Design method for combined die of multi-cavity thin-wall casting

Abstract

The invention relates to a method for designing a combined mold of a multi-cavity thin-wall casting, belongs to the technical field of casting sand molds, and solves the problems of insufficient dimensional precision, poor casting quality and the like caused by a large number of sand cores, difficulty in positioning and easiness in deformation in the traditional casting technology in the prior art. The invention provides a design method for a combined mold of a multi-cavity thin-wall casting. The design method comprises the following steps that S1, the preset number of risers and the preset parting number of a sand mold are determined; s2, parting design is conducted on the sand mold according to the number of dead heads and the modulus, and a double-row wooden comb type exhaust unit is arranged in each sand mold parting; and S3, a wooden main mold is designed according to the overall shape of the sand mold. According to the combined mold designed through the design method, the parting number is greatly reduced compared with a traditional sand core, and therefore operation simplification, accurate positioning and error reduction are achieved; the exhaust effect is good, and air holes are not easily generated in castings; and the sand mold is high in inner molded surface precision, accurate in casting size, good in surface quality and the like.

Description

Technical Field

[0001] The invention relates to the technical field of casting sand molds, and in particular to a combined mold design method for multi-cavity thin-wall castings. Background Art

[0002] The bow is one of the most important parts of a ship. It is located at the front end of the hull. Because it is located at the bow, it is the first to be impacted by the water, and bears water pressure, wave impact force and external collision force, and has strict requirements on structure, strength, line and life. Cast steel bow is generally a slender variable cross-section "rod-shaped" part, which can generally reach about 7 meters. The bow of some large ships can even reach 21 meters, and most of them have a "C" type structure and a "V" type cross-section. According to the manufacturing method, it can be divided into forged steel bow, cast steel bow, steel plate bow and hybrid bow. Among them, cast steel bow is widely used due to its advantages of being able to be made into more complex cross-sectional shapes and bending states.

[0003] The cast steel bow is a typical multi-cavity thin-walled casting. The current casting method for similar castings is: first make a partial solid sample main mold and a core box with wood, then hit the main mold in a sand pit, and then place the sand cores obtained by hitting the molding sand in the core box in sequence according to the core setting order, and finally assemble the cores in a sand box or a pit to form the cavity of the cast steel bow / multi-cavity thin-walled casting.

[0004] The existing casting technology has the following defects: on the one hand, as the ship type increases, the longer the length of the cast steel bow column, the more sand cores are required, and the longer the production cycle; and the use of wooden molds leads to increased costs, high labor intensity for workers, and environmental pollution; on the other hand, the positioning of the core box is difficult to control during the compaction process, the core assembly gap is large, and it is easy to deform, which will seriously affect the dimensional accuracy of the cast steel bow column. In addition, the existing general exhaust system for casting sand molds is relatively simple, and the exhaust effect is poor during the casting of multi-cavity thin-walled castings, which easily leads to defects such as pores in the castings. Summary of the invention

[0005] In view of the above analysis, an embodiment of the present invention aims to provide a method for designing a combination mold for multi-cavity thin-walled castings, so as to solve at least one of the problems in the prior art of casting multi-cavity thin-walled castings, that is, there are too many sand mold components / sand cores, which leads to the core box being difficult to control the positioning during the compaction process, large core assembly gap, easy deformation, thereby affecting the dimensional accuracy of the casting, and poor exhaust effect during the casting process.

[0006] The present invention provides a method for designing a combined mold for a multi-cavity thin-wall casting, wherein the combined mold includes a 3D printed sand mold and a wooden main mold, and comprises the following steps:

[0007] S1: Determine the number of preset risers 1 and the number of sand mold parts according to the size and shape of the multi-cavity thin-wall casting and the heat node during the casting process; the sand mold is divided into two layers, each layer of the sand mold is composed of a number of parts;

[0008] S2: The sand mold is designed according to the number and modulus of risers 1. A "double-row wooden comb" exhaust unit is set inside each sand mold;

[0009] S3: Designing a wooden master mold according to the overall shape of the sand mold, wherein the wooden master mold is used to pre-shape a groove in a sand box for setting the sand mold.

[0010] Specifically, the design principle of the number of risers 1 in step S1 is to set a riser 1 at both ends of the length direction of the multi-cavity thin-wall casting, and the number of risers 1 in the middle position must meet the continuity of 45% to 55%; the cross-sectional shape of the riser 1 is one of an ellipse, a square, a rectangle or an irregular polygon; the riser 1 is also provided with a reinforcing rib plate 7.

[0011] Specifically, the number of risers 1 in each layer of sand mold is determined according to the number of risers 1, the size and shape of the multi-cavity thin-wall casting, and the strength of the printing material used; the number of risers 1 included in a single sand mold is not more than 3, and the aspect ratio is not more than 2.

[0012] Specifically, the "double-row wooden comb type" exhaust unit includes an air collecting channel 2, an air guide channel 3 and an exhaust channel 4;

[0013] The air guide channel 3 is arranged according to the shape of the inner cavity of the sand mold parting;

[0014] One end of the air collecting channel 2 is connected to the air guiding channel 3, and the other end points to the inner cavity and keeps a certain distance from the surface of the inner cavity;

[0015] One end of the exhaust channel 4 is connected to the air guide channel 3, and the other end points to the outer surface of the sand mold parting and communicates with the atmosphere;

[0016] The mutually interconnected air collecting channel 2, air guide channel 3 and exhaust channel 4 constitute a complete "double-row wooden comb type" exhaust unit; at least one "double-row wooden comb type" exhaust unit is arranged in a single sand mold.

[0017] Specifically, the total cross-sectional area of ​​the air collecting duct 2 in each "double-row comb-type" exhaust unit is S1, the total cross-sectional area of ​​the air guide duct 3 is S2, and the total cross-sectional area of ​​the exhaust duct 4 is S3, S1:S2:S3=(1.25~2.5):1:(2.0~3.0).

[0018] Specifically, the end of the air collecting channel 2 close to the cavity is 150 to 250 mm away from the inner cavity surface.

[0019] Preferably, a chill iron reserved cavity 5 and a fixing through hole 6 are also provided in the sand mold parting; the chill iron reserved cavity 5 is arranged on the inner mold cavity surface between adjacent risers 1, and the chill iron reserved cavity 5 is connected to the outer surface of the sand mold parting through the fixing through hole 6.

[0020] Specifically, the shape of the wooden main mold is the same as the outer shape of the lower half of the overall sand mold in the assembled state; the height of the wooden main mold is 1 / 5 to 1 / 3 of the height of the overall sand mold.

[0021] The present invention also discloses a combined mold, which comprises a 3D printing sand mold designed by the design method and a wooden main mold.

[0022] The present invention also discloses a casting method for a multi-cavity thin-wall casting, which is characterized in that the casting method adopts the combined mold to obtain the multi-cavity thin-wall casting after molding, pouring and demoulding.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] 1. The present invention creatively adopts the combination of "wooden master mold + 3D printed sand mold" to cast multi-cavity thin-walled castings, especially large castings (cast steel bow column), which greatly reduces the number of sand cores, reduces the operation difficulty and improves the operation efficiency, while greatly improving the positioning accuracy and the surface quality of the cavity, thereby improving the accuracy and surface quality of the casting.

[0025] Existing 3D printing technology is mainly used for the rapid manufacturing of small and medium-sized complex castings. In general sand casting, it is mainly used for small castings such as engine cylinders, and medium-sized castings such as mixed-flow runners weighing more than 2 tons, but it is less used in large steel castings. Cast steel bow columns have the characteristics of many cavities, long length, and thin wall thickness. If the sand mold is completely made of 3D printed sand molds, the sand core forming the outer surface of the bow column also needs to be printed, which will result in long production time and high cost. The existing technology is a combination of traditional wooden main molds and wooden core box sand cores. Each cavity is formed by a separate sand core, which results in a large number of sand cores and a long core setting time.

[0026] The present invention uses 3D printed sand molds to form complex areas of the cast steel bow column, and the main mold is made of traditional wooden main mold. The combination of the two methods can greatly improve the molding efficiency of the cast steel bow column, and greatly improve the positioning accuracy and casting quality.

[0027] 2. The 3D printing sand mold designed by the present invention is equipped with a "double-row wooden comb" exhaust system (the exhaust system is composed of multiple exhaust units), which has a good exhaust effect. According to the characteristics of the cast steel bow column, such as multiple cavities, long length, and thin wall thickness, the present invention creatively designs a "double-row wooden comb" exhaust unit / system composed of an air collecting duct, an air guide duct, and an exhaust duct. Among them, one end of the air collecting duct is close to the inner mold cavity, which can efficiently collect the gas generated during the casting and characterization process; after the exhaust gas is collected by the air collecting duct, it enters the air guide duct set with the mold, and is finally discharged to the outside atmosphere through the exhaust duct. The exhaust efficiency of the exhaust system is significantly improved compared with the existing general exhaust system, which can reduce or even avoid the generation of porosity defects in castings.

[0028] Furthermore, when the cross-sectional area relationship of the gas collecting duct, the air guiding duct and the exhaust duct satisfies S1:S2:S3=(1.25-2.5):1:(2.0-3.0), the exhaust effect is better, and gas congestion and poor exhaust can be avoided when a large amount of gas is discharged.

[0029] 3. The 3D printing sand mold designed by the present invention also has a reserved cavity for chiller and a through hole for fixing. In actual implementation, the chiller can be connected to the steel bar by spot welding and fixed at a preset position of the inner cavity through the through hole for fixing, thereby accelerating the solidification rate of the casting, refining the grain structure, and improving the mechanical properties of the casting during the pouring process. The chiller fixing method is simple and easy, and the fixing is firm and the thermal conductivity is good.

[0030] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0032] Figure 1 This is a schematic diagram of the structure of the cast steel bow casting;

[0033] Figure 2 The sand core parting process diagram of the cast steel bow casting in the prior art (34 pieces in total);

[0034] Figure 3 It is a schematic diagram of the structure of a single exhaust unit;

[0035] Figure 4 The 3D printing sand mold parting design diagram in Example 1;

[0036] Figure 5 This is an enlarged view of parting a in the 3D printed sand mold parting in Example 1 (perspective rendering);

[0037] Figure 6 This is an enlarged view of parting a in the 3D printed sand mold parting in Example 1 (perspective line drawing);

[0038] Figure 7 Schematic diagram of the 3D printed sand mold and wooden master mold structure.

[0039] Reference numerals:

[0040] 1. Riser; 2. Air collecting duct; 3. Air guide duct; 4. Exhaust duct; 5. Cold iron reserved cavity; 6. Through hole for fixing; 7. Reinforcing rib plate. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0042] The existing cast steel bow casting (a large multi-cavity thin-walled casting) has the following problems during the casting process:

[0043] 1. In the casting process, the existing cast steel bow casting forms a cavity by making a main mold and a core box with a wooden model. When the bow is long, the number of sand cores increases, the operation is cumbersome, and there are many core seams, which makes it difficult to control the size. Since the shape of the cast steel bow is curved and easy to deform, the size problem may cause deformation during later processing;

[0044] 2. At present, there are still many problems in using 3D printed sand molds for large multi-cavity thin-walled castings, such as how to perform sand mold parting and design, how to achieve exhaust, how to achieve the placement of chillers, etc. In addition, if the 3D printing method is used entirely for manufacturing, the pouring system and chillers are difficult to prefabricate into the 3D printed sand cores, and improper handling may even cause sparks; and if the sand mold is completely made with 3D printed sand cores, the sand core forming the outer surface of the bow column also needs to be printed, which will result in a long production time and high cost.

[0045] Based on the defects of the prior art, the researchers of the present invention have proposed a casting method for large multi-cavity thin-walled castings that combines "wooden master mold + 3D printed sand mold" after a lot of research, theoretical analysis and experimental adjustment. This method has achieved efficient, high-precision and cost-controlled preparation of large multi-cavity thin-walled castings. The core of the casting method lies in the design of the 3D printed sand mold.

[0046] The present invention provides a method for designing a combined mold for a multi-cavity thin-wall casting, wherein the combined mold includes a 3D printed sand mold and a wooden main mold, and comprises the following steps:

[0047] S1: Determine the number of preset risers 1 and the number of sand mold parts according to the size and shape of the multi-cavity thin-wall casting and the heat node during the casting process; the sand mold is divided into two layers, each layer of the sand mold is composed of a number of parts;

[0048] S2: The sand mold is designed according to the number and modulus of risers 1. A "double-row wooden comb" exhaust unit is set inside each sand mold;

[0049] S3: Designing a wooden master mold according to the overall shape of the sand mold, wherein the wooden master mold is used to pre-shape a groove in a sand box for setting the sand mold.

[0050] Specifically, the cast steel bow is a typical large multi-cavity thin-walled casting. The traditional core splitting method divides the main body cavity structure into multiple sand cores. The sand core interface is generally the middle dividing surface of the middle rib plate. In this way, the number of sand cores increases, the molding process is complicated, and it is very easy to cause dimensional deviation when the core is lowered, resulting in the problem of one side thickening and the other side missing in the later cleaning process. It can only be refined by repair welding and carbon planing and polishing. Due to the narrow cavity space, the repair welding operation is difficult. On the other hand, large-area repair welding is easy to cause deformation of the bow body. The 3D printed sand mold (composed of multiple sand mold partings) in the combined mold designed by the present invention is significantly reduced compared to the traditional sand core number (taking the embodiment as an example, it is reduced from the traditional 34 sand cores to 6 sand mold partings), which effectively avoids the occurrence of the above problems.

[0051] Specifically, since the hot spots of different castings are closely related to the casting shapes, the composition of the molten steel, the angle of the inner cavity of the mold, etc., they cannot be generalized. The hot spot information can be obtained by computer simulation or reference to casting experience, and the number and position of the risers can be determined based on the hot spot information. Furthermore, the present invention proposes a universal riser design principle, which is suitable for the inner cavity / mold design of most multi-cavity thin-walled castings.

[0052] Specifically, the design principle of the number of risers in step S1 is: a riser is set at both ends of the multi-cavity thin-walled casting in the length direction, and the number of risers in the middle position must meet the continuity of 45% to 55% (the continuity of the riser is the ratio of the sum of the length of the root of the riser to the circumference of the wheel shape, which is called the continuity of the riser); the cross-sectional shape of the riser is one of elliptical, square, rectangular or irregular polygonal; the riser is also provided with a reinforcing rib plate (such as Figure 1As shown). The above design principle can not only meet the shrinkage compensation needs of the multi-cavity thin-walled casting, but also avoid the insufficient strength of the sand mold caused by too many risers; the role of the reinforcing rib plate is to further improve the structural strength and avoid structural defects in the casting during the shaping and demoulding process. In the specific implementation, the setting of the reinforcing rib plate can refer to the existing technology. The final product will cut off and polish the excess parts such as the riser and rib plate, and the riser and rib plate are not part of the final product.

[0053] Specifically, the number of sand mold partings in each layer is determined according to the number of risers, the size and shape of the multi-cavity thin-wall casting, and the strength of the printing material used.

[0054] First, the number of sand mold partings is determined according to the determined number of risers. The number of risers included in a single sand mold parting is not more than 3, for example, 1, 2, 3, and the aspect ratio is not more than 2; as shown in Example 1, the number of risers is 6, and each sand mold parting is set to contain 2 risers, the aspect ratio is 1.8, and the sand mold is divided into two layers as a whole, and the final number of sand mold partings is 6.

[0055] It is worth noting that the structural dividing surface of a single sand mold parting is closely related to the shape of a specific casting. After the approximate number of sand mold partings is determined according to the number of risers, the parting surface of the sand mold parting is formed by naturally extending along the structural dividing surface of the casting. For example, it is divided along a rib extension surface of a multi-cavity thin-walled casting. For example, the d, e, and f sand mold partings in Example 1 are formed by naturally extending according to the shape of the protruding part, while the upper sand molds a, b, and c have hollow inner cavities and no protruding structures, so they can be directly cut vertically. In addition, the parting surfaces of the upper and lower sand molds can be determined according to the shape of the inner cavity / casting (such as Figure 4 shown).

[0056] Furthermore, the number of sand mold partings per layer is also related to the strength of the printing material used. If the strength of the printing material is high, the number of sand mold partings can be appropriately reduced on the basis of the number of sand mold partings determined by the number of risers, and the aspect ratio of a single sand mold parting can be appropriately enlarged, such as 1.5 to 2; if the material strength is low, in order to prevent the sand mold from collapsing, the number of sand mold partings should be appropriately increased on the basis of the number of sand mold partings determined by the number of risers, and the aspect ratio of a single sand mold parting should be appropriately reduced, such as 1.0 to 1.5. It is worth noting that unless there are special requirements for the casting material, such as appropriately reducing the material strength in order to pursue shear resistance, most common high-temperature resistant materials for 3D printing are suitable for aspect ratios below 2, and sand mold collapse and other phenomena will not occur.

[0057] Exemplarily, common high temperature resistant printing materials include high temperature alloys such as nickel-based alloys and cobalt-based alloys. These alloys have extremely high creep resistance and oxidation resistance and are suitable for extreme high temperature environments. In addition, there are ceramic materials such as alumina and silicon nitride, which are not only resistant to high temperatures, but also have good electrical insulation and wear resistance. In specific implementations, appropriate high temperature resistant printing materials can be selected based on factors such as casting temperature, casting surface quality requirements, and cost control.

[0058] Specifically, the "double-row wooden comb type" exhaust unit includes an air collecting duct, an air guide duct and an exhaust duct;

[0059] The air guide channel is arranged according to the shape of the inner cavity of the sand mold parting;

[0060] One end of the air collecting channel is connected to the air guiding channel, and the other end points to the inner cavity and keeps a certain distance from the surface of the inner cavity;

[0061] One end of the exhaust channel is connected to the air guide channel, and the other end points to the outer surface of the sand mold parting and is connected to the atmosphere;

[0062] The mutually interconnected air collecting duct, air guide duct and exhaust duct constitute a complete "double-row wooden comb type" exhaust unit; at least one "double-row wooden comb type" exhaust unit is arranged in a single sand mold.

[0063] Specifically, one end of the gas collecting channel is close to the surface of the inner cavity, which helps to collect the gas generated during the pouring and solidification process. After the gas is collected by the gas guide channel, it is finally discharged to the external atmosphere through the exhaust channel. It is worth noting that the gas collecting channel and the exhaust channel should not be connected to the gas guide channel at the same node, but should be staggered to avoid structural defects.

[0064] It is worth noting that after the 3D printed sand mold is assembled, if the exhaust port corresponding to the exhaust duct is located on the upper surface of the sand mold, exhaust can be achieved without additional treatment; if the exhaust port corresponding to the exhaust duct is located inside the sand box (for example, the exhaust hole of the lower sand mold parting is generally located on the side), it is necessary to directly pierce the air hole or place a hollow nylon rope during the sand placing process in the sand box to connect the exhaust hole to the external atmosphere.

[0065] Specifically, the total cross-sectional area of ​​the air collecting duct in each "wooden comb type" exhaust unit is S1, the total cross-sectional area of ​​the air guide duct is S2, and the total cross-sectional area of ​​the exhaust duct is S3, S1:S2:S3 = (1.25-2.5):1:(2.0-3.0). When the above relationship is satisfied, the exhaust effect of the exhaust unit is optimal, and it is not easy to have poor gas discharge; on this basis, the total cross-sectional area of ​​the exhaust system (which may include multiple exhaust units) cannot be too large, otherwise it may cause the structural strength of the sand mold to decrease.

[0066] It is worth emphasizing that in actual implementation, in order to further improve the exhaust effect, different exhaust units can be connected (the specifications of the connecting air duct are the same as those of the air guide duct), so that multiple exhaust units in a single sand mold are interconnected, and the exhaust effect is improved when the gas production in the inner cavity is uneven; but it is worth noting that in the design process, the multiple connected exhaust units still need to meet the above cross-sectional area ratio relationship separately instead of being calculated as a whole. In addition, the connecting air duct itself can independently become a complete exhaust unit (that is, including air collecting ducts, air guide ducts and exhaust ducts) or it can be used only as a connecting air duct (including air guide ducts, which may include air collecting ducts or exhaust ducts). The specific setting can be flexibly set according to the shape of the casting / inner cavity.

[0067] Specifically, the end of the gas collecting channel close to the cavity is 150 to 250 mm away from the inner cavity surface. One end of the gas collecting channel is close to the inner cavity surface to more efficiently collect the gas generated during the pouring process, but the end surface should not be too close to the inner cavity surface to avoid the metal liquid overflowing into the gas collecting channel.

[0068] Preferably, a chill iron reserved cavity and a fixing through hole are also provided in the sand mold parting; the chill iron reserved cavity is arranged on the inner mold cavity surface between adjacent risers, and the chill iron reserved cavity is connected with the outer surface of the sand mold parting through the fixing through hole.

[0069] Specifically, the edge size of the chiller reserved cavity is 2-3mm larger than the edge of the chiller to facilitate the subsequent chiller installation; the diameter of the fixing through hole is 10-20mm, which is used to pass the fixing steel bar; the corresponding position of the fixing through hole on the outer surface of the sand mold parting is also provided with a fixture avoidance hole with a diameter of 100-350mm and a depth of 100-150mm. In actual implementation, the sand mold / sand mold parting is first printed, and then the fixing steel bar is passed through the fixing through hole. One end of the fixing steel bar is spot welded to the chiller, and the other end is spot welded to the fixture (such as a short steel bar or a rectangular iron sheet of suitable thickness). The fixing method is simple and easy to operate and has low cost.

[0070] Specifically, the shape of the wooden main mold is the same as the shape of the lower half of the overall sand mold in the assembled state (such as Figure 7 The height of the wooden master mold is 1 / 5 to 1 / 3 of the height of the whole sand mold. The function of the wooden master mold is to pre-press a groove matching the sand mold in the sand box, which is convenient for inserting the 3D printed sand mold / sand mold parting, and helps to improve the accuracy of sand mold assembly and positioning.

[0071] Preferably, the sand mold parting surface of the lower layer is provided with a positioning slope, the specific slope is 1:8-12, the wooden main mold matches the sand mold parting surface of the lower layer, the positioning slope is used to facilitate the lowering and assembly of the 3D printing sand mold / sand mold parting, and the positioning is more accurate and stable.

[0072] The present invention also discloses a casting mold combination, which includes a 3D printing sand mold designed by the design method and a wooden main mold.

[0073] The invention also discloses a casting method for a multi-cavity thin-wall casting. The casting method adopts the casting mold combination to obtain the multi-cavity thin-wall casting after molding, pouring and demoulding.

[0074] Example 1

[0075] This embodiment provides a 3D printing sand mold design process and a casting process for a multi-cavity thin-wall casting, including:

[0076] S1: According to the thermal node of the multi-cavity thin-walled cast steel bow column (obtained according to computer simulation and experience), a waist-shaped riser with a diameter of 300mm is set. According to the riser design principle, a riser is set at both ends of the length direction. The total length of the cast steel bow column is 6014mm. According to the continuation of 50%, 6014×50%÷500=6.014≈6, so 6 waist-shaped risers of φ300mm are placed evenly in the middle position; a single sand mold parting includes 2 waist-shaped risers and the sand mold includes upper and lower layers, with a total of 6 sand mold partings; after the 6 sand mold partings are combined, the inner mold cavity is the shape of the casting (including auxiliary components such as risers and ribs), wherein the upper sand mold parting can be vertically cut, and the lower sand mold parting is naturally extended at the shape segment of the protruding part to form a cutting surface / parting surface, and the length-to-width ratio of a single sand mold parting is 1.8;

[0077] S2: After determining the number of risers, chillers should be installed between every two risers for zone shrinkage compensation. The wall thickness of the cast steel bow column is 80mm, and the thickness of the chiller is 0.5-0.85 times of that, which is 40mm.

[0078] S3: The sand mold parting position is as close as possible to one side of the cavity rib plate, the number of sand mold parting layers is 2, and the inner cavity structure is in the sand mold parting of the lower layer; the positioning slope of each lower layer sand mold parting is 1:10, the height is 120mm, and there are 6 sand molds in total (3 upper layers and 3 lower layers);

[0079] S4: When printing the sand mold, a chiller reserved cavity is required. The gap between the chiller reserved cavity and the chiller is 2mm. A 20mm hole is printed behind the chiller reserved cavity, which goes straight to the back of the sand mold. A fixture avoidance hole with a diameter of 250mm and a depth of 150mm is reserved behind the sand mold. After the sand mold is printed, a φ12 steel bar is first passed through the small hole and spot welded to the chiller, and then disconnected at the fixture avoidance hole. A short steel bar with a diameter of 30mm and a length of 220mm is spot welded to fix the chiller.

[0080] S5: When printing the sand mold, directly print the "double-layer wooden comb" exhaust channel. The sand intake of the adjacent casting live surface of the air collecting channel is 200mm. Two exhaust units are set for each upper sand mold parting. The cross-section of the air collecting channel is φ6mm, and they are all connected to a φ10mm air guide channel, which is connected to the external atmosphere through a φ15mm exhaust channel. The three are staggered with each other, and S1:S2:S3=1.8:1:2.5 in each exhaust unit; the exhaust system of the lower sand mold parting (composed of exhaust units) is the same size as that of the upper sand mold parting, and the shape is set according to the live surface / inner mold cavity of the casting (where the two exhaust units in sand molds a and c are connected by connecting air channels); alumina ceramic materials are used for 3D printing and a matching wooden main mold is prepared. The height of the wooden main mold is 1 / 5 of the total height of the sand mold;

[0081] S6: The wooden sand box of the main mold is knocked flat and turned over to remove the main mold. The 3D printed sand mold / sand mold parting mold are then put into the mold in sequence. The sand mold is then knocked flat around with furan resin sand. The entire molding operation takes 2 days (the molding process of the prior art takes 7 days). After that, pouring is performed to obtain a multi-cavity thin-walled cast steel bow column.

[0082] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for designing a combined mold for a multi-cavity thin-walled casting, characterized in that: The combined mold includes a 3D printed sand mold and a wooden master mold, and includes the following steps: S1: according to the size and shape of the multi-cavity thin-wall casting and the heat node during the casting process, the number of preset risers (1) and the number of sand mold parts are determined; the sand mold is divided into two layers, upper and lower, and each layer of the sand mold is composed of a plurality of parts; S2: Design the sand mold according to the number and modulus of the risers (1), and a "double-row wooden comb" exhaust unit is provided inside each sand mold; S3: Designing a wooden master mold according to the overall shape of the sand mold, wherein the wooden master mold is used to pre-shape a groove in a sand box for setting the sand mold.

2. The design method according to claim 1, characterized in that: The design principle of the number of risers (1) in step S1 is to respectively set a riser (1) at both ends along the length direction of the multi-cavity thin-wall casting, and the number of risers (1) in the middle position must meet the continuity of 45-55%.

3. The design method according to claim 1, characterized in that: The number of sand mold splitting layers is determined according to the number of risers (1), the size and shape of the multi-cavity thin-wall casting, and the strength of the printing material used.

4. The design method according to claim 1, characterized in that: The "double-row wooden comb type" exhaust unit comprises an air collecting duct (2), an air guide duct (3) and an exhaust duct (4); The air guide channel (3) is arranged according to the shape of the inner cavity of the sand mold; One end of the air collecting channel (2) is connected to the air guiding channel (3), and the other end points to the inner cavity and maintains a certain distance from the surface of the inner cavity; One end of the exhaust channel (4) is connected to the air guide channel (3), and the other end points to the outer surface of the sand mold and communicates with the atmosphere; The mutually connected air collecting channel (2), air guide channel (3) and exhaust channel (4) form a complete "double-row wooden comb type" exhaust unit; at least one "double-row wooden comb type" exhaust unit is arranged in a single sand mold.

5. The design method according to claim 4, characterized in that: The total cross-sectional area of ​​the air collecting duct (2) in each "double-row comb-type" exhaust unit is S1, the total cross-sectional area of ​​the air guide duct (3) is S2, and the total cross-sectional area of ​​the exhaust duct (4) is S3, S1:S2:S3=(1.25-2.5):1:(2.0-3.0).

6. The design method according to claim 4, characterized in that: The end of the air collecting channel (2) close to the cavity is 150 to 250 mm away from the inner cavity surface.

7. The design method according to claim 1, characterized in that: The sand mold parting is also provided with a chill iron reserved cavity (5) and a fixing through hole (6); the chill iron reserved cavity (5) is arranged on the inner mold cavity surface between adjacent risers (1), and the chill iron reserved cavity (5) is connected to the outer surface of the sand mold parting through the fixing through hole (6).

8. The design method according to claim 1, characterized in that: The shape of the wooden main mold is the same as the outer shape of the lower half of the overall sand mold in the assembled state; the height of the wooden main mold is 1 / 5 to 1 / 3 of the height of the overall sand mold.

9. A combined mold, characterized in that: The combined mold includes a 3D printed sand mold and a wooden master mold designed by the design method described in any one of claims 1 to 8.

10. A casting method for a multi-cavity thin-walled casting, characterized in that: The casting method adopts the combined mold described in claim 9 to obtain the multi-cavity thin-wall casting after molding, pouring and demoulding.

Images