Casting construction method based on 3D printing

Abstract

The invention relates to the technical field of 3D casting, in particular to a casting construction method based on 3D printing, which comprises the following steps: constructing a three-dimensional model of a part to be manufactured; layering the three-dimensional model to obtain slices of each layer; a central axis and a skeleton line of the slice are obtained, the central axis is a point set which is equidistant from two or more points on different edges or extension lines of the edges on the profile of the slice, and the skeleton line is a connecting line of a certain point on the central axis and a certain point on the profile of the corresponding slice; a layered manufacturing mode is adopted, fine machining of parts can be achieved, the manufacturing precision is improved, waste of materials can be reduced to the maximum extent through a layer-by-layer stacking mode, the material utilization rate is improved, a printing path can be optimized according to actual needs, the optimal path point number can be determined according to the requirements of different parts, and the production efficiency is improved. Therefore, the printing path is flexibly adjusted.

Description

Technical Field

[0001] The invention relates to the technical field of 3D casting, and in particular to a casting construction method based on 3D printing. Background Art

[0002] With the rapid development of 3D printing technology, the three-dimensional model of the product can be directly imported into the printing equipment to directly obtain the casting prototype wax mold to replace the traditional wax mold.

[0003] In the field of sand casting, the current sand molds for 3D printing use sand + curing agent + binder as raw materials. According to the input three-dimensional model, the molds are prepared layer by layer, which can replace the modeling process in the traditional sand casting process. However, after the sand mold is formed, it still needs coating, baking, assembling and other processes before pouring molten steel.

[0004] During the post-waxing process of 3D printing, the deformation and size changes of the wax mold and the fracture of the thin-walled weak positions also affect the pass rate of wax mold printing. At the same time, it increases material waste, reduces material utilization, fails to highlight the shape and texture of the casting, and reduces details and texture. Summary of the invention

[0005] In view of this, an embodiment of the present invention hopes to provide a casting construction method based on 3D printing to solve or alleviate the technical problems existing in the prior art and to provide at least a beneficial option for the above technical problems.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A casting construction method based on 3D printing comprises the following steps:

[0008] S1. Build a three-dimensional model of the part to be manufactured;

[0009] S2, layering the three-dimensional model to obtain slices of each layer;

[0010] S3, obtaining a central axis and a skeleton line of the slice, wherein the central axis is a set of points equidistant from two or more points on different sides or extensions of sides on the slice contour, and the skeleton line is a line connecting a point on the central axis and a corresponding point on the slice contour;

[0011] S4, dividing the skeleton line obtained in S3 into two parts with the central axis as the center, the skeleton line located on one side of the central axis is recorded as the first half area, and the skeleton line located on the other side of the central axis is recorded as the second half area;

[0012] S5, respectively, arranging the skeleton lines of the first half region and the second half region obtained in S4 in sequence along the direction of the central axis;

[0013] S6, respectively calculating the maximum skeleton line length and the minimum skeleton line length in the skeleton lines of the sorted first half area and the second half area, and determining the optimal path points of the first half area and the second half area according to the maximum printing width and the minimum printing width limited by the actuator;

[0014] S7, according to the optimal number of path points of the first half area obtained in S6, determine the position of each path point on the skeleton line of the first half area, ensure that the distance between each path point is the length of the skeleton line divided by the optimal number of path points, and then sequentially connect the corresponding path points on the skeleton line of the first half area to generate a printing path for the first half area, and simultaneously use this method to generate a printing path for the second half area;

[0015] S8. Grind and clean the casting surface. Use a pneumatic grinding head to grind the sand holes or pores on the surface defects and expand the openings. Then use high-pressure gas to blow out the sand holes or pores to remove impurities.

[0016] S9, using 3D printing metal powder as molding powder, spraying binder micro droplets layer by layer through a micro droplet jet bonding method to stack the 3D printing powder layer by layer into the sand holes or pores;

[0017] S10, sintering the 3D printing powder at high temperature in a reducing atmosphere to sinter the metal powder into a whole and fill the sand holes or pores;

[0018] S11, repeat S9 and S10 until the sand holes or pores are completely filled and slightly higher than the casting surface;

[0019] S12. Mill or grind the protruding parts on the casting surface until they meet the casting surface quality requirements.

[0020] As a further solution of the present invention: the method for determining the region to which the skeleton line belongs in S4 is: substituting the coordinates of the two endpoints of the skeleton line into formula (1), classifying the skeleton line with a positive result as the first half region, and classifying the skeleton line with a negative result as the second half region;

[0021] MAx×OUTy-MAy×OUTx (1);

[0022] Wherein, MAx is the abscissa of the endpoint MA on the central axis of the skeleton line, MAy is the ordinate of the endpoint MA, OUTy is the ordinate of the endpoint OUT on the slice contour of the skeleton line, and OUTx is the abscissa of the endpoint OUT.

[0023] As a further solution of the present invention: the binder microdroplets used in S9 include water-soluble polymer materials or water.

[0024] As a further solution of the present invention: the water-soluble polymer material includes polyvinyl pyrrolidone or polyvinyl alcohol.

[0025] As a further solution of the present invention: the high temperature sintering of S10 is carried out by laser melting or oxyacetylene sintering, and hydrogen or carbon monoxide is introduced as a reducing agent.

[0026] As a further solution of the present invention: the 3D printing metal powder includes iron powder or a mixed powder of iron powder and stainless steel powder.

[0027] As a further solution of the present invention: the high temperature sintering is carried out by gradually increasing the temperature, and the maximum temperature is controlled between 1000°C and 1350°C.

[0028] As a further solution of the present invention: the method further comprises the following steps:

[0029] Step 1: divide a triangle in a blank polygonal image according to a preset division rule, and divide the other regions of the polygon except the triangle into at least three regions: light, gray and dark. The blank polygonal image has the characteristics of equal side lengths, equal internal angles and axial symmetry;

[0030] Step 2: extracting the target color with the largest color proportion from the target cover image, and filling the blank image of the polygon with the target color;

[0031] Step 3: adjusting the transparency of the area corresponding to the triangle to a preset value, and adjusting the transparency values ​​of the light, gray and dark areas from low to high according to the transparency values;

[0032] Step 4: Add outline strokes to the triangle corresponding area and the light, gray and dark areas to generate a polygonal 3D effect covering template;

[0033] Step 5: Overlay the polygonal 3D effect overlay template on the target cover image to form a 3D visual effect of the target cover image.

[0034] As a further solution of the present invention: extracting the target color with the largest color proportion from the target cover image and filling the target color in the blank image of the polygon includes: extracting the color with the largest color proportion from the target cover image;

[0035] The brightness of the color with the largest proportion is reduced by a preset percentage value, and the transparency value of the color with the largest proportion is set to a preset fourth value, so as to obtain a target color;

[0036] Fill the blank image of the polygon with the target color.

[0037] As a further solution of the present invention: adding outline strokes to the area corresponding to the triangle and the three areas of light, gray and dark to generate a polygonal 3D effect overlay template includes: adding outline strokes to the area corresponding to the triangle, and adding the outline strokes to the areas corresponding to one of the first triangles and two of the first sub-triangles included in the bright area;

[0038] and, adding the outline stroke to an area corresponding to one of the second triangles and two of the second sub-triangles included in the gray area;

[0039] And, adding the outline stroke to the area corresponding to one of the third triangles and two of the third sub-triangles included in the dark area to generate a polygonal 3D effect overlay template.

[0040] The embodiment of the present invention has the following advantages due to the adoption of the above technical solution:

[0041] 1. High manufacturing precision: This solution adopts a layered manufacturing method, which can achieve fine processing of parts and improve manufacturing precision.

[0042] 2. Save materials: This solution can minimize material waste and improve material utilization by stacking layer by layer.

[0043] 3. Strong flexibility: This solution can optimize the printing path according to actual needs, and can determine the optimal number of path points according to the requirements of different parts, so as to flexibly adjust the printing path.

[0044] 4. High surface quality: This solution carries out grinding, cleaning, sintering and other treatments in the final process steps, which can ensure the quality requirements of the casting surface and improve the overall quality of the parts.

[0045] 5. Wide application: This solution can be printed with different metal powders, including iron powder or mixed powder, and is suitable for the manufacture of castings of different materials.

[0046] 6. Environmental protection and energy saving: This solution uses water-soluble polymer materials as binder droplets and adopts high-temperature sintering under a reducing atmosphere, which is more environmentally friendly and energy-saving than traditional casting processes.

[0047] 7. Division rules and color filling: Through the preset division rules, a triangle is divided in the blank polygonal image, and the other areas are divided into three areas: light, gray and dark. Then, the target color with the largest color proportion is extracted from the target cover image, and the target color is filled in the blank polygonal image. In this way, partial areas of the casting can be colored, which increases the visual effect and aesthetics.

[0048] 8. Transparency adjustment: adjust the transparency of the triangular area according to the preset value, and adjust the transparency of the light, gray and dark areas in order from low to high. This transparency adjustment can make different areas of the casting appear layered and three-dimensional, further enhancing the 3D visual effect.

[0049] 9. Outline stroke: By adding outline strokes to the triangular area and the light, gray and dark areas, a polygonal 3D effect overlay template can be generated. This can further highlight the shape and texture of the casting, increase the details and texture, and make the visual effect more realistic.

[0050] The above summary is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the present invention will be readily apparent by reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1 A workflow of a casting construction method based on 3D printing proposed by the present invention;

[0053] Figure 2 The present invention provides a workflow of an embodiment of a casting construction method based on 3D printing. DETAILED DESCRIPTION

[0054] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0055] It should be noted that the terms "first", "second", "symmetrical", "array", etc. are only used to distinguish between description and position description purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the definition of "first", "symmetrical", etc. can explicitly or implicitly include one or more of these features; similarly, when the quantity of certain features is not limited in the form of words such as "two" or "three", it should be noted that this feature also explicitly or implicitly includes one or more feature quantities;

[0056] In the present invention, unless otherwise clearly specified and limited, the terms such as "installation", "connection", "fixation" and the like should be understood in a broad sense; for example, it can be a fixed connection, a detachable connection, or an integral molding; it can be a mechanical connection, a direct connection, welding, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood based on the description and drawings combined with specific circumstances.

[0057] like Figure 1 As shown, the present invention provides a casting construction method based on 3D printing, comprising the following steps:

[0058] S1. Constructing a three-dimensional model of the part to be manufactured. First, a three-dimensional model of the part to be manufactured needs to be constructed, which can usually be done through computer-aided design software (CAD);

[0059] S2, layering the three-dimensional model to obtain slices of each layer, layering the three-dimensional model to obtain slices of each layer, in order to prepare data for a subsequent 3D printing process;

[0060] S3, obtaining the central axis and skeleton line of the slice, wherein the central axis is a set of points equidistant from two or more points on different sides or extensions of the sides on the slice contour, and the skeleton line is a line connecting a point on the central axis and a point on the slice contour corresponding to the central axis, and obtaining the central axis and skeleton line of the slice, wherein the acquisition of these lines may involve knowledge of mathematical modeling and computational geometry, so as to ensure the stability and consistency of the component during the 3D printing process;

[0061] S4, the skeleton line obtained in S3 is divided into two parts with the central axis as the center, the skeleton line located on one side of the central axis is recorded as the first half area, and the skeleton line located on the other side of the central axis is recorded as the second half area, and the method for determining the area to which the skeleton line belongs in S4 is: substitute the coordinates of the two end points of the skeleton line into formula (1), classify the skeleton line with a positive result as the first half area, and classify the skeleton line with a negative result as the second half area;

[0062] MAx×OUTy-MAy×OUTx (1);

[0063] In the formula, MAx is the abscissa of the endpoint MA on the central axis of the skeleton line, MAy is the ordinate of the endpoint MA, OUTy is the ordinate of the endpoint OUT on the slice contour of the skeleton line, OUTx is the abscissa of the endpoint OUT. The skeleton line is divided into two parts according to the central axis, and the area to which the skeleton line belongs is determined according to formula (1) in order to optimize the printing path of the component and ensure the strength and stability of the component;

[0064] S5, respectively sorting the skeleton lines of the first half area and the second half area obtained in S4 in sequence along the direction of the central axis, and sorting the skeleton lines to prepare for subsequent path planning;

[0065] S6, respectively calculating the maximum skeleton line length and the minimum skeleton line length in the skeleton lines of the sorted first half area and the second half area, and determining the optimal path points of the first half area and the second half area according to the maximum printing width and the minimum printing width limited by the actuator, and calculating and determining the optimal path points of each area to ensure that the printing width meets the requirements;

[0066] S7, according to the optimal number of path points of the first half area obtained in S6, determine the position of each path point on the skeleton line of the first half area, ensure that the distance between each path point is the length of the skeleton line divided by the optimal number of path points, and then sequentially connect the corresponding path points on the skeleton line of the first half area to generate a printing path for the first half area, and at the same time use this method to generate a printing path for the second half area, determine the position of the path point on the skeleton line of each area according to the optimal number of path points, and generate a printing path, in order to guide the movement path of the 3D printing device;

[0067] S8. Grind and clean the surface of the casting. Use a pneumatic grinding head to grind the sand holes or pores of the surface defects and expand the openings. Then use high-pressure gas to blow out the sand holes or pores to remove impurities. Grind and clean the surface of the casting to prepare for the subsequent 3D printing process.

[0068] S9, using 3D printing metal powder as molding powder, spraying binder micro-droplets layer by layer through a droplet jet bonding method so that the 3D printing powder is stacked layer by layer into the sand holes or pores, the binder micro-droplets used in S9 include water-soluble polymer materials or water, the water-soluble polymer materials include polyvinyl pyrrolidone or polyvinyl alcohol, the 3D printing metal powder includes iron powder or a mixed powder of iron powder and stainless steel powder, using 3D printing metal powder as molding powder, stacking the powder layer by layer through a droplet jet bonding method, and using water-soluble polymer materials or water as binder micro-droplets, involving powder stacking and bonding technology;

[0069] S10, sintering the 3D printing powder at high temperature in a reducing atmosphere to form a whole and fill the sand holes or pores. The high temperature sintering of S10 adopts laser melting or oxyacetylene sintering, and hydrogen or carbon monoxide is introduced as a reducing agent. The high temperature sintering is carried out in a stepwise heating manner, and the maximum temperature is controlled between 1000° C. and 1350° C. The 3D printing powder is sintered at high temperature in a reducing atmosphere to form a whole and fill the sand holes or pores. This step is the curing process of the 3D printing metal powder, which usually adopts laser melting or oxyacetylene sintering.

[0070] S11, repeat S9 and S10 until the sand holes or pores are completely filled and slightly higher than the surface of the casting, and repeat the bonding and sintering process until the sand holes or pores are completely filled and slightly higher than the surface of the casting;

[0071] S12. Mill or grind the protruding parts on the casting surface until they meet the casting surface quality requirements.

[0072] The working principle of this method is as follows: first, a three-dimensional model of the part to be manufactured needs to be constructed, and then the model is layered to obtain slices of each layer.

[0073] Next, for each slice, its central axis and skeleton line are obtained.

[0074] The central axis is a set of equidistant points on different sides or extensions of sides on the slice contour, while the skeleton line is a line connecting a point on the central axis and a point on the corresponding slice contour.

[0075] The skeleton line is divided into two parts with the central axis as the center, and the skeleton line of each part is sorted to determine the optimal number of path points.

[0076] Then, based on these path points, a printing path is generated to achieve layer-by-layer stacking of parts.

[0077] Next, the casting surface is ground and cleaned, and a pneumatic grinding head is used to grind away surface defects and remove impurities.

[0078] Subsequently, 3D printing metal powder is used as the molding powder, and the binder micro-droplets are sprayed layer by layer through the micro-droplet jet bonding method, so that the 3D printing powder is stacked layer by layer into the sand holes or pores.

[0079] The binder droplets used include water-soluble polymer materials or water.

[0080] Finally, the 3D printing powder is sintered at high temperature under a reducing atmosphere to sinter the metal powder into a whole and fill the sand holes or pores.

[0081] High temperature sintering adopts laser melting or oxyacetylene sintering, and hydrogen or carbon monoxide is introduced as a reducing agent.

[0082] The whole process requires gradual temperature increase, with the maximum temperature controlled between 1000℃ and 1350℃.

[0083] Repeat the above steps until the sand holes or pores are completely filled and slightly higher than the surface of the casting, and then mill or grind the protruding parts of the casting surface until they meet the casting surface quality requirements.

[0084] like Figure 2 As shown, in one embodiment, the method further comprises the following steps:

[0085] Step 1: divide a triangle in a blank polygonal image according to a preset division rule, and divide other areas in the polygon except the triangle into at least three areas of light, gray and dark. The blank polygonal image has the characteristics of equal side length, equal internal angle and axial symmetry. According to the preset division rule, divide a triangle in the blank polygonal image and divide other areas into three areas of light, gray and dark. This involves knowledge related to image processing and geometry.

[0086] Step 2: extract the target color with the largest color proportion from the target cover image, and fill the target color in the blank image of the polygon. Extract the color from the target cover image and fill it into the blank image of the polygon, which requires color extraction and filling algorithms;

[0087] Step 3: adjusting the transparency of the area corresponding to the triangle to a preset value, and adjusting the transparency values ​​of the light, gray and dark areas from low to high according to the transparency values. The transparency adjustment also involves image processing and transparency processing technology, and the outline stroke in step 4 requires edge detection and stroke algorithms;

[0088] Step 4: Add outline strokes to the triangle corresponding area and the light, gray and dark areas to generate a polygonal 3D effect covering template;

[0089] Step 5: Overlay the polygonal 3D effect overlay template on the target cover image to form a 3D visual effect of the target cover image.

[0090] The step of extracting the target color with the largest color proportion from the target cover image and filling the target color in the blank image of the polygon includes: extracting the color with the largest color proportion from the target cover image;

[0091] The brightness of the color with the largest proportion is reduced by a preset percentage value, and the transparency value of the color with the largest proportion is set to a preset fourth value, so as to obtain a target color;

[0092] Fill the blank image of the polygon with the target color.

[0093] Adding outline strokes to the area corresponding to the triangle and the three areas of light, gray and dark to generate a polygonal 3D effect overlay template includes: adding outline strokes to the area corresponding to the triangle, and adding the outline strokes to areas corresponding to one of the first triangles and two of the first sub-triangles included in the bright area;

[0094] and, adding the outline stroke to an area corresponding to one of the second triangles and two of the second sub-triangles included in the gray area;

[0095] And, adding the outline stroke to the area corresponding to one of the third triangles and two of the third sub-triangles included in the dark area to generate a polygonal 3D effect overlay template.

[0096] In this embodiment, specifically: this workflow also includes a processing step of extracting the target color with the largest color proportion from the target cover image, and a detailed description of adding outline strokes to the triangular area and the light, gray and dark areas.

[0097] This embodiment realizes the 3D effect by processing and superimposing images.

[0098] 1. Sand mold is a structure with certain structural strength produced by bonding sand (generally silica sand, ceramsite sand, water glass sand, etc.) with binder (generally alkali phenolic resin, urethane resin, furan resin and water glass, etc.) under the catalytic reaction of curing agent. It can be used to receive high-temperature molten steel and form the required casting products.

[0099] 2. The coating layer is mainly a mixture of high-temperature resistant sand powder (usually zircon powder) and solvent (usually water and alcohol). It is usually applied to the inner surface of the sand mold by manual or mechanical methods to form a high-temperature resistant coating, which plays a protective role when molten steel is poured into the sand mold cavity;

[0100] 3. Explanation of the process before traditional casting:

[0101] Modeling process: mix sand, curing agent and binder in a certain proportion, spread them into the corresponding mold, wait for a period of curing, and then remove the mold to form a sand mold;

[0102] Coating process: brush the above alcohol coating or water-based coating onto the surface of the sand mold;

[0103] Combining process: combine the separate sand molds together to form the product cavity.

[0104] Pouring process: the process of pouring molten metal into the sand mold cavity.

[0105] 4. Sand mold 3D printing process:

[0106] Refer to the video below. The sand mold 3D printing process is to use a sand spreader to evenly spread the sand mixed with curing agent (the laying height is between 0.2-0.5mm), and then use a printing nozzle (each nozzle has 512 or 1024 inkjet holes) to selectively spray the binder in the 3D design area to form a product with a certain structure and shape.

[0107] In the several embodiments provided in the present application, it should be understood that the disclosed terminals, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0108] In addition, each functional unit in each embodiment of the present application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of software functional units. The above is only an implementation method of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the description and drawings of this application, or directly or indirectly used in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A casting construction method based on 3D printing, It is characterized in that The following steps are involved: S1. Build a three-dimensional model of the part to be manufactured; S2, layering the three-dimensional model to obtain slices of each layer; S3, obtaining a central axis and a skeleton line of the slice, wherein the central axis is a set of points equidistant from two or more points on different sides or extensions of sides on the slice contour, and the skeleton line is a line connecting a point on the central axis and a corresponding point on the slice contour; S4, dividing the skeleton line obtained in S3 into two parts with the central axis as the center, the skeleton line located on one side of the central axis is recorded as the first half area, and the skeleton line located on the other side of the central axis is recorded as the second half area; S5, respectively, arranging the skeleton lines of the first half region and the second half region obtained in S4 in sequence along the direction of the central axis; S6, respectively calculating the maximum skeleton line length and the minimum skeleton line length in the skeleton lines of the sorted first half area and the second half area, and determining the optimal path points of the first half area and the second half area according to the maximum printing width and the minimum printing width limited by the actuator; S7, according to the optimal number of path points of the first half area obtained in S6, determine the position of each path point on the skeleton line of the first half area, ensure that the distance between each path point is the length of the skeleton line divided by the optimal number of path points, and then sequentially connect the corresponding path points on the skeleton line of the first half area to generate a printing path for the first half area, and simultaneously use this method to generate a printing path for the second half area; S8. Grind and clean the casting surface. Use a pneumatic grinding head to grind the sand holes or pores on the surface defects and expand the openings. Then use high-pressure gas to blow out the sand holes or pores to remove impurities. S9, using 3D printing metal powder as molding powder, spraying binder micro droplets layer by layer through a micro droplet jet bonding method to stack the 3D printing powder layer by layer into the sand holes or pores; S10, sintering the 3D printing powder at high temperature in a reducing atmosphere to sinter the metal powder into a whole and fill the sand holes or pores; S11, repeat S9 and S10 until the sand holes or pores are completely filled and slightly higher than the casting surface; S12. Mill or grind the protruding parts on the casting surface until they meet the casting surface quality requirements.

2. A casting construction method based on 3D printing according to claim 1, It is characterized in that The method for determining the region to which the skeleton line belongs in S4 is: substituting the coordinates of the two endpoints of the skeleton line into formula (1), classifying the skeleton line with a positive result as the first half region, and classifying the skeleton line with a negative result as the second half region; MAx×OUTy-MAy×OUTx(1); Wherein, MAx is the abscissa of the endpoint MA on the central axis of the skeleton line, MAy is the ordinate of the endpoint MA, OUTy is the ordinate of the endpoint OUT on the slice contour of the skeleton line, and OUTx is the abscissa of the endpoint OUT.

3. A casting construction method based on 3D printing according to claim 1, Features: The binder droplets used in S9 include water-soluble polymer materials or water.

4. A casting construction method based on 3D printing according to claim 3, Features: The water-soluble polymer material includes polyvinyl pyrrolidone or polyvinyl alcohol.

5. A casting construction method based on 3D printing according to claim 1, Features: The high temperature sintering of S10 is performed by laser melting or oxyacetylene sintering, while hydrogen or carbon monoxide is introduced as a reducing agent.

6. A casting construction method based on 3D printing according to claim 1, Features: The 3D printing metal powder includes iron powder or a mixed powder of iron powder and stainless steel powder.

7. A casting construction method based on 3D printing according to claim 5, Features: The high temperature sintering is carried out in a step-by-step heating manner, with the highest temperature being controlled between 1000°C and 1350°C.

8. A casting construction method based on 3D printing according to claim 7, It is characterized in that The method further comprises the following steps: Step 1: divide a triangle in a blank polygonal image according to a preset division rule, and divide the other regions of the polygon except the triangle into at least three regions: light, gray and dark. The blank polygonal image has the characteristics of equal side lengths, equal internal angles and axial symmetry; Step 2: extracting the target color with the largest color proportion from the target cover image, and filling the blank image of the polygon with the target color; Step 3: adjusting the transparency of the area corresponding to the triangle to a preset value, and adjusting the transparency values ​​of the light, gray and dark areas from low to high according to the transparency values; Step 4: Add outline strokes to the triangle corresponding area and the light, gray and dark areas to generate a polygonal 3D effect covering template; Step 5: Overlay the polygonal 3D effect overlay template on the target cover image to form a 3D visual effect of the target cover image.

9. A casting construction method based on 3D printing according to claim 8, Features: The step of extracting the target color with the largest color proportion from the target cover image and filling the target color in the blank image of the polygon includes: extracting the color with the largest color proportion from the target cover image; The brightness of the color with the largest proportion is reduced by a preset percentage value, and the transparency value of the color with the largest proportion is set to a preset fourth value, so as to obtain a target color; Filling the blank image of the polygon with the target color; Adding outline strokes to the area corresponding to the triangle and the three areas of light, gray and dark to generate a polygonal 3D effect overlay template includes: adding outline strokes to the area corresponding to the triangle, and adding the outline strokes to areas corresponding to one of the first triangles and two of the first sub-triangles included in the bright area; and, adding the outline stroke to an area corresponding to one of the second triangles and two of the second sub-triangles included in the gray area; And, adding the outline stroke to the area corresponding to one of the third triangles and two of the third sub-triangles included in the dark area to generate a polygonal 3D effect overlay template.

10. A casting construction method based on 3D printing according to claim 8, It is characterized in that The following steps are also included: During the sand laying process, the software can distinguish the contour line directly, and an auxiliary sand laying head can be added in the contour line area to lay a certain width of zircon sand, and then the print head can be used for inkjet printing. The grid refractory sand spreader is located at the front end of the sand spreader. The software is used to control the switches in each grid. The refractory sand is spread along the trajectory in advance (the sand spreading width d, t is related to the layer thickness, d, t = K * sand spreading thickness, K = 2-50). The subsequent original sand is spread on this basis and scraped to complete the sand spreading operation.

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