3D printing integral sand core manufacturing method

Abstract

The 3D printing integral sand core manufacturing method comprises the steps that an integral sand core model is designed according to the size of an integral sand core to be manufactured, and an integral sand core sample piece is printed; the actual size of the whole sand core sample piece is obtained and compared with the size of the whole sand core model, and the deformation position and the deformation amount of the whole sand core sample piece are obtained; according to the deformation position and the deformation amount of the whole sand core sample piece, a reverse deformation sand core model is designed; and according to the reverse deformation sand core model, a whole sand core finished product is printed and manufactured. According to the method, the deformation position and the deformation amount are analyzed, the reverse deformation amount of the deformation position is designed, then the deformation amount of the deformation position is subjected to reverse size design in advance according to a whole sand core finished product printed according to the reverse deformation sand core model, the size precision of the 3D printing whole sand core is improved, and the production efficiency is improved. And the finally prepared casting is closer to the design size, and the one-time inspection qualification rate of the casting is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing sand cores, and more specifically, to a method for manufacturing a 3D printing integral sand core. Background Art

[0002] The rapid development of aerospace technology has led to an increasing demand for large, complex, high-strength and tough aluminum alloy castings. Large, complex, high-strength and tough aluminum alloy castings have the advantages of low production costs and high degree of structural and functional integration. Pylon castings are typical aluminum alloy castings for external suspension devices of aircraft. They are widely used because they have the functions of bearing and protecting aircraft and are highly versatile.

[0003] For example, Figure 1 A large aluminum alloy rack casting is shown, which consists of a main rack 01, two auxiliary racks 02 and two groups (two in each group) of wing-shaped structures 03. The two auxiliary racks 02 are located on both sides of the main rack 01 and are connected to the main rack 01 through a group of wing-shaped structures 03. The casting is an internal cavity structure with an outline size of 2580×600×400mm and a wall thickness of 4~45mm.

[0004] Figure 2 Shown Figure 1 A traditional core making scheme for the casting shown in the figure. First, the whole sand core is divided into 6 parts, each part is parted from the symmetric surface or near the symmetric surface (to facilitate leaving an exhaust channel on the parting surface, and the exhaust channels of the 6 parts of the sand core are interconnected), the whole sand core is divided into 12 sub-sand cores, core box molds are made for each, and then 12 sub-sand cores are made from the core box mold. Then, after the exhaust channel is made on the parting surface of the sub-sand core, the sub-sand cores of each group of sand cores are glued at the parting surface by core glue (note that the core glue cannot block the exhaust channel). Finally, the 6 parts of the sand core are placed in the sand mold outer mold in a specific order. The disadvantages of this core making method are: the sand core has more blocks and more positioning structures, which makes the cumulative error larger, resulting in reduced dimensional accuracy of the casting, and even dimensional deviation; seams and burrs are prone to appear on the parting surface of the sand core of the casting, which is difficult to clean; the core making and assembly and cleaning of seams and burrs are labor-intensive and inefficient.

[0005] In order to overcome the defects of the above-mentioned traditional core making scheme, a 3D printing integral sand core scheme has emerged in the prior art. Because it is an integral sand core, compared with the traditional sand core that is divided into multiple parts and then assembled, there is no problem of error accumulation and burrs.

[0006] However, the 3D printed integral sand core, in addition to factors such as the number of mold sand meshes, the amount of resin added, and the amount of curing agent added that affect the dimensional accuracy of the sand mold / sand core, is also easily deformed and scrapped due to the size effect and its own complex structure.

[0007] Therefore, how to improve the dimensional accuracy of 3D printed integral sand cores has become a technical problem that needs to be urgently solved by technical personnel in this field. Summary of the invention

[0008] In view of this, an object of the present invention is to provide a method for manufacturing a 3D printed integral sand core to improve the dimensional accuracy of the 3D printed integral sand core.

[0009] To achieve the above object, the present invention provides the following technical solutions: A method for manufacturing a 3D printing integral sand core, comprising: Printing an integral sand core sample step, designing an integral sand core model according to the size of the integral sand core to be manufactured, and printing the integral sand core sample; The step of obtaining the deformation position and deformation amount is to obtain the actual size of the integral sand core sample and compare it with the size of the integral sand core model to obtain the deformation position and deformation amount of the integral sand core sample; The reverse deformation sand core model designing step includes designing the reverse deformation sand core model according to the deformation position and deformation amount of the overall sand core sample; The step of printing the integral sand core finished product is to print and manufacture the integral sand core finished product according to the reverse deformed sand core model.

[0010] Optionally, in the above-mentioned 3D printing integral sand core manufacturing method, the step of printing the integral sand core sample is specifically: using 3D modeling software to design an integral sand core model according to the size of the integral sand core to be manufactured, and using a sand mold 3D printing device to print the integral sand core sample; The step of obtaining the deformation position and deformation amount is specifically as follows: obtaining the actual size of the overall sand core sample by laser three-dimensional scanning, and comparing it with the size of the overall sand core model to obtain the deformation position and deformation amount of the overall sand core sample.

[0011] Optionally, in the above-mentioned 3D printing integral sand core manufacturing method, the integral sand core is a sand core of a hanger-type casting, and the integral sand core includes a main hanger sand core, a sub-hanger sand core located on both sides of the main hanger sand core, and a wing-shaped structure sand core connecting the main hanger sand core and the sub-hanger sand core.

[0012] Optionally, in the above-mentioned 3D printing integral sand core manufacturing method, the step of obtaining the deformation position and deformation amount is specifically: obtaining the actual size of the integral sand core sample, and comparing it with the size of the integral sand core model, obtaining the warping of the main rack sand core sample of the integral sand core sample in the vertical direction as a, the non-parallelism of the two rack sand core samples in the horizontal direction as b, and the warping in the vertical direction as c; The steps of designing the reverse deformation sand core model are specifically as follows: according to the deformation position and deformation amount of the overall sand core sample, the reverse deformation sand core model is designed, so that the reverse deformation sand core model is based on the overall sand core model, the warping of the main hanger sand core model along the vertical direction is -a, the non-parallelism of the two hanger sand core models along the horizontal direction is -b, and the warping along the vertical direction is -c.

[0013] Optionally, in the above-mentioned 3D printing integral sand core production method, the molding sand selected for the integral sand core finished product is 70-140 mesh, the selected resin addition amount is 2%-3% of the molding sand weight, and the selected curing agent addition amount is 0.2%-0.3% of the resin addition amount.

[0014] Optionally, in the above-mentioned 3D printing integral sand core manufacturing method, the reverse deformation sand core model includes a sand core model body and an exhaust structure, and the exhaust structure includes a main exhaust channel and a branch exhaust channel; The main exhaust channel is arranged along the sand core model body, and the main exhaust channels at various positions are interconnected. There are multiple branch exhaust channels, which are arranged at intervals along the main exhaust channel. One end of the branch exhaust channel is connected to the main exhaust channel, and the other end passes through the surface of the sand core model body and is connected to the mold cavity. The branch exhaust channel is an hourglass-shaped structure.

[0015] Optionally, in the above-mentioned 3D printing integral sand core manufacturing method, the branch exhaust channels include multiple groups, each group of branch exhaust channels are arranged at intervals along the main exhaust channel, and the branch exhaust channels in the same group are arranged at the same cross-section of the main exhaust channel, and include branch exhaust channels extending in multiple directions and perpendicular to the main exhaust channel.

[0016] Optionally, in the above-mentioned 3D printing integral sand core manufacturing method, the diameter of the main exhaust channel is 10 mm to 20 mm, and the distance from the edge of the main exhaust channel to the edge of the sand core model body is not less than 20 mm; and / or, Each group of branch exhaust channels is arranged along the main exhaust channel at intervals of 100 mm to 200 mm; and / or, The branch exhaust channel includes an outer branch exhaust channel section and an inner branch exhaust channel section that are connected in the direction from the surface of the sand core model body to the main exhaust channel, and the outer branch exhaust channel section and the inner branch exhaust channel section are both conical structures. The large diameter end of the outer branch exhaust channel section is arranged close to the surface of the sand core model body, and the large diameter end of the inner branch exhaust channel section is arranged close to the main exhaust channel. The small diameter end of the outer branch exhaust channel section has the same diameter as the small diameter end of the inner branch exhaust channel section, and is connected.

[0017] Optionally, in the above-mentioned 3D printing integral sand core manufacturing method, the branch exhaust channel also includes an equal diameter channel connected between the inner branch exhaust channel section and the main exhaust channel, and the equal diameter channel has the same diameter as the large diameter end of the inner branch exhaust channel section; and / or, The large diameter end of the outer branch exhaust channel section extends to the surface of the sand core model body and has a diameter of 4-6 mm, the small diameter end of the outer branch exhaust channel section has a diameter of 2.5-3.5 mm, and the length of the outer branch exhaust channel section in the axial direction is 5 mm-10 mm; and / or, The diameter of the large diameter end of the inner branch exhaust channel section is 4-6 mm, the diameter of the small diameter end of the inner branch exhaust channel section is 2.5-3.5 mm, and the length of the inner branch exhaust channel section along the axial direction is 5 mm-10 mm.

[0018] Optionally, in the above-mentioned 3D printing integral sand core manufacturing method, a sand cleaning step is also included, and after the sand cleaning step is completed, the mouth of the branch exhaust channel is filled with resin sand; The sand cleaning step includes at least one of the following steps: The finished integral sand core is erected to allow the loose sand in the main exhaust passage to flow out; Compressed air is introduced into one end of the main exhaust channel, so that negative pressure is formed at the connection point between the main exhaust channel and the branch exhaust channel, so as to suck the loose sand in the branch exhaust channel into the main exhaust channel and discharge it with the compressed air; A tool is inserted into the branch exhaust channel and reciprocated to assist in cleaning the loose sand in the branch exhaust channel.

[0019] The 3D printing integral sand core manufacturing method provided by the present invention first prints the integral sand core sample according to the integral sand core model, and analyzes the deformation position and deformation amount of the integral sand core sample compared to the integral sand core model. Then, reverse design is performed according to the deformation position and deformation amount of the integral sand core sample to obtain a reverse deformation sand core model, and the integral sand core finished product is printed and manufactured according to the reverse deformation sand core model. The present invention analyzes the deformation position and deformation amount, designs the reverse deformation amount of the deformation position, and then makes the integral sand core finished product printed according to the reverse deformation sand core model, and makes the deformation amount of the deformation position reversely dimensionally designed in advance. Therefore, the prepared integral sand core finished product is closer to the integral sand core model initially designed according to the size of the integral sand core, thereby improving the dimensional accuracy of the 3D printed integral sand core, and making the finally prepared casting closer to the design size, thereby improving the one-time inspection pass rate of the casting. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a structural schematic diagram of an aluminum alloy bracket casting; Figure 2 For casting Figure 1 An exploded view of a conventional core making scheme for a casting is shown; Figure 3 For casting Figure 1 A schematic diagram of the structure of a 3D printed integral sand core of a casting is shown; Figure 4 It is a schematic structural diagram of the exhaust structure disclosed in an embodiment of the present invention; Figure 5 A cross-sectional view of an exhaust structure disclosed in an embodiment of the present invention; Figure 6 This is a microstructure photograph of a casting prepared by using a 3D printed integral sand core according to an embodiment of the present invention.

[0022] The meanings of the reference numerals in the figures are as follows: 01-main rack; 02-secondary rack; 03-wing-shaped structure; 1-main rack sand core; 2-auxiliary rack sand core; 3-wing-shaped structure sand core; 4-main exhaust channel; 5-branch exhaust channel; 501-external branch exhaust channel section; 502-inner branch exhaust channel section; 503-equal diameter channel. DETAILED DESCRIPTION

[0023] The core of the present invention is to provide a method for manufacturing a 3D printed integral sand core to improve the dimensional accuracy of the 3D printed integral sand core.

[0024] The following embodiments are described with reference to the accompanying drawings. In addition, the embodiments shown below do not limit the invention contents described in the claims. In addition, the entire contents of the structures represented by the following embodiments are not limited to those necessary as solutions to the inventions described in the claims. It should be noted that, for ease of description, only the parts related to the inventions are shown in the accompanying drawings. The embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0025] Although the 3D printing of integral sand cores can overcome the problem of cumulative errors caused by supporting multiple sub-sand cores and then assembling them in the traditional core making solution, for castings with complex structures, deformation will occur after printing according to the set dimensions, resulting in the prepared integral sand core being different from the set dimensions. Figure 3 Taking the scheme shown as an example, after testing, it was found that the main hanger sand core 1 was warped by 3~4mm in the vertical direction, the non-parallelism of the two auxiliary hangers 2 was 1.5~2.5mm in the horizontal direction, and the warping was 2~3mm in the vertical direction. The dimensional requirements of the corresponding positions of the casting are that the warping of the main hanger is within the range of ±2mm, the non-parallelism of the two auxiliary hangers in the horizontal direction should be <2mm, and the warping in the vertical direction is within the range of ±2mm. Figure 3 The probability of the overall sand core size of the 3D printing being out of tolerance is shown to be about 30-40%.

[0026] In order to overcome the above-mentioned problem of out-of-tolerance size of 3D printed integral sand cores and improve dimensional accuracy, the present embodiment discloses a method for producing 3D printed integral sand cores, which includes: a step of printing an integral sand core sample, a step of obtaining a deformation position and a deformation amount, a step of designing a reverse deformation sand core model, and a step of printing an integral sand core finished product.

[0027] Specifically, the step of printing the integral sand core sample includes: designing an integral sand core model according to the size of the integral sand core to be manufactured, and printing the integral sand core sample.

[0028] The overall sand core model should be designed according to the requirements. For example, the size of the overall sand core to be made can be obtained by considering the structural shape of the actual casting, and the overall sand core model can be designed through the corresponding software according to the size of the overall sand core to be made, and the overall sand core sample can be 3D printed. The overall sand core sample is not the final overall sand core product, but a sand core printed according to the ideal design model before obtaining the overall sand core product. From the previous discussion, it can be known that although the overall sand core sample is a sand core printed according to the ideal design model, the sand core will inevitably undergo a certain deformation. For some sand cores with complex structures, the dimensional accuracy will be excessive due to excessive deformation.

[0029] The step of obtaining the deformation position and deformation amount includes: obtaining the actual size of the overall sand core sample, and comparing it with the size of the overall sand core model to obtain the deformation position and deformation amount of the overall sand core sample.

[0030] The actual size of the integral sand core sample is obtained by measurement, and then compared with the size of the integral sand core model to determine the deformation position and deformation amount of the integral sand core sample (the deformation amount here is directional, that is, the deformation value in which direction). It should be noted that the deformation position and deformation amount are one-to-one corresponding. Since the integral sand core sample and the integral sand core sample are printed with the same material and the same equipment, they theoretically have the same, or at least similar, deformation position and deformation amount. Therefore, the deformation position and deformation amount of the integral sand core sample can be used as a reverse design reference for the sand core model of the printed integral sand core product.

[0031] The steps of designing the reverse deformation sand core model include: designing the reverse deformation sand core model according to the deformation position and deformation amount of the whole sand core sample.

[0032] The reverse deformation sand core model needs to be designed according to the deformation position and deformation amount of the overall sand core sample, that is, based on the deformation amount of a certain deformation position of the overall sand core sample, the deformation in the opposite direction of the deformation position is designed on the basis of the overall sand core model, and the deformation amount in the opposite direction can be designed according to the tolerance of the casting. For example, if the deformation amount of a certain deformation position of the overall sand core sample is a, the deformation amount of the reverse deformation sand core model in the opposite direction of the deformation position can be designed as b, as long as ab can meet the tolerance range of the casting. Preferably, b can be designed to be equal to a and opposite in direction, so that the casting obtains the optimal size. The purpose of designing the reverse deformation sand core model is that when the overall sand core finished product is printed according to the reverse deformation sand core model, if a certain deformation position has a corresponding deformation amount in the corresponding direction again, because the corresponding reverse deformation is performed at the deformation position (that is, the size of this position is reduced or increased), when deformation occurs again, this deformation will instead cause the final overall sand core finished product to shift in the direction of the designed size, thereby improving the dimensional accuracy of the overall sand core finished product.

[0033] The step of printing the integral sand core finished product includes printing and manufacturing the integral sand core finished product according to the reverse deformation sand core model.

[0034] Furthermore, in this embodiment, in the step of printing the integral sand core sample, a 3D modeling software can be used to design the integral sand core model according to the size of the integral sand core to be produced, and the size of the integral sand core to be produced is derived from the size of the casting. In the step of printing the integral sand core sample, a sand mold 3D printing device can be used to print the integral sand core sample.

[0035] In the step of obtaining the deformation position and deformation amount, the actual size of the overall sand core sample can be obtained by laser three-dimensional scanning, and compared with the size of the overall sand core model to obtain the deformation position and deformation amount of the overall sand core sample.

[0036] In this embodiment, if Figure 3As shown, the integral sand core can be a sand core of a hanger type casting, and the integral sand core includes a main hanger sand core 1, a sub-hanger sand core 2 located on both sides of the main hanger sand core 1, and a wing-shaped structure sand core 3 connecting the main hanger sand core 1 and the sub-hanger sand core 2. It should be noted that the embodiment of the present invention is not limited to the sand core of the hanger type casting, and any sand core with dimensional tolerance problems caused by deformation can be manufactured using the 3D printing integral sand core manufacturing method disclosed in the embodiment of the present invention to improve the dimensional accuracy of the finished sand core, and then improve the dimensional accuracy of the casting.

[0037] In this embodiment, the steps of obtaining the deformation position and deformation amount are as follows: obtaining the actual size of the overall sand core sample and comparing it with the size of the overall sand core model, obtaining the warpage of the main hanger sand core sample of the overall sand core sample in the vertical direction as a, the non-parallelism of the two hanger sand core samples in the horizontal direction as b, and the warpage in the vertical direction as -c. The vertical direction refers to the direction in which the casting is located when it is in use, that is, the vertical direction; correspondingly, the horizontal direction refers to the horizontal direction when the casting is in use.

[0038] The specific steps for designing the reverse deformation sand core model are as follows: according to the deformation position and deformation amount of the overall sand core sample, the reverse deformation sand core model is designed, so that the reverse deformation sand core model is based on the overall sand core model, the warping of the main hanger sand core model along the vertical direction is -a, the non-parallelism of the two auxiliary hanger sand core models along the horizontal direction is -b, and the warping along the vertical direction is -c, that is, the same deformation amount is designed in opposite directions for the main hanger sand core model and the auxiliary hanger sand core model.

[0039] In a specific embodiment, the main hanger sand core sample of the integral sand core sample has a warping of 3 to 4 mm in the vertical direction, the two hanger sand core samples have a non-parallelism of 1.5 to 2.5 mm in the horizontal direction, and a warping of 2 to 3 mm in the vertical direction.

[0040] When designing the reverse deformation sand core model, the main hanger sand core model is warped to -3~-4mm in the vertical direction, the two hanger sand core models are non-parallel to -1.5~-2.5mm in the horizontal direction, and are warped to -2~-3mm in the vertical direction.

[0041] It should be noted that the above-mentioned specific deformation amount scheme is based on a specific scheme to obtain the deformation amount and the designed reverse deformation amount. Therefore, the specific deformation amount and deformation position are not limited to this embodiment. Technical personnel in this field can design a reverse deformation sand core model based on the actual sand core, and the actual deformation position and deformation amount of the sand core.

[0042] In this embodiment, the mold sand selected for the integral sand core product is 70-140 mesh, the selected resin addition amount is 2%-3% of the weight of the mold sand, and the selected curing agent addition amount is 0.2%-0.3% of the resin addition amount. It should be noted that the integral sand core product and the integral sand core sample should use the same molding sand material for 3D printing. After experimental verification, the integral sand core product prepared by selecting the above-mentioned material has a smaller deformation amount, which can further improve the dimensional accuracy of the casting.

[0043] During casting, the finished integral sand core will be exposed to high-temperature alloy liquid, causing the finished integral sand core to heat up quickly. The high temperature will cause the resin binder of the finished integral sand core to thermally decompose and produce a large amount of gas. The higher the temperature, the more violent the reaction to form gas, and the greater the gas pressure. The gas will diffuse from the high-pressure area to the low-pressure area in the middle of the finished integral sand core. Based on this, the finished integral sand core usually needs to be equipped with an exhaust structure to discharge the gas generated by the high temperature to avoid affecting the quality of the casting.

[0044] In a specific embodiment of the present invention, the reverse deformation sand core model includes a sand core model body and an exhaust structure, and the sand core model body and the exhaust structure are formed at one time by 3D printing. Figure 4 and Figure 5 As shown, the exhaust structure includes a main exhaust channel 4 and a branch exhaust channel 5.

[0045] The main exhaust channel is arranged along the main body of the sand core model, and the main exhaust channels at various positions are interconnected to form a channel network. Taking the reverse deformation sand core model as a hanger sand core model as an example, it is necessary to design the main exhaust channel 4 in the main hanger sand core model, the auxiliary hanger sand core model and the wing-shaped structure sand core model, so that these positions can be exhausted through the main exhaust channel 4. The main exhaust channels at various positions are interconnected to facilitate the discharge of gas in the main exhaust channel out of the sand core.

[0046] In this embodiment, there are multiple branch exhaust channels 5, which are arranged at intervals along the main exhaust channel 4. One end of the branch exhaust channel 5 is connected to the main exhaust channel 4. The branch exhaust channel 5 can be connected to the main exhaust channel 4 at a certain angle. Preferably, the branch exhaust channel 5 can be connected to the main exhaust channel 4 vertically, and the other end penetrates the surface of the sand core model body and is connected to the cavity. The branch exhaust channel 5 is an hourglass-shaped structure.

[0047] When the 3D printed integral sand core product with the above exhaust structure is used for casting, the main exhaust channel 4 of the integral sand core product is connected to the through holes reserved in the sand mold outer mold through the core heads at both ends of the integral sand core product to discharge the gas outside the sand mold outer mold. That is, the gas generated by the sand on the surface of the integral sand core product diffuses inward, flows into the branch exhaust channel 5, and then flows into the main exhaust channel 4. The main exhaust channel 4 is connected to the sand mold outer mold, so that the gas generated by the integral sand core product is discharged into the atmosphere.

[0048] In addition, in this embodiment, the branch exhaust channel 5 is designed as an hourglass-shaped structure, which is convenient for cleaning the loose sand therein on the one hand, and for filling the surface pits formed by the branch exhaust channel 5 on the surface of the integral sand core product with resin sand on the other hand, and then scraping it flat according to the shape. In this way, the air permeability of the integral sand core product can be improved, and the inner surface quality of the casting can be improved.

[0049] Specifically, Figure 5 As shown, the branch exhaust channel 5 includes an outer branch exhaust channel section 501 and an inner branch exhaust channel section 502 connected in the direction from the surface of the sand core model body to the main exhaust channel 4, and the outer branch exhaust channel section 501 and the inner branch exhaust channel section 502 are both conical structures. That is, the outer branch exhaust channel section 501 and the inner branch exhaust channel section 502 form an hourglass structure.

[0050] The large diameter end of the outer exhaust channel section 501 is arranged close to the surface of the main body of the sand core model, the large diameter end of the inner exhaust channel section 502 is arranged close to the main exhaust channel 4, and the small diameter end of the outer exhaust channel section 501 is the same diameter as the small diameter end of the inner exhaust channel section 502, and is connected. Since the large diameter end of the outer exhaust channel section 501 is arranged close to the surface of the main body of the sand core model, the diameter of the mouth of the outer exhaust channel section 501 is relatively large, and the diameter gradually decreases with the increase of depth. When the mouth of the branch exhaust channel 5 is filled with resin sand, since the diameter of the outer exhaust channel section 501 gradually decreases with the depth, its side wall has a supporting effect on the resin sand filled in, and can be attached and retained in the outer exhaust channel section 501, which is convenient for blocking the outer exhaust channel section 501 to avoid the alloy material from entering the outer exhaust channel section 501 during casting and forming burrs.

[0051] The inner exhaust channel section 502 is just the opposite to the outer exhaust channel section 501. As the depth increases, the diameter of the inner exhaust channel section 502 gradually increases, that is, the diameter of the side facing the main exhaust channel 4 is larger, which makes it easier to clear the loose sand in the outer exhaust channel section 501 and the main exhaust channel 4.

[0052] In addition, the branch exhaust channel 5 not only includes an hourglass-shaped structure, but also includes an equal-diameter channel 503 connected between the inner branch exhaust channel section 502 and the main exhaust channel 4, that is, in this embodiment, the hourglass-shaped structure is designed only at one end of the branch exhaust channel 5 close to the surface of the sand core model body, and the other part is an equal-diameter channel 503. In order to ensure a smooth transition, the equal-diameter channel 503 has the same diameter as the large-diameter end of the inner branch exhaust channel section 502.

[0053] like Figure 4As shown, in this embodiment, in order to ensure that the gas generated by the main body of the sand core model can be quickly merged into the main exhaust channel 4 through the branch exhaust channel 5. The branch exhaust channels 5 may include multiple groups, each group of branch exhaust channels 5 is arranged at intervals along the main exhaust channel 4, each group of branch exhaust channels 5 may be arranged at equal intervals, or may be arranged at unequal intervals according to requirements, and the interval between two adjacent groups of branch exhaust channels 5 should be designed according to actual products.

[0054] The same group of branch exhaust channels 5 is arranged at the same cross section of the main exhaust channel 4, that is, the branch exhaust channels 5 located at the same cross section of the main exhaust channel 4 are the same group of branch exhaust channels 5. There are multiple branch exhaust channels 5 in a group of branch exhaust channels 5, and they extend in multiple directions. Figure 4 In the illustrated solution, one group of branch exhaust channels 5 includes four branch exhaust channels 5, and the four branch exhaust channels 5 are arranged vertically in pairs. It should be noted that those skilled in the art can set other numbers of branch exhaust channels 5 for each group of branch exhaust channels 5 according to needs, and are not limited to the above-mentioned four solutions, and the angle between two adjacent branch exhaust channels is not limited to the vertical angle.

[0055] Furthermore, in a specific embodiment, the diameter of the main exhaust channel 4 can be designed to be 10mm~20mm, and the distance from the edge of the main exhaust channel 4 to the edge of the sand core model body is not less than 20mm, that is, the depth of the main exhaust channel 4 in the sand core model body should be ensured, that is, the amount of sand at any position of the main exhaust channel 4 should not be less than 20mm, so as to avoid the problem of collapse of the overall sand core product caused by the main exhaust channel 4 being too shallow.

[0056] Each group of branch exhaust channels 5 can be arranged at intervals of 100mm to 200mm along the main exhaust channel 4. The large diameter end of the outer branch exhaust channel section 501 extends to the surface of the sand core model body and has a diameter of 4 to 6mm. The diameter of the small diameter end of the outer branch exhaust channel section 501 is 2.5 to 3.5mm, and the length of the outer branch exhaust channel section 501 along the axial direction is 5mm to 10mm. The diameter of the large diameter end of the inner branch exhaust channel section 502 is 4 to 6mm, the diameter of the small diameter end of the inner branch exhaust channel section 502 is 2.5 to 3.5mm, and the length of the inner branch exhaust channel section 502 along the axial direction is 5mm to 10mm.

[0057] It should be noted that the above size range is an example, which is related to the size of the specific overall sand core product. Those skilled in the art can design the size range of the exhaust structure according to the size of the sand core.

[0058] In a specific embodiment of the present invention, the 3D printing integral sand core manufacturing method may also include a sand cleaning step. After the sand cleaning step is completed, the mouth of the branch exhaust channel 5 is filled with resin sand. That is, before the outer branch exhaust channel section 501 of the branch exhaust channel 5 is filled with resin sand, the loose sand in the exhaust structure needs to be cleared out to avoid the loose sand affecting the exhaust.

[0059] In this embodiment, the sand cleaning step includes at least one of the following steps: 1) Stand up the finished integral sand core so that the loose sand in the main exhaust channel 4 flows out; 2) Compressed air is introduced into one end of the main exhaust channel 4, so that negative pressure is formed at the connection point between the main exhaust channel 4 and the branch exhaust channel 5, so as to suck the loose sand in the branch exhaust channel 5 into the main exhaust channel 4 and discharge it with the compressed air; 3) Use a tool to insert into the branch exhaust channel 5 and move it back and forth to assist in cleaning the loose sand in the branch exhaust channel 5.

[0060] Among them, in the first step, after the integral sand core product is formed, the integral sand core product is erected to ensure that the main exhaust channel 4 with the longest path remains vertical or nearly vertical, so that the loose sand in the main exhaust channel 4 in the main hanger sand core and the auxiliary hanger sand core can flow out directly.

[0061] In the second step, compressed air is introduced into one end of the main exhaust channel 4 in the main hanger sand core and the auxiliary hanger sand core, and the fast-flowing gas forms a negative pressure in the main exhaust channel 4, sucking the loose sand in the branch exhaust channel 5 into the main exhaust channel 4, and finally discharged together with the airflow.

[0062] In the third step, a steel needle is inserted into the branch exhaust channel 5 and reciprocated to assist in cleaning the loose sand in the branch exhaust channel 5 .

[0063] It should be noted that the above three sand cleaning steps can be performed simultaneously. If the sand cleaning is performed in the above order, the sand cleaning effect and efficiency can be improved.

[0064] The 3D printing integral sand core manufacturing method disclosed in the embodiment of the present invention is suitable for casting large and complex rack-type structural parts. Among them, large refers to structural parts with a length of not less than 2.5m and a weight of not less than 500kg; complex refers to structural parts with complex structures, large differences in wall thickness, and wing-shaped structures that conform to aerodynamic design; rack-type structural parts refer to structural parts composed of multiple load-bearing beams, and the load-bearing beams are connected by wing-shaped structures, which are usually placed outside the aircraft and used to hang or carry items.

[0065] The integral sand core product is manufactured by the 3D printing integral sand core manufacturing method disclosed in this embodiment, and the casting is prepared by the integral sand core product. Figure 1As shown, the casting can be placed on the outside of the aircraft to suspend or carry missiles. The outline dimensions of the casting are 2580mm in length, 600mm in width, 400mm in height, 45mm in maximum wall thickness, and 4mm in minimum wall thickness. After X-ray inspection, the metallurgical quality of the casting meets the requirements of HB963-2005 Class I parts. The cutting performance of the specified area on the casting reaches tensile strength σb=480MPa and elongation δ=13%; the metallographic photograph of the specified area on the casting is as follows Figure 6 As shown in the figure, it shows that the casting has fine grains and uniform structure; when the maximum stress σmax=120MPa, loading type R=0.1, specimen notch Kt=1, and loading frequency f=100Hz, the number of fatigue cycles is greater than 10 7 , indicating that the casting has good dynamic load bearing capacity.

[0066] Compared with the prior art, the 3D printed integral sand core manufacturing method disclosed in the embodiment of the present invention reduces the defects of high cost of split sand core box molds, low core making efficiency, and easy generation of burrs on the parting surface, solves the key problems of deformation and exhaust of large and complex 3D printed integral sand cores, reduces the probability of scrapping castings due to dimensional tolerances or pore inclusion defects, and significantly improves the first-time inspection pass rate of large and complex castings.

[0067] As shown in this application and claims, unless the context clearly indicates an exception, the words "a", "an", "a kind" and / or "the" do not refer to the singular, but also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements. The elements defined by the sentence "includes a..." do not exclude the existence of other identical elements in the process, method, commodity or device that includes the elements.

[0068] In the description of this application, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in this application based on the specific content of the technical solution.

[0069] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0070] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for making a 3D printed integral sand core, characterized in that: include: Printing an integral sand core sample step, designing an integral sand core model according to the size of the integral sand core to be manufactured, and printing the integral sand core sample; The step of obtaining the deformation position and deformation amount is to obtain the actual size of the integral sand core sample and compare it with the size of the integral sand core model to obtain the deformation position and deformation amount of the integral sand core sample; The reverse deformation sand core model designing step includes designing the reverse deformation sand core model according to the deformation position and deformation amount of the overall sand core sample; The step of printing the integral sand core finished product is to print and manufacture the integral sand core finished product according to the reverse deformed sand core model.

2. The 3D printing integral sand core manufacturing method according to claim 1, characterized in that: The step of printing the integral sand core sample is specifically as follows: using 3D modeling software to design an integral sand core model according to the size of the integral sand core to be manufactured, and using a sand mold 3D printing device to print the integral sand core sample; The step of obtaining the deformation position and deformation amount is specifically as follows: obtaining the actual size of the overall sand core sample by laser three-dimensional scanning, and comparing it with the size of the overall sand core model to obtain the deformation position and deformation amount of the overall sand core sample.

3. The 3D printing integral sand core manufacturing method according to claim 1, characterized in that: The integral sand core is a sand core of a hanger type casting, and the integral sand core comprises a main hanger sand core, auxiliary hanger sand cores located on both sides of the main hanger sand core, and a wing-shaped structure sand core connecting the main hanger sand core and the auxiliary hanger sand core.

4. The 3D printing integral sand core manufacturing method according to claim 3, characterized in that: The step of obtaining the deformation position and deformation amount is specifically as follows: obtaining the actual size of the integral sand core sample and comparing it with the size of the integral sand core model, obtaining that the warpage of the main hanger sand core sample of the integral sand core sample along the vertical direction is a, the non-parallelism of the two hanger sand core samples along the horizontal direction is b, and the warpage along the vertical direction is c; The steps of designing the reverse deformation sand core model are specifically as follows: according to the deformation position and deformation amount of the overall sand core sample, the reverse deformation sand core model is designed, so that the reverse deformation sand core model is based on the overall sand core model, the warping of the main hanger sand core model along the vertical direction is -a, the non-parallelism of the two hanger sand core models along the horizontal direction is -b, and the warping along the vertical direction is -c.

5. The 3D printing integral sand core manufacturing method according to claim 1, characterized in that: The molding sand selected for the integral sand core finished product is 70-140 mesh, the selected resin addition amount is 2%-3% of the molding sand weight, and the selected curing agent addition amount is 0.2%-0.3% of the resin addition amount.

6. The method for making a 3D printed integral sand core according to any one of claims 1 to 5, characterized in that: The reverse deformation sand core model comprises a sand core model body and an exhaust structure, wherein the exhaust structure comprises a main exhaust channel and a branch exhaust channel; The main exhaust channel is arranged along the sand core model body, and the main exhaust channels at various positions are interconnected. There are multiple branch exhaust channels, which are arranged at intervals along the main exhaust channel. One end of the branch exhaust channel is connected to the main exhaust channel, and the other end passes through the surface of the sand core model body and is connected to the mold cavity. The branch exhaust channel is an hourglass-shaped structure.

7. The method for making a 3D printed integral sand core according to claim 6, wherein: The branch exhaust channels include a plurality of groups, each group of the branch exhaust channels are arranged at intervals along the main exhaust channel, and the branch exhaust channels in the same group are arranged at the same cross-section of the main exhaust channel, and include the branch exhaust channels extending in multiple directions and perpendicular to the main exhaust channel.

8. The method for making a 3D printing integral sand core according to claim 7, characterized in that: The diameter of the main exhaust channel is 10 mm to 20 mm, and the distance from the edge of the main exhaust channel to the edge of the sand core model body is not less than 20 mm; and / or, Each group of branch exhaust channels is arranged along the main exhaust channel at intervals of 100 mm to 200 mm; and / or, The branch exhaust channel includes an outer branch exhaust channel section and an inner branch exhaust channel section that are connected in the direction from the surface of the sand core model body to the main exhaust channel, and the outer branch exhaust channel section and the inner branch exhaust channel section are both conical structures. The large diameter end of the outer branch exhaust channel section is arranged close to the surface of the sand core model body, and the large diameter end of the inner branch exhaust channel section is arranged close to the main exhaust channel. The small diameter end of the outer branch exhaust channel section has the same diameter as the small diameter end of the inner branch exhaust channel section, and is connected.

9. The method for making a 3D printing integral sand core according to claim 8, characterized in that: The branch exhaust channel further includes an equal-diameter channel connected between the inner branch exhaust channel section and the main exhaust channel, wherein the equal-diameter channel has the same diameter as the large-diameter end of the inner branch exhaust channel section; and / or, The large diameter end of the outer branch exhaust channel section extends to the surface of the sand core model body and has a diameter of 4-6 mm, the small diameter end of the outer branch exhaust channel section has a diameter of 2.5-3.5 mm, and the length of the outer branch exhaust channel section in the axial direction is 5 mm-10 mm; and / or, The diameter of the large diameter end of the inner branch exhaust channel section is 4-6 mm, the diameter of the small diameter end of the inner branch exhaust channel section is 2.5-~3.5 mm, and the length of the inner branch exhaust channel section along the axial direction is 5 mm~10 mm.

10. The method for making a 3D printing integral sand core according to claim 6, characterized in that: The invention also comprises a sand cleaning step, and after the sand cleaning step is completed, the mouth of the branch exhaust channel is filled with resin sand; The sand cleaning step includes at least one of the following steps: The finished integral sand core is erected to allow the loose sand in the main exhaust passage to flow out; Compressed air is introduced into one end of the main exhaust channel, so that negative pressure is formed at the connection point between the main exhaust channel and the branch exhaust channel, so as to suck the loose sand in the branch exhaust channel into the main exhaust channel and discharge it with the compressed air; A tool is inserted into the branch exhaust channel and reciprocated to assist in cleaning the loose sand in the branch exhaust channel.

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