, intelligent dense sand molds are used. During the solidification process of the molten metal, the computer intelligently controls the start and stop of the intelligent sand mold cooling fans and heating materials in both sections, achieving consistent solidification processes across all parts of the casting. This reduces thermal stress caused by differences in solidification rates, minimizing casting deformation and subsequent hot and cold cracking defects. Simultaneously, the lower casting thermal stress also reduces residual stress in the casting, which helps shorten the stress-relieving aging time and the production cycle of machine tool castings.

[0016] 2. This invention, through the segmented manufacturing of machine tool structure castings using sand molds, systematically monitors the temperature changes of each part of the casting and sand mold, recording temperature change data for each location. This enables the rapid creation of a casting database for a specific type of machine tool structure casting, providing precise comparative data for subsequent machine tool casting manufacturing and design. The discretization of the sand mold allows for precise quality control of each part of the casting. Combined with the previously recorded casting database, it intelligently controls the cooling and solidification process of each component of the casting, reducing performance differences between batches of machine tool castings and achieving high-stability manufacturing of machine tool structure castings. This provides support for the production design of large, single-piece machine tool structural components. Attached Figure Description

[0017] Figure 1 Schematic diagram of intelligent low-stress sand casting design and manufacturing method for CNC machine tool structural parts; Figure 2 Intelligent low-stress sand molding system; Figure 3 Schematic diagram of intelligent hollow sand mold structure; Figure 4 Schematic diagram of intelligent dense sand mold structure; The attached diagrams are labeled as follows: 1- Sand mold module for thick-walled castings; 2- Sand mold module for thin-walled castings; 3- Sand mold module for uniform-thickness castings; 4- Casting cavity; 5- Gating system cavity; 6- Partial sand mold module for the gating system; 1-1 Cooling fan A; 1-2 Hollowed-out sand mold structure; 1-3 Sand mold thermocouple A; 1-4 Surface contact layer; 1-5 Active cooling channel; 1-6 Cooling fan B; 2-1 Sand mold thermocouple B; 2-2 Heating material; 2-3 Dense sand mold. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should be noted that these drawings are simplified schematic diagrams, illustrating only the basic structure of the invention in a schematic manner, and therefore only show the components relevant to the invention.

[0019] The present invention proposes an intelligent low-stress sand casting method for large basic components of high-end CNC machine tools, the process of which is as follows: Figure 1 As shown.

[0020] Step 1: Based on the actual machine tool casting model, analyze the wall thickness characteristics of each part, and use the formula M = (casting volume / casting heat dissipation surface area) to calculate the equivalent modulus of each part and the average equivalent modulus of the entire casting. Step 2: Based on the wall thickness, modulus calculation and analysis results and the structural characteristics of the casting, the area in the casting that is more than 50% higher than the average equivalent modulus is called the thick-walled large modulus area, and the area that is less than 50% higher than the average equivalent modulus is called the thin-walled small modulus area. Based on this, multiple sand mold modules are divided into the thick-walled large modulus area sand mold module 1, the thin-walled small modulus area sand mold module 2, and other sand mold modules that need to be processed (sand mold module 3 for the uniform wall thickness part, sand mold module 6 for the gating system part). Step 3: Design the intelligent hollow sand mold structure for the thick-walled, large-modulus area. Select the sand material for the surface contact area 1-4 according to the actual alloy type. For alloys with higher pouring temperatures, use high-cooling-rate sand such as zircon sand and chromite sand. For alloys with lower pouring temperatures, use low-cooling-rate sand such as sand sand and pearl sand. Step 4: Design the hollow structure features 1-2 based on the specific dimensions of a certain intelligent hollow module. The hollow structure can be selected as a grid, face-centered cubic, body-centered cubic lattice, etc. Step 5: Combine the above-mentioned hollow structure design with the active heat dissipation air duct 1-5 and the installation positions of fans 1-1 and 1-6, and set up thermocouple A (1-3) to monitor the solidification process of molten metal. Step 6: Design the intelligent dense sand mold structure of the thin-walled small-modulus region 2, select a profile material with a large heat storage coefficient to manufacture this part of the sand mold, and set the heating material 2-2 and the monitoring thermocouple B (2-1) in the sand mold.

[0021] Step 7: Process and manufacture each sand mold module, use sand mold additive manufacturing equipment to manufacture intelligent hollow sand molds, and use sand mold cutting equipment to prepare other modules; Step 8: Assemble the sand mold modules and install active cooling fans 1-1 and 1-6, heating material 2-2, and temperature monitoring thermocouples A (1-3) and B (2-1) to form an intelligent low-stress sand casting system; Step 9: Spray paint inside the entire sand mold and dry it to complete the preparation of the sand mold before pouring; Step 10: Pour molten metal into the intelligent low-stress sand casting system; Step 11: The monitoring thermocouples A (1-3) and B (2-1) set in each area collect the temperature of the sand mold and the temperature of the molten metal in that part, and input them into the control computer to calculate the solidification fraction of the molten metal in that part; Step 12: Compare the differences in the solidification fraction of the molten metal in each part. The computer automatically controls the start of the active cooling fans 1-1 and 1-6 and the heating material 2-2 to achieve forced heat dissipation in the thick-walled area and heat preservation in the thin-walled area, balance the solidification rate of the molten metal in each part, achieve simultaneous solidification of each part of the casting, and reduce the generation and accumulation of stress during the solidification process. Step 13: Monitor the solidification process of the casting until it is completely solidified; Step 14: When the casting temperature cools down to below 400~500℃, promptly carry out sand removal and cleaning. Step 15: After the casting has cooled further, it is polished to obtain a low-stress machine tool structure casting. Step 16: Save the temperature curves of each part of the casting and the time curve of the intelligent sand mold process, and establish a database for this type of product; Step 17: When producing this type of product again, repeat steps 1-8 and directly call the existing data to control the operation of the intelligent low-stress sand casting system to ensure the stability of different batches of products.

[0022] This invention addresses large machine tool structural parts with significant differences in module thickness, and is not limited to machine tool castings. The method utilizes resin sand molds to manufacture an intelligent low-stress sand casting system, including but not limited to clay sand molds, cryogenic sand molds, ceramic sand molds, and ceramic cores. This method is applicable to metallic materials suitable for sand casting, including but not limited to high-pouring-temperature ferrous metals and low-pouring-temperature non-ferrous metals.

[0023] Among them, intelligent hollow sand molds are used in the thick-walled areas of the components, and intelligent dense sand molds are used in the thin-walled areas. The intelligent hollow sand mold uses two parts, hollow structure and intelligent flow channel wind speed control, to achieve precise control of cooling in this area. The intelligent dense sand mold uses dense structure and heating material to quantitatively control the heat release in this area, and accurately keep it warm.

[0024] In actual casting, temperature curves and intelligent sand mold process time curves for various parts of a certain type / class of casting are established, and a database of this type of product is created. When producing a certain type of product again, the existing data can be directly called to control the operation of the intelligent sand mold system, ensuring the stability of different batches of products.

[0025] The intelligent hollow sand mold in the intelligent low-stress sand casting system of the present invention consists of three parts: a surface contact area, a hollow sand mold area, and an intelligent control unit. It includes five components: a cooling fan, a hollow sand mold structure, a sand mold temperature measuring thermocouple, a surface contact layer, and an active cooling channel.

[0026] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims

1. An intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools, characterized by: First, an intelligent low-stress sand casting system is designed. Then, low-stress sand casting is completed based on the intelligent low-stress sand casting system, including the following steps: Step 1: Based on the actual machine tool casting model, analyze the wall thickness characteristics of each part, and use the formula M = (casting volume / casting heat dissipation surface area) to calculate the equivalent modulus of each part and the average equivalent modulus of the entire casting. Step 2: Based on the wall thickness, modulus calculation and analysis results and the structural characteristics of the casting, the area in the casting that is more than 50% higher than the average equivalent modulus is called the thick-walled large modulus area, and the area that is less than 50% of the average equivalent modulus is called the thin-walled small modulus area. Based on this, multiple sand mold modules for the thick-walled large modulus area, sand mold modules for the thin-walled small modulus area, and other sand mold modules that need to be processed are divided. Step 3: Design the intelligent hollow sand mold structure for the thick-walled, large-modulus area. Select the molding sand material for the surface contact area according to the actual alloy type. For alloys with higher pouring temperatures, use high-cooling-rate molding sand such as zircon sand and chromite sand, and for alloys with lower pouring temperatures, use low-cooling-rate molding sand such as silica sand and alumina sand. Step 4: Design the hollow structure features based on the specific dimensions of a certain intelligent hollow sand mold structure. The hollow structure includes, but is not limited to, grid-like, face-centered cubic, and body-centered cubic lattices. Step 5: Combine the above-mentioned hollow structure design with the active heat dissipation air duct and fan installation position, and set up thermocouples to monitor the solidification process of molten metal; Step 6: Design an intelligent dense sand mold structure for the thin-walled, small-modulus region, select a profile material with a large heat storage coefficient to manufacture this part of the sand mold, and set heating materials and monitoring thermocouples in the sand mold; Step 7: Process and manufacture each sand mold module, use sand mold additive manufacturing equipment to manufacture intelligent hollow sand molds, and use sand mold cutting equipment to prepare other modules; Step 8: Assemble the sand mold modules, install the active cooling fan, heating material, and temperature monitoring thermocouple to form an intelligent low-stress sand casting system; Step 9: Spray paint inside the entire sand mold and dry it to complete the preparation of the sand mold before pouring; Step 10: Pour molten metal into the intelligent low-stress sand casting system; Step 11: The monitoring thermocouples set up in each area collect the temperature of the sand mold and the temperature of the molten metal in that part, and input them into the control computer. The computer uses the Newton baseline method to quickly process and calculate the solidification fraction of the molten metal in that part. Step 12: By comparing the solidification fraction of the molten metal in each part, the computer automatically controls the start and speed of the active cooling fan to achieve precise control of the cooling rate of the area and control the heating of the insulation material to achieve forced heat dissipation in the thick-walled area and active heat preservation in the thin-walled area, balance the solidification rate of the molten metal in each part, achieve simultaneous solidification of all parts of the casting, and reduce the generation and accumulation of stress during the solidification process. Step 13: Monitor the solidification process of the casting until it is completely solidified; Step 14: When the casting temperature cools down to below 400~500℃, promptly carry out sand removal and cleaning. Step 15: The casting is further cooled and then polished to obtain a low-stress machine tool structure casting; Step 16: Save the temperature curves of each part of the casting and the time curve of the intelligent sand mold process, and establish a database for this type of product; Step 17: When producing this type of product again, repeat steps 1-8 and directly call the existing data to control the operation of the intelligent low-stress sand casting system to ensure the stability of different batches of products.

2. The intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools according to claim 1, characterized in that, The method is applicable to large machine tool structural parts with large differences in module thickness among different parts, and is not limited to machine tool castings.

3. The intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools according to claim 1, characterized in that, The method manufactures an intelligent low-stress sand casting system using resin sand molds, including but not limited to clay sand molds, frozen sand molds, ceramic sand molds, and ceramic cores.

4. The intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools according to claim 1, characterized in that, The method is applicable to metallic materials suitable for sand casting, including but not limited to high pouring temperature materials of ferrous metals and low pouring temperature materials of non-ferrous metals.

5. The intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools according to claim 1, characterized in that, Intelligent hollow sand molds are used in thick-walled areas of the components, while intelligent dense sand molds are used in thin-walled areas. The intelligent hollow sand mold uses two parts, hollow structure and intelligent flow channel wind speed control, to achieve precise control of cooling in this area. The intelligent dense sand mold uses dense structure and heating material to quantitatively control the heat release in this area, achieving precise heat preservation.

6. The intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools according to claim 1, characterized in that, In actual casting, temperature curves and intelligent sand mold process time curves for various parts of a certain type / class of casting are established, and a database of this type of product is created. When producing a certain type of product again, the existing data can be directly called to control the operation of the intelligent sand mold system, ensuring the stability of different batches of products.

7. An intelligent low-stress sand casting method for large foundation components of high-end CNC machine tools, characterized in that, The intelligent hollow sand mold in the intelligent low-stress sand casting system consists of three parts: surface contact area, hollow sand mold area, and intelligent control unit. It includes five components: cooling fan, sand mold hollow structure, sand mold temperature measuring thermocouple, surface contact layer, and active cooling channel.

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