A 3DP forming method for precision casting gypsum mold

Abstract

The present application relates to a kind of precision casting gypsum type 3DP forming method, belong to the field of precision casting of gypsum type.The present application is directly formed by the three-dimensional digital model of gypsum type and is used for pouring, avoids complex moulding, and turns type process, can greatly improve the production efficiency of gypsum type casting method, reduces production cost;And the present application can directly form precision casting gypsum type, for non-ferrous metal casting field.Through 3DP method, gypsum type can be formed to fully utilize the high forming freedom of 3D printing technology forming complex lattice structure, can be designed in the interior of gypsum type Hollow structure, while ensuring that gypsum type has enough strength, change the poor air permeability of gypsum type, the shortcoming that gypsum type is difficult to remove.

Description

Technical Field

[0001] This invention belongs to the field of gypsum mold precision casting, specifically relating to a 3DP molding method for precision casting gypsum molds. Background Technology

[0002] Since the 1950s, plaster mold casting technology has been gradually applied to the casting industry. Currently, plaster mold casting is mainly used in the field of non-ferrous metal casting, especially aluminum alloy casting. Plaster mold castings have high dimensional accuracy, good surface quality, and low residual strength of the mold. They can be used for the mass production of small castings, as well as for the single-piece and small-batch production of large castings.

[0003] Traditional plaster mold casting techniques typically involve pouring plaster slurry into rubber, metal, wooden, or wax molds. After the slurry solidifies, the mold is removed, and the plaster mold is dried before casting. In recent years, with the rise of 3D printing technology, although some researchers have used 3D-printed rapid melting molding to replace wax molds for plaster mold casting, this method is not significantly different from traditional processes. The production process is complex, requiring multiple steps to form the plaster mold, resulting in higher production costs and longer production cycles.

[0004] With the continuous development of 3D printing technology, the three-dimensional droplet jet molding method (3DP method) has become increasingly advantageous in terms of high molding efficiency compared to other 3D printing methods. In recent years, this technology has been applied to various materials such as casting sand molds and powder metal forming, further promoting the development of 3D printing technology.

[0005] Therefore, how to provide a precision casting 3DP plaster mold molding method to simplify the process and reduce production costs is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention addresses the shortcomings of existing plaster mold casting processes, such as complex preparation processes, low production efficiency, and poor permeability before obtaining plaster molds. It provides a method that applies the 3DP method to the field of precision plaster mold casting, directly forming plaster molds from three-dimensional digital models of plaster molds for casting, avoiding complex mold making and casting processes, which can greatly improve the production efficiency of plaster mold casting methods and reduce production costs.

[0007] It should be noted that the purpose of this invention is to shorten the production process of the gypsum mold precision casting process, improve production efficiency, reduce production costs, and fully utilize the molding advantages of the 3D printing method. The invention provides a 3D printing method for precision casting gypsum molds, which can directly form gypsum molds for precision casting in the non-ferrous metal casting field. Furthermore, forming gypsum molds using the 3D printing method fully utilizes the advantages of 3D printing technology, such as high molding freedom and the ability to form complex lattice structures. Designing a hollow structure inside the gypsum mold can overcome the disadvantage of poor air permeability.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for precision casting plaster mold 3DP, the method specifically includes the following steps:

[0010] Step 1: Digital Model Preparation

[0011] Taking into account both the casting process design and the characteristics of the 3DP molding method, the digital model of the precision casting plaster mold was processed using 3D modeling software. This included adding shrinkage allowance to compensate for shrinkage during the drying process of the plaster mold and the shrinkage of the casting during solidification. Reasonable parting was implemented to ensure the dimensional and shape accuracy of the casting while also ensuring easy cleaning of powder from the mold cavity after molding. Simultaneously, a hollow structure was designed inside the plaster mold to improve its poor permeability; this hollow structure must be open to facilitate the cleaning of powder inside.

[0012] It should be noted that the term "open" in the open-type hollow structure means that the hollow structure directly penetrates the outer surface of the mold, and the holes of the hollow structure are open to the atmosphere. Near the surface of the mold cavity, there is a non-hollow structure to ensure that the inner surface of the mold has sufficient capacity to withstand the mechanical and thermal shocks of filling. The normal distance between the starting surface of the hollow structure and the inner surface of the mold is maintained at 3-10mm, and the appropriate size is selected according to the size of the mold. The hollow structure used is mainly to ensure the overall structural strength of the gypsum mold while achieving communication between the inside of the mold and the external environment. The shape of a single unit of the hollow structure can be arbitrarily selected, but the hollow structure designed in this invention is a gradient hollow structure. All holes are connected inside and outside. The diameter of the holes formed by the structure is smaller near the surface of the mold and gradually increases outward along the normal of the surface of the mold, ultimately ensuring that the volume ratio of holes in the mold is not less than 60%.

[0013] Step 2: Powder Material Preparation

[0014] To prepare gypsum-type powder materials, 200-325 mesh α-hemihydrate gypsum (α-CaSO4·1 / 2H2O) is selected as the main material, and short glass fibers, ceramic fibers or SiO2-Al2O3 series gypsum refractory fillers are added, including but not limited to silica powder, sillimanite, mullite, kaolin, bauxite, alumina and zircon sand powder.

[0015] The main powder material for the gypsum mold is 200-325 mesh α-hemihydrate gypsum (α-CaSO4·1 / 2H2O), with an addition amount of 20%-60%; bauxite powder is selected as filler, with an addition amount of 40%-80%, and 0.05-0.5% of short glass fiber or ceramic fiber is added at the same time. After thorough mixing, the powder material for 3DP printing gypsum mold is prepared.

[0016] Step 3: Adhesive Preparation

[0017] The main component of the binder is deionized water, accounting for 60-90%, with polyvinylpyrrolidone (PVP) added, accounting for 1%-10%; magnesium sulfate 0-0.5% as a coagulant aid, borax 0-0.5% as a retarder, and appropriate amounts of humectants, pH adjusters, etc., to formulate a binder for 3DP method molding of gypsum plaster.

[0018] Step 4: Shaping the plaster mold

[0019] The 3DP method is used to form plaster molds. The slice file of the digital model obtained in step one is imported into the molding control software. The plaster powder prepared in step two is spread evenly on the surface of the molding cylinder by a powder spreading cart. The binder prepared in step three is sprayed evenly onto the surface of the plaster powder by the printing nozzle according to the image obtained from the model slices to form a plaster mold. Then the molding cylinder descends to a layer thickness of 0.1-0.2mm, the powder spreading cart spreads powder again, and the printing nozzle sprays binder again. This cycle is repeated until the entire plaster mold is printed.

[0020] Step 5: Post-treatment of plaster molds

[0021] After the plaster mold formed in step four has cured in the molding cylinder for 4-12 hours, use an industrial vacuum cleaner to remove the uncured powder from the molding cylinder. After sieving, the powder can be reused. After the plaster mold has cured, remove it and clean off any residual powder adhering to the surface. Transfer the plaster mold to a drying oven and dry it at a temperature of 100-400℃ for 12-36 hours to ensure complete dehydration.

[0022] Step Six: Pouring

[0023] Remove the completely dehydrated plaster mold from the drying oven, check its strength, and quickly pour the plaster. Avoid excessive temperature drop in the plaster mold. Hot pouring ensures sufficient fluidity of the liquid metal in the mold cavity, which is beneficial for the molding of thin-walled castings. The pouring method can be flexibly selected according to the process characteristics of the casting, either gravity pouring or anti-gravity pouring.

[0024] Step 7: Post-processing of castings

[0025] After the casting has cooled, the plaster mold can be removed. The removed casting can then undergo post-processing steps such as cutting and grinding to obtain a qualified plaster mold casting.

[0026] As can be seen from the above technical solution, compared with the prior art, the precision casting plaster mold 3DP molding method provided by the present invention has the following superior effects:

[0027] 1) The precision casting plaster mold disclosed in this invention is an organic combination of three-dimensional spray forming technology (3DP) and plaster mold casting process, which can shorten the production process of traditional plaster mold casting process and change the shortcomings of traditional plaster mold process.

[0028] 2) This invention utilizes 3DP technology to spray an adhesive for forming plaster molds onto a uniformly laid bed of plaster powder in the correct geometric pattern. By spraying the adhesive layer by layer and laying the plaster powder layer by layer, the powder in the area where the adhesive is sprayed is bonded together, and finally a plaster mold that can be applied to precision casting is formed.

[0029] 3) This invention can fully utilize the high degree of freedom in 3D printing technology. By designing a hollow structure inside the plaster mold, a pore structure similar to that of foamed plaster mold is formed inside the plaster mold. At the same time, while ensuring the strength of the plaster mold, various hollow structures can be freely designed. Compared with the uncontrollability of the pores inside foamed plaster, it is more regular, the connection between the pores is higher, and the degree of communication between the inside and outside of the plaster mold is higher than that of traditional plaster molds. The plaster mold produced by the process of this invention has higher air permeability and a higher casting yield. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the 3DP method molding principle.

[0032] Figure 2This is an assembly drawing for a plaster casting mold.

[0033] Figure 3 This is a drawing of the casting.

[0034] Figure 4 This is a casting process diagram.

[0035] Figure 1 middle,

[0036] 1 is the material collection box, 2 is the forming cylinder, 3 is the printing nozzle, 4 is the plaster mold, 5 is the powder spreading cart, and 6 is the equipment casing. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention discloses a method for precision casting plaster mold 3DP molding.

[0039] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0040] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0041] Example 1

[0042] The method of this invention for forming casting plaster molds is implemented as follows:

[0043] 1) Model Design: First, using NX 3D modeling software, the model is designed as follows... Figure 3 The casting process design for the shown parts is complete, employing a casting process using an upper plaster mold and a lower metal mold. Simultaneously, a 3D digital model of the plaster mold is generated; at this stage, the 3D model does not include any hollow structures. Based on the structure and dimensions of the casting parts, a continuous hollow structure is established, starting from a position 3mm away from the normal distance of the inner surface of the casting cavity. The hollow structure is based on hexahedral units, with the inner (closer to the inner cavity surface) hexahedron having a side length of 2mm and the outer (outer surface of the casting cavity) hexahedron having a side length of 5mm. The hollow structure connects from the inside out.

[0044] 2) Preparation of gypsum powder: 325 mesh α-hemihydrate gypsum was selected as the main material, accounting for 59.9% by mass. 325 mesh bauxite powder was added, accounting for 40% by mass. Ceramic fiber was added, accounting for 0.1% by mass. The mixture was stirred in a bowl mixer for 3 hours. After being mixed evenly, it was transferred to a drying oven for drying at 100℃ for 5 hours.

[0045] 3) Adhesive preparation: The main component of the adhesive is deionized water, accounting for 80% by mass. Add 5% polyvinylpyrrolidone (PVP), 0.5% magnesium sulfate, 0.5% borax, and 4% humectant. Stir for 0.5 hours, and then add a pH adjuster as needed to make the pH close to neutral.

[0046] 4) Preparation of plaster mold: Add the prepared binder and plaster powder to the binder bucket and material box of AFS-J380P respectively. Import the three-dimensional data of the designed casting model in STL format into the software control system of the equipment. Set the printing layer thickness to 0.1mm and the binder dosage to medium. Then print the mold layer by layer. After printing, place it in the cylinder for more than 6 hours before taking it out. Then remove the excess powder.

[0047] 5) Post-treatment of plaster molds: After the plaster molds are removed, they are transferred to a drying oven and dried at 120℃ for 10 hours.

[0048] 6) Casting: After the plaster mold has dried, take it out and visually inspect it for cracks or missing parts. If the mold is intact, place it on the lower metal plate. Preheat the metal plate to 200°C, then place the pressure iron and cast immediately.

[0049] 7) Post-casting treatment: After the casting is poured and cooled, the plaster mold can be removed to obtain the casting.

[0050] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for precision casting plaster mold 3DP molding, characterized in that, The method specifically includes the following steps: 1) Digital Model Preparation Using 3D modeling software, shrinkage allowance was added to the digital model of the precision casting plaster mold, and the mold was reasonably parted. At the same time, an open gradient hollow structure was designed inside the plaster mold. 2) Powder material preparation The material is prepared from the following raw materials by weight percentage: 20%-60% α-hemihydrate gypsum (α-CaSO4·1 / 2H2O) of 200-325 mesh, 40%-80% bauxite, and 0.05-0.5% short glass fiber or ceramic fiber; The raw materials are thoroughly mixed to form a 3DP printing plaster powder material. 3) Adhesive preparation Weigh out the raw materials separately according to the following mass percentages: 1-10% polyvinylpyrrolidone, 0-0.5% magnesium sulfate as coagulant aid, 0-0.5% borax as retarder, and 60-80% deionized water. The prescribed amounts of polyvinylpyrrolidone, magnesium sulfate, and borax were added to deionized water, along with a humectant and a pH adjuster, to formulate a binder for 3DP method molding of plaster molds. 4) Molding plaster mold Import the slice file of the digital model obtained in step 1) into the molding control software. Spread the powder material prepared in step 2) evenly on the surface of the molding cylinder (2) through the powder spreading cart (5). Spray the binder prepared in step 3) evenly onto the surface of the powder material through the printing nozzle (3) according to the image obtained by the model slice to form a plaster mold (4). Then the molding cylinder (2) descends to a layer thickness of 0.1-0.2mm, the powder spreading cart (5) spreads powder again, and the printing nozzle (3) sprays binder again. Repeat this process until the entire plaster mold printing is completed. 5) Post-treatment of plaster molds After the plaster mold formed in step 4) has been cured in the molding cylinder (2) for 12-24 hours, the uncured powder in the molding cylinder (2) is sucked out, and the cured plaster mold is taken out and the residual powder attached to the surface is removed; then the plaster mold is dried. 6) Pouring Take out the plaster mold that has been dried in step 5), check its strength, and pour it quickly; 7) Post-treatment of castings After the casting completed in step 6) has cooled, the plaster mold is removed. The removed casting is then cut and polished to obtain a qualified plaster mold casting. In step 1), the open-type gradient hollow structure means that the hollow structure directly penetrates the outer surface of the mold, and the holes of the hollow structure are connected to the atmosphere; near the surface of the mold cavity, there is a non-hollow structure, and the normal distance between the starting surface of the hollow structure and the inner surface of the mold is 3-10mm.

2. The precision casting plaster mold 3DP molding method according to claim 1, characterized in that, The drying temperature in step 5) is 100-400℃, and the drying time is 12-36h.

3. The precision casting plaster mold 3DP molding method according to claim 1, characterized in that, The pouring method in step 6) can be flexibly selected as gravity pouring or anti-gravity pouring according to the process characteristics of the casting.

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