Hot forming and additive manufacturing cold forming apparatus and methods for chilled sand molds special adhesive

Abstract

This invention belongs to the interdisciplinary field of cryogenic sand molding and additive manufacturing technology, specifically relating to a device and method for thermoforming cryogenic sand molds with special binders and cold forming in additive manufacturing. The device includes a support frame, a forming platform, a binder pre-fabrication mechanism, and a printing mechanism. This method effectively improves the penetration ability of water-based binders in molding sand particles by coupling the preheating and insulation processes of the water-based binder. The design of a submerged sand storage tank improves the cold retention effect of the pre-cooled raw sand, while simultaneously optimizing the water-based binder formulation. This device and method can solve the problems of general binder penetration and insufficient precision and strength required by conventional cryogenic sand molding additive manufacturing technology. It enables continuous production of cryogenic sand molds from binder preparation to jet printing, which is of great significance for achieving high-precision and high-efficiency preparation of cryogenic sand molds and promoting the green transformation and upgrading of the foundry industry.

Description

Technical Field

[0001] This invention belongs to the intersection of cryogenic sand molding and additive manufacturing technologies, and specifically relates to an apparatus and method for cryogenic sand molding of special adhesives and cold forming of additive manufacturing. Background Technology

[0002] Cryogenic sand casting is a novel rapid prototyping technology that combines cryogenic sand casting with sand mold 3D printing. Based on the microdroplet jetting principle, cryogenic sand casting uses a water-based solution as a special binder for sand casting. Pre-cooled sand particles are laid layer by layer in a low-temperature environment, and the water-based binder is jetted layer by layer, freezing layer by layer to obtain a cryogenic sand mold. This technology enables the rapid preparation of cryogenic sand molds for complex sand molds.

[0003] On the one hand, cryogenic sand additive manufacturing technology produces less dust and is environmentally friendly, resulting in high-quality castings. On the other hand, it offers advantages such as high manufacturing flexibility and short production cycles. However, currently, achieving high-precision and efficient sand mold preparation using cryogenic sand additive manufacturing technology still faces the following limitations:

[0004] (1) The volume of a single droplet ejected by the nozzle of the cryogenic sand additive manufacturing technology is only tens of picoliters, which has poor penetration ability in the molding sand material. The low temperature forming environment further limits the penetration and spreading ability of microdroplets in the molding sand material. In addition, a large number of microdroplets have solidified during the falling process, which makes them unable to penetrate, ultimately affecting the forming accuracy and strength of the sand mold product.

[0005] (2) The existing frozen sand additive manufacturing technology does not have a heat preservation and cold preservation function in the sand laying box. The pre-cooled molding sand particles are stored in the sand laying box. Under the strong convection heat exchange with the air, the pre-cooled molding sand particles heat up rapidly. When the droplets come into contact with the molding sand particles, they cannot solidify quickly, which seriously limits the forming efficiency of frozen sand additive manufacturing technology.

[0006] (3) In patent CN114769502B, a water-based adhesive formulation for cryogenic sand additive manufacturing was disclosed. This is also a water-based adhesive formulation commonly used in existing cryogenic sand additive manufacturing technology. However, the content of the four additives in this formulation reaches more than 20%, and the isopropanol emissions will cause certain environmental pollution, and pyrrolidone also has certain toxicity. The green level of the adhesive formulation process can be further improved.

[0007] (4) In existing resin sand additive manufacturing equipment in room temperature environment, there have been cases of heating ink with heating rods, but the purpose of heating is limited to adjusting the viscosity of ink so that the ink characteristics meet the requirements of printhead ejection.

[0008] Therefore, how to further improve the penetration ability of water-based adhesives in the frozen sand additive manufacturing process, improve the cold insulation ability of the sand box, and optimize the formulation process of water-based adhesives are important issues that urgently need to be addressed in the current frozen sand additive manufacturing technology. Summary of the Invention

[0009] To address the aforementioned issues, this invention discloses a thermoforming and additive manufacturing cold forming apparatus and method for cryogenic sand molds using special adhesives. By designing an adhesive prefabrication mechanism coupled with a preheating and insulation process for the water-based adhesive, the penetration ability of the adhesive in molding sand particles is improved. Simultaneously, the formulation of the water-based adhesive is optimized, facilitating the preparation of cryogenic sand molds with higher precision and strength. This enables continuous production of cryogenic sand molds from adhesive preparation to jet printing.

[0010] To achieve the above objectives, this invention proposes a cryogenic sand mold special adhesive thermoforming and additive manufacturing cold forming device. The device includes: a support frame, a forming platform, an adhesive pre-forming mechanism, and a printing mechanism. The support frame integrates the forming platform, the adhesive pre-forming mechanism, and the printing mechanism into a single unit, ensuring stable operation of the entire device. The adhesive pre-forming mechanism comprises a feed pipe, a pre-mixing tank, an ink cartridge mounting bracket, an ink delivery pipe a, an insulation tank, an ink delivery pipe b, an insulation shell, a heating resistor, a stirring impeller, and an ink cartridge cover. The pre-mixing tank is composed of an insulation shell and an ink cartridge cover, and is fixed to the ground and connected to the support frame via the ink cartridge mounting bracket. The ink cartridge cover has two holes. One hole connects to the feed pipe, which delivers the prepared pure water and additives to the pre-mixing tank. The other hole connects to ink delivery pipe a, the other end of which is connected to an insulated tank, allowing the prepared water-based adhesive to be transported to the insulated tank for heat preservation before use. The insulated tank is also connected to an ink delivery pipe b, through which the water-based adhesive enters the ink circulation system for inkjet printing. A resistance heater is installed below the ink cartridge cover to heat the additives in the pre-mixing tank. The stirring impeller is installed at the bottom of the insulated shell and is driven by a rotary motor to achieve rotation and stirring functions. Both ink delivery pipes a and b are covered with insulation cotton.

[0011] As a further design of this solution, the printing mechanism includes a structural beam, slide rail a, slide rail b, a printhead box, and a scraper. The printhead box is mounted on one side of the structural beam via slide rail b, and can slide along slide rail b. The printhead box contains a printhead, and the printing ink comes from the water-based adhesive that enters the ink circulation system from the ink supply pipe b. The structural beam is fixed above the support frame via slide rail a, which drives the printhead box to slide as a whole. The scraper is located below the structural beam, with its lower edge horizontal, and is used to level the bed of molding sand powder during printing.

[0012] As a further design of this solution, the forming platform includes a sand storage box, a cold air insulation box, an air inlet, a waste sand collection box, a sealing lifting platform, a sand spreading lifting platform, a servo electric cylinder, a lifting motor, support guide columns, a screw structure, a lifting slide, and lifting guide columns. The sealing lifting platform is connected and fixed to the lifting slide via four lifting guide columns, and the sealing lifting platform and the lifting slide move synchronously. The lifting slide can slide up and down under the drive of the screw structure and the lifting motor. The four support guide columns passing through the lifting slide play a guiding and structural support role, thereby realizing the vertical movement of the sealing lifting platform. One sand storage box and three waste sand collection boxes are arranged around the sealing lifting platform. The bottom plate of the sand storage box is a sand spreading lifting platform that can be raised and lowered, driven by a servo electric cylinder. Four cold air insulation boxes are also arranged on the outside of the sand storage box and the waste sand collection box, and several air inlets are opened on the outer wall of the cold air insulation box.

[0013] This invention also provides a method for thermoforming and additive manufacturing cold forming of a special adhesive using a frozen sand mold, the method comprising the following steps:

[0014] Step 1: Design a sand mold STL 3D model based on the geometric characteristics of the casting product, slice it using computer slicing software, output information such as slice shape and slice thickness, and import it into the printing system;

[0015] Step 2: Add pure water and additives to the pre-mixing tank, start the stirring impeller and heating resistor. The stirring impeller mixes the pure water and additives evenly, and the heating resistor accelerates the dissolution of the additives in the water by heating and ensures that the additives are completely dissolved. The pure water and additives are mixed evenly to obtain a water-based adhesive with a certain temperature, and then it is transferred to an insulated tank to keep it warm for later use.

[0016] Step 3: Select the appropriate type of molding sand according to the shape of the casting, mix the raw sand particles with the pre-cooling medium evenly, pre-cool to the required temperature, and fill the pre-cooled molding sand particles into the sand storage box for later use.

[0017] Step 4: Continuously supply cold air into the cold air insulation box to adjust the temperature of the forming platform to a suitable low temperature.

[0018] Step 5: The sealing lifting platform moves down a certain distance, the sand-laying lifting platform moves up a certain distance, and the printing mechanism slides to lay a layer of pre-cooled molding sand as the base sand. After the base sand is laid, the printing mechanism returns to the starting position.

[0019] Step 6: The sealing lifting platform moves down by one layer thickness, the sand-laying lifting platform rises to a certain height, the printing mechanism slides, the scraper smooths and completes the sand-laying, and the printing nozzle sprays water-based adhesive at a certain temperature as needed according to the current layer cross-sectional information of the sand mold to complete the printing of the current layer sand mold. The printing mechanism returns to the starting position.

[0020] Step 7: Repeat step 6. When the amount of pre-cooled molding sand in the sand storage box is insufficient to lay a layer of molding sand, fill the sand storage box with pre-cooled molding sand, lay the sand layer by layer, and print layer by layer until all layers of sand are laid and printed to complete the sand mold preparation. During the printing process, while consuming the water-based adhesive in the insulation tank, continuously add pure water and additives to the pre-mixing tank, continuously stir and heat, and continuously send the prepared water-based adhesive into the insulation tank for insulation.

[0021] Step 8: Leave the printed sand mold in the forming platform for a period of time until the sand mold reaches the required specifications. Raise the sealing lifting platform to the highest position, clean and recycle the unbonded molding sand particles, and take out the sand mold along with the sealing lifting platform and put it into the cold storage for later use.

[0022] Step 9: Reinstall the sealing lifting platform to prepare for printing the next frozen sand mold.

[0023] As a further design of this scheme, the additive in step 2 consists of polyvinyl alcohol and acetylation diol surfactant. The polyvinyl alcohol selected is polyvinyl alcohol 1788, and the content of added polyvinyl alcohol is 3-4% of the mass of pure water, which is used to improve the viscosity of the water-based adhesive. The content of added acetylation diol surfactant is 0.1% of the mass of pure water, which is used to improve the surface tension of the water-based adhesive.

[0024] As a further design of this scheme, in step 2, the stirring speed of the stirring impeller is 60-300 r / min, the heating temperature of the heating resistor is 80-100℃, and the temperature of the initially prepared water-based adhesive is 80-100℃.

[0025] As a further design of this solution, the outer surfaces of the pre-mixing bucket and the heat-insulating bucket in step 2 are both covered with heat-insulating material to ensure that the water-based adhesive does not lose too much heat during the heating preparation and heat-insulating storage process, thus preventing the temperature from becoming too low.

[0026] As a further design of this scheme, the raw sand particles in step 3 are refractory molding sand for casting, including one or more of quartz sand, ceramsite sand, chromite sand, zircon sand, corundum sand, and olivine sand. The pre-cooling medium is liquid nitrogen or dry ice, which pre-cools the molding sand particles to -50 to 0°C.

[0027] As a further design of this scheme, in step 4, the cold air insulation box is made of low-temperature steel or other materials with excellent low-temperature resistance, and the cold air introduced is low-temperature nitrogen obtained by vaporizing liquid nitrogen.

[0028] As a further design of this scheme, the water-based binder sprayed in step 6 contains 3-8% of the molding sand mass.

[0029] The beneficial effects of this invention are:

[0030] (1) This invention preheats and insulates the water-based adhesive by designing a pre-mixing tank and a heat preservation tank. The preheated microdroplets sprayed from the nozzle have a certain heat dissipation and cooling during the falling process, and still have a high temperature when they reach the surface of the molding sand particles, so that they can better penetrate and spread in the molding sand particles. During the penetration and spreading process, they gradually cool and solidify, and the sand molds prepared have higher precision and strength.

[0031] (2) The present invention continuously introduces cold air into the sand storage chamber. Combined with the sunken sand storage chamber design, it has a good cold preservation effect on the pre-cooled molding sand particles. The molding sand particles can still maintain a low temperature when laid. The droplets can quickly solidify and adhere when they come into contact with the molding sand particles. At the same time, the good cold preservation effect means that more pre-cooled molding sand particles can be filled into the sand storage chamber at one time, reducing the number of times the molding sand material is manually filled into the sand storage chamber, and effectively improving the efficiency of sand mold printing.

[0032] (3) The novel water-based adhesive proposed in this invention introduces only two additives, polyvinyl alcohol and acetylsene glycol surfactant, into pure water, which simplifies the formulation process of the water-based adhesive. Moreover, the additive content can be controlled below 5 wt.%, and its performance parameters such as viscosity and surface tension can still meet the printing nozzle deposition requirements and fully wet the powder bed, greatly reducing the amount of additives used. At the same time, polyvinyl alcohol is inexpensive, non-toxic and odorless, and the water-based adhesive has a higher level of greenness.

[0033] (4) This invention couples the formulation and preheating process of water-based adhesives. Water-based adhesives with added polyvinyl alcohol need to be completely dissolved and formulated in a heated environment. In order to make the adhesives have better penetration ability, the adhesives also need to be preheated. The water-based adhesives prepared by heating are directly kept warm and sprayed for printing. The resource consumption generated during the heating process is greatly reduced. At the same time, the digitalization level of the production and preparation of water-based adhesives to the frozen sand additive manufacturing process is improved, and continuous production is realized.

[0034] (4) In this invention, the heating process for the ink, besides adjusting viscosity, has two unique functions: first, heating is necessary because polyvinyl alcohol can only dissolve in water at relatively high temperatures; second, heating enhances the penetration ability of the modified adhesive, ensuring that it can fully penetrate the pre-cooled sand particles in the low-temperature special environment of cryogenic sand additive manufacturing, thus guaranteeing the overall bonding ability of the printed sand mold. The heating resistance process of this invention simultaneously possesses three functions and integrates multiple processes. Attached Figure Description

[0035] Figure 1This is a schematic diagram of a cryogenic sand mold special adhesive thermoforming and additive manufacturing cold forming apparatus according to an embodiment of the present invention.

[0036] Figure 2 This is a schematic diagram illustrating the basic steps of a cryogenic sand mold special adhesive thermoforming and additive manufacturing cold forming method according to an embodiment of the present invention.

[0037] Figure 3 This is a schematic diagram of the adhesive prefabrication mechanism described in an embodiment of the present invention.

[0038] Figure 4 This is a cross-sectional view of the pre-mixing barrel described in an embodiment of the present invention.

[0039] Figure 5 This is a side view of the printing mechanism described in an embodiment of the present invention.

[0040] Figure 6 This is a side or bottom view of the structural beam described in an embodiment of the present invention.

[0041] Figure 7 This is a side and top view of the forming platform described in an embodiment of the present invention.

[0042] Figure 8 This is a side or bottom view of the forming platform described in an embodiment of the present invention.

[0043] Figure 9 In this embodiment, four groups of samples were placed in a magnetic stirrer and stirred at a heating temperature of 95°C for 1 hour until they were uniformly stirred. The viscosity of the four groups of water-based adhesives was then tested.

[0044] Figure 10 In this embodiment, four groups of samples were placed in a magnetic stirrer and stirred at a heating temperature of 95°C for 1 hour until they were uniformly mixed. The surface tension diagrams of the four groups of water-based adhesives were then tested.

[0045] Figure Descriptions: 1-Supporting frame; 2-Forming platform; 3-Adhesive prefabrication mechanism; 4-Printing mechanism; 5-Feeding pipe; 6-Premixing tank; 7-Ink cartridge mounting bracket; 8-Ink delivery pipe a; 9-Insulation tank; 10-Ink delivery pipe b; 11-Insulation shell; 12-Heating resistor; 13-Stirring impeller; 14-Ink cartridge cover; 15-Structural beam; 16-Slide rail a; 17-Slide rail b; 18-Printhead box; 19-Scraper; 20-Sand storage box; 21-Cold air insulation box; 22-Air inlet; 23-Waste sand collection box; 24-Sealed lifting platform; 25-Sand spreading lifting platform; 26-Servo electric cylinder; 27-Lifting motor; 28-Supporting guide column; 29-Screw screw structure; 30-Lifting slide; 31-Lifting guide column. Detailed Implementation

[0046] 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.

[0047] like Figure 1 and Figures 3-8 As shown, this embodiment provides a cryogenic sand mold special adhesive thermoforming and additive manufacturing cold forming device, including a support frame 1, a forming platform 2, an adhesive prefabrication mechanism 3, and a printing mechanism 4. The support frame 1 integrates the forming platform 2, the adhesive prefabrication mechanism 3, and the printing mechanism 4 into one unit. The adhesive prefabrication mechanism 3 includes a feeding pipe 5, a pre-mixing tank 6, an ink cartridge mounting bracket 7, an ink delivery pipe a 8, an insulation tank 9, an ink delivery pipe b 10, an insulation shell 11, a heating resistor 12, and a stirring impeller. 13 and ink cartridge cover 14; the pre-mixing tank 6 is composed of an insulated outer shell 11 and an ink cartridge cover 14, and is fixed to the ground by an ink cartridge mounting bracket 7 and connected to the support frame 1; the ink cartridge cover 14 has two holes, one of which is connected to the feed pipe 5, and the other is connected to the ink delivery pipe a8, which transports the proportioned pure water and additives into the pre-mixing tank, and the other end of the ink delivery pipe a8 is connected to the insulated tank 9; now the prepared water-based adhesive is transported into the insulated tank for insulation and later use; the insulated tank 9 is also connected to A single ink delivery pipe b10 allows the water-based adhesive to enter the ink circulation system for inkjet printing. A heating resistor 12 is installed below the ink cartridge cover 14 to heat the additives in the pre-mixing container. The heating temperature of the heating resistor is 80-100℃. A stirring impeller 13 is installed at the bottom of the insulation shell 11, with a stirring speed of 60-300 r / min, driven by a rotary motor to achieve rotation and stirring functions. Both ink delivery pipes a8 and b10 are covered with insulation cotton to ensure that the water-based adhesive does not lose too much heat during heating, preparation, transportation, and insulation storage, preventing the temperature from dropping too low. The additives consist of polyvinyl alcohol and acetylsene glycol surfactants. The polyvinyl alcohol used is polyvinyl alcohol 1788, and the added polyvinyl alcohol content is 3-4% of the mass of pure water to improve the viscosity of the water-based adhesive. The added acetylsene glycol surfactant content is 0.1% of the mass of pure water to improve the surface tension of the water-based adhesive.

[0048] The printing mechanism 4 includes a structural beam 15, a slide rail a16, a slide rail b17, a printhead box 18, and a scraper 19. The printhead box 18 is mounted on one side of the structural beam 15 via the slide rail b17, and slides along the slide rail b17. The printhead box 18 contains a printhead, and the printing ink comes from the water-based adhesive that enters the ink circulation system from the ink supply pipe b10. The structural beam 15 is fixed above the support frame 1 via the slide rail a16, which drives the printhead box 18 to slide as a whole. The scraper 19 is located below the structural beam 15, and its lower edge is horizontal. During the printing process, the scraper 19 is used to level the bed of molding sand powder.

[0049] The forming platform 2 includes a sand storage box 20, a cold air insulation box 21, an air inlet 22, a waste sand collection box 23, a sealed lifting platform 24, a sand spreading lifting platform 25, a servo electric cylinder 26, a lifting motor 27, a support guide column 28, a lead screw structure 29, a lifting slide 30, and a lifting guide column 31. The sealed lifting platform 24 is connected and fixed to the lifting slide 30 through four lifting guide columns, and the sealed lifting platform 24 and the lifting slide 30 rise and fall synchronously. The lifting slide 30 moves up and down under the drive of the lead screw structure and the lifting motor, and the four guide columns passing through the lifting slide 30... The supporting guide column serves as a guide and structural support. The sealing lifting platform 24 is surrounded by a sand storage box 20 and three waste sand collection boxes 23. The bottom plate of the sand storage box 20 is a sand-laying lifting platform that can be raised and lowered, driven by a servo electric cylinder. Four cold air insulation boxes 21 are also provided on the outside of the sand storage box 20 and the waste sand collection box 23. Several air inlets 22 are opened on the outer wall of the cold air insulation box 21. The cold air insulation box is made of low-temperature steel or other materials with excellent low-temperature resistance. The cold air introduced is low-temperature nitrogen obtained by vaporizing liquid nitrogen.

[0050] Four groups of water-based adhesive formulation experiments were designed. The specific additive formulations are shown in the table below. Polyvinyl alcohol 1788 is used to change the viscosity of the solution, and acetylacetic diol surfactant is used to change the surface tension of the solution.

[0051]

[0052] Four groups of samples were placed in a magnetic stirrer and stirred at 95°C for 1 hour until homogeneous. The viscosity and surface tension of the four groups of water-based adhesives were then tested. Results Figure 9 and Figure 10 As shown:

[0053] The results showed that when the content of polyvinyl alcohol 1788 reached 3%, the viscosity of the adhesive met the requirements of the nozzle spraying. The surface tension of the three groups of samples with a content of 0.1% acetylsadiol surfactant was within the allowable range of nozzle spraying. The modified water-based adhesive had good dispersing ability. The modified formula was initially obtained, that is, the lower limit of the addition of polyvinyl alcohol 1788 is 3% and the addition of acetylsadiol surfactant is 0.1%.

[0054] like Figure 2 As shown, a method for thermoforming and additive manufacturing cold forming of a special adhesive using cryogenic sand molds is described. This method prints a batch of cryogenic sand mold cylindrical specimens with a diameter of 50 mm, a height of 50 mm, and a moisture content of 5 wt.% for measuring compressive strength. The method includes the following steps:

[0055] Based on the geometric characteristics of the casting product, a sand mold STL 3D model is designed. The model is then sliced ​​using computer slicing software. Since the cylindrical sample has a relatively simple shape, the traditional equal-thickness slicing method is used for slicing. The cylindrical sample has a height of 50mm, and the layer thickness is set to 0.5mm, resulting in 100 slice layers. The slice shape, slice thickness, and other information are output and imported into the printing system.

[0056] Pure water and additives were added to a pre-mixing tank. The additives consisted of 3 wt.% polyvinyl alcohol 1877 and 0.1 wt.% acetylsene glycol surfactant (by weight of pure water). The impeller and heating resistor were started, with the impeller speed set to 120 r / min to mix the pure water and additives evenly. The heating resistor was set to 95℃ to accelerate the dissolution of the additives in the water and ensure complete dissolution. The pure water and additives were mixed evenly to obtain a water-based adhesive at 95℃. The viscosity of the prepared water-based adhesive was measured to be 7.64 mPa·s, and the surface tension was 31.25 mN / m, meeting the requirements of the printing nozzle. The adhesive was then transferred to an insulated container for later use. 70 / 140 mesh quartz sand particles were selected and mixed evenly with dry ice at a dry ice to original sand particle mass ratio of 1:20. The mixture was pre-cooled to -20℃, and the pre-cooled sand particles were filled into a sand storage box for later use. The mixture was then cooled by cold air. Cold air, specifically low-temperature nitrogen obtained from the vaporization of liquid nitrogen, is continuously circulated into the cold box to set the forming platform temperature to -20℃. The sealing lifting platform moves down a certain distance, and the sand-laying lifting platform moves up a certain distance. The printing mechanism slides to lay a layer of pre-cooled molding sand as the base sand. After the base sand is laid, the printing mechanism returns to the starting position. The sealing lifting platform moves down 0.5mm, and the sand-laying lifting platform rises a certain height. The printing mechanism slides, and the scraper smooths the sand to complete the sand laying. At the same time, the printing nozzle sprays water-based adhesive at a certain temperature as needed, based on the cross-sectional information of the current layer of the sand mold. The mass of the adhesive is 5% of the mass of the laid molding sand. At this time, the temperature of the sprayed water-based adhesive is about 50℃, completing the printing of the current layer of the sand mold. The printing mechanism returns to the starting position. When the amount of pre-cooled molding sand in the sand storage tank is insufficient to lay a layer of molding sand, pre-cooled molding sand is added to the sand storage tank. Sand is laid layer by layer, and printing is done layer by layer until all layers of sand are laid and printed, completing the sand mold preparation.

[0057] During the printing process, while consuming the water-based adhesive in the insulation tank, pure water and additives are continuously added to the pre-mixing tank, and the mixture is continuously stirred and heated. The prepared water-based adhesive is continuously fed into the insulation tank for heat preservation. The printed sand mold is left to stand on the forming platform for a period of time until the cylindrical sand mold reaches the required specifications. The sealing lifting platform is then raised to its highest position, and the unbonded molding sand particles are cleaned and recycled. The cylindrical sand mold, along with the sealing lifting platform, is taken out and placed in a cold storage for later use. The sealing lifting platform is then reinstalled to prepare for printing the next frozen sand mold.

[0058] 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 cryogenic sand mold special adhesive thermoforming and additive manufacturing cold forming apparatus, comprising a support frame (1), a forming platform (2), an adhesive preforming mechanism (3), and a printing mechanism (4), wherein the support frame (1) integrates the forming platform (2), the adhesive preforming mechanism (3), and the printing mechanism (4) into one unit; characterized in that, The adhesive prefabrication mechanism (3) includes a feed pipe (5), a pre-mixing tank (6), an ink cartridge mounting bracket (7), an ink delivery pipe a (8), an insulation tank (9), an ink delivery pipe b (10), an insulation shell (11), a heating resistor (12), a stirring impeller (13), and an ink cartridge cover (14). The pre-mixing tank (6) is composed of an insulation shell (11) and an ink cartridge cover (14), and is fixed to the ground by the ink cartridge mounting bracket (7) and connected to the support frame (1). The ink cartridge cover (14) has two holes, one of which is connected to the feed pipe (5), and the other hole is connected to the ink delivery pipe a (8). The other end of the ink delivery pipe a (8) is connected to the insulation tank (9). The insulation tank (9) is also connected to a... Ink delivery pipe b (10) allows water-based adhesive to enter the ink circulation system for inkjet printing; a heating resistor (12) is installed below the ink cartridge cover (14) to heat the additives in the pre-mixing tank; the stirring impeller (13) is installed at the bottom of the insulation shell (11) and driven by a rotary motor to achieve rotation and stirring functions; both ink delivery pipe a (8) and ink delivery pipe b (10) are covered with insulation cotton; the printing mechanism (4) includes a structural beam (15), slide rail a (16), slide rail b (17), printhead box (18), and scraper (19); the printhead box (18) is set on one side of the structural beam (15) via slide rail b (17), and the printhead box ( 18) The print head is installed in the print head box (18) and the printing ink comes from the water-based adhesive that enters the ink circulation system from the ink supply pipe b (10); the structural beam (15) is fixed above the support frame (1) by the slide rail a (16) and drives the print head box (18) to slide as a whole; the scraper (19) is set below the structural beam (15) and the lower edge of the scraper (19) is horizontal, and it scrapes the laid molding sand powder bed during the printing process; the forming platform (2) includes a sand storage box (20), a cold air insulation box (21), an air inlet (22), a waste sand collection box (23), a sealing lifting platform (24), a sand laying lifting platform (25), and a servo electric cylinder ( 26), lifting motor (27), support guide column (28), screw structure (29), lifting slide (30) and lifting guide column (31); the sealed lifting platform (24) is connected and fixed to the lifting slide (30) through 4 lifting guide columns, and the sealed lifting platform (24) and the lifting slide (30) rise and fall synchronously; the lifting slide (30) moves up and down under the drive of the screw structure and the lifting motor, and the 4 support guide columns passing through the lifting slide (30) play a guiding and structural support role. The sealed lifting platform (24) is provided with 1 sand storage box (20) and 3 waste sand collection boxes (23) around its perimeter. The bottom plate of the sand storage box (20) is a sand-laying lifting platform that can be raised and lowered, driven by a servo electric cylinder.The sand storage box (20) and waste sand collection box (23) are each equipped with four cold air insulation boxes (21) on their outer sides, and several air inlets (22) are opened on the outer wall of the cold air insulation boxes (21).

2. A method for thermoforming and cold forming of a cryogenic sand mold special adhesive for additive manufacturing, based on the apparatus for thermoforming and cold forming of a cryogenic sand mold special adhesive for additive manufacturing as described in claim 1, characterized in that, The method includes the following steps: Step 1: Design a sand mold STL 3D model based on the geometric characteristics of the casting product, slice it using computer slicing software, output the slice shape and thickness information, and import it into the printing system; Step 2: Add pure water and additives to the pre-mixing tank, start the stirring impeller and heating resistor. The stirring impeller mixes the pure water and additives evenly, and the heating resistor accelerates the dissolution of the additives in the water by heating and ensures that the additives are completely dissolved. The pure water and additives are mixed evenly to obtain a water-based adhesive with a certain temperature, and then it is transferred to an insulated tank to keep it warm for later use. Step 3: Select the appropriate type of molding sand according to the shape of the casting, mix the raw sand particles with the pre-cooling medium evenly, pre-cool to the required temperature, and fill the pre-cooled molding sand particles into the sand storage box for later use. Step 4: Continuously supply cold air into the cold air insulation box to adjust the temperature of the forming platform to a suitable low temperature. Step 5: The sealing lifting platform moves down a certain distance, the sand-laying lifting platform moves up a certain distance, and the printing mechanism slides to lay a layer of pre-cooled molding sand as the base sand. After the base sand is laid, the printing mechanism returns to the starting position. Step 6: The sealing lifting platform moves down by one layer thickness, the sand-laying lifting platform rises to a certain height, the printing mechanism slides, the scraper smooths and completes the sand-laying, and the printing nozzle sprays water-based adhesive at a certain temperature as needed according to the current layer cross-sectional information of the sand mold to complete the printing of the current layer sand mold. The printing mechanism returns to the starting position. Step 7: Repeat step 6. When the amount of pre-cooled molding sand in the sand storage box is insufficient to lay a layer of molding sand, fill the sand storage box with pre-cooled molding sand, lay the sand layer by layer, and print layer by layer until all layers of sand are laid and printed to complete the sand mold preparation. During the printing process, while consuming the water-based adhesive in the insulation tank, continuously add pure water and additives to the pre-mixing tank, continuously stir and heat, and continuously send the prepared water-based adhesive into the insulation tank for insulation. Step 8: Leave the printed sand mold in the forming platform for a period of time until the sand mold reaches the required specifications. Raise the sealing lifting platform to the highest position, clean and recycle the unbonded molding sand particles, and take out the sand mold along with the sealing lifting platform and put it into the cold storage for later use. Step 9: Reinstall the sealing lifting platform to prepare for printing the next frozen sand mold.

3. The method for thermoforming and additive manufacturing cold forming of a special adhesive using a frozen sand mold according to claim 2, characterized in that, The additives in step 2 consist of polyvinyl alcohol and acetylation diol surfactants. The polyvinyl alcohol used is polyvinyl alcohol 1788, and the amount of polyvinyl alcohol added is 3-4% of the mass of pure water, which is used to improve the viscosity of the water-based adhesive. The amount of acetylation diol surfactant added is 0.1% of the mass of pure water, which is used to improve the surface tension of the water-based adhesive.

4. The method for thermoforming and additive manufacturing cold forming of a special adhesive using a frozen sand mold according to claim 2, characterized in that, In step 2, the stirring speed of the impeller is 60-300 r / min, the heating temperature of the heating resistor is 80-100℃, and the temperature of the initially prepared water-based adhesive is 80-100℃.

5. The method for thermoforming and additive manufacturing cold forming of a special adhesive using a frozen sand mold according to claim 2, characterized in that, In step 2, the outer surfaces of both the pre-mixing container and the insulation container are covered with insulation cotton to ensure that the water-based adhesive does not lose too much heat during the heating preparation and insulation storage process, thus preventing the temperature from becoming too low.

6. The method for thermoforming and additive manufacturing cold forming of a special adhesive using a frozen sand mold according to claim 2, characterized in that, In step 3, the raw sand particles are refractory molding sand for casting, including one or more of quartz sand, ceramsite sand, chromite sand, zircon sand, corundum sand, and olivine sand. The pre-cooling medium is liquid nitrogen or dry ice, which pre-cools the molding sand particles to -50 to 0°C.

7. The method for thermoforming and additive manufacturing cold forming of a special adhesive using a frozen sand mold according to claim 2, characterized in that, In step 4, the cold air insulation box is made of low-temperature steel, and the cold air introduced is low-temperature nitrogen obtained by vaporizing liquid nitrogen.

8. The method for thermoforming and additive manufacturing cold forming of a special adhesive using a frozen sand mold according to claim 2, characterized in that, The water-based adhesive sprayed in step 6 contains 3-8% of the molding sand mass.

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