Iron mold coated sand core and its manufacturing method

Abstract

An iron mold coated with sand core, comprising: a metal mold, the outer surface of the metal mold having an outer shape corresponding to the shape of the product to be cast; and sand for coating the outer surface of the metal mold, wherein the sand for coating is formed on the outer surface of the metal mold by a 3D printing device, and a plurality of micro air exhaust channels are formed in the sand for coating, the micro air exhaust channels communicate with each other and communicate with the gap at the parting surface of the sand box during casting, the micro air exhaust channels are formed during the 3D printing process using the 3D printing device, and the plurality of micro air exhaust channels are formed as a whole over the entire extension dimension of the sand for coating so that the gas generated during the casting process of the casting can be discharged out of the sand box along the air exhaust channels. The present application also relates to a method for manufacturing the iron mold coated with sand core.

Description

Technical Field

[0001] This application relates to the field of casting, and particularly to the manufacture of iron mold coated sand cores in casting processes, which forms micro-exhaust channels by 3D printing the required coated sand on an iron mold. Background Art

[0002] The casting industry is a basic industry of the manufacturing industry and plays an indispensable role in the development of the national economy. In recent years, the casting industry has developed rapidly, especially the iron mold coated sand manufacturing technology has been widely applied. However, in the traditional iron coated sand process, the manufacturing equipment for coated sand and sand cores is complex, with high energy consumption. The sand cores made have poor air permeability, resulting in some stubborn defects such as multi-porosity in casting products, and can only manufacture products with relatively simple spatial structures. For this reason, 3D printing technology has been applied and developed to a certain extent in the casting field.

[0003] CN201711188955 discloses a high-temperature resistant 3D printing coated sand molding curing agent and its preparation process, which mentions the component ratio of the molding curing agent, that is, mainly including modified phenolic resin, polyvinyl butyral, etc. by weight parts to improve the bonding strength and aging resistance of the coated sand and extend the service life of the coated sand.

[0004] CN108296420A discloses a coated sand for laser 3D printing and its preparation method, and also involves the raw material components by weight parts to improve the overall strength, high-temperature resistance, fire resistance persistence and its own structural stability of the coated sand.

[0005] CN108296442A discloses a 3D printing coated sand molding process. In its embodiments, several steps of the 3D printing coated sand molding process are disclosed: original sand drying, pickling, re-drying, preparing mixed sand in a sand mixer, injecting the mixed sand into a mold, introducing 100°C steam into the mold to obtain a 3D printing coated sand semi-finished product, and drying and curing to obtain a formed 3D printing coated sand. The component by weight of the coated sand is also disclosed.

[0006] CN108672660A discloses a 3D printing rapid prototyping machine based on coated sand materials. When using a 3D printing device to make coated sand cores, production raw materials are added, the device is connected to an external circuit, and the staff controls the motor to work through a control panel, moves the spray gun up and down. The raw materials reach the top plate of the limiting plate above the printing table through the spray gun, and the control panel completes the production work of coated sand core making through the cooperation of controlling a booster pump, a motor, a first cylinder and a second cylinder.

[0007] CN207205200U discloses a 3D printing device for making core with coated sand. The data of the core to be printed is imported through a central control device. According to the data, corresponding control electrical signals are generated to adjust the position of the printing workbench to perform printing layer by layer.

[0008] CN104923712A discloses a 3D printing coated sand and its preparation method. It relates to a coated sand used in the casting field and also discloses the components of the coated sand. Among them, melamine formaldehyde resin, cashew shell liquid modified phenolic resin and binder are added to the mixer, and the coated sand is prepared therefrom.

[0009] Obviously, in these traditional 3D printing technologies for making core with iron mold coated with sand, most of them use resin sand for molding. The amount of sand used is large, the molding time is long, the efficiency is low, and the strength is low. Moreover, the biggest drawback of using thermosetting organic resin as the binder is the problem of waste gas emission. Organic resins mostly come from petroleum products or agricultural chemicals, with high prices. During molding and core making, the VOC value is high, which is harmful to the health of operators. During the casting process, a large amount of harmful gases are generated, polluting the environment. Therefore, it is necessary to discharge these harmful gases in time during the casting process.

[0010] Therefore, there is a need to provide a 3D printing coated sand core with improved exhaust function compared with traditional iron mold coated sand cores and traditional 3D printing resin sand cores, which has outstanding performance advantages, economic advantages and environmental protection advantages. Summary of the Invention

[0011] This application aims to solve the following problems in the existing casting technology: the problems of complex sand core manufacturing equipment, high energy consumption, high cost of sand cores, airtightness, and gas evolution; in the iron mold coated sand process, the problems of complex coated sand molding equipment, high energy consumption, high cost, airtightness, and gas evolution; the problems of long molding time, high cost, low efficiency, small strength, and environmental protection problems of waste gas emission in 3D printing resin sand.

[0012] Therefore, this application provides an iron mold coated sand core, including: a metal mold, the outer surface of the metal mold has an outer shape corresponding to the shape of the product to be cast; and a coated sand covering the outer surface of the metal mold, wherein the coated sand is formed on the outer surface of the metal mold by a 3D printing device, and a plurality of micro exhaust channels are formed in the coated sand. The micro exhaust channels communicate with each other and communicate with the gap at the parting surface of the sand box during casting. The micro exhaust channels are formed during the 3D printing process using the 3D printing device. The plurality of micro exhaust channels are formed as a whole over the entire extension dimension of the coated sand so that the gas generated during the casting process of the casting can be discharged out of the sand box along the exhaust channels.

[0013] Optionally, the shape, size, and distribution of the plurality of micro-exhaust channels in the coated sand are determined by a CAD modeling process for a 3D printing device.

[0014] Optionally, the coated sand is formed of an inorganic material having a certain particle size or the inorganic material is formed into a porous structure, and the gaps between the particles of the inorganic material or the small holes of the porous structure together constitute the exhaust channels.

[0015] Optionally, the coated sand material is made of silica sand and an inorganic binder or a small amount of organic binder.

[0016] Optionally, the inorganic material includes silicate.

[0017] Optionally, the metal mold is made of a metal with high strength and resistance to casting high temperature, such as cast iron.

[0018] Optionally, the metal mold is made into a solid or hollow structure.

[0019] Optionally, the cross-section of the micro-exhaust channel is circular, oval, rectangular, polygonal, or irregular.

[0020] Optionally, the layer thickness of the coated sand is about 7 mm.

[0021] This application also relates to a method for manufacturing a coated sand core in an iron mold as described above, including the following steps: designing an iron mold that matches the shape of the product to be cast according to the shape of the product to be cast, so that the iron mold has external shape data corresponding to the shape of the product; designing a CAD model of the coated sand according to the external shape data, wherein a plurality of micro-exhaust channels are designed in the coated sand; preparing a coated sand material for 3D printing; loading the prepared coated sand material into a mixer of a 3D printing device; printing a coated sand product on the formed iron mold with the 3D printing device; and removing the loose sand on the surface of the coated sand product to obtain the final coated sand core.

[0022] Optionally, the micro-exhaust channels are designed to be distributed along the entire extension range of the coated sand.

[0023] Optionally, the exhaust channels are formed by the pores between the materials by selecting a coated sand material that can form a porous structure during 3D printing.

[0024] The coated sand core of this application is 3D printed on an iron mold with a substantially inorganic material, so that the coated sand has a microporous exhaust function. The exhaust channels are connected by interconnected microscopic channels. The exhaust channels can also be optimized and designed using 3D modeling software. The 3D printed coated sand core in an iron mold is formed by laser 3D printing of silica sand and an inorganic binder or a small amount of organic binder.

[0025] That is, by using 3D printing technology, an inorganic environmentally friendly 3D printed iron mold coated sand core with micro-exhaust channels is quickly produced on an iron mold, eliminating the molds and equipment for core making and molding (including auxiliary equipment such as heating), and eliminating the mold design and manufacturing processes in traditional casting, basically realizing moldless casting. In addition, since the inorganic binder or a small amount of organic binder is used in this application, the emissions of waste gas and dust can be greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] This application will become apparent and easy to understand in conjunction with the following drawings and detailed description, in which:

[0027] Figure 1 is a printing device for printing a coated sand core according to this application;

[0028] Figure 2 is according to Figure 1 a detailed view of a part of the coated sand printed by the printing device shown;

[0029] Figure 3 is a more detailed view of a part of the coated sand core according to this application;

[0030] Figure 4 is a schematic diagram of gas exhaust in a sand box during the casting process including the coated sand core according to this application;

[0031] Figure 5 is a schematic diagram of a traditional sand box used in the casting process; and

[0032] Figure 6 is for Figure 5 a schematic diagram after improving the traditional sand box shown into the coated sand box of this application and mass-producing it. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The exemplary embodiments disclosed in this application will be described in more detail below with reference to the drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present application can be more thoroughly understood and the scope of the present application can be completely conveyed to those skilled in the art.

[0034] Figure 1Shown is a printing device 100 for 3D printing a sand-coated core in an iron mold according to the present application. The printing device 100 includes a base 1 and a gantry 2 standing upright above the base and movable along a track 15 in the direction shown by the arrow Y in the figure. A printing platform 3 is provided on the base 1, and a three-dimensional moving workbench 4 is placed on the printing platform 3. The item to be printed is placed on the three-dimensional moving workbench 4. A laser printing device 5 is provided on the gantry 2. The gantry 2 has a horizontal guide rail 6 above the three-dimensional moving workbench 4 and parallel to the three-dimensional moving workbench 4. A horizontally moving support platform 8 moves horizontally on the horizontal guide rail 6 as shown by the arrow X in the figure. The horizontally moving support platform 8 has a vertical guide groove, and a vertically moving support platform 7 carrying the laser printing device 5 moves vertically in the vertical guide groove as shown by the arrow Z in the figure, so that the laser printing device 5 can move omnidirectionally.

[0035] The laser printing device 5 is connected to a laser 11, and a mixing tank 10 is connected to the laser printing device 5 to supply the mixed sand-coated mold material to the laser printing device 5. An air source 12 is connected to the mixing tank 10 to assist in mixing the materials. A plurality of supply ports are provided in the mixing tank 10 for feeding the coated sand material and the binder respectively, such as a silica sand supply port 13 and an inorganic binder supply port 14.

[0036] The printing device 100 further has a control system 9, which controls the operations of the laser printing device 5, the laser 11, the air source 12, and the mixing tank 10 respectively according to the item to be printed and different process conditions.

[0037] In the present application, the above printing device 100 is used to manufacture a sand-coated core in an iron mold as follows. First, determine the product specifications to be cast (including dimensions, materials, process requirements, etc.); then perform corresponding product CAD design according to the determined product specifications to design the specific parameters of the product; perform three-dimensional design of the iron mold for casting to be used with the product according to the specific parameters of the determined product; perform three-dimensional design of the sand-coated mold according to the parameters of the iron mold and the parameters of the final product, and layer the three-dimensional design data to generate a scanning trajectory for use by the printing device; load various constituent materials for manufacturing the sand-coated mold material into the mixing tank according to the designed ratio as needed, and use the printing device 100 to print the sand-coated mold on the iron mold through, for example, 3DP adhesive jetting technology and SLS selective laser sintering technology to form a preliminary core, and then remove the loose sand on the core and apply a coating to obtain a sand-coated core in an iron mold. This core can be used in the next manufacturing process, such as core setting, mold closing, and pouring, to obtain the final casting.

[0038] The traditional sand-coated iron mold process can only manufacture products with relatively simple spatial structures, while using 3D printing to make a sand-coated core in an iron mold can manufacture complex structures that are difficult or even impossible to manufacture by traditional processes.

[0039] However, in the traditional iron mold sand coating process, the sand core and the sand mold have no air permeability. During the casting production process, the gas generated due to high-temperature gas evolution cannot be discharged from the cavity in time, which is extremely likely to cause harmful defects such as product pores and pinholes. In severe cases, the product is directly scrapped.

[0040] Therefore, this application has been improved on this basis. During the process of 3D printing the sand coating, a kind of micro-exhaust channel is created in the sand coating. The micro-exhaust channel is connected by interconnected microscopic channels. When this kind of core is cast and poured, it can quickly exhaust gas through the micro-exhaust channel and the exhaust channel set on the parting surface of the sand box, which can effectively improve the air permeability of the mold, reduce gas retention and gas evolution, avoid the generation of casting pore defects, and improve the overall quality of the casting.

[0041] On Figure 1 the three-dimensional moving workbench 4 shown in, an iron mold sand-coated core 20 printed by 3D is exemplarily shown. An enlarged view of a part of the iron mold sand-coated core 20 is shown in Figure 2 to schematically show the micro-exhaust channel 23 in the sand coating.

[0042] The iron mold sand-coated core 20 includes an iron mold 21 and a layer of sand coating 22 printed on the surface of the iron mold 21. A number of micro-exhaust channels 23 are designed in the sand coating 22. These micro-exhaust channels 23 are carried out during the three-dimensional design process of the sand coating according to the parameters of the iron mold and the parameters of the final product and during the process of generating the scanning trajectory by stratifying the three-dimensional design data, and can also be realized through the material selection of the sand coating.

[0043] Figure 3 The micro-exhaust channel 23 and the gas flow path 24 in the sand coating 22 are shown in an enlarged view with a larger ratio.

[0044] The shape and size of the micro-exhaust channel 23 can be designed according to the material and size to be cast, as long as these micro-exhaust channels 23 can work together to transport the gas generated during the casting process to the parting surface between the sand boxes and then to the outside of the sand boxes. In practice, on the one hand, the micro-exhaust channel 23 can be designed as a channel with a circular, square, rectangular, polygonal cross-section, etc. The micro-exhaust channel 23 can also be an irregular shape, but the micro-exhaust channels 23 are interconnected with each other and communicate with the parting surface. On the other hand, the micro-exhaust channel 23 can be formed by the material selection of the sand coating itself. For example, the sand coating 22 is made of a porous material or made into a porous structure, and the pores therein are interconnected, which constitutes the micro-exhaust channel 23.

[0045] Figure 4Shows a schematic diagram of the air flow direction of the iron mold coated sand core during the casting process according to the present application. As shown in the figure, the two parts of the casting sand box, namely the upper box and the lower box, are respectively composed of the iron mold coated sand cores according to the present application. The upper box includes an iron mold 21 and coated mold sand 22, and the lower box includes an iron mold 21' and coated mold sand 22'. After the sand boxes are combined together, a mold cavity is formed between the coated mold sands 22 and 22' for pouring liquid. During the casting process, the gas generated will flow along the micro-exhaust channels in the coated mold sand as shown by the arrow 24 in Figure 4 and finally discharged through the gap of the parting surface between the upper and lower boxes.

[0046] The iron mold coated sand core is formed by 3D printing the coated mold sand 22 on the outer surface of the iron mold 21. Therefore, the thickness of the coated mold sand 22 can be selected according to needs. As shown in Figure 4 , compared with the entire mold, the layer thickness of the coated mold sand 22 is very small, which can be, for example, less than 7 mm.

[0047] Figure 5 Shows a schematic diagram of the structure of the sand box 40 formed by traditional 3D resin printing of the mold. It is composed of an upper box 41 and a lower box 42. Among them, the core is directly printed layer by layer in the upper box 41 and the lower box 42. It can be seen that for such a core, the overall sand consumption is large, the printing efficiency is low, the time is long, the energy consumption is large, the actual application benefit is poor, and the cost is very high.

[0048] From Figure 4 and Figure 5 structural comparison, it can be seen that the core of the present application saves significantly on sand consumption compared to it.

[0049] In addition, the iron mold coated sand core of the present application is also suitable for mass production, and only needs to be implemented by modifying the existing iron mold 21.

[0050] Figure 6 Shows the structure diagram after mass production of the iron mold coated sand core improved on the basis of the traditional sand box shown in Figure 5 . It only needs to print the coated mold sands 22 and 22' on the iron molds 21 and 21' through the printing device 100 shown in Figure 1 . Whether it is single-piece small-batch production or medium- and large-batch production, the most flexible manufacturing production can be achieved, and the cost is much lower than the traditional casting process. For single-piece small-batch production of new products, there is no need to design a dedicated iron mold sand box for new products. A general iron mold sand box can be used as a carrier, and the shape / core can be printed through 3D printing, and the product can be obtained after pouring, greatly reducing the development cycle from drawing to physical object and reducing material consumption. When the product structure needs to be adjusted and modified, it can be quickly adjusted according to customer needs without generating additional costs. After the produced sample parts are approved by the customer, the general sand box can be replaced with a dedicated iron mold sand box matching the product.

[0051] Regarding the material of the coated sand 22 of the present application, inorganic materials such as silicates can be selected as the molding sand, and these inorganic materials can be mixed with inorganic binders in the mixing tank 10 to form the coated sand material for 3D printing. This overcomes the problems that occur when using organic resin sand as the molding sand in traditional iron mold coated sand. That is, when producing complex cast products, due to the limitation of the fluidity of the sand, the sand shooting may not be solid, resulting in the direct scrapping of the product. In addition, the biggest drawback of using thermosetting organic resin as the binder in the traditional process is the problem of exhaust gas emissions. Organic resins mostly come from petroleum products or agricultural chemicals, with high prices, high VOC values during molding and core making, which are harmful to the health of operators. During the pouring process, a large amount of harmful gases are generated, polluting the environment. All of these have been effectively solved by the micro-exhaust channels 23 designed in the coated sand of the present application.

[0052] The present application uses 3D printing to coat the iron mold with sand to form a core. During the printing process, it is instantaneously cured by selective laser sintering, eliminating the need for a huge heating device and reducing the labor intensity of workers; only an iron mold sand box is required, eliminating the production of iron mold tools, and greatly reducing the cost; since the time required for heating and curing is eliminated, the production efficiency is greatly improved, making it suitable for mass production.

[0053] Although the present application is described by taking the iron mold coated sand as an example, that is, 3D printing the coated sand on the iron mold, however, the material of the iron mold can be other materials as long as its melting point is higher than the casting temperature and it has sufficient mechanical strength. That is, other high-temperature and high-strength metal materials can be selected, not limited to iron.

[0054] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. An iron mold coated with sand core, comprising: A metal mold, the outer surface of which has a shape corresponding to the shape of the product to be cast; And The sand for coating the outer surface of the metal mold, wherein, The sand for coating is formed on the outer surface of the metal mold by a 3D printing device, and a number of micro-exhaust channels are formed in the sand for coating. The micro-exhaust channels communicate with each other and communicate with the gap at the parting surface of the sand box during casting. The micro-exhaust channels are formed during the 3D printing process using a 3D printing device. The number of micro-exhaust channels is formed throughout the sand for coating so that the gas generated during the casting process of the casting flows out of the sand box along the micro-exhaust channels.

2. The iron mold coated with sand core according to claim 1, wherein the shape, size and distribution of the number of micro-exhaust channels in the sand for coating are determined by the CAD modeling process for the 3D printing device.

3. The iron mold coated with sand core according to claim 1, wherein the sand for coating is formed by an inorganic material having a certain particle size or the inorganic material is formed into a porous structure, and the gaps between the particles of the inorganic material or the small holes of the porous structure together constitute the micro-exhaust channels.

4. The iron mold coated with sand core according to any one of claims 1-3, wherein the material of the sand for coating is made of silica sand and an inorganic binder or a small amount of organic binder.

5. The iron mold coated with sand core according to claim 3, wherein the inorganic material includes silicate.

6. The iron mold coated with sand core according to any one of claims 1-3, wherein the metal mold is made of a metal with high strength and resistance to casting high temperature.

7. The iron mold coated with sand core according to claim 6, wherein the metal mold is made of cast iron.

8. The iron mold coated with sand core according to any one of claims 1-3, wherein the metal mold is made into a solid or hollow structure.

9. The iron mold coated with sand core according to any one of claims 1-3, wherein the cross section of the micro-exhaust channel is circular, elliptical, rectangular, polygonal or irregular.

10. The iron mold coated with sand core according to any one of claims 1-3, wherein the layer thickness of the sand for coating is about 7 mm.

11. A method for manufacturing the iron mold coated with sand core according to any one of claims 1-10, comprising the following steps: Design an iron mold matching the shape of the product according to the shape of the product to be cast, so that the iron mold has shape data corresponding to the product shape; Design a CAD model of the sand for coating according to the shape data, wherein a number of micro-exhaust channels are designed in the sand for coating; Prepare the sand for coating material for 3D printing; Load the prepared sand for coating material into the mixer of the 3D printing device; Print the sand for coating product on the formed iron mold with a 3D printing device; Remove the loose sand on the surface of the sand for coating product to obtain the final sand for coating core.

12. The method according to claim 11, wherein the micro-exhaust channels are designed to be formed throughout the sand for coating.

13. The method according to claim 11 or 12, wherein The micro-exhaust channels are formed by the pores between the materials by selecting the sand for coating material to form a porous structure during 3D printing.

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