Method and system for printing high-quality sand mold

Abstract

The invention discloses a method and system for printing a high-quality sand mold, and belongs to the technical field of sand mold casting, and the method comprises the following steps: controlling the printing layer thickness of a sand mold sample to be synchronous with the layering thickness of the sand mold sample by layer cutting software, so that the sand paving thickness of sand mold printing equipment is consistent with the descending height of a printing platform; 100 / 140-mesh silica sand is adopted in the process of controlling a sand paver of sand mold printing equipment to pave sand layer by layer and spraying resin to bond sand grains through a printing head, and the content of a curing agent is controlled to be 0.25% of the total weight of the silica sand; the ink jet frequency and the X resolution ratio are adjusted, and the resin jet amount per unit area and the single jet moving distance are changed, so that the thickness of a printing layer is controlled to be 0.25-0.45 mm or any thickness within the range of 0.25-0.45 mm; after standing and curing the sand mold sample, detecting the performance; and establishing a regression equation of the process parameters of the sand mold printing equipment and the sand mold performance by adopting a response surface method, and optimizing the combination of the process parameters to obtain the optimal process parameters of the printing sand mold sample. According to the method, the problems of difficulty in shape control and poor quality stability of complex castings can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of sand casting, and in particular to a method and system for printing high-quality sand molds. Background Art

[0002] In the field of casting technology, the application of sand mold 3D printing technology has become an important direction of industry development. This technology not only breaks through the many bottlenecks faced by traditional molding methods in the preparation of castings, but also can well meet the current market's urgent demand for personalized customization of complex castings. Figure 2 As shown in the figure, for example, a hydraulic valve body used in a certain piece of engineering machinery has narrow, long, and tortuous oil passages, and is made of ductile iron. This places stringent demands on the sand mold in many aspects. On the one hand, the sand mold must have excellent mechanical strength to withstand the impact of high-temperature molten metal; on the other hand, because the oil passages cannot be machined internally and there are a large number of oil ports, the sand mold must also have high surface quality and dimensional accuracy.

[0003] However, most existing technologies only improve the casting performance of printed sand molds by simply adjusting the ratio of raw materials. However, this method has obvious limitations. It has very limited room for improvement in the strength and dimensional accuracy of the sand mold, and it is unable to stably control the surface quality of the sand mold. Specifically, in actual applications, sand molds prepared using existing technologies are prone to core breakage during the pouring process, have dimensional deviations and surface roughness problems, and cannot meet the mechanical strength requirements of complex castings for sand molds; at the same time, the dimensional accuracy of the sand mold is low, making it difficult to ensure the positioning accuracy of complex structures such as oil channels; in addition, the surface quality of the sand mold is poor, resulting in a rough surface of the casting that does not meet the use standards. Summary of the Invention

[0004] In order to solve some or all of the technical problems existing in the above-mentioned prior art, the present invention provides a method and system for printing high-quality sand molds, so that the tensile strength of the sand mold samples printed by the method and system of the present invention is improved and the gas evolution is reduced. When the sand molds printed by the method and system of the present invention are used to cast castings, the surface of the cast castings is smooth and the performance meets the use requirements, which solves the problems of difficult shape control and poor quality stability of complex castings and reduces process costs.

[0005] The technical solutions of the present invention are as follows:

[0006] In a first aspect, a method for printing high-quality sand molds is provided, comprising:

[0007] The thickness of the printed layer of the sand mold sample is controlled synchronously with the layer thickness of the sand mold sample by the layer cutting software, so that the sand laying thickness of the sand mold printing device is consistent with the height of the printing platform descending. In the process of controlling the sand spreading device of the sand mold printing device to lay sand layer by layer and the print head to spray resin to bond the sand grains, the raw sand used is silica sand with a particle size of 100 / 140 mesh, and the curing agent content used is controlled to be 0.25% of the total weight of the silica sand;

[0008] Dynamically adjust the inkjet frequency and X resolution, change the resin injection volume per unit area and the single injection movement distance to control the printing layer thickness between 0.25mm and 0.45mm or any thickness among 0.25mm, 0.30mm, 0.35mm and 0.45mm;

[0009] After the sand mold sample is printed and allowed to solidify, the performance is tested;

[0010] The response surface methodology was used to establish the tensile strength regression equation and gas evolution regression equation related to the resin inkjet volume, print layer thickness, curing agent content of the sand mold printing equipment and the sand mold performance. The central composite design was used to optimize the process parameter combination. The sand mold parameters after performance testing were compared with the sand mold parameters obtained from the tensile strength regression equation and the gas evolution regression equation to obtain the optimal process parameters for printing the sand mold sample.

[0011] Furthermore, in the above method for printing high-quality sand molds, the tensile strength regression equation includes:

[0012] Y1=2.44+0.4786A-0.1128B+0.0257C+0.0075AB-0.01AC+0.0075BC+0.0079A 2 +0.0097B 2 -0.0098C 2 ;

[0013] Wherein, Y1 represents the tensile strength regression equation, A represents the resin inkjet amount, B represents the printing layer thickness, and C represents the curing agent addition amount.

[0014] Furthermore, in the above-mentioned method for printing high-quality sand molds, the gas generation regression equation includes:

[0015] Y2=10.74+1.72A-0.165B+0.3358C-0.0225AB-0.06AC-0.0175BC-0.1793A 2 -0.0326B 2 -0.0891C 2 ;

[0016] Wherein, Y2 represents the regression equation of gas emission.

[0017] In some optional implementations, the optimal process parameters for printing sand mold specimens include:

[0018] The resin inkjet amount is 1.46%, the curing agent addition amount is 0.25%, and the printing layer thickness is 0.35mm.

[0019] In a second aspect, a system for printing high-quality sand molds is provided, comprising:

[0020] A control module, which is used to synchronize the thickness of the printed layer of the sand mold sample with the thickness of the layer of the sand mold sample by the layer cutting software, so that the sand laying thickness of the sand mold printing device is consistent with the height of the printing platform;

[0021] A dynamic adjustment module, which is used to dynamically adjust the inkjet frequency and X resolution, change the resin injection volume per unit area and the single injection movement distance, so as to control the printing layer thickness to be within a preset thickness or a preset thickness range;

[0022] A performance testing module is used to test the performance of the sand mold sample after it is printed and allowed to solidify;

[0023] The optimization module is used to establish a tensile strength regression equation and a gas evolution regression equation for the resin inkjet amount, print layer thickness, and curing agent content of the sand mold printing equipment using the response surface method, and to optimize the process parameter combination through central composite design. The sand mold parameters after performance testing are compared with the sand mold parameters obtained from the tensile strength regression equation and the gas evolution regression equation to obtain the optimal process parameters for printing the sand mold sample.

[0024] The main advantages of the technical solution of the present invention are as follows:

[0025] The present invention provides a method and system for printing high-quality sand molds, which controls the layer thickness synchronization during the sand mold sample printing process, that is, the sand laying thickness = the platform descent height, thereby avoiding the "step effect" caused by the layer thickness misalignment in the traditional process, ensuring that the sand laying thickness of the sand spreader is strictly consistent with the descent height of the printing platform each time, avoiding uneven sand accumulation or resin injection misalignment due to layer thickness deviation, thereby ensuring the interlayer bonding strength and dimensional accuracy of the sand mold structure, using silica sand with a particle size of 100 / 140 mesh to provide a denser sample stacking, and 0.25% of the curing agent balances the strength and gas emission, and the dimensional accuracy is improved to ±0.24mm, which is higher than the existing technology. The inkjet frequency and X-resolution are dynamically adjusted to change the resin injection volume per unit area and the distance traveled per single injection. This results in an increase in the injection volume per unit time and, consequently, in the resin volume per unit area when the inkjet frequency increases. This reduces the distance traveled per single injection as the X-resolution increases, which in turn reduces the droplet spacing and, consequently, the effective layer thickness. When the layer thickness is set to 0.35 mm, the tensile strength reaches 2.20 MPa, an 18.3% increase compared to the existing technology. Adjusting the X-resolution also enables precise control of the droplet spacing, eliminating the surface roughness problem associated with traditional fixed layer thicknesses. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the embodiments of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0027] Figure 1 A schematic flow chart of a method for printing high-quality sand molds provided by one embodiment of the present invention;

[0028] Figure 2 A three-dimensional structural diagram of a valve core of a prior art hydraulic valve body casting provided in accordance with an embodiment of the present invention;

[0029] Figure 3 A schematic structural diagram of a sand mold sample printed in a method for printing high-quality sand molds provided by one embodiment of the present invention from one perspective;

[0030] Figure 4 A schematic structural diagram of a sand mold sample printed in a method for printing high-quality sand molds provided by one embodiment of the present invention from another perspective;

[0031] Figure 5 A schematic diagram of the structure of a sand mold sample printed by a method for printing high-quality sand molds provided by an embodiment of the present invention;

[0032] Figure 6aA schematic diagram of a response surface of the interaction between the printing layer thickness and the amount of resin ink jetted on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by one embodiment of the present invention;

[0033] Figure 6b A schematic diagram of contour lines corresponding to a response surface of the interaction between the printing layer thickness and the amount of resin ink jetted on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention;

[0034] Figure 7a A response surface diagram of the interaction between the curing agent and resin inkjet amount on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by one embodiment of the present invention;

[0035] Figure 7b A schematic diagram of contour lines corresponding to a response surface of the interaction between the curing agent and resin inkjet amounts on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention;

[0036] Figure 8a A schematic diagram of a response surface of the interaction between the curing agent and the printing layer thickness on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by one embodiment of the present invention;

[0037] Figure 8b A schematic diagram of contour lines corresponding to a response surface of the interaction between the curing agent and the printing layer thickness on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention;

[0038] Figure 9a A response surface diagram of the interaction between the printing layer thickness and the amount of resin ink jetted on the gas generation of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by one embodiment of the present invention;

[0039] Figure 9b A schematic diagram of contour lines corresponding to a response surface of the interaction between the print layer thickness and the resin inkjet amount on the gas generation amount of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by one embodiment of the present invention;

[0040] Figure 10a A response surface diagram of the interaction between the amount of resin inkjet and the curing agent on the gas evolution of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by one embodiment of the present invention;

[0041] Figure 10bA schematic diagram of contour lines corresponding to a response surface of the interaction between the amount of resin inkjet and the curing agent on the amount of gas evolution of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by one embodiment of the present invention;

[0042] Figure 11a A response surface diagram of the interaction between the printing layer thickness and the curing agent on the gas evolution of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention;

[0043] Figure 11b A schematic diagram of contour lines corresponding to a response surface of the interaction between the printing layer thickness and the curing agent on the gas generation amount of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention;

[0044] Figure 12 A schematic diagram of the structure of a system for printing high-quality sand molds provided by an embodiment of the present invention.

[0045] Description of reference numerals:

[0046] 100, control module; 200, dynamic adjustment module; 300, performance detection module; 400, optimization module. DETAILED DESCRIPTION

[0047] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] The following is combined with Figure 1 -Attached Figure 12 , describes in detail the technical solution provided by the embodiments of the present invention.

[0049] As attached Figure 1 As shown in FIG11 , an embodiment of the present invention provides a method for printing high-quality sand molds, particularly a method for controlling the process performance of 3D printing sand molds for valve body castings with complex internal structures. The method includes the following steps S1 to S4:

[0050] Step S1: Controlling the printing layer thickness of the sand mold sample and the layer thickness of the sand mold sample by the layer cutting software to synchronize, so that the sand laying thickness of the sand mold printing device is consistent with the height of the printing platform descending, wherein, in the process of controlling the sand spreader of the sand mold printing device to lay sand layer by layer and the print head to spray resin to bond the sand grains, the raw sand used is silica sand with a particle size of 100 / 140 mesh, and the curing agent content used is controlled to be 0.25% of the total weight of the silica sand;

[0051] Combining practical applications and 3D printing technology, when 3D printing any model, it is necessary to first model the part to be printed and then perform corresponding slicing on it. For sand mold printing, it is also necessary to establish a three-dimensional model and perform corresponding slicing operations.

[0052] For example, the model data is imported into the layer cutting software of the printing system for layer processing. At the same time, in the embodiment of the present invention, the raised and recessed sand mold samples of letter shapes or the standard sample of "8" shape are designed, such as Figure 3-Figure 5 As shown, in order to observe and measure the surface quality and dimensional accuracy of the sand mold.

[0053] This setup synchronizes the print layer thickness with the layer thickness specified by the slicing software, i.e., the sanding thickness = the platform descent height. This ensures that the sanding thickness of each sanding operation is strictly consistent with the platform descent height. For example, when the layer thickness is 0.35mm, the platform drops 0.35mm. This prevents uneven sand accumulation or misaligned resin injection due to layer thickness deviations, thereby ensuring the interlayer bonding strength and dimensional accuracy of the sand mold structure. The use of 100 / 140 mesh silica sand, with a particle size distribution of approximately 197–241μm, results in a high sand packing density, making it easier for the resin to fill the gaps between particles, forming a uniform bonding network. A curing agent content of 0.25% (relative to silica sand) ensures sufficient resin curing while avoiding increased brittleness in the sand mold due to excessive curing agent, achieving a balance between strength and toughness.

[0054] Step S2: Dynamically adjust the inkjet frequency and X resolution, change the resin injection volume per unit area and the single injection movement distance, so as to control the printing layer thickness to be between 0.25 mm and 0.45 mm or to control the printing layer thickness to be any one of 0.25 mm, 0.30 mm, 0.35 mm and 0.45 mm;

[0055] In some optional implementations of this embodiment, in order to improve the tensile strength, reduce gas evolution, and achieve a smooth casting surface when casting sand mold samples printed by a sand mold printing device, such as a sand mold 3D printer, with performance meeting usage requirements, the preset thickness range is set to any thickness range of 0.25 mm to 0.45 mm. Most preferably, the preset thickness range is set to any one of 0.25 mm, 0.30 mm, 0.35 mm, and 0.45 mm.

[0056] In order to further improve the quality of the sand mold printed by the embodiment of the present invention, so that the sand mold of the embodiment of the present invention meets the requirements of quality, strength, precision and roughness after printing, in the process step of controlling the printing layer thickness of the sand mold sample and synchronizing the layer thickness of the sand mold sample by the layer cutting software, so that the sand laying thickness of the sand mold printing equipment is consistent with the lowering height of the printing platform, the raw sand used is set to silica sand with a particle size of 100 / 140 mesh, and the curing agent content used is 0.25% of the total weight of the silica sand.

[0057] In practical applications, for example, the digital panel adjusts the printhead's inkjet frequency and X-resolution, changing the amount of resin sprayed per unit area and the distance traveled per jet, thereby varying the print layer thickness. For example, each layer's control signal is converted and transmitted to the 3D printer, controlling the sander to apply sand layer by layer, and the printhead to spray resin to bond the sand grains. The sand mold's printed layer thickness is synchronized with the layer thickness set by the slicing software, with a layer thickness of 0.25mm to adjust printing efficiency. The raw sand used is 100 / 140 mesh silica sand, and the curing agent is added to the sand mold with process parameters such as 0.25% of the total silica sand.

[0058] Specifically, the dynamic adjustment principle includes the following: the inkjet frequency determines the number of resin injections per unit time. The higher the frequency, the more resin is injected per unit area, and the stronger the sand grain bond strength is. The X resolution controls the movement distance of the print head during a single injection. For example, the higher the resolution, the smaller the movement distance. By adjusting this parameter, the falling distance of the resin droplets can be changed, which in turn affects the thickness of the printed layer. For example, the smaller the spacing, the thinner the layer thickness.

[0059] In some optional implementations of this embodiment, layer thickness control methods include: Because layer thickness directly affects printing efficiency and sand mold density, in this embodiment of the present invention, setting a layer thickness range of 0.25mm–0.45mm takes into account both production efficiency (thick layers print quickly) and surface quality (thin layers print with high precision). For example, a layer thickness of 0.25mm is suitable for high-precision sand molds, while a layer thickness of 0.45mm is suitable for rapid prototyping of large sand molds.

[0060] Therefore, in an embodiment of the present invention, the signal frequency of the circuit in the nozzle driving system can be changed, and the driving system can send an inkjet instruction to control the nozzle, so that the amount of adhesive sprayed per unit area can be changed on the basis of a fixed amount of adhesive added; the moving distance when spraying the adhesive once can be adjusted to change the falling distance between the adhesive droplets.

[0061] Step S3: After the sand mold sample is printed and allowed to stand and solidify, the performance is tested;

[0062] In combination with actual applications, each time a layer of printing is completed, the printing platform is lowered a certain distance according to the layer thickness until the sample is printed, and then the sample is taken out for testing after standing in the working box. For example, after the sample is printed, it is left in the working box for 60 minutes to completely solidify, and then the performance is taken out for testing, including tensile strength, gas evolution and dimensional accuracy.

[0063] In some optional implementations of this embodiment, the tensile strength is tested by a SWY-B digital hydraulic strength testing machine, and the gas emission volume is tested using a GET-Ⅲ intelligent gas emission tester, with the aim of comparing the test results with the following regression equation experimental results after the test is completed.

[0064] Step S4: Response surface methodology is used to establish regression equations for the tensile strength and gas evolution of the sand mold performance, which are related to the resin inkjet volume, print layer thickness, and curing agent content of the sand mold printing equipment. The process parameter combination is optimized through central composite design, and the sand mold parameters after performance testing are compared with the sand mold parameters obtained from the tensile strength regression equation and the gas evolution regression equation to obtain the optimal process parameters for printing the sand mold sample.

[0065] In some optional implementations of this embodiment, the printing equipment process parameters include: resin inkjet volume, print layer thickness, and curing agent content. Specifically, in this embodiment of the present invention, a response surface methodology is used to establish a regression equation for the resin inkjet volume, print layer thickness, curing agent content, and sand mold properties.

[0066] In order to achieve precise control and detection of sand mold accuracy, the tensile strength regression equation and the gas evolution regression equation are used in the embodiment of the present invention to control it. Among them, the tensile strength regression equation includes:

[0067] Y1=2.44+0.4786A-0.1128B+0.0257C+0.0075AB-0.01AC+0.0075BC+0.0079A 2 +0.0097B 2 -0.0098C 2 ;

[0068] Wherein, Y1 represents the tensile strength regression equation, A represents the resin inkjet amount, B represents the printing layer thickness, and C represents the curing agent addition amount.

[0069] The gas production regression equation includes:

[0070] Y2=10.74+1.72A-0.165B+0.3358C-0.0225AB-0.06AC-0.0175BC-0.1793A 2 -0.0326B 2 -0.0891C 2 ;

[0071] Wherein, Y2 represents the regression equation of gas emission.

[0072] In this way, by applying the response surface methodology to the optimization of 3D printing sand mold process parameters, a regression equation between process parameters and sand mold performance was established, which can scientifically explain the influence of each parameter on performance, realize the accurate prediction and control of sand casting performance, and change the limitations of the traditional single adjustment of raw material ratio.

[0073] Specifically, in order to further determine the influence of the parameter selection and setting of the embodiment of the present invention on the printing accuracy and quality of the sand mold sample, different test parameters were used for testing. The selected test parameters are shown in Table 1 below.

[0074] Table 1: Test parameters

[0075]

[0076] It should be noted that the meaning of α in the above Table 1 is a variable factor, which has the same meaning as -1, 0, and 1. It can be seen from the experimental parameter table in the above Table 1 that the embodiment of the present invention adopts three-factor five-level experimental parameters.

[0077] Among them, in the embodiment of the present invention, the performance data of the printed sand mold under different process parameters obtained based on the central composite design are shown in Table 2 below.

[0078] Table 2: Printed sand mold performance data under different process parameters based on central composite design

[0079]

[0080]

[0081] According to the central composite design and experimental results of the 3D printing process parameters in Table 2, the variance analysis of the tensile strength of the printed sand mold was performed using the ANOVA function of the response surface optimization analysis in the Design Expert software. The analysis method is shown in Table 3, which is a data table of the variance analysis results of the tensile strength. In this way, the regression model equation between the tensile strength and the resin inkjet amount A, the printing layer thickness B, and the curing agent addition amount C was obtained.

[0082] Table 3: Tensile strength variance analysis results table

[0083] source sum of squares degrees of freedom mean square error F-number P-value Significance Model 3.32 9 0.3685 65.84 <0.0001 ** A 3.13 1 3.13 558.92 <0.0001 ** B 0.1737 1 0.1737 31.03 0.0002 ** C 0.009 1 0.009 1.61 0.2336 - AB 0.0004 1 0.0004 0.0804 0.7825 - AC 0.0008 1 0.0008 0.1429 0.7133 - BC 0.0005 1 0.0005 0.0804 0.7825 - <![CDATA[A 2 ]]> 0.0009 1 0.0009 0.1610 0.6967 - <![CDATA[B 2 ]]> 0.0013 1 0.0013 0.2401 0.6341 - <![CDATA[C 2 ]]> 0.0014 1 0.0014 0.2459 0.6307 - residual 0.056 10 0.056 - - - Lack of Fit 0.0392 5 0.0078 2.34 0.1861 - Pure error 0.0167 5 0.0033 - - - Total deviation 3.37 19 - - - - <![CDATA[R 2 ]]> 0.9834 - - - - - <![CDATA[Adj.R 2 ]]> 0.9685 - - - - -

[0084] The data in Table 3 were analyzed and the P and F values ​​of the model and the lack of fit term were used to determine whether the regression model was statistically significant. The model P < 0.0001 < 0.005, the F value was 65.84, and the model was very significant; the lack of fit term P = 0.1861 > 0.0392, the F value was 2.34, and the lack of fit term was not significant relative to the pure error. According to the correlation coefficient R 2 , Corrected determination coefficient Adj.R 2 and coefficient of variation C v It can reflect the fit of the model. 2 =0.9834, indicating that the fit between the measured and predicted values ​​of tensile strength is high; Adj.R 2 =0.9685, indicating that only no more than 4% of the tensile strength cannot be explained by this model; C v =3.06%, the deviation between the measured value and the predicted value is very low, and the experimental results are reliable. Therefore, the model's regression equation can be used to explain and predict the response results. Analyzing the influence of each factor model on tensile strength, it can be seen that the resin inkjet volume and the printing layer thickness have a significant effect on the tensile strength, with the influence degree being: A>B. The effect of the curing agent addition on the tensile strength is weak; the interaction term and the square term have no significant effect on the tensile strength. For example Figure 6a and Figure 6b As shown in the curve, the peak tensile strength requirement is A↑+B↓, and the minimum gas emission window requirement is A↓+C↓. The interaction of the three factors of print layer thickness, resin inkjet volume, and curing agent content on the tensile strength response surface trend diagram is shown in Figures 6 to 8, where: Figure 6a A schematic diagram of a response surface of the interaction between the printing layer thickness and the amount of resin ink jetted on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention; Figure 6b A schematic diagram of contour lines corresponding to a response surface of the interaction between the printing layer thickness and the amount of resin ink jetted on the tensile strength of a high-quality sand mold sample printed using a method for printing a high-quality sand mold provided by an embodiment of the present invention; Figure 7a A response surface diagram of the interaction between the curing agent and resin inkjet amount on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention; Figure 7b A schematic diagram of contour lines corresponding to a response surface of the interaction between the curing agent and resin inkjet amounts on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention; Figure 8a A schematic diagram of the response surface of the interaction between the curing agent and the printing layer thickness on the tensile strength of a high-quality sand mold sample printed using a method for printing high-quality sand molds provided by an embodiment of the present invention; Figure 8bA schematic diagram of the contour lines corresponding to the response surface of the interaction between the curing agent and the printing layer thickness on the tensile strength of a high-quality sand mold sample printed by a method for printing high-quality sand molds provided by an embodiment of the present invention; taking FIG6 as an example, Figure 6a represents the response surface plot, Figure 6b For Figure 6a The contour map corresponding to the response surface plot, Figure 6a and Figure 6b The relationship between the two is: Figure 6a The more inclined the response surface is, the more significant the effect of the printing layer thickness and the amount of resin inkjet on the tensile strength is. Figure 6b The more it resembles an ellipse, the stronger the interaction between the two factors.

[0085] It should also be noted that the principles of the following Figures 7 to 11 are similar to the principles illustrated in Figure 6. They are all schematic diagrams of the response surfaces of the interaction between print layer thickness and resin inkjet volume, curing agent and resin inkjet volume, and curing agent and print layer thickness on tensile strength and gas emission, as well as the contour lines corresponding to the tensile strength response surface, as well as the display results of tensile strength and gas emission under different influencing factors.

[0086] Combining the central composite design of 3D printing process parameters in Table 2 with the experimental results, the variance analysis of the gas emission of the printed sand mold was performed using the ANOVA function of the response surface optimization analysis in the Design Expert software, and the regression model equation between the above gas emission and the resin inkjet amount A, the printing layer thickness B, and the curing agent addition amount C was obtained.

[0087] In order to further verify the influence of the interaction of process parameters on the gas emission of high-quality sand mold samples printed by a method for printing high-quality sand molds provided by an embodiment of the present invention, the gas emission was also analyzed and verified in an embodiment of the present invention, and the analytical verification data used are shown in Table 4 below.

[0088] Table 4: Gas emission variance analysis results table

[0089] source sum of squares degrees of freedom mean square error F-number P-value Significance Model 42.97 9 6.26 229.51 <0.0001 ** A 40.49 1 40.49 1946.11 <0.0001 ** B 0.3719 1 0.3719 17.87 0.0017 ** C 1.54 1 1.54 74.03 <0.0001 ** AB 0.0041 1 0.0041 0.1947 0.6684 ** AC 0.0288 1 0.0288 1.38 0.2666 * BC 0.0025 1 0.0025 0.1178 0.7386 - <![CDATA[A 2 ]]> 0.4632 1 0.4632 22.27 0.0008 ** <![CDATA[B 2 ]]> 0.0153 1 0.0153 0.7346 0.4115 - <![CDATA[C 2 ]]> 0.1145 1 0.1145 5.50 0.0409 * residual 0.2080 10 0.2080 - - - Lack of Fit 0.1770 5 0.0354 5.69 0.3960 - Pure error 0.0311 5 0.0062 - - - Total deviation 43.18 19 - - - - <![CDATA[R 2 ]]> 0.9952 - - - - - <![CDATA[Adj.R 2 ]]> 0.9908 - - - - -

[0090] It should also be noted that in Tables 3 and 4, “**” indicates highly significant (P<0.01); “*” indicates significant (P<0.05).

[0091] Analysis of the data in Table 4 shows that the model P < 0.0001 < 0.005, the F value is 229.51, and the model is very significant; the lack of fit term P = 0.3960 > 0.1770, the F value is 5.69, and the lack of fit term is not significant relative to the pure error. 2 =0.9952, indicating that the measured and predicted values ​​of gas emission are highly consistent; the correction coefficient of determination Adj.R 2=0.9908, indicating that no more than 1% of the gas emission cannot be explained by this model; the coefficient of variation C v =1.37%, the deviation between the measured value and the predicted value is very low, and the experimental results are reliable. Therefore, the model regression equation can be used to explain and predict the response results. Analyzing the influence of each factor model on the gas emission, it can be seen that the resin inkjet volume and the amount of curing agent added have the same significant effect on the gas emission; the effect of the printing layer thickness on the gas emission is weak; the effect of the interaction term on the gas emission is not significant; in the square phase, the resin inkjet volume and the amount of curing agent added have a significant effect on the gas emission, and the degree of influence A 2 >C 2 The response surface trend diagrams of the interaction between the three factors of print layer thickness, resin inkjet volume, and curing agent content on gas emission are shown in Figures 9 to 11.

[0092] Therefore, using the above method of the embodiment of the present invention, the optimal process parameter combination obtained under the central composite design is shown in Table 5 below.

[0093] Table 5: Optimal process parameter combination data obtained under central composite design

[0094]

[0095] Analyzing Table 5, combined with Tables 1 to 4 and Figures 6 to 11, the optimal combination of A = 1.46%, B = 0.35 mm, and C = 0.25% achieves a tensile strength of 2.13 MPa, which is lower than the baseline group of 2.41 MPa when A = 1.6%, B = 0.35 mm, and C = 0.30%. The gas evolution is 9.32 mL·g -1 Lower than the baseline group's 10.73 mL·g -1 At the same time, the dimensional accuracy is stable at ±0.24mm, meeting the ±0.3mm requirement of the valve body oil passage. Combined with Figures 6 to 11, the method of the embodiment of the present invention is used to print the sand mold sample. Combined with item A in Y1, increasing the resin inkjet amount by 1% can increase the tensile strength by 0.4786MPa; combined with item B in Y1, for every 0.1mm increase in layer thickness, the tensile strength decreases by 0.1128MPa; combined with item C in Y2, increasing the curing agent by 0.1% increases the gas emission by 0.3358mL·g -1 .

[0096] Therefore, the experiment was arranged by central composite design (CCD), with the resin inkjet volume A, printing layer thickness B, and curing agent content C as independent variables, and the tensile strength Y1 and gas emission Y2 as dependent variables. The above-mentioned multiple regression equation for tensile strength was established, revealing the joint effect of sand mold printing process parameters. For example, A had the most significant effect on Y1, with P < 0.0001. The above-mentioned multiple regression equation for gas emission was also established, indicating that A and C had a significant effect on Y2, and A2 and C 2 Item P < 0.01. Using DesignExpert software, we analyzed the response surface curve to find the parameter combination that maximizes Y1 and minimizes Y2. Compared with traditional single-factor optimization, the method of this embodiment of the present invention can simultaneously consider parameter interactions, reducing the number of experiments by over 40% (combined with actual experiments and applications, 20 sets of experiments can cover the entire parameter space).

[0097] Therefore, according to Table 5, the method provided by the embodiment of the present invention improves the dimensional accuracy of the sand mold from ±0.37 mm of the traditional method to ±0.24 mm by precisely matching the layer thickness, meeting the positioning requirement of the oil passage of the hydraulic valve body of ±0.25 mm, thereby significantly improving the dimensional accuracy. In addition, in the embodiment of the present invention, by setting the layer thickness uniform, the sand mold layers are evenly bonded, and the fluctuation range of the tensile strength is reduced from ±0.9 MPa to ±0.13 MPa. When the resin inkjet amount increases from 1.2% to 1.46%, the tensile strength is increased from 1.56 MPa to 2.13 MPa ( Figure 6a and Figure 6b Surface peak), because more resin fills the gaps between sand particles to form a continuous bonding phase, too high an inkjet volume will lead to an increase in gas emission (for example, the gas emission is 13.00 mL / g when the inkjet volume is 2.0%). By optimizing it to 1.46%, the gas emission is reduced to 9.32 mL / g ( Figure 9a and Figure 9b valley area) to reduce porosity defects in castings.

[0098] Comparing the data in Table 2, we can see that sand molds printed with finer-grained silica sand exhibit superior overall performance. Optimizing 3D printing process parameters can effectively improve the mechanical strength, dimensional accuracy, and surface quality of the sand molds. The data in Tables 2 and 3 also reveal the influence of 3D printing process parameters on sand casting performance, helping to systematically explain the combined effects of various printing process parameters on sand casting performance. This demonstrates that the methods provided by the present invention reduce the cost of process improvements, address the challenges of difficult shape control and poor quality stability in complex castings, and promote the widespread application of 3D printing technology in the foundry industry.

[0099] Preferably, through the above method of the embodiment of the present invention, the optimal process parameters for printing the sand mold sample include:

[0100] The resin inkjet amount is 1.46%, the curing agent addition amount is 0.25%, and the printing layer thickness is 0.35mm.

[0101] With this configuration, the optimal parameters achieve the following comprehensive sand mold performance: tensile strength of 2.13 MPa (a 36% increase), capable of withstanding the impact of 1500°C molten metal without breaking; gas generation of 9.32 mL / g (a 28% decrease), meeting the requirements for ductile iron casting; dimensional accuracy of ±0.24 mm (a 35% increase), and oil channel positioning error of ≤0.15 mm. Combined with practical applications, the method provided by this embodiment of the present invention uses a mathematical model to predict sand mold performance under different parameters, eliminating the need for trial and error. This reduces the process debugging cycle from the traditional 20–30 days to 7 days, reducing costs by over 50%.

[0102] In summary, the embodiment of the present invention provides a method for printing high-quality sand molds, combined with mathematical statistical methods, to establish a regression equation between various process parameters and the casting performance of the printed sand molds. The tensile strength is controlled by controlling the amount of grease inkjet, and the overall strength is controlled by the layer thickness. The influencing laws are scientifically explained and predicted, thereby achieving stable control of the casting performance of the printed sand molds and obtaining the optimal 3D printing process parameters. The high-temperature strength and dimensional accuracy of the obtained printed sand molds are significantly improved, the castings do not experience core breakage during the pouring process, the oil channel structure has high dimensional accuracy, the casting surface is smooth, and the performance meets the use requirements.

[0103] Second, as Figure 12 As shown, an embodiment of the present invention further provides a system for printing high-quality sand molds, comprising: a control module 100, a dynamic adjustment module 200, a performance detection module 300 and an optimization module 400, wherein:

[0104] The control module 100 is used to control the printing layer thickness of the sand mold sample and synchronize it with the layer thickness of the sand mold sample by the slicing software, so that the sand laying thickness of the sand mold printing device is consistent with the height of the printing platform descending; the dynamic adjustment module 200 is used to dynamically adjust the inkjet frequency and X resolution, change the resin injection volume per unit area and the single injection movement distance, so as to control the printing layer thickness within a preset thickness or a preset thickness range; the performance detection module 300 is used to detect the performance of the sand mold sample after it is printed and allowed to solidify; the optimization module 400 is used to use the response surface method to establish the tensile strength regression equation and the gas evolution regression equation of the sand mold performance of the sand mold printing device, optimize the process parameter combination through central composite design, and compare the sand mold parameters after the performance test with the sand mold parameters obtained from the tensile strength regression equation and the gas evolution regression equation to obtain the optimal process parameters for printing the sand mold sample.

[0105] Therefore, the present invention provides a system for printing high-quality sand molds, so that the tensile strength of the sand mold samples printed by the system of the present invention is improved and the gas evolution is reduced. When the sand molds printed by the system of the present invention are used to cast castings, the surface of the cast castings is smooth and the performance meets the use requirements, which solves the problems of difficult shape control and poor quality stability of complex castings and reduces process costs.

[0106] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In addition, "front", "back", "left", "right", "upper" and "lower" in this document are all referenced to the placement states shown in the accompanying drawings.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for printing high-quality sand molds, characterized in that: include: The thickness of the printed layer of the sand mold sample is controlled synchronously with the layer thickness of the sand mold sample by the layer cutting software, so that the sand laying thickness of the sand mold printing device is consistent with the height of the printing platform descending. In the process of controlling the sand spreading device of the sand mold printing device to lay sand layer by layer and the print head to spray resin to bond the sand grains, the raw sand used is silica sand with a particle size of 100 / 140 mesh, and the curing agent content used is controlled to be 0.25% of the total weight of the silica sand; Dynamically adjust the inkjet frequency and X resolution, change the resin injection volume per unit area and the single injection movement distance to control the printing layer thickness between 0.25mm and 0.45mm or any thickness among 0.25mm, 0.30mm, 0.35mm and 0.45mm; After the sand mold sample is printed and allowed to solidify, the performance is tested; The response surface methodology was used to establish the tensile strength regression equation and gas evolution regression equation related to the resin inkjet volume, print layer thickness, curing agent content of the sand mold printing equipment and the sand mold performance. The central composite design was used to optimize the process parameter combination. The sand mold parameters after performance testing were compared with the sand mold parameters obtained from the tensile strength regression equation and the gas evolution regression equation to obtain the optimal process parameters for printing the sand mold sample.

2. A method for printing high-quality sand molds according to claim 1, characterized in that: The tensile strength regression equation includes: Y1=2.44+0.4786A-0.1128B+0.0257C+0.0075AB-0.01AC+0.0075BC+0.0079A 2 +0.0097B 2 -0.0098C 2 ; Wherein, Y1 represents the tensile strength regression equation, A represents the resin inkjet amount, B represents the printing layer thickness, and C represents the curing agent addition amount.

3. A method for printing high-quality sand molds according to claim 1, characterized in that: The gas generation regression equation includes: <h2 style=";text-align:left;direction:ltr">Y2 = 10.74 + 1.72A - 0.165B + 0.3358C - 0.0225AB - 0.06AC - 0.0175BC - 0.1793A<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -0.0326B<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -0.0891C<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> ; Wherein, Y2 represents the regression equation of gas emission.

4. A method for printing high-quality sand molds according to any one of claims 2-3, characterized in that: The optimal process parameters for printing sand mold specimens include: The resin inkjet amount is 1.46%, the curing agent addition amount is 0.25%, and the printing layer thickness is 0.35mm.

5. A system for printing high-quality sand molds, characterized in that: include: A control module, which is used to synchronize the thickness of the printed layer of the sand mold sample with the thickness of the layer of the sand mold sample by the layer cutting software, so that the sand laying thickness of the sand mold printing device is consistent with the height of the printing platform; A dynamic adjustment module, which is used to dynamically adjust the inkjet frequency and X resolution, change the resin injection volume per unit area and the single injection movement distance, so as to control the printing layer thickness to be within a preset thickness or a preset thickness range; A performance testing module is used to test the performance of the sand mold sample after it is printed and allowed to solidify; The optimization module is used to establish a tensile strength regression equation and a gas evolution regression equation for the resin inkjet amount, print layer thickness, and curing agent content of the sand mold printing equipment using the response surface method, and to optimize the process parameter combination through central composite design. The sand mold parameters after performance testing are compared with the sand mold parameters obtained from the tensile strength regression equation and the gas evolution regression equation to obtain the optimal process parameters for printing the sand mold sample.

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