A cold source energy field dot matrix scanning sand mold additive manufacturing method

Abstract

The present invention provides a cold source energy field dot matrix scanning sand mold additive manufacturing method, which belongs to the field of frozen sand mold and additive manufacturing technology. This method directly lays water-containing wet sand in the forming chamber, and adopts a cold air direct writing nozzle to print the edge shape in combination with array-type low-temperature cold source dot matrix scanning to freeze the interior, and prints layer by layer to prepare the frozen sand mold. At the same time, in view of the poor fluidity of water-containing wet sand, an extrusion sand laying device is proposed to achieve quantitative laying of water-containing wet sand. This method solves the problem of insufficient penetration of water-based adhesives in the molding sand material in traditional frozen sand mold additive manufacturing technology, improves the forming accuracy and strength of sand mold products, and significantly improves the forming environment, greatly reduces resource consumption, and achieves high-precision and efficient preparation of frozen sand molds, which meets the requirements of green development of the manufacturing industry and is conducive to the transformation and upgrading of the foundry industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of frozen sand molds and additive manufacturing, and specifically relates to a cold source energy field lattice scanning sand mold additive manufacturing method. Background Art

[0002] Frozen sand casting technology uses water as a binder to bond the sand particles together at low temperatures to create sand molds, and high-quality castings are obtained by low-temperature pouring. Frozen sand molds produce less dust during molding, and the sand molds automatically collapse after pouring, without producing irritating odors. They effectively solve problems such as organic adhesive pollution, waste sand recycling, and dust emissions, and have promoted the green development and transformation and upgrading of my country's foundry industry. The frozen sand mold additive manufacturing technology was developed by combining frozen sand molds with sand mold printing technology. It is a new process for printing frozen sand molds layer by layer based on the principle of droplet injection, which realizes the preparation of frozen sand molds for complex sand molds and sand cores. However, existing frozen sand mold additive manufacturing technologies all use a printing nozzle to spray water-based adhesives for rapid manufacturing of frozen sand molds, and their application and promotion still have the following deficiencies:

[0003] 1. The water-based adhesive used in frozen sand additive manufacturing technology has a complex formula design. Existing industrial printheads on the market cannot print with pure water. Before printing, additives must be added to ensure that the water-based adhesive has appropriate parameters such as conductivity, pH value, viscosity, and surface tension to meet the requirements of printhead deposition and fully wet the powder bed for proper penetration. However, the addition of too many additives will increase environmental hazards, deviating from the original intention of green environmental protection.

[0004] 2. Frozen sand additive manufacturing technology has strict requirements on the forming environment. Conventional frozen sand additive manufacturing technology can only print in a negative pressure low-temperature forming chamber. The control of pressure and temperature affects the forming accuracy of the frozen sand mold. The low temperature environment will cause the water-based adhesive to freeze prematurely at the nozzle and damage the nozzle. At the same time, it will cause a large amount of resource waste, pollute the environment, and greatly increase production costs.

[0005] (3) The forming accuracy and strength of sand mold products produced by frozen sand additive manufacturing technology are limited. Cryoprinting relies on the nozzle to spray water-based adhesives. The volume of a single droplet is in the range of tens of picoliters, and the penetration pressure is closely related to the spray volume. As a result, the sprayed droplets have poor penetration ability in the sand material, affecting the forming accuracy and strength of the product, thereby affecting the quality of the casting.

[0006] Based on this, a cold source energy field dot matrix scanning sand mold additive manufacturing method is proposed to solve the problem of water-based adhesive penetration in the molding sand material, improve the forming environment, improve the forming accuracy and strength of the sand mold product, save resources and reduce costs. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a cold source energy field lattice scanning sand mold additive manufacturing method in view of the shortcomings of the above-mentioned prior art, so as to solve the problems raised in the above-mentioned background technology.

[0008] To solve the above technical problems, the present invention adopts a technical solution: a cold source energy field lattice scanning sand mold additive manufacturing method, comprising the following steps:

[0009] S1. Design a sand mold STL 3D model according to the geometric characteristics of the casting product, slice it through a computer, and output the slice shape and slice thickness information;

[0010] S2. Divide the slice shape of each layer into a shape-conforming scanning area and a dot-matrix scanning area, and import the slice shape and slice thickness information of the divided areas into the printing system;

[0011] S3, pre-cooling the molding sand particles, and evenly mixing them with a certain amount of pure water, and then placing the mixed molding sand material into the extrusion sand laying device;

[0012] S4, the refrigeration chamber wall starts refrigeration until the temperature of the forming area stabilizes;

[0013] S5. The lifting platform moves down a certain distance, and a layer of molding sand material is laid on the extrusion sand laying device as the bottom sand. The compaction roller scrapes it flat. After the bottom sand is laid, the extrusion sand laying device and the compaction roller return to the starting position.

[0014] S6. The lifting platform moves down one layer thickness, adjusts the height of the lifting base plate of the extrusion sand paving device, and lays a layer of molding sand material in a quantitative manner. The compaction roller scrapes it flat. After the sand paving is completed, the extrusion sand paving device and the compaction roller return to the starting position.

[0015] S7, start the cold air direct writing nozzle to perform cold air scanning on the conformal scanning area, freeze the edge of the current layer of sand mold to form a shell mold, and after printing is completed, the cold air direct writing nozzle returns to the starting position;

[0016] S8, start the array of low-temperature cooling sources to perform dot scanning on the dot scanning area, freeze the inner area of ​​the current layer of sand mold through the free diffusion of the cold field, and connect it with the frozen shell mold. After printing is completed, the array of low-temperature cooling sources returns to the starting position;

[0017] S9, repeat S6-S8, printing each layer until the preparation of the frozen sand mold is completed;

[0018] S10. After printing is completed, clean the unfrozen molding sand material and store the prepared sand mold in a cold storage.

[0019] Furthermore, in S2, the area division means that after removing all 2 mm wide edge parts close to the surface sand part, the remaining parts of the slice shape of each layer are divided into a series of array-distributed grids, and the size of each grid is equal to the array-type low-temperature cooling source, wherein all complete grids together constitute the dot matrix scanning area, and the other areas of the slice shape excluding the dot matrix scanning area constitute the shape-adaptive scanning area.

[0020] Furthermore, the molding sand particles in S3 are at least one of quartz sand, chromite sand, zircon sand, corundum sand, and forsterite sand, and the mass fraction of water in the molding sand particles is 4% to 8%.

[0021] Furthermore, in S3, the pre-cooling treatment is to cool the molding sand particles in advance by passing cold air, and the temperature of the molding sand particles obtained by the treatment is 2-5°C.

[0022] Furthermore, the extrusion sand-laying device includes a back plate, an electric cylinder, a pressure block, a sand storage bin and a lifting base plate, wherein the electric cylinder, the pressure block, the sand storage bin and the lifting base plate are sequentially installed on the back plate from top to bottom, wherein the lifting base plate is used to control the size of the sand falling opening by adjusting the height up and down, and the electric cylinder and the pressure block are used to control the pressing speed of the pressure block, and the amount of sand falling is controlled by extrusion by adjusting the size of the sand falling opening and the pressing speed of the pressure block, thereby realizing quantitative sand falling.

[0023] Furthermore, in S4, the refrigeration cavity wall is made of low-temperature steel, and the refrigeration temperature is 2-10°C.

[0024] Furthermore, the outer layers of the compacting roller and the extrusion sand-laying device are thermally sprayed with a hydrophobic Teflon coating to prevent sand from sticking during the sand-laying and compaction processes.

[0025] Furthermore, the nozzle of the cold air direct writing nozzle is replaceable, and the nozzle outlet is in the shape of a circular hole with a hole diameter of 0.2 to 2 mm. The low-temperature gas ejected from the nozzle is low-temperature carbon dioxide with a temperature not exceeding -50°C.

[0026] Furthermore, the array-type low-temperature cooling source has 36 cold air nozzles distributed in an array, and the working range of the cooling source is a 30mm×30mm square. The nozzles outside the array-type low-temperature cooling source can be selectively closed, and the middle 25 cold air nozzles are retained.

[0027] Furthermore, the low-temperature gas ejected from the nozzles of the array-type low-temperature cooling source is low-temperature nitrogen, and the temperature does not exceed -80°C.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The present invention uses cold air to scan wet sand for printing, replacing the traditional frozen printing nozzle to spray water-based adhesives, eliminating the proportioning process of water-based adhesives, reducing the amount of additives used, and further improving the green level of frozen sand additive manufacturing technology.

[0030] 2. The frozen sand additive manufacturing technology proposed in the present invention does not need to be carried out in a negative pressure environment during the forming process, nor does it need to set the ambient temperature below 0°C, effectively reducing resource loss.

[0031] 3. Compared with industrial nozzles that spray water-based adhesives, the cold air direct writing nozzle and array-type low-temperature cold source used in the present invention have low cost, low loss rate, and easy maintenance, which greatly reduces the printing cost of frozen sand molds.

[0032] 4. This invention uses a cold air direct writing nozzle to conformally print the sand mold's edges and surface, ensuring high surface precision. It also employs an array of low-temperature cooling sources for dot scanning to freeze the sand mold's interior, resulting in higher efficiency than traditional frozen sand additive manufacturing techniques. Furthermore, the cold air freezing of wet sand addresses the poor penetration of water-based binders in traditional frozen sand additive manufacturing techniques, further improving the strength of the frozen sand mold.

[0033] 5. Aiming at the problem of poor fluidity and difficulty in laying wet sand, the present invention proposes a sand extrusion laying device and designs a lifting bottom plate with adjustable sand dropout size, thus achieving quantitative laying of wet sand. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the basic steps of the cold source energy field dot matrix scanning sand mold additive manufacturing method of the present invention.

[0035] Figure 2 This is a schematic diagram of the apparatus involved in the cold source energy field dot matrix scanning sand mold additive manufacturing method of the present invention.

[0036] Figure 3 It is a side view of the extrusion sand-laying device of the present invention.

[0037] Figure 4 It is a cross-sectional view of the extrusion sand-laying device of the present invention.

[0038] Figure 5 This is a schematic diagram of area division when printing a cylindrical sand mold according to an embodiment of the present invention.

[0039] Figure 6 This is a schematic diagram of the area division when printing a flange sand mold according to an embodiment of the present invention.

[0040] Description of reference numerals:

[0041] 1-Cryogenic gas storage tank a; 2-Cryogenic gas storage tank b; 3-Array type cryogenic cold source; 4-Cold gas direct writing nozzle; 5-Extrusion sand spreading device; 6-Compacting roller; 7-Refrigeration chamber wall; 8-Lifting platform; 9-Back plate; 10-Electric cylinder; 11-Pressing block; 12-Sand storage bin; 13-Lifting bottom plate; 14-Sand dropout port. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] like Figure 1-6 As shown, the present invention provides a technical solution: a cold source energy field lattice scanning sand mold additive manufacturing method, comprising the following steps:

[0044] S1. Design a sand mold STL 3D model according to the geometric characteristics of the casting product, slice it through a computer, and output the slice shape and slice thickness information;

[0045] S2. Divide the slice shape of each layer into a conformal scanning area and a dot matrix scanning area, and import the slice shape and slice thickness information of the divided areas into the printing system. In S2, the area division means that after removing all 2mm wide edge parts close to the surface sand, the slice shape of each layer is divided into a series of array-distributed grids, and each grid size is equal to the array-type low-temperature cooling source. All complete grids together constitute the dot matrix scanning area, and the other areas of the slice shape excluding the dot matrix scanning area constitute the conformal scanning area.

[0046] S3, pre-cooling the molding sand particles and mixing them evenly with a certain amount of pure water, and then loading the mixed molding sand material into the extrusion sand paving device 5; the molding sand particles are at least one of quartz sand, chromite sand, zircon sand, corundum sand, and forsterite sand, and the mass fraction of water in the molding sand particles is 4% to 8%;

[0047] The pre-cooling treatment is to cool the molding sand particles by passing cold air in advance, and the temperature of the molding sand particles obtained by the treatment is 2-5℃;

[0048] S4, the refrigeration cavity wall 7 is turned on for refrigeration until the temperature of the forming area is stable. The refrigeration cavity wall is made of low-temperature steel and the refrigeration temperature is 2-10°C;

[0049] S5, the lifting platform 8 moves down a certain distance, the extrusion sand laying device 5 lays a layer of molding sand material as the bottom sand, and the compaction roller 6 scrapes it flat. After the bottom sand is laid, the extrusion sand laying device 5 and the compaction roller 6 return to the starting position;

[0050] Among them, the extrusion sand laying device 5 includes a back plate 9, an electric cylinder 10, a pressing block 11, a sand storage bin 12 and a lifting bottom plate 13. The electric cylinder 10, the pressing block 11, the sand storage bin 12 and the lifting bottom plate 13 are sequentially installed on the back plate from top to bottom, wherein the lifting bottom plate 13 is used to control the size of the sand falling opening 14 by adjusting the height up and down, and the electric cylinder 10 and the pressing block 11 are used to control the pressing speed of the pressing block 11. By adjusting the size of the sand falling opening 14 and the pressing speed of the pressing block 11, the amount of sand falling is controlled by extrusion, thereby realizing quantitative sand falling;

[0051] S6, the lifting platform 8 moves down one layer thickness, adjusts the height of the lifting base 13 of the extrusion sand paving device 5, and quantitatively lays a layer of molding sand material. The compaction roller 6 scrapes it flat. After the sand paving is completed, the extrusion sand paving device 5 and the compaction roller 6 return to the starting position;

[0052] The outer layers of the compacting roller 6 and the extrusion sand-laying device 5 are uniformly sprayed with a hydrophobic Teflon coating to prevent sand from sticking during the sand-laying and compaction process.

[0053] S7, start the cold air direct writing nozzle 4 to perform cold air scanning on the conformal scanning area. The cold air direct writing nozzle 4 is connected to the first low-temperature gas storage tank 1 to freeze the edge of the current layer of sand mold to form a shell mold. After the printing is completed, the cold air direct writing nozzle 4 returns to the starting position;

[0054] The nozzle of the cold air direct writing nozzle 4 is replaceable, and the nozzle outlet is in the shape of a circular small hole with a hole diameter of 0.2 to 2 mm. The low-temperature gas ejected from the nozzle is low-temperature carbon dioxide with a temperature not exceeding -50°C.

[0055] S8, start the array type low temperature cooling source 3 to perform a dot matrix scanning on the dot matrix scanning area. The array type low temperature cooling source 3 is connected to the second low temperature gas storage tank 2. The internal area of ​​the current layer of sand mold is frozen by the free diffusion of the cold field and connected to the frozen shell mold. After the printing is completed, the array type low temperature cooling source returns to the starting position;

[0056] The array-type low-temperature cooling source 3 has 36 cold air nozzles distributed in an array. The working range of the cold source is a 30mm×30mm square. The nozzles outside the array-type low-temperature cooling source can be closed, and the 25 cold air nozzles in the middle are retained.

[0057] The low-temperature gas ejected from the nozzle of the array-type low-temperature cooling source 3 is low-temperature nitrogen, and the temperature does not exceed -80°C;

[0058] S9, repeat S6-S8, printing each layer until the preparation of the frozen sand mold is completed;

[0059] S10. After printing is completed, clean the unfrozen molding sand material and store the prepared sand mold in a cold storage.

[0060] Example 1: A cylindrical frozen sand mold with a diameter of 200 mm and a height of 200 mm was prepared.

[0061] According to the geometric characteristics of the casting product, the sand mold STL three-dimensional model is designed through SolidWorks software, and it is sliced ​​through computer slicing software to output information such as slice shape and slice thickness;

[0062] The cylindrical model is relatively simple, so the thickness of each slice is set to 0.5mm, and a total of 400 slice layers are obtained after slicing. The slice shape of each layer is divided into a conformal scanning area and a lattice scanning area. The specific division method is to remove all 2mm wide edge parts close to the surface sand of the slice shape of each layer, and then divide the remaining parts into a series of array-distributed grids. The size of each grid is equal to the array-type low-temperature cooling source, which is a 30mm×30mm square grid. All complete grids together constitute the lattice scanning area, and the other areas of the slice shape excluding the lattice scanning area constitute the conformal scanning area.

[0063] S1, taking the 100th slice of the printed cylindrical sand mold as an example, the area division results are as follows Figure 5 As shown, area a is the conformal scanning area, and area b is the dot matrix scanning area;

[0064] S2, importing information such as the slice shape and slice thickness of the divided area into the printing system;

[0065] S3, select 70 / 140 mesh quartz sand for molding sand particles, pre-cool it with cold air to obtain pre-cooled molding sand particles with a surface temperature of 2°C, mix it evenly with pure water, wherein the mass fraction of water is 4%, and put the mixed molding sand material into the extrusion sand laying device 5;

[0066] S4, the refrigeration chamber wall 7 starts refrigeration and sets the refrigeration temperature to 2°C until the temperature of the forming area stabilizes at 2°C before the next process begins;

[0067] S5, the lifting platform 8 moves down 50mm, the extrusion sand laying device 5 lays a layer of molding sand material as the bottom sand, and the compaction roller 6 scrapes it flat. After the bottom sand is laid, the extrusion sand laying device 5 and the compaction roller 6 return to the starting position;

[0068] S6, the lifting platform 8 moves down 0.5mm, the height of the lifting bottom plate 13 of the extrusion sand laying device 5 is adjusted, and a layer of molding sand material is quantitatively laid. The compaction roller 6 scrapes it flat. After the sand laying is completed, the extrusion sand laying device 5 and the compaction roller 6 return to the starting position. The extrusion sand laying method effectively solves the problem of poor fluidity of wet sand and difficulty in sand laying;

[0069] S7. Start the cold air direct writing nozzle 4 with a nozzle aperture of 1mm. Perform cold air scanning on the conformal scanning area. After the dry ice evaporates and is dried, low-temperature carbon dioxide gas is ejected from the nozzle. The gas temperature at the nozzle is -65°C, and the cold air temperature on the sand surface is -50°C. The edge of the current layer of sand mold is frozen and formed into a shell mold. After printing is completed, the cold air direct writing nozzle 4 returns to the starting position.

[0070] S8, start the array type low temperature cold source 3, close the outer nozzles of the array type low temperature cold source 3, and keep only the 25 nozzles in the middle of the array type low temperature cold source 3 working. The array type low temperature cold source 3 sprays cold air to the center of each grid in the dot matrix scanning area in turn. The liquid nitrogen evaporates and sprays low temperature nitrogen after drying. The gas temperature at the nozzle is about -95°C, and the cold air temperature on the sand surface is about -80°C. Although the working range of the array type low temperature cold source is smaller than the grid size, the free diffusion of the cold field can achieve freezing of the entire area inside the current layer of sand mold until it is connected to the shell mold. After printing is completed, the array type low temperature cold source 3 returns to the starting position;

[0071] S9, repeat S6-S8, printing layer by layer until all layers are printed, completing the preparation of the cylindrical frozen sand mold;

[0072] S10. After printing is completed, clean the unfrozen molding sand material and store the prepared sand mold in a cold storage.

[0073] Example 2: Prepare a frozen sand mold of a flange with an outer diameter of 400 mm, an inner diameter of 200 mm, a through-hole diameter of 50 mm, and a thickness of 80 mm.

[0074] S1. Based on the geometric characteristics of the casting product, a sand mold STL 3D model was designed using SolidWorks software. The model was sliced ​​using computer slicing software, and information such as slice shape and slice thickness was output. The thickness of each slice layer was set to 0.4 mm, and a total of 200 slice layers were obtained after slicing.

[0075] S2. Divide the slice shape of each layer into a conformal scanning area and a dot matrix scanning area. The specific division method is to remove all 2mm wide edge parts close to the surface sand of the slice shape of each layer, and divide the remaining parts into a series of array-distributed grids. The size of each grid is equal to the array-type low-temperature cooling source, which is a 30mm×30mm square. All complete grids together constitute the dot matrix scanning area. The other areas of the slice shape excluding the dot matrix scanning area constitute the conformal scanning area. Taking the 153rd slice of the printed cylindrical sand mold as an example, the regional division results are as follows: Figure 6 As shown, the c area is the shape scanning area, and the d area is the dot matrix scanning area. The slice shape and slice thickness information of the divided areas are imported into the printing system;

[0076] S3, select 70 / 140 mesh quartz sand for molding sand particles, pre-cool it with cold air to obtain pre-cooled molding sand particles with a surface temperature of 2°C, mix it evenly with pure water, wherein the mass fraction of water is 4%, and put the mixed molding sand material into the extrusion sand laying device 5;

[0077] S4, the refrigeration chamber wall 7 starts refrigeration and sets the refrigeration temperature to 2°C until the temperature of the forming area stabilizes at 2°C before the next process begins;

[0078] S5, the lifting platform 8 moves down 50mm, the extrusion sand laying device 5 lays a layer of molding sand material as the bottom sand, and the compaction roller 6 scrapes it flat. After the bottom sand is laid, the extrusion sand laying device 5 and the compaction roller 6 return to the starting position;

[0079] S6, the lifting platform 8 moves down 0.4mm, the height of the lifting base 13 of the extrusion sand laying device 5 is adjusted, and a layer of molding sand material is quantitatively laid. The compaction roller 6 scrapes it flat. After the sand laying is completed, the extrusion sand laying device 5 and the compaction roller 6 return to the starting position. The extrusion sand laying method effectively solves the problem of poor fluidity of wet sand and difficulty in sand laying;

[0080] S7. Start the cold air direct writing nozzle 4 with a nozzle aperture of 0.5 mm. Perform cold air scanning on the conformal scanning area. After the dry ice evaporates and is dried, low-temperature carbon dioxide gas is ejected from the nozzle. The gas temperature at the nozzle is -65°C, and the cold air temperature on the sand surface is -50°C. The edge of the current layer of sand mold is frozen to form a shell mold. After printing is completed, the cold air direct writing nozzle 4 returns to the starting position.

[0081] S8, start the array type low temperature cooling source 3, and the 36 cold air nozzles of the array type low temperature cooling source 3 work simultaneously. The array type low temperature cooling source 3 sprays cold air to the center of each grid in the dot matrix scanning area in turn. The liquid nitrogen evaporates and is dried before spraying out low temperature nitrogen. The gas temperature at the nozzle is about -95°C, and the cold air temperature on the sand surface is about -80°C. Although the working range of the array type low temperature cooling source is smaller than the grid size, the free diffusion of the cold field can achieve freezing of the entire area inside the current layer of sand mold until it is connected to the shell mold. After printing is completed, the array type low temperature cooling source returns to the starting position;

[0082] S9, repeat S6-S8, printing layer by layer until all layers are printed, completing the preparation of the flange frozen sand mold;

[0083] S10. After printing is completed, clean the unfrozen molding sand material and store the prepared sand mold in a cold storage.

[0084] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0085] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A cold source energy field lattice scanning sand mold additive manufacturing method, characterized by: The following steps are involved: S1. Design a sand mold STL 3D model according to the geometric characteristics of the casting product, slice the sand mold STL 3D model through a computer, and output the slice shape and slice thickness information; S2. Divide the slice shape of each layer into a shape-conforming scanning area and a dot-matrix scanning area, and import the slice shape and slice thickness information of the divided areas into the printing system; S3, pre-cooling the molding sand particles and mixing them evenly with a certain amount of pure water, and then placing the mixed molding sand material into the extrusion sand laying device (5); S4, the refrigeration chamber wall (7) starts refrigeration until the temperature of the forming area stabilizes; S5, the lifting platform (8) moves down a certain distance, the extrusion sand laying device (5) lays a layer of molding sand material as the bottom sand, and the compaction roller (6) scrapes it flat. After the bottom sand is laid, the extrusion sand laying device (5) and the compaction roller (6) return to the starting position; S6, the lifting platform (8) moves down by one layer thickness, adjusts the height of the lifting base plate (13) of the extrusion sand paving device (5), quantitatively lays a layer of molding sand material, and the compaction roller (6) scrapes it flat. After the sand paving is completed, the extrusion sand paving device (5) and the compaction roller (6) return to the starting position; S7, start the cold air direct writing nozzle (4) to perform cold air scanning on the shape-following scanning area, freeze the edge of the current layer of sand mold to form a shell mold, and after the printing is completed, the cold air direct writing nozzle (4) returns to the starting position; S8, start the array type low temperature cooling source (3) to perform a dot matrix scanning on the dot matrix scanning area, freeze the inner area of ​​the current layer sand mold through the free diffusion of the cold field, and connect it with the frozen shell mold. After the printing is completed, the array type low temperature cooling source returns to the starting position; S9, repeat S6-S8, printing each layer until the preparation of the frozen sand mold is completed; S10. After printing is completed, clean the unfrozen molding sand material and store the prepared sand mold in a cold storage.

2. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: In S2, the area division means that after removing all 2mm wide edge parts close to the surface sand part, the remaining parts of the slice shape of each layer are divided into a series of array-distributed grids. The size of each grid is equal to the array-type low-temperature cooling source. All complete grids together constitute the dot matrix scanning area, and the other areas of the slice shape excluding the dot matrix scanning area constitute the shape-adaptive scanning area.

3. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: The molding sand particles in S3 are at least one of quartz sand, chromite sand, zircon sand, corundum sand, and forsterite sand, and the mass fraction of water in the molding sand particles is 4% to 8%.

4. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: In S3, the pre-cooling treatment is to cool the molding sand particles by passing cold air in advance, and the temperature of the molding sand particles obtained by the treatment is 2-5°C.

5. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: The extrusion sand laying device (5) comprises a back plate (9), an electric cylinder (10), a pressing block (11), a sand storage bin (12) and a lifting base plate (13). The electric cylinder (10), the pressing block (11), the sand storage bin (12) and the lifting base plate (13) are sequentially mounted on the back plate from top to bottom, wherein the lifting base plate (13) is used to control the size of a sand falling opening (14) by adjusting the height up and down, and the electric cylinder (10) and the pressing block (11) are used to control the downward pressing speed of the pressing block (11). By adjusting the size of the sand falling opening (14) and the downward pressing speed of the pressing block (11), the amount of sand falling is controlled by an extrusion method, thereby realizing quantitative sand falling.

6. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: In S4, the refrigeration cavity wall is made of low-temperature steel, and the refrigeration temperature is 2 to 10°C.

7. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: The outer layers of the compacting roller (6) and the extruding sand-laying device (5) are uniformly sprayed with a hydrophobic Teflon coating to prevent sand from sticking during the sand-laying and compacting processes.

8. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: The nozzle of the cold air direct writing nozzle (4) is replaceable, and the nozzle outlet is in the shape of a circular small hole with a hole diameter of 0.2 to 2 mm. The low-temperature gas ejected from the nozzle is low-temperature carbon dioxide with a temperature not exceeding -50°C.

9. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: The array type low temperature cold source (3) has 36 cold air nozzles distributed in an array, and the cold source working range is a 30mm×30mm square, wherein the nozzles outside the array type low temperature cold source can be selectively closed, and the middle 25 cold air nozzles are retained.

10. The cold source energy field lattice scanning sand mold additive manufacturing method according to claim 1, characterized in that: The low-temperature gas ejected from the nozzles of the array-type low-temperature cooling source (3) is low-temperature nitrogen gas, the temperature of which does not exceed -80°C.

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