Sand mold three-dimensional interconnected high-flexibility channel rapid freezing device and method

Abstract

The invention provides a sand mold three-dimensional interconnected high-flexibility channel rapid freezing device and method.The device comprises a frozen sand mold printing system and a frozen sand mold post-processing system, and the frozen sand mold post-processing system comprises a pore positioning module, a pore sand cleaning module and a rapid freezing module; a belt conveyor is arranged between the frozen sand mold printing system and the frozen sand mold post-processing system, and a printed frozen sand mold is transferred from the frozen sand mold printing system to the frozen sand mold post-processing system through the belt conveyor. On the basis of an airflow scanning positioning and closed-loop sand cleaning system, the pore three-dimensional shape is precisely reduced, residual sand is removed, micron-sized pore control and overall frozen sand mold rapid freezing are achieved, the consumable cost is reduced, the frozen sand mold whole-process machining efficiency is effectively improved, and the product quality is improved. And a high-precision, short-period and zero-waste green casting solution is provided for the fields of aerospace, automobiles and the like.

Description

Technical Field

[0001] This invention belongs to the intersection of cryogenic sand mold and additive manufacturing technology, specifically relating to a rapid freezing device and method for three-dimensional interconnected highly flexible channels in sand molds. Background Technology

[0002] Cryo-sand additive manufacturing is a near-net-shape technology that uses 3D printing to build sand molds layer by layer and then solidifies the sand particles with a binder at low temperatures to create castings with complex geometries. Based on the discrete-stacking principle, this technology uses slicing software to discretize and layer the 3D sand mold model, layer by layer laying sand and selectively spraying binder. The binder is typically pure water or other modified water-based solutions. At low temperatures, the binder freezes the sand particles to obtain a solid sand mold, enabling the rapid fabrication of complex cryo-sand molds. Cryo-sand additive manufacturing offers significant advantages such as high precision, ability to handle complex shapes, rapid manufacturing, and environmental friendliness, making it suitable for modern manufacturing industries, especially in aerospace, automotive, and medical sectors, where it has broad application potential.

[0003] In the cryogenic sand molding process, the freezing of the sand blank is one of the key steps in the formation of the cryogenic sand mold, and the freezing efficiency determines the forming efficiency of the sand mold. Currently, the printed sand blank needs to be stored in a cold storage room for more than 24 hours to ensure the sand mold's strength meets actual casting requirements. The long freezing time and the energy consumption issues caused by the freezing process severely hinder the further promotion and application of cryogenic sand mold additive manufacturing technology. To solve these problems, manufacturers often incorporate interlayer cooling technology into the cryogenic sand mold printing process. After each layer of adhesive is sprayed, a low-temperature cold source is used to accelerate the freezing and curing of the current layer's adhesive. However, due to the long printing time, although the overall sand mold has a certain strength after printing, the strength still does not meet the delivery requirements.

[0004] Therefore, how to further accelerate the freezing speed of the binder in the frozen sand mold additive manufacturing process, improve the printing efficiency of frozen sand molds, and shorten the delivery cycle of frozen sand molds are urgent problems that need to be solved in the current frozen sand mold additive manufacturing technology. Summary of the Invention

[0005] To address the aforementioned problems, this invention discloses a rapid freezing device and method for sand-mold three-dimensional interconnected highly flexible channels.

[0006] The specific plan is as follows: The three-dimensional interconnected, highly flexible channel rapid freezing device for sand molds includes a frozen sand mold printing system and a frozen sand mold post-processing system. The frozen sand mold post-processing system includes a pore positioning module, a pore sand cleaning module, and a rapid freezing module. A belt conveyor is provided between the frozen sand mold printing system and the frozen sand mold post-processing system. The printed frozen sand mold is transferred from the frozen sand mold printing system to the frozen sand mold post-processing system via the belt conveyor. The three-dimensional interconnected, highly flexible channel rapid freezing device for sand molds has two workstations. The freezing sand mold printing system is located at the first workstation, and the pore positioning module is located at the second workstation. After the freezing sand mold printing system completes the sand mold printing, its printing platform outlet is adjacent to the feed end of a belt conveyor. The discharge end of this belt conveyor extends and is precisely positioned above the rotating tray of the pore positioning module. The printed frozen sand mold is automatically transferred to the pore positioning module via this belt conveyor. The rotating tray of the pore positioning module is its core component and also serves as a shared platform for sand cleaning and freezing operations. This tray is located in the center of the second workstation. The pore sand cleaning module is fixedly installed in the left frame area of ​​the pore positioning module. The rapid freezing module is fixedly installed in the right frame area of ​​the pore positioning module. The cryogenic sand molding printing system includes a main frame, a printer nozzle, a sand storage tank, a sand spreading device, and a printing platform. The printer nozzle, sand storage tank, sand spreading device, and printing platform are fixed to the main frame via mechanical supports, bolts, or a slide rail system to ensure stability during printing. The printer nozzle is mounted on a nozzle holder, which moves along the X and Y axes on the main frame via a precision slide rail system. The nozzle holder is equipped with a motor and transmission device, enabling the printer nozzle to move precisely along a predetermined path. The sand spreading device includes a sand drop box and low-temperature rollers. Sand particles from the sand storage tank are transferred to the sand drop box via pipes. The printing platform is connected to a ball screw and driven by a servo motor to achieve precise lifting and lowering operations in the Z-axis direction. The pore positioning module includes an airflow generating device, an airflow guiding and regulating device, a sensor array, and a signal processing unit. It is used to reconstruct the three-dimensional morphology of the frozen sand mold and accurately locate the pore structure. The airflow guiding and regulating device includes an airflow duct and an airflow regulating device. The airflow generating device generates a stable airflow, guides the airflow through the airflow duct to precisely control the direction of the airflow, ensuring that the airflow blows towards a specific area, and precisely controls the airflow magnitude through the airflow regulating device. The sensor array detects the changing airflow as it blows onto the sand mold. The signal processing unit includes a data acquisition unit and a data processing unit. The data acquisition unit converts the signals from the airflow sensors into digital signals for subsequent processing and analysis. The data processing unit calculates and analyzes the acquired data to determine the relationship between changes in airflow and the surface features of the object. The pore sand cleaning module includes an electric motor, a wind turbine, a suction pipe, a collection box, a rotating tray, and a sand cleaning robotic arm. The electric motor is connected to the wind turbine, which drives the wind turbine to rotate, accelerates airflow, and generates negative pressure. Dry sand in the pores is sucked into the collection box along the suction pipe under the negative pressure. The collection box is connected to the molding sand storage tank by a pipe, and the dry sand in the collection box enters the molding sand storage tank for recycling through negative pressure. The sand cleaning robotic arm precisely controls the position of the suction pipe. The rotating tray can rotate. The rapid freezing module includes a cryogenic medium storage tank, a spray pipe, a control valve, a nozzle, and a spraying robotic arm; the cryogenic medium stored in the cryogenic medium storage tank is sprayed out from the nozzle along the spray pipe; the control valve is used to adjust the flow rate and pressure of the cryogenic medium, and the cooling intensity of the spray is controlled by adjusting the flow rate; the spraying robotic arm precisely controls the position of the spray pipe.

[0007] Furthermore, the airflow generating device of the pore positioning module includes a diaphragm air pump, an axial flow fan, a screw compressor, and an ultrasonic airflow generator; used to generate stable or controllable airflow required for positioning, with different types of equipment selected according to the application scenario; the sensor array includes a wind speed sensor, a pressure sensor, and a thermal sensor, used to measure the speed, intensity, pressure changes, and temperature changes of the airflow, detect the airflow generated by blowing, and convert it into a processable signal. The airflow generating device is fixed on a vibration-damping base at the bottom or rear side of the second workstation frame to avoid vibration interference with the sensors. The wind speed / pressure sensors are arranged in a ring array on a detection bracket 5-10cm high around the rotating tray, with a total of 8-12 measuring points, evenly covering the side surface of the sand mold. The thermal sensor is embedded inside the wind speed sensor housing.

[0008] Furthermore, the impeller of the pore sand cleaning module includes a centrifugal impeller, an axial flow impeller, a turbine impeller, a multi-blade impeller, and an oblique flow impeller.

[0009] Furthermore, the cryogenic medium includes liquid nitrogen, liquid helium, dry ice, liquid fluorine, liquid ammonia, and liquid hydrogen. The choice of medium depends on the cooling temperature requirement, cooling rate, and cost factors.

[0010] Furthermore, the nozzle is a pinhole or atomizing nozzle so that the cryogenic medium is better dispersed in the air.

[0011] A rapid freezing method for sand-mold three-dimensional interconnected highly flexible channels includes the following steps: Step 1: Sand Mold Structure Design: A preliminary model is created in CAD software, designing a sand mold model with a gating system. Based on the functional requirements, mechanical properties, and assembly requirements of the casting, the preliminary model is optimized in detail, including optimizing wall thickness, eliminating stress concentration, and adding ventilation holes. Finally, based on the sand mold model structure, a highly flexible three-dimensional interconnected pore structure is designed inside the sand mold. Thermodynamic, fluidity, and shrinkage simulation analysis is performed on the above-mentioned frozen sand mold using casting simulation software to predict potential problems during the casting process and to provide feedback for optimization of the frozen sand mold model. The designed three-dimensional sand mold model is converted into an STL format file and imported into slicing software to complete layer slicing; the slicing information is then imported into the printing system. Step 2: Cryogenic Sand Mold Printing: A layer of base sand is laid on the forming platform, leveled by a low-temperature rotating roller, and adhesive is sprayed as needed according to the slice information; the forming platform descends by one layer thickness, sand particles are laid and leveled, the low-temperature rotating roller initially freezes the printed sand mold, and adhesive is sprayed according to the slice information of the current layer; the forming platform continues to descend, laying sand layer by layer and spraying adhesive layer by layer, until the cryogenic sand mold printing is completed; Step 3: Pore Structure Sand Removal: The printed frozen sand mold is transferred to the frozen sand mold post-processing system. The airflow generator of the pore positioning module first blows a high-power airflow onto the surface of the frozen sand mold, causing the loose molding sand particles on the surface of the pore structure to fall off. After almost no particles have fallen off, the working power of the airflow generator is reduced, and the airflow continues to blow onto the surface of the frozen sand mold. At this point, no molding sand particles are blown away, and the surface condition of the frozen sand mold remains almost unchanged. The surface morphology of the frozen sand mold affects the distribution of airflow, changing the speed, direction, and intensity of the airflow. The wind speed sensor installed in the sensor array... The airflow changes are captured by instruments, pressure sensors, or thermal sensors. The airflow change information is correlated with the surface morphology of the frozen sand mold to obtain a three-dimensional model, so as to achieve precise positioning of the pore structure of the frozen sand mold. The vacuum negative pressure pipeline of the pore cleaning module is connected to the pore structure outlet of the sand mold on the outer surface, and the unfrozen sand powder inside is removed, leaving a large number of pore structures. After the sand cleaning of one side surface is completed, the rotating tray drives the frozen sand mold to rotate a certain angle until the other side surface is aligned with the airflow generating device, and the sand cleaning of the front side begins until the sand cleaning of all side surface pores is completed. Step 4: Rapid Freezing and Shaping: Based on the pore positions obtained from the air blowing positioning above, the rapid freezing module continuously introduces low-temperature medium into the pores through the nozzles. To ensure that the freezing medium fills all the pores, after introducing the cooling medium into one side surface for 5-10 minutes, the rotating tray drives the frozen sand mold to rotate at a certain angle (90°, 180°, 270°), and the nozzles introduce the cooling medium into the pores on the other side surfaces of the frozen sand mold to achieve rapid freezing of the frozen sand mold. After freezing is completed, the frozen sand mold is stored in a refrigerator for later use, or it can be directly cast.

[0012] Furthermore, in step 1, when designing a highly flexible three-dimensional interconnected pore structure inside the sand mold, different pore structure forms are selected according to the characteristics of the sand mold structure. These pore structure forms include simple hollow pores, honeycomb structure pores, irregular mesh structure pores, pores with trapezoidal or conical cavities inside, and foam structure pores. When designing frozen sand molds for large castings or castings with relatively uniform stress, simple hollow pores are selected. When the frozen sand mold has a high strength-to-weight ratio and needs to withstand impact or complex stress, honeycomb structure pores are selected. When designing frozen sand molds for medium to large-sized castings, and the castings need to withstand greater pressure during service, irregular mesh structure pores are selected. When the casting needs to withstand gradual loads, including structural components in the automotive and aerospace industries, pores with trapezoidal or conical cavities inside are selected when designing the corresponding frozen sand mold. When the frozen sand mold has complex internal channels or precision details, foam structure pores are selected.

[0013] Furthermore, in step 2, the thickness of the layered slices is 0.2~0.6mm, and the slicing method of equal thickness layering or adaptive layering is selected according to actual needs; the low-temperature roller is filled with a low-temperature medium at a temperature of -10~-5℃, which plays a role in interlayer cooling; the molding sand particles used include one or more of the following: quartz sand, ceramsite sand, chromite sand, zircon sand, corundum sand, and olivine sand, with mesh sizes of 50 / 100 mesh, 100 / 140 mesh, and 140 / 270 mesh, and the appropriate material and mesh size are selected according to the casting requirements; the type of binder includes industrial pure water or other modified solutions mainly composed of pure water; the inkjet amount of the binder is 2~4wt.%.

[0014] Furthermore, in step 3, when the airflow generating device first blows a high-power airflow onto the surface of the frozen sand mold, the gas flow rate is 10~100L / min, and after reducing the working power of the airflow generating device, the flow rate is 1~10L / min.

[0015] The beneficial effects of this invention are as follows: 1. Based on an airflow scanning positioning and closed-loop sand removal system, micron-level pore control is achieved: First, a large airflow of 10-100 L / min is used to remove loose sand, followed by a micro-airflow of 1-10 L / min for non-destructive scanning. An annular array sensor captures airflow disturbances, accurately restoring the three-dimensional morphology of the pores. The centrifugal impeller's negative pressure thoroughly removes residual sand, achieving a porosity ≥99%. It supports five types of adaptive structures, including honeycomb and conical cavities, giving castings lightweight and impact-resistant properties, breaking through the limitations of traditional single sand mold structures.

[0016] 2. Traditional frozen sand molds require over 24 hours of refrigeration for curing. This invention achieves a breakthrough through pore-oriented deep cryogenic freezing technology: using low-temperature media such as liquid nitrogen / dry ice, directly injected into the three-dimensional interconnected pores through atomizing nozzles, combined with multi-angle adjustments of a rotating tray, the freezing speed is increased to 5-10 mm / min, completing the overall freezing of the sand mold within 30 minutes. The sand mold's compressive strength reaches 1.5 MPa (25% higher than the casting standard), energy consumption is reduced by 90%, completely solving the industry's core problems of low freezing efficiency and long delivery cycles.

[0017] 3. Dual-station collaborative architecture enables unmanned production: Frozen sand molds are seamlessly transferred from the printing station to a shared rotating pallet via a belt conveyor. Sand cleaning and freezing robotic arms work collaboratively on opposite sides, completing multiple processes in a single clamping operation, reducing repositioning time by 80%. Dry sand is 100% recycled, reducing consumable costs by 30%. The entire process for a single sand mold takes ≤2 hours, providing high-precision, short-cycle, zero-waste green casting solutions for aerospace, automotive, and other industries. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the sand-type three-dimensional interconnected highly flexible channel rapid freezing device according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the basic steps of the rapid freezing method for sand-mold three-dimensional interconnected highly flexible channels according to an embodiment of the present invention.

[0020] Figure descriptions: 1-Main frame; 2-Molding sand storage tank; 3-Printer nozzle; 4-Sand drop box; 5-Cryogenic roller; 6-Printing platform; 7-Belt conveyor; 8-Signal processing unit; 9-Airflow generator; 10-Airflow guide and adjuster; 11-Sensor array; 12-Electric motor; 13-Sand cleaning robotic arm; 14-Collection box; 15-Sand suction pipe; 16-Nozzle; 17-Spraying robotic arm; 18-Spraying pipe; 19-Control valve; 20-Cryogenic medium storage tank; 21-Rotating tray. Detailed Implementation

[0021] 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 the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0022] like Figure 1As shown, this invention provides a three-dimensional interconnected, highly flexible channel rapid freezing device for sand molds, including a frozen sand mold printing system and a frozen sand mold post-processing system. The frozen sand mold post-processing system includes a pore positioning module, a pore cleaning module, and a rapid freezing module. A belt conveyor is provided between the frozen sand mold printing system and the frozen sand mold post-processing system. The printed frozen sand mold is transferred from the frozen sand mold printing system to the frozen sand mold post-processing system via the belt conveyor. The three-dimensional interconnected, highly flexible channel rapid freezing device for sand molds has two stations: the frozen sand mold printing system is located at the first station, and the pore positioning module is located at the second station. After the frozen sand mold printing system completes the sand mold printing, its printing platform outlet is adjacent to the feed end of a belt conveyor. The discharge end of the belt conveyor extends and is precisely positioned above the rotating tray of the pore positioning module. The printed frozen sand mold is automatically transferred to the pore positioning module via this belt conveyor. The rotating tray of the pore positioning module is its core component and also serves as a shared platform for cleaning and freezing operations. This tray is located at the center of the second station. The pore sand removal module is fixedly installed on the left side of the pore positioning module. The rapid freezing module is fixedly installed on the right side of the pore positioning module. The cryogenic sand molding printing system includes a main frame 1, a printer nozzle 3, a molding sand storage tank 2, a sand spreading device, and a printing platform 6. The printer nozzle, molding sand storage tank, sand spreading device, and printing platform are fixed to the main frame by mechanical supports, bolts, or a slide rail system to ensure their stability during printing. The printer nozzle is mounted on a nozzle holder, which moves along the X and Y axes on the main frame via a precision slide rail system. The nozzle holder is equipped with a motor and a transmission device, enabling the printer nozzle to move precisely along a predetermined path. The sand spreading device includes a sand drop box 4 and a low-temperature roller 5. Molding sand particles in the molding sand storage tank are transferred to the sand drop box through pipes. The printing platform is connected to a ball screw and driven by a servo motor to achieve precise lifting and lowering operations in the Z-axis direction. The pore positioning module includes an airflow generating device 9, an airflow guiding and regulating device 10, a sensor array 11, and a signal processing unit 8, used to reconstruct the three-dimensional morphology of the frozen sand mold and accurately locate the pore structure. The airflow guiding and regulating device includes an airflow duct and an airflow regulating device. The airflow generating device generates a stable airflow, guides the airflow through the airflow duct to precisely control the direction of the airflow, ensuring that the airflow blows to a specific area, and precisely controls the airflow magnitude through the airflow regulating device. The sensor array detects the airflow changes as it blows onto the sand mold. The signal processing unit includes a data acquisition unit and a data processing unit. The data acquisition unit converts the signals from the airflow sensors into digital signals for subsequent processing and analysis. The data processing unit calculates and analyzes the acquired data to determine the relationship between changes in airflow and the surface features of the object. The pore sand cleaning module includes an electric motor 12, a wind turbine, a sand suction pipe 15, a collection box 14, a rotating tray 21, and a sand cleaning mechanical arm 13. The electric motor is connected to the wind turbine, which drives the wind turbine to rotate, accelerates airflow, and generates negative pressure. Dry sand in the pores is sucked into the collection box along the sand suction pipe under the action of negative pressure. The collection box is connected to the molding sand storage tank by a pipe, and the dry sand in the collection box enters the molding sand storage tank for recycling through negative pressure. The sand cleaning mechanical arm precisely controls the position of the sand suction pipe. The rotating tray can rotate. The rapid freezing module includes a cryogenic medium storage tank 20, a spray pipe 18, a control valve 19, a nozzle 16, and a spraying robotic arm 17; the cryogenic medium stored in the cryogenic medium storage tank is sprayed out from the nozzle along the spray pipe; the control valve is used to adjust the flow rate and pressure of the cryogenic medium, and the cooling intensity of the spray is controlled by adjusting the flow rate; the spraying robotic arm precisely controls the position of the spray pipe.

[0023] In this embodiment, the airflow generating device of the pore positioning module includes a diaphragm air pump, an axial flow fan, a screw compressor, and an ultrasonic airflow generator; used to generate stable or controllable airflow required for positioning, with different types of equipment selected according to the application scenario; the sensor array includes a wind speed sensor, a pressure sensor, and a thermal sensor, used to measure the speed, intensity, pressure changes, and temperature changes of the airflow, detect the airflow generated by blowing, and convert it into a processable signal. The airflow generating device is fixed on a vibration-damping base at the bottom or rear side of the second workstation frame to avoid vibration interference with the sensors. The wind speed / pressure sensors are arranged in a ring array on a detection bracket 5-10cm high around the rotating tray, with a total of 8-12 measuring points, evenly covering the side surface of the sand mold. The thermal sensor is embedded inside the wind speed sensor housing.

[0024] In this embodiment, the impeller of the pore sand cleaning module includes a centrifugal impeller, an axial flow impeller, a turbine impeller, a multi-blade impeller, and an oblique flow impeller.

[0025] In this embodiment, the cryogenic medium includes liquid nitrogen, liquid helium, dry ice, liquid fluorine, liquid ammonia, and liquid hydrogen. The choice of medium depends on the cooling temperature requirement, cooling rate, and cost factors.

[0026] In this embodiment, the nozzle is a pinhole or atomizing nozzle so that the cryogenic medium is better dispersed in the air.

[0027] like Figure 2 As shown, this invention provides a rapid freezing method for sand-mold three-dimensional interconnected highly flexible channels, comprising the following steps: Step 1: Sand Mold Structure Design: A preliminary model is created in CAD software, designing a sand mold model with a gating system. Based on the functional requirements, mechanical properties, and assembly requirements of the casting, the preliminary model is optimized in detail, including optimizing wall thickness, eliminating stress concentration, and adding ventilation holes. Finally, based on the sand mold model structure, a highly flexible three-dimensional interconnected pore structure is designed inside the sand mold. Thermodynamic, fluidity, and shrinkage simulation analysis is performed on the above-mentioned frozen sand mold using casting simulation software to predict potential problems during the casting process and to provide feedback for optimization of the frozen sand mold model. The designed three-dimensional sand mold model is converted into an STL format file and imported into slicing software to complete layer slicing; the slicing information is then imported into the printing system. The specific structural design of the sand mold includes: 1. Function-oriented wall thickness optimization: Based on the casting's load-bearing requirements (e.g., thickening the base of bearing seats) and heat dissipation requirements (e.g., thinning the cooling fins of engine cylinder blocks), gradient wall thicknesses (typical range 3-25mm) are set in CAD to avoid abrupt change zones. 2. Mechanical property enhancement: Eliminating stress concentration: Automatically adding R2-R5mm fillets to edges / holes, and using rounded transitions in T-shaped connection areas; Stiffness compensation: Embedding reinforcing ribs in high-load areas (rib thickness ≈ 0.8 × main wall thickness, height ≤ 3 times wall thickness). 3. Assembly compatibility adjustment: Positioning bosses / grooves are designed according to the tolerance of mating parts ±0.1mm; parting surfaces avoid bolt hole positions ≥ 3mm. 4. Process optimization: Vent hole layout: Φ3-5mm vent holes are set at the highest point of the cavity (every 100cm²) and in thicker areas (arrayed with a spacing ≤ 50mm); Shrinkage compensation: 1.2-1.5% anti-deformation is pre-added to the simulated shrinkage porosity area. 5. Pore structure generation: Based on the optimized model, three-dimensional interconnected pores (pore diameter 0.5-2mm, porosity 40-70%) are constructed in non-critical areas (such as the core), and the flow / solidification behavior is verified by casting simulation (such as ProCAST), and the pore distribution is iteratively corrected.

[0028] Step 2: Cryogenic Sand Mold Printing: A layer of base sand is laid on the forming platform, leveled by a low-temperature rotating roller, and adhesive is sprayed as needed according to the slice information; the forming platform descends by one layer thickness, sand particles are laid and leveled, the low-temperature rotating roller initially freezes the printed sand mold, and adhesive is sprayed according to the slice information of the current layer; the forming platform continues to descend, laying sand layer by layer and spraying adhesive layer by layer, until the cryogenic sand mold printing is completed; Step 3: Pore Structure Sand Removal: The printed frozen sand mold is transferred to the frozen sand mold post-processing system. The airflow generator of the pore positioning module first blows a high-power airflow onto the surface of the frozen sand mold, causing the loose molding sand particles on the surface of the pore structure to fall off. After almost no particles have fallen off, the working power of the airflow generator is reduced, and the airflow continues to blow onto the surface of the frozen sand mold. At this point, no molding sand particles are blown away, and the surface condition of the frozen sand mold remains almost unchanged. The surface morphology of the frozen sand mold affects the distribution of airflow, changing the speed, direction, and intensity of the airflow. The wind speed sensor installed in the sensor array... The airflow changes are captured by instruments, pressure sensors, or thermal sensors. The airflow change information is correlated with the surface morphology of the frozen sand mold to obtain a three-dimensional model, so as to achieve precise positioning of the pore structure of the frozen sand mold. The vacuum negative pressure pipeline of the pore cleaning module is connected to the pore structure outlet of the sand mold on the outer surface, and the unfrozen sand powder inside is removed, leaving a large number of pore structures. After the sand cleaning of one side surface is completed, the rotating tray drives the frozen sand mold to rotate a certain angle until the other side surface is aligned with the airflow generating device, and the sand cleaning of the front side begins until the sand cleaning of all side surface pores is completed. Step 4: Rapid Freezing and Shaping: Based on the pore positions obtained from the air blowing positioning above, the rapid freezing module continuously introduces low-temperature medium into the pores through the nozzles. To ensure that the freezing medium fills all the pores, after introducing the cooling medium into one side surface for 5-10 minutes, the rotating tray drives the frozen sand mold to rotate at a certain angle (90°, 180°, 270°), and the nozzles introduce the cooling medium into the pores on the other side surfaces of the frozen sand mold to achieve rapid freezing of the frozen sand mold. After freezing is completed, the frozen sand mold is stored in a refrigerator for later use, or it can be directly cast.

[0029] In this embodiment, when designing a highly flexible three-dimensional interconnected pore structure inside the sand mold in step 1, different pore structure forms are selected according to the characteristics of the sand mold structure. The pore structure forms include simple hollow pores, honeycomb structure pores, irregular mesh structure pores, pores with trapezoidal or conical cavity structures inside, and foam structure pores. When designing frozen sand molds for large castings or castings with relatively uniform stress, simple hollow pores are selected. When the frozen sand mold has a high strength-to-weight ratio and needs to withstand impact or complex stress, honeycomb structure pores are selected. When designing frozen sand molds for medium to large-sized castings, and the castings need to withstand large pressures during service, irregular mesh structure pores are selected. When the casting needs to withstand gradual loads, including structural parts in the automotive and aerospace industries, pores with trapezoidal or conical cavity structures inside are selected when designing the corresponding frozen sand mold. When the frozen sand mold has complex internal channels or precision details, foam structure pores are selected.

[0030] In this embodiment, the layered slicing thickness in step 2 is 0.2~0.6mm, and the slicing method of equal thickness layering or adaptive layering is selected according to actual needs; the low-temperature roller is filled with a low-temperature medium at a temperature of -10~-5℃, which plays a role in interlayer cooling; the molding sand particles used include one or more of the following: quartz sand, ceramsite sand, chromite sand, zircon sand, corundum sand, and olivine sand, with mesh sizes of 50 / 100 mesh, 100 / 140 mesh, and 140 / 270 mesh, and the appropriate material and mesh size are selected according to the casting requirements; the binder includes industrial pure water or other modified solutions mainly composed of pure water; the inkjet amount of the binder is 2~4wt.%.

[0031] In this embodiment, in step 3, when the airflow generator first blows a high-power airflow onto the surface of the frozen sand mold, the gas flow rate is 10~100L / min. After reducing the working power of the airflow generator, the flow rate is 1~10L / min.

[0032] 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. A sand-mold three-dimensional interconnected high-flexibility channel rapid freezing device, characterized in that, It includes a frozen sand mold printing system and a frozen sand mold post-processing system. The frozen sand mold post-processing system includes a pore positioning module, a pore sand cleaning module, and a rapid freezing module. The three-dimensional interconnected, highly flexible channel rapid freezing device for sand molds has two workstations. The freezing sand mold printing system is located at the first workstation, and the pore positioning module is located at the second workstation. After the freezing sand mold printing system completes the sand mold printing, its printing platform outlet is closely connected to the inlet end of a belt conveyor. The outlet end of this belt conveyor extends and is precisely positioned above the rotating tray of the pore positioning module. The printed frozen sand mold is automatically transferred to the pore positioning module via this belt conveyor. The rotating tray of the pore positioning module is its core component and also serves as a shared platform for sand cleaning and freezing operations. This tray is located at the center of the second workstation. The pore sand cleaning module is fixedly installed in the left frame area of ​​the pore positioning module, and the rapid freezing module is fixedly installed in the right frame area of ​​the pore positioning module. The cryogenic sand molding printing system includes a main frame, a printer nozzle, a sand storage tank, a sand spreading device, and a printing platform. The printer nozzle, sand storage tank, sand spreading device, and printing platform are fixed to the main frame via mechanical supports, bolts, or a slide rail system to ensure stability during printing. The printer nozzle is mounted on a nozzle holder, which moves along the X and Y axes on the main frame via a precision slide rail system. The nozzle holder is equipped with a motor and transmission device, enabling the printer nozzle to move precisely along a predetermined path. The sand spreading device includes a sand drop box and low-temperature rollers. Sand particles from the sand storage tank are transferred to the sand drop box via pipes. The printing platform is connected to a ball screw and driven by a servo motor to achieve precise lifting and lowering operations in the Z-axis direction. The pore positioning module includes an airflow generating device, an airflow guiding and regulating device, a sensor array, and a signal processing unit. It is used to reconstruct the three-dimensional morphology of the frozen sand mold and accurately locate the pore structure. The airflow guiding and regulating device includes an airflow duct and an airflow regulating device. The airflow generating device generates a stable airflow, guides the airflow through the airflow duct to precisely control the direction of the airflow, ensuring that the airflow blows towards a specific area, and precisely controls the airflow magnitude through the airflow regulating device. The sensor array detects the changing airflow as it blows onto the sand mold. The signal processing unit includes a data acquisition unit and a data processing unit. The data acquisition unit converts the signals from the airflow sensors into digital signals for subsequent processing and analysis. The data processing unit calculates and analyzes the acquired data to determine the relationship between changes in airflow and the surface features of the object. The pore sand cleaning module includes an electric motor, a wind turbine, a suction pipe, a collection box, a rotating tray, and a sand cleaning robotic arm. The electric motor is connected to the wind turbine, which drives the wind turbine to rotate, accelerates airflow, and generates negative pressure. Dry sand in the pores is sucked into the collection box along the suction pipe under the negative pressure. The collection box is connected to the molding sand storage tank by a pipe, and the dry sand in the collection box enters the molding sand storage tank for recycling through negative pressure. The sand cleaning robotic arm precisely controls the position of the suction pipe. The rotating tray can rotate. The rapid freezing module includes a cryogenic medium storage tank, a spray pipe, a control valve, a nozzle, and a spraying robotic arm; The cryogenic medium stored in the cryogenic medium storage tank is sprayed out from the nozzle along the spray pipe; the control valve is used to adjust the flow rate and pressure of the cryogenic medium, and the cooling intensity of the spray is controlled by adjusting the flow rate. The spraying robotic arm precisely controls the position of the spray pipes.

2. The sand-mold three-dimensional interconnected highly flexible channel rapid freezing device according to claim 1, characterized in that, The airflow generating device of the pore positioning module includes a diaphragm air pump, an axial fan, a screw compressor, and an ultrasonic airflow generator, used to generate stable or controllable airflow required for positioning. Different types of equipment are selected according to the application scenario. The sensor array includes a wind speed sensor, a pressure sensor, and a thermal sensor, used to measure the speed, intensity, pressure changes, and temperature changes of the airflow, detect the airflow generated by blowing, and convert it into a processable signal. The airflow generating device is fixed on a vibration isolation base at the bottom or rear side of the second workstation frame to avoid vibration interference with the sensors. The wind speed / pressure sensors are arranged in a ring array on a detection bracket 5-10cm high around the rotating tray, with a total of 8-12 measuring points, evenly covering the side surface of the sand mold. The thermal sensor is embedded inside the wind speed sensor housing.

3. The sand-mold three-dimensional interconnected highly flexible channel rapid freezing device according to claim 1, characterized in that, The impeller of the pore sand cleaning module is one of the following: centrifugal impeller, axial flow impeller, turbine impeller, multi-blade impeller, or oblique flow impeller.

4. The sand-mold three-dimensional interconnected highly flexible channel rapid freezing device according to claim 1, characterized in that, The cryogenic medium includes liquid nitrogen, liquid helium, dry ice, liquid fluorine, liquid ammonia, and liquid hydrogen. The choice of medium depends on the cooling temperature requirement, cooling rate, and cost factors.

5. The sand-mold three-dimensional interconnected highly flexible channel rapid freezing device according to claim 1, characterized in that, The nozzle is a pinhole or atomizing nozzle to better disperse the cryogenic medium in the air.

6. A rapid freezing method for sand-mold three-dimensional interconnected highly flexible channels, characterized in that, The apparatus according to any one of claims 1-5 includes the following steps: Step 1: Sand Mold Structure Design: A preliminary model is created in CAD software, designing a sand mold model with a gating system. Based on the functional requirements, mechanical properties, and assembly requirements of the casting, the preliminary model is optimized in detail, including optimizing wall thickness, eliminating stress concentration, and adding ventilation holes. Finally, based on the sand mold model structure, a highly flexible three-dimensional interconnected pore structure is designed inside the sand mold. Thermodynamic, fluidity, and shrinkage simulation analysis is performed on the above-mentioned frozen sand mold using casting simulation software to predict potential problems during the casting process and to provide feedback for optimization of the frozen sand mold model. The designed three-dimensional sand mold model is converted into an STL format file and imported into slicing software to complete layer slicing; the slicing information is then imported into the printing system. Step 2: Cryogenic Sand Printing: Lay a layer of base sand on the forming platform, smooth it with a low-temperature rotating roller, and spray adhesive as needed according to the slice information; The forming platform descends by one layer thickness, lays out molding sand particles and smooths them, and the low-temperature rotating rollers initially freeze the printed sand mold. Adhesive is sprayed according to the current layer slice information. The forming platform continues to descend, laying sand layer by layer and spraying adhesive layer by layer until the frozen sand mold printing is completed. Step 3: Pore Structure Sand Removal: The printed frozen sand mold is transferred to the frozen sand mold post-processing system. The airflow generator of the pore positioning module first blows a high-power airflow onto the surface of the frozen sand mold, causing the loose molding sand particles on the surface of the pore structure to fall off. After almost no particles have fallen off, the working power of the airflow generator is reduced, and the airflow continues to blow onto the surface of the frozen sand mold. At this point, no molding sand particles are blown away, and the surface condition of the frozen sand mold remains almost unchanged. The surface morphology of the frozen sand mold affects the distribution of airflow, changing the speed, direction, and intensity of the airflow. The wind speed sensor installed in the sensor array... The airflow changes are captured by instruments, pressure sensors, or thermal sensors. The airflow change information is correlated with the surface morphology of the frozen sand mold to obtain a three-dimensional model, so as to achieve precise positioning of the pore structure of the frozen sand mold. The vacuum negative pressure pipeline of the pore cleaning module is connected to the pore structure outlet of the sand mold on the outer surface, and the unfrozen sand powder inside is removed, leaving a large number of pore structures. After the sand cleaning of one side surface is completed, the rotating tray drives the frozen sand mold to rotate a certain angle until the other side surface is aligned with the airflow generating device, and the sand cleaning of the front side begins until the sand cleaning of all side surface pores is completed. Step 4: Rapid Freezing and Shaping: Based on the pore positions obtained from the air blowing positioning above, the rapid freezing module continuously introduces low-temperature medium into the pores through the nozzles. To ensure that the freezing medium fills all the pores, after introducing the cooling medium into one side surface for 5-10 minutes, the rotating tray drives the frozen sand mold to rotate 90°, 180°, and 270°, and the nozzles introduce the cooling medium into the pores on the other side surfaces of the frozen sand mold to achieve rapid freezing of the frozen sand mold. After freezing is completed, the frozen sand mold is stored in a refrigerator for later use or directly cast.

7. The rapid freezing method for sand mold three-dimensional interconnected highly flexible channels according to claim 6, characterized in that, In step 1, when designing a highly flexible three-dimensional interconnected pore structure inside the sand mold, different pore structure forms are selected according to the characteristics of the sand mold structure. The pore structure forms include simple hollow pores, honeycomb structure pores, irregular mesh structure pores, pores with trapezoidal or conical cavity structures inside, and foam structure pores. When designing frozen sand molds for large castings or castings with relatively uniform stress, simple hollow pores are selected. When the frozen sand mold has a high strength-to-weight ratio and needs to withstand impact or complex stress, honeycomb structure pores are selected. When designing frozen sand molds for medium to large-sized castings, and the castings need to withstand greater pressure during service, irregular mesh structure pores are selected. When castings need to withstand gradual loads, including structural components in the automotive and aerospace industries, pores with trapezoidal or conical cavities are selected when designing the corresponding cryogenic sand molds; when cryogenic sand molds have complex internal channels or precision details, pores with foam structures are selected.

8. The rapid freezing method for sand mold three-dimensional interconnected highly flexible channels according to claim 6, characterized in that, In step 2, the layered slicing thickness is 0.2~0.6mm, and the slicing method of equal thickness layering or adaptive layering is selected according to actual needs; the low-temperature roller is filled with a low-temperature medium at a temperature of -10~-5℃, which plays a role in interlayer cooling; the molding sand particles used include one or more of the following: quartz sand, ceramsite sand, chromite sand, zircon sand, corundum sand, and olivine sand, with mesh sizes of 50 / 100 mesh, 100 / 140 mesh, and 140 / 270 mesh, and the appropriate material and mesh size are selected according to the casting requirements; the binder includes industrial pure water or other modified solutions mainly composed of pure water; the inkjet amount of the binder is 2~4wt.%.

9. The rapid freezing method for sand mold three-dimensional interconnected highly flexible channels according to claim 6, characterized in that, In step 3, when the airflow generator first blows a high-power airflow onto the surface of the frozen sand mold, the gas flow rate is 10~100L / min. After reducing the working power of the airflow generator, the flow rate is 1~10L / min.

10. The rapid freezing method for sand mold three-dimensional interconnected highly flexible channels according to claim 6, characterized in that, In step 4, the injection flow rate of the cryogenic medium is 5~50 L / min.

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