CN114918370B - Sand mold forming method suitable for manufacturing adaptive slices by increasing and decreasing materials - Google Patents
Sand mold forming method suitable for manufacturing adaptive slices by increasing and decreasing materials Download PDFInfo
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- CN114918370B CN114918370B CN202210498571.7A CN202210498571A CN114918370B CN 114918370 B CN114918370 B CN 114918370B CN 202210498571 A CN202210498571 A CN 202210498571A CN 114918370 B CN114918370 B CN 114918370B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/02—Sand moulds or like moulds for shaped castings
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C19/00—Components or accessories for moulding machines
- B22C19/04—Controlling devices specially designed for moulding machines
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y10/00—Processes of additive manufacturing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y50/00—Data acquisition or data processing for additive manufacturing
- B33Y50/02—Data acquisition or data processing for additive manufacturing for controlling or regulating additive manufacturing processes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Abstract
The invention discloses a sand mold forming method suitable for manufacturing adaptive slices by increasing and decreasing materials
Judging the inner and outer contours according to the coordinates of the triangular patch of the inner and outer contours, and using the normal vector of the triangular patch
And parallel printing direction
Angle between vectors
And minimum printable thickness
And maximum thickness
Determining the thickness of a slice, simulating the slice, slicing again according to the result of the simulation slice to determine the proper thickness of the slice, finally exporting the profile of the slice, importing the profile of each layer and the corresponding layer thickness value into a printing system or a cutting system through the data stored in the slice, importing the data of the layer thickness and the profile into the printing system or the cutting system through identifying the png profile file of each layer by a computer, accurately controlling the printing platform to descend to the proper height by a printing PLC control system, adjusting the ink jet frequency of an ink jet system, and finally jetting the corresponding resin content according to the layer thickness information.
Description
Technical Field
The invention mainly belongs to the field of additive manufacturing and subtractive manufacturing; in particular to a sand mold forming method suitable for the self-adaptive slicing of material increase and decrease composite manufacturing.
Background
The sand mold cutting technology is based on CAD model driving, then model discretization slicing, material reduction manufacturing is carried out on a sand blank mixed with a curing agent and a bonding agent by adopting a numerical control removal principle, and material reduction manufacturing of a sand mold is realized by adjusting the feeding depth of a cutting knife through the thickness of the slicing. The slice thickness discretized by the CAD model based on the principle also has an important influence on the cutting depth of the sand mold.
Sand mold 3D printing technology is a typical 3D printing technology for powdered (or granular) materials, which was first proposed by american college of labor and technology in 1989 in US5204055 A1. The method comprises the specific processes that a CAD three-dimensional model is triangulated into an STL format, then the STL model is divided into a plurality of slices through a slicing algorithm, then path planning and inputting of slice information are carried out, then a layer of powder is uniformly paved on a platform, a printing head scans and sprays a liquid material in a specific area, the powder of the spraying part is bonded together, then the printing platform descends by a corresponding layer thickness distance, and the steps are repeated until powder paving and printing work of all layers is completed.
In summary, the current STL mold slicing methods manufactured by adding and subtracting materials have the following problems;
(1) The STL model parting mode generally adopts even isopachous layering, if the layering thickness is little, then can directly lead to follow-up printing time extension, when the layering thickness is big, obvious step effect can appear, this produces harmful effects to foundry goods final forming, but the little position of curvature change produces step effect hardly in the direction of printing, can not produce step effect during the cutting yet, and the sand mould printing thickness scope is at 0.20mm ~ 0.6mm, and the sand mould performance is all qualified.
(2) Aiming at the complex sand mold, the linear function relationship between the layering thickness and the inner and outer contours of the complex sand mold is difficult to satisfy, and the method has very important significance for developing a self-adaptive slicing method with specific engineering application for the complex sand mold.
(3) And (3) by creating a thickness matrix corresponding to the slice outline, corresponding different thicknesses to the slice outline one by one, outputting the slice file in the png format, and importing the slice file into an operating system. The sand moulds with different thicknesses and different process parameters can be realized.
Disclosure of Invention
In order to solve the problems, the invention provides a self-adaptive slicing sand mold forming method suitable for material increase and decrease manufacturing, which can ensure that the printing time is reduced while the mold precision is kept in sand mold printing, and meanwhile, the overall performance of the sand mold is improved by time-varying thickness process printing and cutting manufacturing. And is applicable to other 3D printing fields.
A sand mould forming method suitable for increasing and decreasing materials to manufacture self-adaptive slices comprises the following steps;
the method comprises the following steps: and reading the point set and the face set matrix of the triangular face patch of the STL model by using the stlread function embedded in MATLAB, and creating unit vectors of normal vectors of all triangular face patches of the model.
Step two: if the angle theta between the normal vector of the triangular patch and the positive direction of the Z axis fz >90 deg., then proceed with theta fz ＝180°-θ i Operation if theta fz <Theta at 0 DEG fz ＝-θ i Negating operation of θ fz The value range is determined to be [0 DEG, 90 DEG ]]In the meantime.
Thirdly, judging the inner and outer contours of the sand mold, wherein the included angle between the normal vector of the triangular surface patch of the outer contour of the sand mold STL model and the printing direction is theta fz =90 °, internal profile θ fz ＝[0°，90°]If θ is the inner contour fz (= 90 °) θ of outer profile fz And if the values are equal, judging according to the z value of the internal triangular patch matrix set, wherein the z value of the coordinates (x, y, z) of the triangular patch in the model is always smaller than the z value of the triangular patch of the external contour of the whole model, and dividing the sand mould into an inner part and an outer part by the method.
Step four: determination of slice thickness, wherein the unit Z vector parallel to the printing direction and the unit normal vector N of the triangle patch of the STL model f Angle of (2)
Wherein Z and N f Are all unit vectors, i.e. theta fz ＝arccos(|z i I), when theta fz When the angle is not less than 0 deg., the triangular plate is perpendicular to the Z axis, and the minimum layer thickness H of the sand mold printer is taken min If theta fz =90 °, i.e. no step effect in the model printing, slice thickness being taken to be maximum thickness H max In STL modeThe intra-type should find the minimum value of each triangular patch normal vector, i.e. find the maximum value | Z of the absolute value of each triangular patch unit normal vector Z coordinate i | max To determine the layer thickness of the adaptive slice. I.e. Δ H = H min +(H max -H min )*(1-|z i | max )。
Step five: the introduced STL model was sliced by simulation. First, the maximum slice thickness H is input max And minimum H min Then determining the slice range of the model, and taking the maximum value of the z coordinates of the triangular patch stored by the STL model as the highest point z of the model max Minimum z of triangular patch z during slicing min I.e. the bottom surface is the starting layer thickness, and the intersecting profile of each layer is calculated. When theta is fz =90 °, the cut H is made with the maximum layer thickness max When the inner contour is layered in thickness, Δ H = H min +(H max -H min )*(1-|z i | max ) To calculate the layer thickness of the next layer, δ = Δ H + H i Let i = i +1 if H > z max And stopping slicing, and if not, continuing to circularly slice until the slicing is finished.
Step six: outputting slice data and slice profiles, wherein the slice profiles correspond to the slice thickness values one by one, and checking the slice thickness values due to the theta of the inner profile fz And (3) the data processing is carried out, the precision range of 2 bits after the decimal point is reserved, and then formal slicing is carried out.
Step seven: and importing the png profile picture and the corresponding slice profile and slice thickness data into a printing system, and reducing according to the slice thickness through a PLC control system, and simultaneously adjusting the optimal numerical ink jet quantity of each layer to realize variable thickness printing.
Further, the method comprises the following steps of; the method is suitable for the field of sand mold cutting, the output slice profile and data can be led into a cutting operation system, the layering thickness information is converted into cutting depth, and the method can be applied to sand mold cutting to prepare sand molds.
Further, the method comprises the following steps of; the thickness range of sand mould printing is between 0.20 mm-0.60 mm, and the precision is set at two digits after the decimal point.
Further, the method comprises the following steps of; when the contour is internally and externally divided, if there is a non-theta outside fz In the case of =90 °, the triangular patch θ inside and outside is compared fz The value and the size of the z coordinate of the triangular patch matrix of the inner contour and the outer contour are used for carrying out the self-adaptive slicing algorithm of other models; the minimum slice thickness can be set to be 0.01mm, a proper printing layer thickness range is selected according to different printing processes, the method is suitable for 3D printing and manufacturing of other models, and certain expansibility is achieved.
Further, the method comprises the following steps of; and after path planning is carried out on the output png file of the printing contour, the stored layer thickness information is led into a printing operation system, and the printing operation system adjusts the descending distance and the ink jetting amount of the Z axis during printing according to the file and the data information, so that variable-thickness printing is realized.
The invention has the beneficial effects that:
the implementation of the sand mold forming method suitable for adaptive layering in material increase and decrease manufacturing is applied to the field of microdrop jet sand mold printing, the model precision is guaranteed, meanwhile, the printing time is shortened, by taking self-adaptive slicing of a turbine fan blade sand mold as an example, a 0.2mm model slicing method and a 0.2 mm-0.6 mm slicing method are used, on the premise that the model precision is guaranteed and the step effect is reduced, the printing efficiency is improved by 97%, different printing processes are preferably selected for each layer, the sand mold precision and the strength are improved, the sand mold forming method is applied to the field of sand mold cutting, the axial feeding depth of a cutter is selected according to the difference of the thicknesses of the slices, the excellent aspect ratio is controlled, and flexible manufacturing of the sand mold is realized.
Description of the drawings:
FIG. one is a drawing; STL model triangular patch unit normal vector N f Schematic diagram of included angle with Z vector;
FIG. 2; a flow chart of a sand mold forming method suitable for adaptive layering in material increase and decrease manufacturing;
FIG. 3; an illustration chart of a self-adaptive slicing of a turbine fan blade sand mold;
description of the drawings: 1-STL model outer contour triangular patch, where N f Is a unit normal vector perpendicular to the triangular patch; z is a Z-direction unit vector [0 ] parallel to the printing direction,0,1]；θ fz Is a Z vector and N f The angle between the vectors.
Detailed Description
The present invention will be further illustrated with reference to the accompanying drawings and specific embodiments, which are to be understood as merely illustrative of the invention and not as limiting the scope of the invention.
The sand mold forming method suitable for manufacturing the adaptive slices by increasing and decreasing materials in the embodiment takes printing of a turbofan sand mold as an example, and comprises the following operation steps:
step 1: the CAD size of the turbofan sand mold is 500mm × 500mm × 240mm, the mold is converted into an STL model, as shown in (a) and (b) of FIG. 3, the converted STL model is read by MATLAB, a face set matrix of 42260 × 3 dimensions and a point set matrix of 21122 × 3 dimensions are created, a unit normal vector matrix of 42260 × 3 dimensions is calculated, and the value of θ is used fz =90 °, the turbofan sand mold STL model is divided into two parts,
step 2: setting the initial layer thickness to be 0mm and the maximum slice thickness H max 0.60mm, minimum slice thickness H min =0.20mm, as Δ H = H min +(H max -H min )*(1-|z i | max ) The layer thickness of the next layer is calculated and the number of final slicing layers 607. Fig. 3 is a 165 th layer profile png file of 0.25mm, then the slicing profile with thickness information is introduced into a printing operation system after path planning, 5-level gray scale is selected for the ink jet amount of the resin with the thickness of 0.6mm, 3-level gray scale is selected for 0.4mm, 2-level gray scale is selected for 0.2mm for ink jet printing, the printing equipment reduces the corresponding layer thickness according to the layer thickness information, and the precision is kept at 0.01.
And step 3: and after planning the cutting path of the slice profile with the thickness information, introducing the slice profile into a cutting operation system, adjusting the descending height of a cutter by a control system according to the layer thickness information of each profile, and keeping the precision at 0.01mm, wherein the following table is a comparison table of the traditional equal-thickness slice and a sand mold forming method suitable for the adaptive slice manufactured by adding and subtracting materials, and is shown in table 1.
TABLE 1 comparison of different slicing modes
The technical means disclosed in the invention scheme are not limited to the technical means disclosed in the above embodiments, but also include the technical scheme formed by any combination of the above technical features.
Claims (6)
1. A sand mould forming method suitable for increasing and decreasing materials to manufacture self-adaptive slices is characterized by comprising the following steps;
the method comprises the following steps: reading a point set and a face set matrix of a triangular patch of the STL model by using an stlread function embedded in MATLAB, and creating unit vectors of normal vectors of all triangular patches of the model;
step two: if the angle theta between the normal vector of the triangular patch and the positive direction of the Z axis fz > 90 deg., proceed with theta fz ＝180°-θ i Operation if theta fz Theta is carried out at less than 0 DEG fz ＝-θ i Negating operation of θ fz The value range is determined to be [0 DEG, 90 DEG ]]To (c) to (d);
step three: judging the inner and outer contours of the sand mold;
step four: determining the slice thickness;
step five: carrying out simulated slicing on the imported STL model;
step six: outputting slice data and slice profiles, wherein the slice profiles correspond to the slice thickness values one by one, and checking the slice thickness values due to the theta of the inner profile fz The data processing is carried out, the precision range of 2 bits after the decimal point is reserved, and then formal slicing is carried out;
step seven: and importing the png profile picture and the corresponding slice profile and slice thickness data into a printing system, and reducing according to the slice thickness through a PLC control system, and simultaneously adjusting the optimal numerical ink jet quantity of each layer to realize variable thickness printing.
2. The sand mold forming method for manufacturing adaptive slices by increasing or decreasing materials according to claim 1, wherein the method comprisesCharacterized in that: the third step is that: an included angle between a normal vector of the outer contour triangular surface patch of the sand mold STL model and the printing direction is theta fz =90 °, internal profile θ fz ＝[0°，90°]If θ is the inner contour fz (= 90 °) θ of outer profile fz If the values are equal, judging through the z value of the internal triangular patch matrix set, wherein the z value is always smaller than the z value of the triangular patch of the external contour of the whole model in the coordinates (x, y, z) of the triangular patch in the model, and dividing the sand mold into an inner part and an outer part through the method.
3. The sand mold forming method suitable for the adaptive slicing in the material increase and decrease manufacturing according to claim 2, characterized in that: the outer contour is a curved surface, then the inner and outer contours, by collecting θ fz And z of the inner and outer contour triangular patches i The method realizes more complex model self-adaptive segmentation, wherein the minimum slice thickness is set to be 0.01mm, and a proper printing layer thickness range is selected along with different printing processes, so that the method can be applied to the fields of ceramic printing, sand mold cutting or metal printing.
4. The sand mold forming method suitable for the adaptive slicing in the material increase and decrease manufacturing according to claim 1, characterized in that: step four: wherein the unit Z vector parallel to the printing direction and the normal vector N of the triangular patch unit of the STL model f Angle of (2)
Wherein Z and N f Are all unit vectors, i.e. theta fz ＝arccos(|z i When theta) is given fz When the angle is not less than 0 deg., the triangular plate is perpendicular to the Z axis, and the minimum layer thickness H of the sand mold printer is taken min If theta fz =90 °, i.e. no step effect in the model printing, slice thickness being taken to be maximum thickness H max Within the STL model, the minimum of each triangular patch normal vector should be found, i.e., the maximum of the absolute value of each triangular patch unit normal vector Z coordinate | Z i | max To determineLayer thickness of the adaptive slice; i.e. Δ H = H min +(H max -H min )*(1-|z i | max )。
5. The sand mold forming method suitable for the adaptive slicing in the material increase and decrease manufacturing according to claim 1, characterized in that: step five: first, the maximum slice thickness H is input max And minimum H min Then determining the slice range of the model, and taking the maximum value of the z coordinates of the triangular patch stored by the STL model as the highest point z of the model max Minimum z of triangular patch z during slicing min Namely, the bottom surface is the initial layer thickness, and the intersecting outline of each layer is calculated; when theta is fz =90 °, the cut H is made with the maximum layer thickness max When the inner contour is layered in thickness, Δ H = H min +(H max -H min )*(1-|z i | max ) To calculate the layer thickness of the next layer, δ = Δ H + H i Let i = i +1 if H > z max And stopping slicing, and if not, continuing slicing until the slicing is finished.
6. The sand mold forming method suitable for the material increase and decrease manufacturing self-adaptive slicing according to the claim 1, characterized in that; the printing thickness range of the sand mold is 0.20 mm-0.60 mm; the precision is reserved to the last two decimal places.
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