Multi-material precision sanding and multi-gray collaborative printing control method

Abstract

The application discloses a multi-material precise sand laying and multi-gray collaborative printing control method and belongs to the sand mold 3D printing field. The application designs an STL sand mold model according to the solidification characteristics of a casting, adds different sand mold material properties to the read STL file after reading the STL model, then carries out surface coloring editing processing on the sand mold unit triangular facets with different sand mold material properties, subsequently saves the processed multi-material sand mold model and carries out slicing, outputs a slice PNG file with sand mold properties and different regional colors, and a pixel conversion device in a printing control system carries out pixel two-bit gray value conversion and integration on the slice file. Different sand mold units correspond to different colors, different color regions are divided into different gray values, different grays correspond to different resin injection amounts, multi-material sand mold resin content is injected on demand, sand is laid layer by layer, printing is carried out layer by layer, and the printing work of the multi-material sand mold is completed.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of additive manufacturing technology; specifically relates to multi-material precise sand laying and multi-gray collaborative printing control method. BACKGROUND

[0002] Sand 3D printing technology is a typical powder (or particle) material 3D printing technology, which was first proposed by Massachusetts Institute of Technology in the United States in 1989 in US5204055A1 patent. The specific process of this method is to uniformly lay a layer of powder on the platform, the print head scans and sprays a kind of liquid material in the specific area, so that the powder in the sprayed part is bonded together, then the printing platform is lowered by the corresponding layer thickness, and the above steps are repeated until all the layers of powder laying and printing are completed.

[0003] In the patent 201710803799.1 published by Advanced Manufacturing Technology Research Center of Mechanical Science Research Institute, a sand mold self-adaptive gradient printing forming method is disclosed, which uses a single sand and a traditional STL file for layer slicing, and then sprays resin with different gray levels on the sand of each layer according to the contour information and gray information of the current layer section. In the single sand printing, different gray levels are applied. However, the traditional STL file slicing contour has only a single gray level, and cannot be distinguished according to the feature information, so it cannot be applied to multi-material sand multi-region sand printing forming with different resin injection contents.

[0004] At present, the commercial large-scale sand 3D printing equipment is designed based on single material and single ink injection amount, and the advantages of additive manufacturing are not fully exhibited. On the other hand, due to the rapid development of industrial design, higher requirements are put forward for the function and performance of parts, and the sand mold made of single and homogeneous material is difficult to meet the needs of complex part temperature field and solidification process control, so the research on multi-material and gray level printing sand mold manufacturing has become one of the hotspots.

[0005] Multi-material sand additive manufacturing is more complex than single-material additive manufacturing, and new research is needed for multi-material model establishment, accurate identification, efficient slicing and forming method. Through the research on multi-material precise sand laying and multi-gray collaborative printing control method, the local performance of complex castings is further optimized, the real-time adjustment of ink injection amount and the shape-property matching of printed sand mold are realized, and the intelligent manufacturing of sand mold is realized. SUMMARY

[0006] To solve the above problems, the application discloses a multi-material precise sand laying and multi-gray collaborative printing control method, which adopts gray level identification and color identification, feeds back to the sand laying and printing system, and lays sand and sprays ink with different resin contents for multi-region multi-material. The forming and manufacturing of high flexibility and multi-material sand mold are realized.

[0007] Multi-material precision sand laying and multi-gray collaborative printing control method, comprising the following steps:

[0008] Step one: determine the different requirements of different sand acid consumption, gas evolution, strength and shrinkage rate of the casting by the solidification characteristics of the casting, separately determine the best resin binder content required for each casting unit, and correspond the sand material, binder content of each sand mold unit to different colors, and divide the sand mold STL model unit into different regions.

[0009] Step two: read the two-dimensional slice STL file, and build the geometric space of the model with the space region stored in the STL file. The region index value ranges from [1, M]. In order to include sand material information, a sand material list is constructed, which includes material index, material type and material color information, and then the material list is added to the material library. The material index value is used to distinguish the material type, and the index value ranges from [1, N]. And through the preset multi-material sand mold STL model unit, the material index value is input into the triangle facet and extended vertex of the region STL. And generate M-STL file.

[0010] Step three: in order to further increase the display effect of sand unit, by specifying the RGB color space of red, green and blue color system and transparency, add the corresponding color information and transparency information to the triangle facet of sand unit, and save the surface color through the extended vertex and facet attribute.

[0011] Step four: carry out the layering processing of multi-material sand mold STL model. Set the slice layering thickness, carry out equal-thickness layering or adaptive layering. The cutting plane intersects with multiple regions. Generate corresponding two-dimensional region slice png file, and divide each region material type and color into N1, N2, N3…Nn multiple regions. Two-dimensional slice layer inherits the color attribute and material attribute of each region.

[0012] Step five: carry out gray value processing on two-dimensional multi-material region slice layer, convert the color information of each region into gray information according to the different sand acid consumption, gas evolution, strength and shrinkage rate, and feed back to the ink circulation system. The ink circulation system adjusts the ink supply voltage according to the different gray value information, so as to adjust the printing ink circulation system to change the corresponding resin inkjet amount.

[0013] Step six: sand laying control system, through the difference of color information of each region of two-dimensional slice layer, through identification, correspond the color information to the laid sand material, and according to the difference of color region of two-dimensional slice layer, through step control system, control two or more sand laying devices, carry out parallel sand laying. Different sand laying devices carry out accurate quantitative sand laying according to the difference of region color.

[0014] Step seven: layer by layer sand, layer by layer printing until the multi-material sand print is completed, and the sand mold is taken out.

[0015] The further improvement of the present application is that the different sand materials include equal proportion mixed sand or single refractory sand with different mesh and different thermal physical parameters.

[0016] The further improvement of the present application is that the M-STL file, that is, on the basis of the original STL file, represents the geometric characteristics of the sand mold model by triangular facets, stores the vertex coordinates of each triangular facet, and identifies each integer sequence number mark, then stores the triangular facet information through the sequence number mark of the vertex, and extracts the normal vector information of each triangular facet to establish the spatial topological relationship. The M-STL file is composed of file index information and region segments, the file index information includes vertex coordinate ID, facet attribute, region material attribute, color information, and transparency information, and these file index information is stored in the vertex list and the facet list of each region in turn.

[0017] The further improvement of the present application is that the M-STL can be adaptively layered according to the change of the surface curvature of the casting. Since the color information and the material attribute are stored in the triangular facet list and the vertex list, the two-dimensional multi-region segment layer generated by slicing can still output the material attribute and the color information.

[0018] The further improvement of the present application is that after outputting the png format file of the two-dimensional multi-region segment layer, it is imported into the printing system, and the color information is adapted to different gray scale values, the different gray scale value information is fed back to the ink supply voltage system, so that the ink supply voltage is adjusted, different regions are displayed as different gray scales, and the ink path circulation system sprays resins with different contents to ensure the best adaptation of the sand mold materials in each region and the optimal strength.

[0019] The further improvement of the present application is that the sand laying system adopts two or more sand laying devices, and the sand laying system adopts front and rear parallel sand laying according to the difference of different color regions in the displayed two-dimensional segment layer. The multi-material sand is accurately laid according to the segment layer region division.

[0020] The beneficial effects of the present application are as follows:

[0021] 1. The present application provides a multi-material accurate sand laying and multi-gray scale collaborative printing control method, and adopts extension editing on the basis of the original STL file, inputs material information and color information, and defines a multi-material sand mold model file M-STL.

[0022] 2. A multi-region two-dimensional slicing png file with color information is adopted, gray scale recognition and color recognition are adopted, feedback is given to the sand laying and printing system, and multi-region multi-material sand laying and inkjet printing with different resin contents are carried out; high flexibility, multi-material sand mold forming and manufacturing are realized.

[0023] 3. The application integrates process control of multi-color M-STL slicing, multi-material sand laying, and multi-region gray scale printing, breaks through the problem of traditional single material, traditional slicing file information single, and cannot be applied to higher flexibility, multi-region, multi-sand laying sand mold 3D printing.

[0024] 4. The application can match reasonable sand and different resin contents according to the performance requirements of the casting, adopt reasonable sand matching and different resin contents for high-precision and large wall thickness difference castings, and optimize the indicators of the formed sand mold air permeability, strength, and gas generation amount, while the application also provides a laying control method of multi-sand materials, which can effectively regulate the temperature field of the casting, and the performance of the casting is more excellent.

[0025] 5. The application optimizes the local performance precision regulation of complex castings, real-time adjustment of inkjet amount, and shape-property matching of printed sand molds, and realizes intelligent manufacturing of sand molds. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Flow chart of multi-material precision sand laying and multi-gray scale collaborative printing control method;

[0027] Figure 2 Two-dimensional slicing conversion schematic diagram of multi-material precision sand laying and multi-gray scale collaborative printing control method. DETAILED DESCRIPTION

[0028] The application will be further illustrated below in combination with the drawings and specific embodiments, and it should be understood that the following specific embodiments are only used to illustrate the application and not to limit the scope of the application. It should be noted that the words "front", "back", "left", "right", "up" and "down" used in the following description refer to the directions in the drawings, and the words "in" and "out" refer to the directions towards or away from the geometric center of a particular component.

[0029] The multi-material precision sand laying and multi-gray scale collaborative printing control method of the embodiment includes the following steps:

[0030] Step one: determine the different requirements of different sand consumption acid values, gas generation amounts, strengths, and shrinkage rates of the casting according to the solidification characteristics of the casting, separately determine the optimal resin binder content required by each casting unit, and correspond the sand material and binder content of each sand mold unit to different colors, and divide the sand mold STL model unit into different regions.

[0031] Step two: read the two-dimensional slice STL file to build the geometric space of the model stored in the spatial region of the STL file, and the region index value ranges from 1 to M. In order to include the sand material information, a sand material list is constructed, which includes material index, material type and material color information, etc., and then the material list is added to the material library. The material index value is used to distinguish the material type, and its index value ranges from 1 to N. And through the preset multi-material sand mold STL model unit, the material index value is input into the triangular facet and extended vertex of the region STL. And generate M-STL file.

[0032] The M-STL file, that is, on the basis of the original STL file, represents the geometric characteristics of the sand mold model by triangular facets, stores the vertex coordinates of each triangular facet, and identifies each integer sequence number. Then store the triangular facet information through the sequence number of its vertex, and extract the normal vector information of each triangular facet to establish the spatial topological relationship. The M-STL file is composed of file index information and region segments, and the file index information includes vertex coordinate ID, facet attribute, region material attribute, color information, and transparency information. And store these file index information in the vertex list and facet list of each region in turn.

[0033] Step three: In order to further increase the display effect of the sand mold unit, the RGB color space is specified, and the red, green and blue color systems and transparency are added to the triangular facet of the sand mold unit to add response color information and transparency information, and the surface color is saved through the extended vertex and facet attribute.

[0034] Step four: carry out the layered slicing processing of the multi-material sand mold STL model. Set the slicing layer thickness, and carry out equal-thickness layering or adaptive layering slicing. The slicing plane intersects with multiple regions. Generate corresponding two-dimensional region slice png file, and each region material type and color is divided into N1, N2, N3…Nn multiple regions. The two-dimensional slice layer inherits the color attribute and material attribute of each region.

[0035] After outputting the two-dimensional multi-region slice png format file, it is imported into the printing system, and the color information is adapted to different gray scale values. The different gray scale value information is fed back to the ink supply voltage system, so as to adjust the ink supply voltage. Different regions are displayed as different gray scales, and the ink path circulation system sprays resin with different contents to ensure the best adaptation of each region sand material and the optimal strength, etc.

[0036] Step five: carry out gray scale value processing on the two-dimensional multi-material region slice layer, and according to the different acid consumption, gas evolution, strength and shrinkage of the sand mold, the color information of each region is converted into gray scale information, and fed back to the ink path circulation system. The ink path circulation system adjusts the ink supply voltage according to the different gray scale value information, so as to adjust the printing ink path circulation system to change the corresponding resin ink jet amount.

[0037] Step six: sand control system, by two-dimensional slice layer each region of color information is different, by identifying the color information corresponding to the laid sand material, and according to the color area of two-dimensional slice layer is different, by stepping control system, control two or more than two sand, carry out parallel sanding. Different sanding machine according to the color of the region, accurate quantitative sanding.

[0038] Step seven: layer by layer sanding, layer by layer printing until the multi-material sand printing is completed, and the sand mold is taken out.

[0039] As shown in Figure 1 , first of all, the point cloud scanner or CAD modeling software is used to design the STL sand mold model in modules, the material properties and color properties are added by twice editing the STL model, the multi-material sand mold M-STL model is designed, after adaptive layering or equal-thickness layering by slicing software, the image recognition is fed back to the sanding and printing system, the sanding system feeds back to the sanding machine according to the color difference of two-dimensional slice layer to carry out sanding in different regions. By converting the different colors of two-dimensional slice layer into gray scale, on-demand inkjet of different gray scale values is carried out. Layer by layer sanding and layer by layer printing until the multi-sand multi-gray sand mold printing is completed. The process is shown in the accompanying Figure 2 , the high flexibility, multi-material sand mold forming and manufacturing are realized.

[0040] The technical means disclosed in the scheme of the application is not limited to the technical means disclosed in the above-mentioned embodiments, but also includes the technical scheme composed of any combination of the above technical features.

Claims

1. A method for controlling precise sand application of multiple materials and collaborative printing of multiple grayscale levels, characterized by: Includes the following steps: Step 1: Based on the solidification characteristics of the casting, determine the different requirements for acid consumption, gas generation, strength, and shrinkage of different molding sands. Determine the optimal resin binder content for each mold unit separately, and associate the molding sand material and resin binder content of each sand mold unit with different colors. Divide the sand mold STL model unit into different areas. Step 2: Read the STL file and construct the geometric space of the model using the spatial regions stored in the STL file. The region index value ranges from [1, M]. To include molding sand material information, construct a molding sand material list containing material index, material type, and material color information. Then, add the material list to the material library. Differentiate material types by material index values, with an index value range of [1, N]. Input each material index value into the triangular facets and extended vertices of the STL for this region using pre-defined multi-material sand molding STL model elements. Generate an M-STL file. Step 3: To enhance the display effect of the molding sand unit, color and transparency information are added to the triangular facets of the sand molding unit by specifying the red, green, and blue RGB color space and the transparency; and the surface color is saved by extending the properties of vertices and facets. Step 4: Perform layered slicing of the multi-material sand mold STL model; Set the slice layer thickness to perform equal-thickness or adaptive-thickness slicing; the cutting plane intersects with multiple regions; generate corresponding 2D slice layer PNG files, with each region divided into N1, N2, N3...Nn regions based on material type and color; the 2D slice layer inherits the color and material properties of each region. Step 5: Perform grayscale processing on the two-dimensional slice layer. Based on the different gas emission and intensity of the sand mold, convert the color information of each area into grayscale information and feed it back to the ink circulation system. The ink circulation system adjusts the ink supply voltage according to the different grayscale information, thereby adjusting the printing ink circulation system and changing the corresponding amount of resin binder ink ejected. Step Six: Sand Laying Control System. By recognizing the different color information of each area of ​​the two-dimensional slice layer, the system identifies the color information and matches it with the molding sand material being laid. Based on the different color areas of the two-dimensional slice layer, the system controls two or more sand spreaders to lay sand in parallel and sequentially. Different sand spreaders precisely drop sand according to the different colors of the areas. Step 7: Lay sand layer by layer and print layer by layer until the multi-material sand mold is printed, and then remove the sand mold.

2. The method for controlling precise sand application and multi-grayscale collaborative printing of multiple materials according to claim 1, characterized in that: In step one: different molding sand materials include equal proportions of mixed sand or single refractory molding sand with different mesh sizes and different thermophysical parameters.

3. The method for controlling precise sand application and multi-grayscale collaborative printing of multiple materials according to claim 1; characterized in that: In step two: the M-STL file, based on the original STL file, uses triangular facets to represent the geometric features of the sand mold model, stores the vertex coordinates of each triangular facet, identifies each integer sequence number, stores the triangular facet information through its vertex sequence number, and extracts the normal vector information of each triangular facet to establish spatial topological relationships; the M-STL file consists of file index information and region fragments. The file index information includes vertex coordinate ID, facet attributes, region material properties, color information, and transparency information, and these file index information are stored sequentially in the vertex list and facet list of each region.

4. The method for controlling precise sand laying and multi-grayscale collaborative printing of multiple materials according to claim 1; characterized in that: M-STL performs adaptive layering based on the changes in the curvature of the casting surface; since color information and material properties are stored in the list of triangles and vertices, the two-dimensional slice layer generated by its slicing can still output material properties and color information.

5. The method for controlling precise sand laying and multi-grayscale collaborative printing of multiple materials according to claim 1; characterized in that: In step four: after outputting the PNG format file of the two-dimensional slice layer, it is imported into the printing system, and the color information is adapted to different gray values. The different gray values ​​are then fed back to the ink supply voltage system to adjust the ink supply voltage. Different areas are displayed with different gray levels. The ink circulation system sprays resin binders with different contents to ensure optimal compatibility with the molding sand material in each area.

6. The method for controlling precise sand laying and multi-grayscale collaborative printing of multiple materials according to claim 1; characterized in that: In step six: the sand-laying system uses two or more sand-laying devices. The sand-laying system will lay sand in parallel front and back according to the different color areas in the displayed two-dimensional slice layer; to complete the precise sand-laying of multi-material molding sand according to the slice layer area division.

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