Rapid casting development method based on 3D printing model and fine shell roasting casting process

Abstract

The invention belongs to the technical field of casting part processing, and particularly relates to a rapid casting development method based on a 3D printing model and a fine shell roasting casting process, and the rapid casting development method comprises the following steps: S1, casting three-dimensional drawing design; s2, performing 3D printing on the model; s3, preparing a coating layer; s4, roasting to prepare a shell; s5, modeling is carried out; s6, pouring is conducted; and S7, casting forming. According to the invention, required casting products can be quickly developed and produced without opening the mold, and the production requirements of high-end casting products with the requirements of multiple varieties, small batch, short period, low cost, high quality, complex structure and the like are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of casting processing, and in particular relates to a rapid casting development method based on a 3D printing model and a refined shell roasting casting process. Background Art

[0002] In recent years, with the increasing pace of equipment casting upgrades, manufacturing industries such as aerospace, automotive, and shipbuilding have increasingly demanded casting process design for complex castings. Traditional casting methods, due to high mold costs, long production cycles, and difficulty adapting to complex shape design requirements, are gradually failing to meet market demands. 3D printing, as a new manufacturing technology, offers the advantages of eliminating the need for molds, low cost, and high speed. It also has low sensitivity to casting structure, eliminates the need for mold making, and offers freedom in parting. This increases the flexibility of casting process design and is gradually replacing the production method of using molds to create models. However, integrating and matching 3D printed models with existing casting processes to rapidly develop the required casting products still faces resistance, which limits its application in precision casting.

[0003] At the same time, when the casting process is combined with the 3D printing model for method development, the requirements for the casting coating used in the casting process are higher due to the variety and complexity of the structure of the 3D printing model. In the field of casting coatings, invention patent CN104493076B discloses a calcined quartz powder casting coating and its preparation method, which is 80-100 parts of quartz powder, 0-50 parts of corundum powder, 0-100 parts of mullite powder, 0-30 parts of bauxite powder, 0-100 parts of zircon powder, 0-10 parts of flake graphite, 0-20 parts of earthy graphite powder, 0-5 parts of red iron oxide, 6-8 parts of suspending agent, 5-8 parts of resin, and an appropriate amount of solvent. The suspending agent, resin and an appropriate amount of solvent are added into a blender and stirred for 10 minutes. -30 minutes, then add quartz powder, corundum powder, mullite powder, bauxite powder, zircon powder, flake graphite, earthy graphite powder, and red iron oxide, stir for 30-60 minutes, add an appropriate amount of solvent to adjust to a suitable specific gravity, and thus prepare a casting coating; the casting coating of the invention may further oxidize under high temperature conditions due to the presence of flake graphite and earthy graphite powder, resulting in a decrease in coating stability, especially when used in the manufacture of complex structure castings, there may be uneven flow coating, which not only affects the sintering and peeling effect, but also causes defects in the castings. Summary of the Invention

[0004] In response to existing technical problems, the present invention provides a rapid casting development method based on 3D printing models and a refined shell roasting casting process. This method can rapidly develop and produce the required castings without the need for molds, meeting the demand for high-end casting production requiring diverse varieties, small batches, short cycle times, low costs, high quality, and complex structures.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a rapid casting development method based on a 3D printing model and a refined shell roasting casting process, the rapid casting development method comprising the following steps:

[0007] S1: 3D drawing design of castings;

[0008] S2: 3D printing model: 3D printing model based on the three-dimensional drawing of S1;

[0009] S3: coating layer preparation: the 3D printed model obtained in step S2 is subjected to shaping, coating, and drying, and the operation is repeated to obtain a coating layer;

[0010] S4: calcining and shell making: placing the 3D printed model with the coating layer obtained in step S3 in a calcining furnace with a fume exhaust system to calcine the shell to obtain a refined shell;

[0011] S5: shaping: shaping the refined shell baked in step S4;

[0012] S6: Pouring: pouring molten metal into the mold in step S5 under vacuum negative pressure;

[0013] S7: Casting: After step S6, the casting is obtained by turning the box, removing the sand, and removing the pouring head.

[0014] In some embodiments of the present invention, in step S1, when designing the three-dimensional drawing of the casting, the size shrinkage of the 3D printed model by 0.2-0.8% and the size shrinkage of the casting by 0.8-2.5% are added to the three-dimensional drawing of the casting.

[0015] In some embodiments of the present invention, in step S2, the printer for 3D printing the model is an FDM fused deposition model 3D printer, and the nozzle diameter of the printer is 0.25 to 0.8 mm.

[0016] In some embodiments of the present invention, in step S2, the material of the 3D printing model is a thermoplastic material.

[0017] Preferably, the thermoplastic material is at least one of acrylonitrile-butadiene-styrene copolymer, polylactic acid, thermoplastic polyurethane, and polyethylene terephthalate copolyester.

[0018] Further preferably, the diameter of the thermoplastic material wire is ≥1.75 mm.

[0019] Preferably, the parameters of the printer are: a printing layer height of 0.16 to 0.40 mm, a filling density inside the model of 2 to 38%, and a printing movement speed of 30 to 500 mm / s.

[0020] The present invention selects 3D printing materials, print nozzles, and sets printing parameters based on the characteristics of the refined shell roasting casting process, product dimensions, model strength requirements, model surface roughness requirements, and the principle of avoiding residual defects in the model roasting. Then, an FDM fused deposition modeling 3D printer is used to print the model. By selecting specific materials and setting parameters, the surface quality of the 3D printed model is improved, the strength is higher, the density is lower, the printing efficiency is effectively improved, and the roasting residue of the 3D printed model is reduced.

[0021] In some embodiments of the present invention, in step S3, the coating comprises a top layer coating and a back layer coating.

[0022] In some embodiments of the present invention, in step S3, the surface coating comprises the following raw materials in parts by weight: 60 to 80 parts of aggregate, 1 to 5 parts of polyethylene glycol, 2 to 4 parts of sodium bentonite, 2 to 5 parts of attapulgite, 1 to 3 parts of rosin resin, 3 to 6 parts of magnesium aluminum silicate, 1 to 3 parts of additives and 15 to 30 parts of solvent.

[0023] In some embodiments of the present invention, the preparation steps of the topcoat are as follows:

[0024] Add polyethylene glycol, rosin resin and magnesium aluminum silicate into the solvent, stir at 20-30° C. for 10-30 minutes, then add aggregate, sodium bentonite, attapulgite and additives and disperse evenly to obtain the product.

[0025] In some embodiments of the present invention, the aggregate is quartz powder.

[0026] In some embodiments of the present invention, the solvent is water or methanol.

[0027] In some embodiments of the present invention, the additive is prepared by the following steps:

[0028] (1) Under an inert atmosphere, 1,6-hexanediamine and methoxypolyethylene glycol chloride are sequentially added to a solvent, stirred evenly, and then a catalyst is added. The temperature is raised to 80-85°C and the reaction is carried out for 24-26 hours. The modifier is obtained by filtration and rotary evaporation;

[0029] (2) Adding graphite oxide to N,N-dimethylformamide, ultrasonically dispersing until uniform, adding stearic acid, the modifier and catalyst of step (1), raising the temperature to 80-90° C. and reacting for 14-16 hours to obtain an additive. In some embodiments of the present invention, in step (1), the mass ratio of 1,6-hexanediamine to methoxypolyethylene glycol chloride is (0.2-0.35):1.

[0030] In some embodiments of the present invention, in step (2), the mass ratio of the graphite oxide, stearic acid and modifier is 1: (0.5-0.8): (0.2-0.5).

[0031] Preferably, the graphite oxide is graphite oxide flakes.

[0032] The present invention obtains a functional modifier by adding 1,6-hexanediamine and methoxypolyethylene glycol chloride to carry out a nucleophilic substitution reaction. The modifier reacts with the active groups carboxyl and stearic acid on the surface of graphite oxide to form a bond and coat the surface of the graphite oxide. On the one hand, the stability of the graphite oxide at high temperatures is improved, and the obtained surface coating is less likely to swell and crack. On the other hand, the introduction of long carbon chains and ether bonds may balance the dispersibility and fluidity of various components of the casting coating. In combination with the unique lubricity of graphite oxide, the obtained casting surface is smooth, with clear edges and corners and no defects, thereby significantly improving the quality of the casting, reducing the scrap rate, and lowering the cost.

[0033] In some embodiments of the present invention, the back layer coating is an aggregate with a coating mesh size of 10 to 200 meshes and a refractoriness of ≥1700°C.

[0034] In some embodiments of the present invention, in step S3, the steps of applying the coating are as follows: dipping the assembled 3D printed model in the surface coating, drying, applying the back coating, and drying.

[0035] Preferably, the coating operation is repeated until the thickness of the top coating is 0.2 to 0.6 mm and the thickness of the back coating is 2.5 to 7.5 mm, and then the coating is sealed and dried.

[0036] Preferably, the drying is carried out in a drying room at 35-60° C. and humidity ≤28%.

[0037] In some embodiments of the present invention, in step S4, the operation of firing the shell is to liquefy the 3D printed model at 220-320°C and then porcelainize the coating layer shell at 800-1100°C.

[0038] Preferably, in step S4, the refined shell baking temperature curve is set as follows: in the low temperature stage, the temperature is increased from 25-30°C to 220-320°C, kept warm for 20 minutes, the furnace door is opened, and the residue after the mold is heated and melted is taken out; in the high temperature stage, the temperature is continued to be heated to 800-1100°C, kept warm for 20 minutes to porcelainize the coating layer shell.

[0039] Based on the characteristics of the 3D printed model shell firing process, the model firing residue treatment, the requirements for the porcelainization of the shell coating layer, and the shell quality assurance principles, the applicant selected the shell firing furnace, set the shell firing temperature curve, and pre-treated the model before firing. Then, the applicant controlled the heating temperature at different time periods to liquefy the 3D printed model and overflow the shell. The applicant continued to heat the shell firing to porcelainize the coating layer.

[0040] Preferably, in step S4, before the mold is fired, the coating layer at the pouring and rising openings on the workpiece is removed to expose the mold, and overflow openings are drilled out with a drill for locations that are not easily liquefied and overflow.

[0041] In some embodiments of the present invention, in step S5, the molding is to place the refined shell baked in S4 into a sand box, add molding sand, and vibrate it.

[0042] In some embodiments of the present invention, in step S5, the molding sand is artificial ceramsite sand.

[0043] Preferably, the molding sand is a precious sand with an AlO content of ≥70% and a particle size of 20-40 meshes.

[0044] Preferably, the molding sand is recycled after being turned over.

[0045] In some embodiments of the present invention, in step S6, the specific operation is to start pumping negative pressure 3 to 5 minutes before pouring the molten metal, control the pouring negative pressure at -0.03 to -0.045 MPa, maintain the pressure for 5 to 20 minutes, and keep warm for 3 to 8 hours.

[0046] When pouring molten metal, the present invention adopts vacuum negative pressure pouring in the sand box. The ladle used for pouring the molten metal is selected to control the pouring flow, speed, slag avoidance, and preheating, and a neutral or alkaline ramming material matching the pH value of the molten metal is selected to tie the ladle lining. Before the molten metal is discharged from the furnace, the ladle lining is preheated and baked to a temperature of ≥800°C. When using a shaking ladle for pouring, slag should be removed first, and slag-avoiding pouring is performed in the form of a teapot bag.

[0047] Compared with the traditional casting development and production methods that require molds, the present invention successfully achieves the rapid and low-cost development of the required casting products without the need for molds. It has the advantages of no need for molds, low cost, and high speed, and will gradually replace the production method of using molds to make models. At the same time, the use of 3D printing models can make models in an integrated and integral manner, avoiding parting problems caused by the complex shape and structure of the product; the use of the refined shell roasting casting process can completely solve the various unique defects of castings produced by the solid mold casting process, and can greatly improve the quality and grade of various types of steel castings, stainless steel parts, ductile iron parts, and non-ferrous metal castings. Therefore, combining 3D printing models with the refined shell roasting casting process can meet the needs of high-end casting product production with requirements such as multiple varieties, small batches, short cycles, low costs, high quality, and complex structures, thereby improving production efficiency and product quality.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The present invention combines 3D printing models with fine shell roasting casting technology, which can meet the production needs of high-end casting products with requirements such as multiple varieties, small batches, short cycles, low costs, high quality, and complex structures, thereby improving production efficiency and product quality.

[0050] (2) The present invention selects 3D printing materials, print nozzles and sets printing parameters based on the characteristics of the fine shell roasting casting process, product dimensions, model strength requirements, model surface roughness requirements, and the principle of avoiding residual defects in the model roasting. Then, an FDM fused deposition model 3D printer is used to print the model. The selection of specific materials and the setting of parameters make the surface quality of the 3D printed model better, the strength higher, the density lower, the printing efficiency effectively improved, and the roasting residue of the 3D printed model reduced.

[0051] (3) The present invention obtains a functional modifier by adding 1,6-hexanediamine and methoxypolyethylene glycol chloride to carry out a nucleophilic substitution reaction. The modifier reacts with the active groups on the surface of graphite oxide and stearic acid to coat the surface of graphite oxide. On the one hand, the stability of the graphite oxide at high temperatures is improved, so that the obtained surface coating is not prone to swelling and cracking. On the other hand, the introduction of long carbon chains and ether bonds may balance the dispersibility and fluidity of the various components of the casting coating. With the synergistic effect of the unique lubricity of graphite oxide, the surface of the obtained casting is smooth, with clear edges and corners and zero defects, which significantly improves the quality of the casting, reduces the scrap rate, and reduces the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A simplified process flow diagram for developing a method for rapid casting;

[0053] Figure 2This is a time cycle comparison chart between Example 1 and conventional mold manufacturing + casting. DETAILED DESCRIPTION

[0054] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples are illustrative of the present invention and are intended only to illustrate the present invention, not to limit the present invention. Other combinations and various modifications within the scope of the present invention may be made without departing from the spirit or scope of the present invention.

[0055] Unless otherwise specified, the relevant raw materials used in the following specific embodiments can be purchased from the market, wherein the polyethylene glycol used is PEG600, the number average molecular weight of the methoxy polyethylene glycol chloride used is 550; the metal liquid used is aluminum alloy; the graphite oxide used is oxidized flake graphite with a particle size of 1000 mesh.

[0056] Unless otherwise specified, the post-processing operations such as "filtration", "rotary evaporation", "drying", and "sealing" used in the following specific embodiments can be freely selected by those skilled in the art, and the present invention does not limit them.

[0057] Preparation Example 1

[0058] The preparation steps of the additive are as follows:

[0059] (1) Under nitrogen atmosphere, 1.5 g of 1,6-hexanediamine and 5 g of methoxypolyethylene glycol chloride were added to 80 mL of acetonitrile in sequence and stirred evenly. Then, 0.15 g of potassium carbonate and 0.1 g of potassium iodide were added. The temperature was raised to 82°C and the reaction was continued for 25 h. The modifier was obtained by filtration and rotary evaporation.

[0060] (2) 5 g of graphite oxide was added to 50 mL of toluene and ultrasonically dispersed until uniform. 3 g of stearic acid, 1.8 g of modifier and 10 g of dicyclohexylcarbodiimide were added. The temperature was raised to 85° C. and the mixture was reacted for 15 h. The mixture was filtered and dried to obtain the additive.

[0061] Preparation Example 2

[0062] The preparation steps of the additive are the same as those in Preparation Example 1, except that the amount of stearic acid added in step (2) is 4.5 g.

[0063] Preparation Example 3

[0064] The preparation steps of the additive are the same as those in Preparation Example 1, except that the amount of the modifier added in step (2) is 3.7 g.

[0065] Preparation Example 4

[0066] The preparation steps of the additive are as follows:

[0067] 5 g of graphite oxide was added to 50 mL of toluene and ultrasonically dispersed until uniform. 3 g of stearic acid, 1.8 g of 1,6-hexanediamine and 10 g of dicyclohexylcarbodiimide were added. The temperature was raised to 85° C. and the reaction was carried out for 15 h. The additive was obtained by filtering and drying.

[0068] Preparation Example 5

[0069] The preparation steps of the surface coating are as follows, in parts by weight:

[0070] Add 3 parts of polyethylene glycol, 2 parts of rosin resin and 4.5 parts of magnesium aluminum silicate to 20 parts of methanol, stir at 25°C for 20 minutes, then add 70 parts of quartz powder, 3 parts of sodium bentonite, 3.5 parts of attapulgite and 2 parts of additives and disperse until uniform.

[0071] The additives used were obtained from Preparation Example 1.

[0072] Preparation Example 6

[0073] The preparation steps of the surface coating are as follows, in parts by weight:

[0074] Add 1 part of polyethylene glycol, 1 part of rosin resin and 3 parts of magnesium aluminum silicate to 15 parts of methanol, stir at 30°C for 10 minutes, then add 60 parts of quartz powder, 2 parts of sodium bentonite, 2 parts of attapulgite and 1 part of additive and disperse until uniform.

[0075] The additives used were obtained from Preparation Example 1.

[0076] Preparation Example 7

[0077] The preparation steps of the surface coating are as follows, in parts by weight:

[0078] Add 5 parts of polyethylene glycol, 3 parts of rosin resin and 6 parts of magnesium aluminum silicate to 30 parts of methanol, stir at 20°C for 30 minutes, then add 80 parts of quartz powder, 4 parts of sodium bentonite, 5 parts of attapulgite and 3 parts of additives and disperse until uniform.

[0079] The additives used were obtained from Preparation Example 1.

[0080] Preparation Example 8

[0081] The preparation steps of the surface coating are the same as those in Preparation Example 5, except that the additives used are obtained from Preparation Example 2.

[0082] Preparation Example 9

[0083] The preparation steps of the surface coating are the same as those in Preparation Example 5, except that the additives used are obtained from Preparation Example 3.

[0084] Preparation Example 10

[0085] The preparation steps of the surface coating are the same as those in Preparation Example 5, except that the additives used are obtained from Preparation Example 4.

[0086] Preparation Example 11

[0087] The preparation steps of the back layer coating are as follows, in parts by weight:

[0088] 50 parts of silica sol (with a silicon dioxide content of 30%) and 70 parts of mullite powder (with a particle size of 150 meshes) are stirred and mixed until uniform.

[0089] The following performance tests were performed on the above Preparation Examples 5-10. The specific test results are shown in Table 1:

[0090] Performance testing:

[0091] (1) Flow coating performance: Referring to CN108526388B, the above-mentioned coatings were subjected to flow coating performance test according to the standard JB / T 3998-1999, and the flow coating grade was evaluated;

[0092] (2) Anti-cracking performance: The above coatings were placed on a standard sand sample. The surface is evenly coated and dried at 100°C for 1 hour, then cooled naturally and the coating surface is observed to see if there are any cracks.

[0093] Table 1

[0094] project Flow coating performance (grade) Crack resistance (whether it cracks) Preparation Example 5 9～10 no Preparation Example 6 9～10 no Preparation Example 7 9～10 no Preparation Example 8 8～9 yes Preparation Example 9 7～8 yes Preparation Example 10 5～6 no

[0095] As shown in Table 1, the casting coatings obtained in Preparation Examples 5 to 7 have excellent flow coating performance and crack resistance.

[0096] Comparison of Preparation Examples 8 and 9 with Preparation Example 5 shows that when the amount of stearic acid and modifier added changes, the dispersion and fluidity of the additives in the system are affected, resulting in a decrease in the performance of the casting coating. At the same time, in Preparation Example 8, the molecular chains are entangled and agglomerated, which affects the dispersion of the components of the system and the balance of the mobile phase. After the casting coating is formed, the surface cracks due to unevenness. In Preparation Example 9, the stability of the casting coating suspension system is affected, and the flow coating performance is reduced due to the influence of the system viscosity.

[0097] From the comparison between Preparation Example 10 and Preparation Example 5, it can be seen that when the modifier is replaced with an equal amount of 1,6-hexanediamine to prepare the additive, the three-dimensional network structure formed by the casting coating has insufficient resistance to shear damage and its dispersibility is greatly reduced, which in turn affects the flatness and stability of the casting coating, and the flow coating performance and crack resistance are both reduced.

[0098] Example 1

[0099] A rapid casting development method based on a 3D printing model and a refined shell roasting casting process, characterized in that the rapid casting development method comprises the following steps:

[0100] S1: 3D drawing design of castings: When designing the 3D drawing of castings, the dimensional shrinkage of the 3D printed model by 0.2-0.8% and the dimensional shrinkage of the casting by 0.8-2.5% are added to the 3D drawing of castings;

[0101] S2: 3D printing model: The model was 3D printed according to the 3D drawing of S1. The specific conditions were: the printer was an FDM fused deposition model 3D printer, the printer nozzle diameter was 0.5mm, the material of the 3D printing model was acrylonitrile-butadiene-styrene copolymer with a wire diameter of 2mm, the printing layer height was 0.3mm, the model internal filling density was 20%, and the printing movement speed was 300mm / s;

[0102] S3: Preparation of coating layer: The 3D printed model obtained in step S2 is formed, and then the formed 3D printed model is dipped in the top layer coating (obtained in Preparation Example 5), dried in a drying room at 50°C and 28% humidity, and then coated in the back layer coating (obtained in Preparation Example 11), and dried in a drying room at 50°C and 28% humidity. This process is repeated until the top layer coating thickness reaches 0.4 mm and the back layer coating thickness reaches 5 mm. The coating layer is then sealed and dried to obtain the coating layer.

[0103] S4: Firing and shell making: The 3D printed model with the coating layer obtained in step S3 is pre-treated (the coating layer at the pouring riser on the workpiece is removed to expose the model, and an overflow port is drilled out with a drill bit) and then placed in a baking furnace with a smoke exhaust system. The temperature is raised from 28°C to 300°C to liquefy the 3D printed model, and the temperature is kept at this temperature for 20 minutes. The furnace door is opened, and the residue after the model is heated and melted is taken out. The temperature is then raised to 1000°C at the same heating rate and kept at this temperature for 20 minutes to porcelainize the coating layer and obtain a refined shell.

[0104] S5: Shaping: The refined shells calcined in step S4 are placed in a sand box, and Al O content ≥ 70% and 30 mesh granularity gemstone sand is added and compacted to obtain a shape;

[0105] S6: Pouring: Start pumping negative pressure 5 minutes before pouring the molten metal, control the pouring negative pressure at -0.04MPa, maintain pressure for 15 minutes, and keep warm for 5 hours.

[0106] S7: Casting: After step S6, the casting is obtained by turning the box, shaking out the sand and recovering the molding sand, and removing the pouring head.

[0107] The process flow diagram of this embodiment 1 is as follows Figure 1 The method has a short cycle and the obtained casting products are of high quality, with smooth casting surface, clear edges and corners and zero defects.

[0108] The above is only a preferred embodiment of the present invention and does not limit the present application in any form. Although the present application is disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any technician familiar with this profession, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent implementation cases. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution.

Claims

1. A rapid casting development method based on 3D printing model and refined shell roasting casting process, characterized in that: The rapid casting development method comprises the following steps: S1: 3D drawing design of castings; S2: 3D printing model: 3D printing model based on the three-dimensional drawing of S1; S3: coating layer preparation: the 3D printed model obtained in step S2 is subjected to shaping, coating, and drying, and the operation is repeated to obtain a coating layer; S4: calcining and shell making: placing the 3D printed model with the coating layer obtained in step S3 in a calcining furnace with a fume exhaust system to calcine the shell to obtain a refined shell; S5: shaping: shaping the refined shell baked in step S4; S6: Pouring: pouring molten metal into the mold in step S5 under vacuum negative pressure; S7: Casting: After step S6, the casting is obtained by turning the box, removing the sand, and removing the pouring head.

2. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 1 is characterized in that: In step S1, when designing the three-dimensional drawing of the casting, the size shrinkage of the 3D printed model by 0.2-0.8% and the size shrinkage of the casting by 0.8-2.5% are added to the three-dimensional drawing of the casting.

3. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 1 is characterized in that: In step S2, the printer for 3D printing the model is an FDM fused deposition model 3D printer, and the nozzle diameter of the printer is 0.25 to 0.8 mm.

4. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 1 is characterized in that: In step S2, the material of the 3D printing model is a thermoplastic material.

5. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 1 is characterized in that: In step S3, the coating comprises a surface coating and a back coating.

6. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 5 is characterized in that: The surface coating comprises the following raw materials in parts by weight: 60 to 80 parts of aggregate, 1 to 5 parts of polyethylene glycol, 2 to 4 parts of sodium bentonite, 2 to 5 parts of attapulgite, 1 to 3 parts of rosin resin, 3 to 6 parts of magnesium aluminum silicate, 1 to 3 parts of additives and 15 to 30 parts of solvent.

7. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 5 is characterized in that: In step S3, the steps of applying the paint are as follows: dipping the assembled 3D printed model in the surface layer paint, drying it, applying the back layer paint, and drying it.

8. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 1 is characterized in that: In step S4, the operation of firing the shell is to liquefy the 3D printed model at 220-320°C and then porcelainize the coating layer shell at 800-1100°C.

9. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 1 is characterized in that: In step S5, the molding is to put the refined shell baked in S4 into a sand box, add molding sand and vibrate it.

10. The rapid casting development method based on 3D printing model and refined shell roasting casting process according to claim 1 is characterized in that: In step S6, the specific operation of the pouring is to start pumping negative pressure 3 to 5 minutes before pouring the molten metal, control the pouring negative pressure at -0.03 to -0.045 MPa, maintain the pressure for 5 to 20 minutes, and keep warm for 3 to 8 hours.

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