Method for preparing metal casting mold based on steel grit 3D printing

Abstract

The invention discloses a method for preparing a metal casting mold based on steel grit 3D printing, and belongs to the technical field of metal casting mold machining. In order to solve the technical problem that in the prior art, the mechanical strength and collapsibility of a metal casting mold need to be further improved, the method for preparing the metal casting mold based on steel grit 3D printing comprises the following steps that a sand mold three-dimensional model is established according to a metal casting, then casting mold steel grit is filled in an operation box of sand mold 3D printing equipment, and the casting mold steel grit is obtained; the binder storage tank is filled with a binder; and according to the section formation of the sand mold three-dimensional model, a sand paving system of the sand mold 3D printing equipment paves cast steel sand on a printing platform. The casting steel sand and the binder are matched with each other, the metal casting mold blank is prepared through 3D printing and then dried, the normal-temperature mechanical property and high-temperature property of the metal casting mold are effectively improved, the application range of the metal casting mold is widened, and meanwhile the collapsibility of the metal casting mold is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal casting processing, and in particular to a method for preparing a metal casting based on steel sand 3D printing. Background Art

[0002] The preparation of traditional metal castings usually includes mold design, mold manufacturing, casting and other links. Among them, mold manufacturing is one of the key steps, which requires a lot of time and cost. With the continuous development of manufacturing technology, 3D printing technology, as an advanced additive manufacturing technology, has shown great application potential in many fields. Especially in the field of metal casting, 3D printing technology, with its high precision, high efficiency and high degree of design freedom, provides a new solution for the preparation of metal castings.

[0003] In the prior art, a Chinese invention patent with publication number CN107695294B discloses a 3D printing method for casting sand molds, which relates to the field of 3D printing additive manufacturing technology. The method includes the following steps:

[0004] (1) Establish a three-dimensional model of a sand mold for casting; (2) The sand-laying system lays the sand mixed with the catalyst into a thin sand layer at a speed of 40-60 seconds per layer, and controls the thickness of each sand layer to be 0.2-0.5 mm; (3) After the sand-laying and leveling are completed, the printer nozzle accurately and evenly sprays the binder onto the surface of the sand layer according to the cross-sectional shape of the three-dimensional model of the sand mold, and solidifies the sand layer through the cross-linking reaction between the binder and the catalyst; (4) Repeat the process of steps (2) to (3) above, and stack multiple layers until the required sand mold thickness is printed. The method of the present invention can significantly reduce the number of times the nozzle presses ink during the printing process, which can not only reduce the loss of resin and reduce costs, but also effectively improve printing efficiency.

[0005] A Chinese invention patent with publication number CN113695513A discloses a water glass steel sand casting mold and a preparation method. A water glass steel sand casting mold, the raw sand is steel sand, and the steel sand is bonded and shaped by water glass. The preparation method of the water glass steel sand casting mold includes the following steps: A. sand preparation; B. model and sand box preparation; C. sand mixing; D. shaping; D. mold hardening; E. demolding. The steel sand of the casting mold of the present invention has high heat storage and thermal conductivity, and enhances the quenching ability. The obtained casting has fine crystalline structure, dense texture, excellent mechanical properties, high production efficiency and low production cost; the recycling of steel sand reduces the consumption of natural resources compared with mineral sand, and also avoids the generation of a large amount of solid waste sand, which is energy-saving and environmentally friendly.

[0006] Although 3D printing can solve the processing requirements of casting molds with complex structures and high precision requirements, the metal molds currently prepared by 3D printing have poor mechanical strength and are often only suitable for the processing and molding of some small castings. In addition, in order to improve the strength of existing metal molds, the amount of water glass is usually increased, so that the molten steel still has a high residual strength after the pouring is completed, and the collapsibility of the metal mold needs to be further improved.

[0007] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing a metal casting mold based on steel sand 3D printing, which is used to solve the technical problem in the prior art that the mechanical strength and collapsibility of the metal casting mold need to be further improved.

[0009] The purpose of the present invention can be achieved through the following technical solutions:

[0010] A method for preparing a metal casting mold based on steel sand 3D printing comprises the following steps:

[0011] S1. Establish a sand mold three-dimensional model according to the metal casting, then fill the casting steel sand into the working box of the sand mold 3D printing equipment, and fill the binder into the binder storage tank;

[0012] S2. According to the cross-section formation of the sand mold three-dimensional model, the sand paving system of the sand mold 3D printing equipment lays the casting steel sand on the printing platform to form a basic sand layer with a thickness of 0.2-0.5mm;

[0013] S3, the sand mold 3D printing equipment sprays the binder on the surface of the sand layer and starts printing layer by layer;

[0014] S4, repeat step S3 until the printing is completed, obtain the metal casting blank, and dry it to obtain the metal casting mold.

[0015] Further, in step S3, the printing speed of the sand mold 3D printing device is 12-20s / layer, the molding efficiency is 55-60L / h, the sand mold 3D printing device is equipped with a piezoelectric nozzle and a set of sand spreaders, wherein the sand spreader is connected to the working line for laying the casting steel sand, the layer thickness of the sand layer is 0.2-0.5mm, the piezoelectric nozzle is connected to the binder storage tank for spraying the binder, the negative pressure value is 2.3-2.6kPa, and the spraying amount of the binder is 6-9g / m 2 .

[0016] Furthermore, the drying method in step S4 is: putting the metal casting mold body into a drying oven, raising the temperature of the drying oven to 120-180° C., keeping the temperature for 10-40 minutes, and cooling the temperature of the drying oven to room temperature to obtain the metal casting mold.

[0017] Furthermore, the preparation method of casting steel sand is: adding steel sand and curing aid into a reactor and stirring, raising the temperature of the reactor to 75-85°C, adding reinforcing powder into the reactor in batches, keeping warm and mixing for 50-60 minutes, and post-treating to obtain casting steel sand.

[0018] Synthesis reaction mechanism of casting steel sand:

[0019] Under high temperature environment, the reinforcing powder undergoes coupling reaction with the curing aid through the triethoxysilane on its surface, thereby enhancing the bonding force between the steel sand and the reinforcing powder, modifying the reinforcing powder on the surface of the steel sand to form a coating modification, and promoting the formation of casting steel sand.

[0020] Furthermore, the dosage ratio of the steel sand, the curing aid and the reinforcing powder is 1000g:1-4g:6-10g, the curing aid is one or more of propylene glycol triacetate, propylene glycol diacetate, propylene glycol monoacetate, ethylene glycol diacetate, ethylene glycol monoacetate, diethylene glycol diacetate, and diethylene glycol monoacetate, the steel sand is any one of carbon steel, low carbon steel, and stainless steel, and the mesh size is 100-140 meshes.

[0021] Furthermore, the reinforced powder is obtained by processing the following steps:

[0022] A1. Evenly mix nano-aluminum oxide, nano-silicon carbide, nano-yttrium oxide and nano-boron nitride to obtain a mixed powder;

[0023] A2, adding the mixed powder, anhydrous ethanol and KH-540 into the reactor and stirring, raising the temperature of the reactor to 50-60°C, adding alkali solution into the reactor, keeping the temperature for reaction for 50-60min, and post-treating to obtain the pretreated powder;

[0024] A3. Add the pretreated powder and N,N-dimethylformamide into a nitrogen-protected reactor and stir. Raise the temperature of the reactor to 60-70°C. Add isocyanatepropyltriethoxysilane into the reactor and keep the reaction temperature for 60-80 minutes. Post-treat to obtain the enhanced powder.

[0025] Enhanced powder synthesis reaction mechanism:

[0026] The composition of the mixed powder was optimized. After the surface of the mixed powder was modified with active amino groups using KH-540, a condensation reaction occurred between the isocyanate group on isocyanatepropyltriethoxysilane and the amino groups as the active site. A large amount of triethoxysilane was modified on the outside of the mixed powder to improve the reactivity of the enhanced powder.

[0027] Furthermore, in step A1, the weight ratio of nano-alumina, nano-silicon carbide, nano-yttrium oxide, and nano-boron nitride is 8-10:2-3:2-3:2-3; in step A2, the amount ratio of the mixed powder, anhydrous ethanol, KH-540, and alkali solution is 5g:50mL:2g:5mL, and the alkali solution is 0.2-0.3mol / L sodium hydroxide solution. The post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, the filter is filtered, and the filter cake is washed with purified water until neutral and then dried. , the filter cake is transferred to a drying oven at a temperature of 70-80°C, and vacuum dried to constant weight to obtain a pretreated powder; in step A3, the amount ratio of the pretreated powder, N,N-dimethylformamide, and isocyanatepropyltriethoxysilane is 5g:50mL:3g, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, the filter cake is washed twice with anhydrous ethanol and then dried, and the filter cake is transferred to a drying oven at a temperature of 60-70°C, and vacuum dried to constant weight to obtain an enhanced powder.

[0028] Further, the binder is processed by the following steps:

[0029] B1. Add aluminum dihydrogen phosphate and purified water into a reactor and stir until the system is dissolved. The temperature of the reactor is raised to 70-80° C., polyethylene oxide is added into the reactor, and the mixture is stirred for 20-30 min to obtain an aluminum phosphate solution.

[0030] B2. Add the sodium silicate solution into the reactor and stir. Raise the temperature of the reactor to 60-70°C and stir for 20-30 minutes. Add hydroxypropyl methylcellulose into the reactor and stir until the system is dissolved. Add aluminum phosphate solution and 1,2-bistrimethoxysilylethane into the reactor and stir for 20-30 minutes to obtain a binder.

[0031] Furthermore, in step B1, the dosage ratio of the aluminum dihydrogen phosphate, purified water and polyethylene oxide is 3g:10mL:0.5g; in step B2, the dosage ratio of the sodium silicate solution, hydroxypropyl methylcellulose, aluminum phosphate solution and 1,2-bistrimethoxysilylethane is 100-120mL:3-5g:20-30mL:5-7g, the modulus of the sodium silicate solution is 2.0-2.2, and the solid content is 25-45%.

[0032] The present invention has the following beneficial effects:

[0033] 1. The method for preparing a metal mold based on steel sand 3D printing of the present invention comprises the following steps: reinforcing and modifying steel sand by reinforcing powder to prepare casting steel sand, and then reinforcing water glass with aluminum phosphate solution, hydroxypropyl methyl fiber and 1,2-bistrimethoxysilylethane to prepare a binder. The 3D printing device is used to print layer by layer according to the 3D model, and the shape and size of the mold can be very accurately controlled, so that it can be suitable for casting of castings with complex structures and high precision requirements. At the same time, by adjusting the printing parameters such as printing speed, layer thickness, and spraying amount of the binder, the internal porosity and density of the mold are accurately controlled, thereby improving the strength and toughness of the mold and reducing defects such as casting pores and slag inclusions. The metal mold of the present application selects metal sand as the base material, giving the metal mold a higher thermal conductivity, so that it can quickly conduct heat, thereby contributing to the uniform cooling and solidification of the metal liquid, reducing the stress and defects inside the casting, and improving the tissue density and mechanical properties of the casting, so that the metal mold is more suitable for the processing and preparation of large castings.

[0034] 2. The method for preparing metal casting molds based on steel sand 3D printing of the present invention comprises the following steps: coating the steel sand with mixed powder; the high hardness and thermal stability of nano-aluminum oxide and silicon carbide enable the casting mold to maintain good shape and dimensional stability during high-temperature pouring; yttrium oxide can improve the microstructure of the casting steel sand, thereby reducing pores and cracks, and improving the density and strength of the material; the lubricity of nano-boron nitride and the addition of silane coupling agent reduce the interfacial bonding force between the casting mold and the casting, which makes it easier to separate the casting mold from the casting after cooling, thereby improving the collapsibility; the mixed powder modifies the steel sand in the form of coating; the mixed powder forms a uniform on the surface of the steel sand due to its excellent mechanical properties and thermal stability. After the uniform coating layer is formed, the overall structural strength of the metal mold is enhanced, and the mold can better transfer and disperse stress when subjected to external force, promote a more uniform distribution of stress inside the metal mold, improve the cohesion of the metal mold, reduce the risk of stress concentration, and improve the overall performance and durability of the mold. Therefore, when the mold is subjected to pressure, the metal mold can better resist deformation and damage, and the compressive strength, shear strength and bending strength of the metal mold are improved. When preparing the metal mold, the mixed powder is evenly dispersed in the metal mold along with the steel sand. The nanostructure of the mixed powder can reduce the pores and defects in the metal mold, thereby reducing the gas generation, so that the metal mold can be promoted and applied in the processing of large-scale high-quality castings.

[0035] 3. The method for preparing a metal mold based on steel sand 3D printing of the present invention uses aluminum dihydrogen phosphate solution to strengthen water glass. The aluminum dihydrogen phosphate and sodium silicate react to form an aluminum phosphate silicate network structure, which has high strength. Polyethylene oxide and hydroxypropyl methylcellulose are used as additives to improve the fluidity and permeability of the binder, so that the binder can more easily penetrate between the steel sand particles to form a tighter bond and enhance the cohesive force of the binder. 1,2-bistrimethoxysilylethane is used as a coupling agent to improve the interface bonding between the inorganic binder and the steel sand, so that the bonding between the binder and the steel sand is tighter, and a firm bond is formed between the steel sand particles of the mold. The metal After the casting body is dried, the aluminum dihydrogen phosphate and sodium silicate in the binder further react with the curing agent to form a more stable chemical structure with higher thermal stability, which cooperates with the casting steel sand to further improve the overall strength of the metal casting, making it more durable. The polyethylene oxide and hydroxypropyl methylcellulose in the binder decompose in a high temperature environment and produce a small amount of gas. By controlling the dosage ratio of each component in the binder, the gas emission of the metal casting in a high temperature environment is reduced, thereby improving the casting quality of the casting. In addition, the decomposition of polyethylene oxide and hydroxypropyl methylcellulose in a high temperature environment cooperates with the casting steel sand to further improve the disintegration of the metal casting. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The modulus of the sodium silicate solution in the present application is 2.0-2.2, and the solid content is 25-45%; the polyethylene oxide is selected from Wuhan Jushun Chemical Co., Ltd., with a molecular weight of 1 million, density: apparent density 0.2-0.3kg / L, true density 1.15-1.22Kg / L, pH value is neutral (0.5wt% aqueous solution), and is completely soluble in water.

[0038] Example 1

[0039] This embodiment provides a method for preparing a metal casting mold based on steel sand 3D printing, comprising the following steps:

[0040] S1. Preparation of reinforced powder

[0041] Mix nano-aluminum oxide, nano-silicon carbide, nano-yttrium oxide and nano-boron nitride in a weight ratio of 8:2:2:2 and pass through a 150-mesh sieve to obtain a mixed powder;

[0042] Weigh: 100 g of mixed powder, 1000 mL of anhydrous ethanol, and 40 g of KH-540, add them to a reactor and stir, raise the temperature of the reactor to 50°C, add 100 mL of 0.2 mol / L sodium hydroxide solution to the reactor, and keep the reaction for 50 minutes. After the reaction is completed, lower the temperature of the reactor to room temperature, filter, wash the filter cake with purified water until it is neutral, and then drain it. Transfer the filter cake to a drying oven at a temperature of 70°C, and vacuum dry it to constant weight to obtain a pretreated powder;

[0043] Weigh: 100 g of pretreated powder and 1000 mL of N,N-dimethylformamide are added to a nitrogen-protected reactor and stirred. The temperature of the reactor is raised to 60°C. 60 g of isocyanatepropyltriethoxysilane is added to the reactor and the reaction is kept warm for 60 minutes. After the reaction is completed, the temperature of the reactor is lowered to room temperature and filtered. The filter cake is washed twice with anhydrous ethanol and then dried. The filter cake is transferred to a drying oven at a temperature of 60°C and vacuum dried to constant weight to obtain enhanced powder.

[0044] S2. Preparation of casting steel sand

[0045] Select carbon steel fine particles with a mesh size of 100 as steel grit;

[0046] Weigh: 10000 g of steel sand and 10 g of propylene glycol triacetate, add them into a reactor and stir, raise the temperature of the reactor to 75°C, add 60 g of reinforcing powder into the reactor in batches, keep warm and mix for 50 minutes, and obtain casting steel sand.

[0047] S3. Preparation of binder

[0048] Weigh: 30 g of aluminum dihydrogen phosphate and 100 mL of purified water, add them into a reactor and stir until the system is dissolved. The temperature of the reactor is raised to 70°C, 5 g of polyethylene oxide is added into the reactor, and the mixture is stirred for 20 min to obtain an aluminum phosphate solution.

[0049] Weigh: 1000 mL of sodium silicate solution is added to a reactor and stirred. The temperature of the reactor is raised to 60°C and stirred for 20 minutes. 30 g of hydroxypropyl methylcellulose is added to the reactor and stirred until the system is dissolved. 200 mL of aluminum phosphate solution and 50 g of 1,2-bistrimethoxysilylethane are added to the reactor and stirred for 20 minutes to obtain a binder, wherein the modulus of the sodium silicate solution is 2.0 and the solid content is 25%.

[0050] S4. Preparation of metal casting body

[0051] A sand mold 3D model is established according to the metal casting, and then the casting steel sand is filled in the working box of the sand mold 3D printing equipment, and the binder is filled in the binder storage tank. The sand mold 3D printing equipment is equipped with a piezoelectric nozzle and a set of sand spreaders, wherein the sand spreader is connected to the working line for laying the casting steel sand, and the piezoelectric nozzle is connected to the binder storage tank for spraying the binder. The negative pressure value is 2.3kPa, and the spraying amount of the binder is 9g / m 2 ;

[0052] According to the cross-sectional formation of the sand mold three-dimensional model, the sand paving system of the sand mold 3D printing equipment lays the casting steel sand on the printing platform to form a basic sand layer with a thickness of 0.2 mm. After the sand mold 3D printing equipment sprays the binder on the surface of the sand layer, it immediately sprays the casting steel sand and repeats the printing operation until the printing is completed to obtain a metal casting blank. Among them, the printing speed of the sand mold 3D printing equipment is 12s / layer and the molding efficiency is 55L / h.

[0053] S5. Preparation of metal casting mold

[0054] The metal casting mold body is placed in a drying oven, the temperature of the drying oven is raised to 120° C., and the temperature is kept for 10 minutes. The temperature of the drying oven is then lowered to room temperature to obtain a metal casting mold.

[0055] Example 2

[0056] This embodiment provides a method for preparing a metal casting mold based on steel sand 3D printing, comprising the following steps:

[0057] S1. Preparation of reinforced powder

[0058] Mix nano-aluminum oxide, nano-silicon carbide, nano-yttrium oxide and nano-boron nitride in a weight ratio of 9:2.5:2.5:2.5 and pass through a 150-mesh sieve to obtain a mixed powder;

[0059] Weigh: 100 g of mixed powder, 1000 mL of anhydrous ethanol, and 40 g of KH-540, add them to a reactor and stir, raise the temperature of the reactor to 55°C, add 100 mL of 0.25 mol / L sodium hydroxide solution to the reactor, and keep the reaction for 55 minutes. After the reaction is completed, lower the temperature of the reactor to room temperature, filter, wash the filter cake with purified water until it is neutral, and then drain it. Transfer the filter cake to a drying oven at a temperature of 75°C, and vacuum dry it to constant weight to obtain a pretreated powder;

[0060] Weigh: 100 g of pretreated powder and 1000 mL of N,N-dimethylformamide are added to a nitrogen-protected reactor and stirred. The temperature of the reactor is raised to 65°C. 60 g of isocyanatepropyltriethoxysilane is added to the reactor and the reaction is kept warm for 70 minutes. After the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, and the filter cake is washed twice with anhydrous ethanol and then dried. The filter cake is transferred to a drying oven at a temperature of 65°C and vacuum dried to constant weight to obtain enhanced powder.

[0061] S2. Preparation of casting steel sand

[0062] Select low-carbon steel fine particles with a mesh size of 120 mesh as steel grit;

[0063] Weigh: 10000 g of steel sand and 25 g of ethylene glycol diacetate, add into a reactor and stir, raise the temperature of the reactor to 80° C., add 70 g of reinforcing powder into the reactor in batches, keep warm and mix for 55 minutes, and obtain casting steel sand.

[0064] S3. Preparation of binder

[0065] Weigh: 30 g of aluminum dihydrogen phosphate and 100 mL of purified water, add them into a reactor and stir until the system is dissolved. The temperature of the reactor is raised to 75°C, 5 g of polyethylene oxide is added into the reactor, and the mixture is stirred for 25 minutes to obtain an aluminum phosphate solution.

[0066] Weigh: 1100 mL of sodium silicate solution is added to a reactor and stirred. The temperature of the reactor is raised to 65°C and stirred for 25 minutes. 40 g of hydroxypropyl methylcellulose is added to the reactor and stirred until the system is dissolved. 250 mL of aluminum phosphate solution and 60 g of 1,2-bistrimethoxysilylethane are added to the reactor and stirred for 25 minutes to obtain a binder, wherein the modulus of the sodium silicate solution is 2.1 and the solid content is 35%.

[0067] S4. Preparation of metal casting body

[0068] A sand mold 3D model is established according to the metal casting, and then the casting steel sand is filled in the working box of the sand mold 3D printing equipment, and the binder is filled in the binder storage tank. The sand mold 3D printing equipment is equipped with a piezoelectric nozzle and a set of sand spreaders, wherein the sand spreader is connected to the working line for laying the casting steel sand, and the piezoelectric nozzle is connected to the binder storage tank for spraying the binder. The negative pressure value is 2.4kPa, and the spraying amount of the binder is 7g / m 2 ;

[0069] According to the cross-sectional formation of the sand mold three-dimensional model, the sand paving system of the sand mold 3D printing equipment lays the casting steel sand on the printing platform to form a basic sand layer with a thickness of 0.35 mm. After the sand mold 3D printing equipment sprays the binder on the surface of the sand layer, it immediately sprays the casting steel sand and repeats the printing operation until the printing is completed to obtain a metal casting blank. Among them, the printing speed of the sand mold 3D printing equipment is 16s / layer, and the molding efficiency is 58L / h.

[0070] S5. Preparation of metal casting mold

[0071] The metal casting mold body is placed in a drying oven, the temperature of the drying oven is raised to 150° C., and the temperature is kept for 25 minutes. The temperature of the drying oven is then lowered to room temperature to obtain a metal casting mold.

[0072] Example 3

[0073] This embodiment provides a method for preparing a metal casting mold based on steel sand 3D printing, comprising the following steps:

[0074] S1. Preparation of reinforced powder

[0075] Mix nano-aluminum oxide, nano-silicon carbide, nano-yttrium oxide and nano-boron nitride in a weight ratio of 10:3:3:3 and pass through a 150-mesh sieve to obtain a mixed powder;

[0076] Weigh: 100 g of mixed powder, 1000 mL of anhydrous ethanol, and 40 g of KH-540, add them to a reactor and stir, raise the temperature of the reactor to 60°C, add 100 mL of 0.3 mol / L sodium hydroxide solution to the reactor, and keep the reaction for 60 minutes. After the reaction is completed, lower the temperature of the reactor to room temperature, filter, wash the filter cake with purified water until it is neutral, and then drain it. Transfer the filter cake to a drying oven at a temperature of 80°C, and vacuum dry it to constant weight to obtain a pretreated powder;

[0077] Weigh: 100 g of pretreated powder and 1000 mL of N,N-dimethylformamide are added to a nitrogen-protected reactor and stirred. The temperature of the reactor is raised to 70°C. 60 g of isocyanatepropyltriethoxysilane is added to the reactor and the reaction is kept warm for 80 minutes. After the reaction is completed, the temperature of the reactor is lowered to room temperature, filtered, and the filter cake is washed twice with anhydrous ethanol and then dried. The filter cake is transferred to a drying oven at a temperature of 70°C and vacuum dried to constant weight to obtain enhanced powder.

[0078] S2. Preparation of casting steel sand

[0079] Select stainless steel fine particles with a mesh size of 140 mesh as steel grit;

[0080] Weigh: 10000 g of steel sand and 40 g of propylene glycol monoacetate, add into a reactor and stir, raise the temperature of the reactor to 85°C, add 100 g of reinforcing powder into the reactor in batches, keep warm and mix for 60 minutes, and obtain casting steel sand.

[0081] S3. Preparation of binder

[0082] Weigh: 30 g of aluminum dihydrogen phosphate and 100 mL of purified water, add them into a reactor and stir until the system is dissolved. The temperature of the reactor is raised to 80°C, 5 g of polyethylene oxide is added into the reactor, and the mixture is stirred for 30 min to obtain an aluminum phosphate solution.

[0083] Weigh: 1200 mL of sodium silicate solution is added to a reactor and stirred. The temperature of the reactor is raised to 70°C and stirred for 30 minutes. 50 g of hydroxypropyl methylcellulose is added to the reactor and stirred until the system is dissolved. 300 mL of aluminum phosphate solution and 70 g of 1,2-bistrimethoxysilylethane are added to the reactor and stirred for 30 minutes at a temperature of 40 °C to obtain a binder, wherein the modulus of the sodium silicate solution is 2.2 and the solid content is 45%.

[0084] S4. Preparation of metal casting body

[0085] A sand mold 3D model is established according to the metal casting, and then the casting steel sand is filled in the working box of the sand mold 3D printing equipment, and the binder is filled in the binder storage tank. The sand mold 3D printing equipment is equipped with a piezoelectric nozzle and a set of sand spreaders, wherein the sand spreader is connected to the working line for laying the casting steel sand, and the piezoelectric nozzle is connected to the binder storage tank for spraying the binder. The negative pressure value is 2.6kPa, and the spraying amount of the binder is 6g / m 2 ;

[0086] According to the cross-sectional formation of the sand mold three-dimensional model, the sand paving system of the sand mold 3D printing equipment lays the casting steel sand on the printing platform to form a basic sand layer with a thickness of 0.5 mm. After the sand mold 3D printing equipment sprays the binder on the surface of the sand layer, it immediately sprays the casting steel sand and repeats the printing operation until the printing is completed to obtain a metal casting blank. Among them, the printing speed of the sand mold 3D printing equipment is 20s / layer and the molding efficiency is 60L / h.

[0087] S5. Preparation of metal casting mold

[0088] The metal casting mold body is placed in a drying oven, the temperature of the drying oven is raised to 180°C, and the temperature is kept for 40 minutes. The temperature of the drying oven is then lowered to room temperature to obtain a metal casting mold.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 3 is that the steel sand in step S2 is used as the casting steel sand in step S4.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 3 is that the reinforcing powder in step S2 is replaced by the mixed powder in step S1.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 3 is that no aluminum phosphate solution is added to the binder in step S3.

[0095] Comparative Example 4

[0096] The difference between this comparative example and Example 3 is that step S5 is eliminated, and the metal casting mold body in step S4 is used as the metal casting mold.

[0097] Performance Test:

[0098] The room temperature mechanical properties and high temperature properties of the metal castings prepared in Examples 1-3 and Comparative Examples 1-4 were measured with reference to the standard GB / T 43365-2023 "Sand Mold Properties Test Method for Additive Manufacturing Metal Castings", wherein the room temperature mechanical properties include compressive strength, shear strength and flexural strength, and the high temperature properties include high temperature compressive strength, high temperature expansion rate and gas evolution;

[0099] The metal casting was prepared by pouring molten steel into the mold cavity of the metal mold prepared by Examples 1-3 and Comparative Examples 1-4, and then the residual strength of the metal mold was measured, wherein the residual strength was measured by referring to the standard GB / T43365-2023 "Sand Mold Performance Test Method for Additive Manufacturing Metal Castings" to measure the compressive strength of the sample;

[0100] The specific test results are shown in Table 1 below.

[0101] Table 1-Performance test data of samples

[0102]

[0103] Data Analysis:

[0104] A comparative analysis of the data in Table 1 above shows that the room-temperature compressive strength of the metal mold prepared by the present invention reaches 9.96 MPa, the room-temperature shear strength reaches 6.78 MPa, the room-temperature flexural strength reaches 7.12 MPa, the high-temperature compressive strength reaches 7.03 MPa, the high-temperature expansion rate is reduced to 0.15%, the gas evolution is reduced to 3.4 mL / g, and the residual strength is reduced to 0.56 MPa. All performance parameters are better than those of the comparative example, which shows that the present invention prepares casting steel sand by reinforcing and modifying steel sand with reinforcing powder, and then prepares a binder with aluminum phosphate solution, hydroxypropyl methyl fiber and 1,2-bistrimethoxysilylethane reinforced water glass, prepares a metal casting blank by 3D printing equipment, and then performs drying treatment, which not only effectively improves the room-temperature mechanical properties and high-temperature properties of the metal mold, but also improves the disintegration of the metal mold, so that the metal mold can be widely used in the processing of large castings, and the application range of the metal mold is broadened.

[0105] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0106] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0107] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a metal casting mold based on steel sand 3D printing, characterized in that: The following steps are involved: S1. Establish a sand mold three-dimensional model according to the metal casting, then fill the casting steel sand into the working box of the sand mold 3D printing equipment, and fill the binder into the binder storage tank; S2. According to the cross-section formation of the sand mold three-dimensional model, the sand paving system of the sand mold 3D printing equipment lays the casting steel sand on the printing platform to form a basic sand layer with a thickness of 0.2-0.5mm; S3, the sand mold 3D printing equipment sprays the binder on the surface of the sand layer and starts printing layer by layer; S4, repeat step S3 until the printing is completed, obtain the metal casting blank, and dry it to obtain the metal casting mold.

2. A method for preparing a metal casting mold based on steel sand 3D printing according to claim 1, characterized in that: In step S3, the printing speed of the sand mold 3D printing device is 12-20s / layer, the molding efficiency is 55-60L / h, the sand mold 3D printing device is equipped with a piezoelectric nozzle and a set of sand spreaders, wherein the sand spreader is connected to the working line for laying the casting steel sand, the layer thickness of the sand layer is 0.2-0.5mm, the piezoelectric nozzle is connected to the binder storage tank for spraying the binder, the negative pressure value is 2.3-2.6kPa, and the spraying amount of the binder is 6-9g / m 2 .

3. The method for preparing a metal mold based on steel sand 3D printing according to claim 1, characterized in that: The drying method in step S4 is as follows: the metal casting mold body is placed in a drying oven, the temperature of the drying oven is increased to 120-180° C., the temperature is kept for 10-40 minutes, and the temperature of the drying oven is cooled to room temperature to obtain a metal casting mold.

4. The method for preparing a metal casting mold based on steel sand 3D printing according to claim 1, characterized in that: The preparation method of casting steel sand is as follows: adding steel sand and curing aid into a reactor and stirring, raising the temperature of the reactor to 75-85°C, adding reinforcing powder into the reactor in batches, and mixing for 50-60 minutes to obtain casting steel sand.

5. The method for preparing a metal casting mold based on steel sand 3D printing according to claim 4, characterized in that: The dosage ratio of the steel sand, the curing aid and the reinforcing powder is 1000g:1-4g:6-10g, the curing aid is one or more of propylene glycol triacetate, propylene glycol diacetate, propylene glycol monoacetate, ethylene glycol diacetate, ethylene glycol monoacetate, diethylene glycol diacetate, and diethylene glycol monoacetate, the steel sand is any one of carbon steel, low carbon steel, and stainless steel, and the mesh size is 100-140 meshes.

6. The method for preparing a metal casting mold based on steel sand 3D printing according to claim 4, characterized in that: The reinforced powder is obtained by processing the following steps: A1. Evenly mix nano-aluminum oxide, nano-silicon carbide, nano-yttrium oxide and nano-boron nitride to obtain a mixed powder; A2, adding the mixed powder, anhydrous ethanol and KH-540 into the reactor and stirring, raising the temperature of the reactor to 50-60°C, adding alkali solution into the reactor, keeping the temperature for reaction for 50-60min, and post-treating to obtain the pretreated powder; A3. Add the pretreated powder and N,N-dimethylformamide into a nitrogen-protected reactor and stir. Raise the temperature of the reactor to 60-70°C. Add isocyanatepropyltriethoxysilane into the reactor and keep the reaction temperature for 60-80 minutes. Post-treat to obtain the enhanced powder.

7. The method for preparing a metal casting mold based on steel sand 3D printing according to claim 6, characterized in that: In step A1, the weight ratio of nano-alumina, nano-silicon carbide, nano-yttrium oxide, and nano-boron nitride is 8-10:2-3:2-3:2-3; in step A2, the amount ratio of the mixed powder, anhydrous ethanol, KH-540, and alkali solution is 5g:50mL:2g:5mL, and the alkali solution is 0.2-0.3mol / L sodium hydroxide solution; in step A3, the amount ratio of the pretreated powder, N,N-dimethylformamide, and isocyanatepropyltriethoxysilane is 5g:50mL:3g.

8. The method for preparing a metal casting mold based on steel sand 3D printing according to claim 1, characterized in that: The adhesive is processed by the following steps: B1. Add aluminum dihydrogen phosphate and purified water into a reactor and stir until the system is dissolved. The temperature of the reactor is raised to 70-80° C., polyethylene oxide is added into the reactor, and the mixture is stirred for 20-30 min to obtain an aluminum phosphate solution. B2. Add the sodium silicate solution into the reactor and stir. Raise the temperature of the reactor to 60-70°C and stir for 20-30 minutes. Add hydroxypropyl methylcellulose into the reactor and stir until the system is dissolved. Add aluminum phosphate solution and 1,2-bistrimethoxysilylethane into the reactor and stir for 20-30 minutes to obtain a binder.

9. The method for preparing a metal casting mold based on steel sand 3D printing according to claim 8, characterized in that: In step B1, the dosage ratio of the aluminum dihydrogen phosphate, purified water and polyethylene oxide is 3g:10mL:0.5g; in step B2, the dosage ratio of the sodium silicate solution, hydroxypropyl methylcellulose, aluminum phosphate solution and 1,2-bistrimethoxysilylethane is 100-120mL:3-5g:20-30mL:5-7g, the modulus of the sodium silicate solution is 2.0-2.2, and the solid content is 25-45%.

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