Combined die for casting cast steel stem casting

Abstract

The invention relates to a combined mold for casting a cast steel stem casting, belongs to the technical field of casting 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 casting of the cast steel stem casting in the prior art. The invention provides a combined mold for casting a cast steel stem casting. The combined mold comprises a 3D printing sand mold and a wooden main mold; wherein the 3D printing sand mold is composed of a plurality of sand mold sub-molds, and each sand mold sub-mold is provided with at least one'double-row wooden comb type 'exhaust unit; wherein the wooden main mold is designed according to the overall shape of the sand mold. The parting number of the combined mold is greatly reduced compared with that of a traditional sand core, so that operation is simplified, positioning is accurate, and errors are reduced; 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 moulds, in particular to a combined mould for casting a cast steel bow column casting. 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 needed, 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 pouring of cast steel bow column 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 combination mold for casting a cast steel bow column casting, so as to solve at least one of the problems in the prior art of casting a cast steel bow column casting, such as a large number of sand cores, difficult positioning, easy deformation resulting in insufficient dimensional accuracy, poor casting quality, etc.

[0006] The present invention provides a combined mold for casting a cast steel bow column casting, the combined mold comprising a 3D printed sand mold and a wooden main mold;

[0007] The 3D printing sand mold is divided into two layers, each layer is composed of multiple sand mold parts, and each of the sand mold parts is provided with a "double-row wooden comb type" exhaust unit;

[0008] The wooden main mold is designed according to the overall shape of the sand mold and is used to pre-shape a groove in the sand box for setting the sand mold.

[0009] Specifically, the 3D printed sand mold is provided with a plurality of risers 1, including risers at end positions and risers at middle positions, wherein a riser 1 is respectively provided at both ends along the length direction of the cast steel bow column casting, and the number of risers 1 at the middle position must meet a continuity of 45-55%; the riser 1 is provided in the upper sand mold parting.

[0010] Specifically, 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 upper sand mold is 1 to 3, and the length-to-width ratio of a single sand mold is not greater than 2.

[0012] Specifically, the "double-row comb-type" exhaust unit includes an air duct 3, and an air collecting duct 2 and an exhaust duct 4 which are arranged along the extension direction of the air duct 3 and are respectively connected to the inner cavity of the air duct 3;

[0013] The gas during the pouring process is collected through the gas collecting channel 2, enters the air guide channel 3, and is discharged to the outside of the 3D printing sand mold through the exhaust channel 4.

[0014] Specifically, there are multiple air collecting channels 2 arranged along the extending direction of the air guide channel 3, and the multiple air collecting channels 2 point to the inner cavity;

[0015] There are multiple exhaust passages 4 arranged along the extending direction of the air guide passage 3, and the multiple exhaust passages 4 point to the outside of the 3D printing sand mold;

[0016] There is an angle between the air collecting passage 2 and the exhaust passage 4 , and the air collecting passage 2 and the exhaust passage 4 are arranged alternately.

[0017] Specifically, the air guide channel 3 is arranged according to the shape of the inner cavity of the sand mold parting;

[0018] At least one "double-row wooden comb type" exhaust unit is arranged in a single sand mold.

[0019] Specifically, two "double-row wooden comb type" exhaust units are arranged in each sand mold parting, and the two exhaust units are symmetrically distributed on both sides of the inner mold cavity, and the air guide duct 3 of each "double-row wooden comb type" exhaust unit is arranged along the length extension direction of the inner mold cavity; or, more than three "double-row wooden comb type" exhaust units are arranged in each sand mold parting, and the "double-row wooden comb type" exhaust units are connected in sequence and arranged along the length extension direction of the inner mold cavity to form an overall "double-row wooden comb type" exhaust system.

[0020] 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).

[0021] The present invention also discloses a design method of the combined mold, firstly determining the number of risers 1 according to the specific shape and heat node of the cast steel bow casting, then determining the number and shape of the sand mold parting and the exhaust system design, obtaining a 3D printed sand mold design scheme, and then designing a wooden main mold according to the 3D printed sand mold.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] 1. The present invention creatively adopts a combination mold 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.

[0024] 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 a 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.

[0025] 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.

[0026] 2. The 3D printing sand mold designed by the present invention is equipped with a "double-row wooden comb" exhaust system (composed of multiple exhaust units) with good exhaust effect. According to the characteristics of cast steel bow column with multiple cavities, long length and thin wall thickness, the present invention creatively designs a "double-row wooden comb" exhaust 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 arranged with the mold, and is finally discharged to the external 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.

[0027] 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.

[0028] 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.

[0029] 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

[0030] 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.

[0031] Figure 1 This is a schematic diagram of the structure of the cast steel bow casting;

[0032] Figure 2 The sand core parting process diagram of the cast steel bow casting in the prior art (34 pieces in total);

[0033] Figure 3 It is a schematic diagram of the structure of a single exhaust unit;

[0034] Figure 4 The 3D printed sand mold parting design drawings in Example 1 (a total of 6 pieces);

[0035] Figure 5 This is an enlarged view of parting a in the 3D printed sand mold parting in Example 1 (perspective rendering);

[0036] Figure 6 This is an enlarged view of parting a in the 3D printed sand mold parting in Example 1 (perspective line drawing);

[0037] Figure 7 Schematic diagram of the 3D printed sand mold and wooden master mold structure;

[0038] Figure 8 Schematic diagram of the overall structure of the 3D printed sand mold in Example 1 (assembled state).

[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 castings have 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 main mold + 3D printed sand mold" (i.e., combined mold) after a lot of research, theoretical analysis and experimental adjustment. This method has achieved the efficient, high-precision and cost-controlled preparation of large multi-cavity thin-walled castings. The core of the casting method lies in the combined mold and its design.

[0046] The present invention provides a combined mold for casting a cast steel bow column casting, the combined mold comprising a 3D printed sand mold and a wooden main mold;

[0047] The 3D printing sand mold is divided into two layers, each layer is composed of multiple sand mold parts, and each of the sand mold parts is provided with a "double-row wooden comb type" exhaust unit;

[0048] The wooden main mold is designed according to the overall shape of the sand mold and is used to pre-shape a groove in the sand box for setting the sand mold.

[0049] 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.

[0050] Specifically, the 3D printed sand mold is provided with a plurality of risers 1, the risers including risers at the end positions and risers at the middle positions, wherein a riser 1 is respectively provided at both ends along the length direction of the cast steel bow column casting, and the number of risers 1 at the middle position needs to meet a continuity of 45-55% (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 riser 1 is provided in the upper sand mold parting.

[0051] Furthermore, 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. The principle for determining the number of risers proposed in the present invention is a universal principle and is applicable to the inner cavity / mold design of most cast steel bow castings.

[0052] Specifically, 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 .

[0053] Specifically, the number of risers 1 in each upper sand mold is 1 to 3, and the aspect ratio of a single sand mold is not greater than 2. The above-mentioned setting method 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 demolding 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 redundant parts such as the riser and rib plate, and the riser and rib plate are not part of the final product.

[0054] 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).

[0055] Furthermore, the aspect ratio of each layer of sand mold is also related to the strength of the printing material used. If the printing material is strong, the aspect ratio of a single sand mold 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 aspect ratio of a single sand mold can 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 an aspect ratio of less than 2, and sand mold collapse will not occur.

[0056] 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.

[0057] 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 naturally extended along the structural dividing surface of the casting, such as the parting surface of the cast steel bow casting rib (corresponding to the gap between the protruding parts of the mold cavity) extending outward naturally (such as Figure 4 shown).

[0058] Specifically, the "double-row comb-type" exhaust unit includes an air duct 3, and an air collecting duct 2 and an exhaust duct 4 which are arranged along the extension direction of the air duct 3 and are respectively connected to the inner cavity of the air duct 3;

[0059] The gas during the pouring process is collected through the gas collecting channel 2, enters the air guide channel 3, and is discharged to the outside of the 3D printing sand mold through the exhaust channel 4.

[0060] Furthermore, the "double-row wooden comb type" exhaust system includes an air collecting duct, an air guide duct and an exhaust duct;

[0061] The air guide channel is arranged according to the shape of the inner cavity of the sand mold parting;

[0062] 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;

[0063] 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;

[0064] 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.

[0065] 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.

[0066] 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.

[0067] Specifically, there are multiple air collecting channels 2 arranged along the extending direction of the air guide channel 3, and the multiple air collecting channels 2 point to the inner cavity;

[0068] There are multiple exhaust passages 4 arranged along the extending direction of the air guide passage 3, and the multiple exhaust passages 4 point to the outside of the 3D printing sand mold;

[0069] There is an angle between the air collecting passage 2 and the exhaust passage 4 , and the air collecting passage 2 and the exhaust passage 4 are arranged alternately.

[0070] Specifically, the air guide channel 3 is arranged according to the shape of the inner cavity of the sand mold; at least one "double-row wooden comb type" exhaust unit is arranged in a single sand mold.

[0071] Specifically, two "double-row wooden comb type" exhaust units are arranged in each sand mold parting, and the two exhaust units are symmetrically distributed on both sides of the inner mold cavity, and the air guide duct 3 of each "double-row wooden comb type" exhaust unit is arranged along the length extension direction of the inner mold cavity; or, more than three "double-row wooden comb type" exhaust units are arranged in each sand mold parting, and the "double-row wooden comb type" exhaust units are connected in sequence and arranged along the length extension direction of the inner mold cavity to form an overall "double-row wooden comb type" exhaust system.

[0072] Specifically, the total cross-sectional area of ​​the air collecting channel 2 in each "double-row comb-type" exhaust unit is S1, the total cross-sectional area of ​​the air guide channel 3 is S2, and the total cross-sectional area of ​​the exhaust channel 4 is S3, S1:S2:S3 = (1.25-2.5):1:(2.0-3.0). When the above relationship is met, the exhaust effect of the exhaust system is the best, and it is not easy to have poor gas discharge; on this basis, the total cross-sectional area of ​​the exhaust system cannot be too large, otherwise it may cause the structural strength of the sand mold to decrease.

[0073] It is worth emphasizing that in actual implementation, in order to further improve the exhaust effect, different groups of 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] Specifically, the shape of the wooden master mold is the same as the lower part of the 3D printed sand mold; the height of the wooden master mold is 1 / 5 to 1 / 3 of the height of the entire 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.

[0078] Preferably, the lower sand mold parting surface is provided with a positioning slope, the specific slope is 1:8-12, the wooden main mold matches the lower sand mold parting surface, the positioning slope is used to facilitate the insertion and assembly of the 3D printing sand mold / sand mold parting, and the positioning is more accurate and stable

[0079] The present invention also discloses a design method of the combined mold, firstly determining the number of risers 1 according to the specific shape and heat node of the cast steel bow casting, then determining the number and shape of the sand mold parting and the exhaust system design, obtaining a 3D printed sand mold design scheme, and then designing a wooden main mold according to the 3D printed sand mold.

[0080] The specific steps of the design method are:

[0081] 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;

[0082] S2: The sand mold is designed according to the number and modulus of the risers 1. A "double-row wooden comb" exhaust system (composed of several exhaust units) is provided inside each sand mold;

[0083] 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.

[0084] 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.

[0085] Example 1

[0086] This embodiment provides a possible design of a combined mold for a cast steel bow casting, as well as a design process of the combined mold and a subsequent casting process.

[0087] S1: According to the cast steel bow casting (casting shape such as Figure 1 As shown in the figure, a heat node (obtained according to computer simulation and experience) with a waist-shaped riser of 300 mm in diameter 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 6014 mm. According to the continuation of 50%, 6014×50%÷500=6.014≈6, so 6 waist-shaped risers of φ300 mm are placed in the middle position on average; 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 (as shown in the figure). Figure 4 , Figure 8 As shown); after the 6 sand molds are combined, the inner cavity is the shape of the cast steel bow casting (including auxiliary components such as risers and ribs), where the upper sand mold can be divided vertically, and the lower sand mold is naturally extended along the shape segment of the protruding part (corresponding to the ribs of the cast steel bow casting) to form a cutting surface / parting surface. The aspect ratio of a single sand mold is 1.8; (as shown Figure 4 (shown)

[0088] 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.

[0089] 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);

[0090] 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.

[0091] 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 (consisting of 2 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 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;

[0092] S6: The wooden sand box of the main mold is flattened and turned over, the main mold is taken out, and then the 3D printed sand mold / sand mold parting are put into it in sequence, and then the sides of the sand mold are flattened with furan resin sand. The whole molding operation process takes 2 days (the molding process of the existing technology takes 7 days), and then pouring is carried out to obtain a cast steel bow column casting.

[0093] 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 combined mold for casting a cast steel bow casting, characterized in that: The combined mold includes a 3D printed sand mold and a wooden main mold; The 3D printing sand mold is divided into two layers, each layer is composed of multiple sand mold parts, and each of the sand mold parts is provided with a "double-row wooden comb type" exhaust unit; The wooden main mold is designed according to the overall shape of the sand mold and is used to pre-shape a groove in the sand box for setting the sand mold.

2. The combined mold according to claim 1, characterized in that: The 3D printing sand mold is provided with a plurality of risers (1), the risers comprising risers at end positions and risers at middle positions, wherein a riser (1) is respectively provided at both ends along the length direction of the cast steel bow column casting, and the number of risers (1) at the middle position needs to meet a continuity of 45-55%; the risers (1) are provided in the upper sand mold parting.

3. The combined mold according to claim 2, characterized in that: 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).

4. The combined mold according to claim 2, characterized in that: The number of risers (1) in each upper sand mold is 1 to 3, and the length-to-width ratio of a single sand mold is not greater than 2.

5. The combined mold according to claim 1, characterized in that: The "double-row wooden comb type" exhaust unit comprises an air duct (3), and an air collecting duct (2) and an exhaust duct (4) which are arranged along the extension direction of the air duct (3) and are respectively connected to the inner cavity of the air duct (3); Gas during the casting process is collected through the gas collecting channel (2), enters the air guide channel (3), and is discharged to the outside of the 3D printing sand mold through the exhaust channel (4).

6. The combined mold according to claim 5, characterized in that: There are a plurality of air collecting channels (2) arranged along the extending direction of the air guide channel (3), and the plurality of air collecting channels (2) point toward the inner cavity; There are a plurality of exhaust ducts (4) arranged along the extension direction of the air guide duct (3), and the plurality of exhaust ducts (4) point to the outside of the 3D printing sand mold; There is an included angle between the air collecting duct (2) and the exhaust duct (4), and the air collecting duct (2) and the exhaust duct (4) are arranged in a staggered manner.

7. The combined mold according to claim 5, characterized in that: The air guide channel (3) is arranged according to the shape of the inner cavity of the sand mold; At least one "double-row wooden comb type" exhaust unit is provided in a single sand mold.

8. The combined mold according to claim 7, characterized in that: Two "double-row wooden comb-type" exhaust units are arranged in each sand mold, and the two exhaust units are symmetrically distributed on both sides of the inner mold cavity, and the air guide channel (3) of each "double-row wooden comb-type" exhaust unit is arranged along the direction of the inner mold cavity; or, more than three "double-row wooden comb-type" exhaust units are arranged in each sand mold, and the "double-row wooden comb-type" exhaust units are connected in sequence and arranged along the direction of the inner mold cavity to form an overall "double-row wooden comb-type" exhaust system.

9. The combined mold according to any one of claims 1 to 8, 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).

10. A method for designing a combined mold according to any one of claims 1 to 9, characterized in that: Firstly, the number of risers (1) is determined according to the specific shape and heat node of the cast steel bow casting, and then the number and shape of the sand mold parting and the exhaust system design are determined to obtain a 3D printing sand mold design scheme, and then the wooden main mold is designed according to the 3D printing sand mold.

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