Sand printing green forming method and device based on digital light projection

Abstract

The present application relates to a kind of sand printing green forming method and device based on digital light projection;The device includes integrated vibration compaction sand laying mechanism, ball screw mechanism, vacuum sanding material box, base, protective panel support frame, digital light projection mechanism, printing lifting platform.Adopt double-roller extrusion discharge chute to realize quantitative sanding, sand laying box is equipped with vibration compaction plate, vibration flattening compaction plane, the surface of premixed photosensitive resin is radiated using digital light projection technology, resin polymerization crosslinking in projection area, form net structure between sand particles, realize sand mold efficient forming, can reduce sand printing layer thickness, improve sand mold overall precision, and waste sand can be directly reused after recycling, environmental protection and pollution-free.

Description

Technical Field

[0001] This invention relates to the intersection of 3DP printing and DLP photopolymerization printing of casting sand molds, and particularly to a green forming method and apparatus for sand mold printing based on digital light projection. Background Technology

[0002] Traditional sand mold 3D printing technology is a rapid prototyping technology mainly based on microdroplet jetting. It involves slicing a 3D digital model into layers, then using a multi-nozzle print head to spray a binder-cured powder, layer by layer, to rapidly form the physical object of the digital model. Currently, most sand mold 3D printing equipment is based on powder bed rapid prototyping. The forming process involves the storage, supply, laying, and recycling of molding sand, as well as the on-demand spraying of resin binder. When the sprayed resin binder encounters the pre-mixed curing agent in the molding sand, the sand particles bond and solidify to form the desired sand mold. Sand mold 3D printing technology has advantages such as high manufacturing flexibility and low complexity sensitivity, enabling rapid manufacturing of sand molds, shells, and cores. It is particularly suitable for the development and research of single-piece, small-batch, personalized, and complex-shaped castings.

[0003] Because sand mold 3D printing technology uses a special forming principle that uses a print head to spray binder to bond loose sand layer by layer, it causes problems such as high sand mold porosity, low dimensional accuracy, and low printing efficiency, which affect the surface quality and performance of castings and make it difficult to meet the high-precision manufacturing requirements of some complex castings.

[0004] Sand mold integral printing equipment based on microdroplet jetting technology has the following shortcomings:

[0005] (1) In actual production, multiple printheads may cause problems such as uneven ink spraying and splashing, resulting in low sand mold precision and unstable quality of finished products in the same batch.

[0006] (2) The printing efficiency of sand mold 3D printing is not high due to the limitations of the speed of moving parts and the printing width, which cannot meet the growing production demand.

[0007] The basic principle of photopolymerization molding technology is to selectively irradiate photosensitive resin with light of a specific wavelength controlled by a computer, curing it to form a single-layer outline. This process is repeated layer by layer until the final solid model is obtained. DLP technology projects this layer image directly onto the entire area, achieving surface curing and significantly increasing printing speed, while also being less demanding on the viscosity of the resin. Combining photopolymerization with sand mold printing can shorten the process, improve the overall accuracy of the sand mold, and allow for direct reuse of waste sand, making it environmentally friendly and pollution-free. This device and method can solve the problems of traditional sand mold 3D printing equipment being limited by nozzle performance, and the sand mold accuracy and printing efficiency failing to meet the growing production demands. It is of great significance for achieving precise sand mold forming and high-efficiency, green, and sustainable printing. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] This invention addresses the problems of traditional sand mold 3D printing equipment in the prior art, such as limitations imposed by nozzle performance, low sand mold precision, low printing efficiency, and serious waste of molding sand materials. It provides a green forming method and device for sand mold printing based on digital light projection, so as to improve the printing precision and production efficiency of sand mold overall printing forming equipment.

[0010] (II) Technical Solution

[0011] To achieve the above objectives, a green forming device for sand mold printing based on digital light projection is provided, comprising: an integrated vibration compaction and sand spreading mechanism, a ball screw mechanism, a vacuum sand feeding box, a base, a protective panel support frame, a digital light projection mechanism, and a printing lifting platform.

[0012] In the vacuum sand feeding box, the vacuum sand suction hopper has a built-in air switch valve to control the sand to enter the sand storage tank. The sand storage tank has a built-in screw propeller. The servo motor b controls the screw propeller to evenly spread the sand in the sand storage tank. The sand storage amount can be observed through the sand quantity monitoring window. Cylinders are installed on both sides of the sand storage tank. The cylinders control the opening of the sand storage tank switch plate to drop sand to the double roller extrusion trough.

[0013] In the integrated vibratory compaction sand spreading mechanism, the double roller extrusion discharge trough is connected to the vibratory compaction mechanism through a fixed plate, which can flatten and compact the sand surface while spreading sand, thereby improving the performance of the sand mold;

[0014] The digital light projection mechanism moves the projection screen through a mechanical motion module, and after sand is laid, light projection is applied to the sand surface in the designated projection area to cure the resin.

[0015] The printing platform descends to a certain thickness via lifting guide columns, and through layer-by-layer sand laying and irradiation, achieves precise and efficient sand mold forming.

[0016] Furthermore, the integrated vibration compaction sand-spreading mechanism consists of a double-roller extrusion discharge trough and a vibration compaction mechanism. The double-roller extrusion discharge trough is equipped with double rollers for extruding material. The gap and rotation speed of the two rollers are adjusted according to the required discharge volume to achieve quantitative sand spreading. A movable slide table connected to a ball screw mechanism is used below the double-roller extrusion discharge trough for movement. The vibration compaction mechanism consists of a vibration compaction plate, a servo motor, a cam, and a small lifting guide column. It is connected to the double-roller extrusion discharge trough via a fixed plate and moves together with the sand-spreading mechanism on a slide rail. While spreading sand, it compacts and flattens the sand surface, improving sand-spreading printing efficiency.

[0017] Furthermore, the digital light projection mechanism consists of a mechanical motion module and a projection device, connected to the protective panel support frame via a fixed connecting plate, replacing the traditional 3D sand mold printing nozzle. The projection area of ​​the projection device should be able to fully cover the printing platform, and different wavelength light sources can be replaced for irradiation according to actual curing requirements. The projection screen is moved parallel to the printing platform via a mechanical structure to project the required two-dimensional image for the current layer. The light source on the projection device uses UV LED, and the replaceable light source wavelength range is 280-380nm. The mechanical motion module consists of a servo motor a, an electric telescopic rod, a ball joint, a support rod, and a fixed support. The support rod provides fixed support. When moving the projection device, the servo motor a controls the upper electric telescopic rod and the ball joint to lower the projection screen, and the lower ball joint moves accordingly until the projection screen is parallel to the printing platform.

[0018] This invention also provides a green forming method for sand mold printing based on digital light projection, which is carried out according to the following steps:

[0019] Step 1: Select molding sand, binder, and their mixing formula according to the casting requirements;

[0020] Step 2: Design the three-dimensional geometric model of the sand mold and perform layer-by-layer slicing to obtain the two-dimensional slice information of each layer; set the layer thickness (0.1-0.6mm), and pre-lay a certain layer thickness of molding sand to prevent it from sticking to the printing platform;

[0021] Step 3: Put the proportioned raw sand particles and the corresponding amount of photosensitive resin binder (2-8 wt.%) into a sand mixer and stir evenly to obtain premixed molding sand particles with binder.

[0022] Step 4: The premixed molding sand particles are fed into the sand storage tank through a vacuum sand suction hopper; the sand storage tank has a built-in screw propeller to evenly load the premixed sand into the double roller extrusion discharge trough, and the sand loading process is completed;

[0023] Step 5: The integrated vibration compaction sand spreading mechanism moves from left to right through the ball screw mechanism, and the molding sand particles premixed with binder are squeezed and quantitatively dropped onto the printing platform by two rollers.

[0024] Step 6: The compaction mechanism moves behind the sand-laying mechanism, patting and flattening the premixed molding sand particles with curing agent on the printing platform to complete the sand-laying process.

[0025] Step 7: The digital light projection mechanism moves parallel to the printing platform through a mechanical structure to project the current layer's two-dimensional image, exposing the current layer's resin for 30-60 seconds to catalyze the reaction and promote resin curing.

[0026] Step 8: Stop the current layer irradiation and lower the printing platform by one layer thickness;

[0027] Step 9: Repeat steps 5 to 8, exposing and printing layer by layer until the sand mold is prepared;

[0028] Step 10: Remove the sand mold, recycle the waste sand, and post-process the sand mold as needed.

[0029] Furthermore, in step 1, molding sand, binder, and their mixing formula are selected. The types of molding sand that can be selected include quartz sand, magnesium olivine sand, zircon sand, etc.; the mesh size of the molding sand can be selected from 140 to 600 mesh; the viscosity range of the photosensitive resin binder can be selected from 20 to 300 mPa·s; and the mixing formula of molding sand and binder can be formulated according to printing requirements.

[0030] Furthermore, in steps 5 and 6, the sand spreading is done by using a double roller extrusion to quantitatively discharge the sand, which saves raw materials for molding sand and avoids severe bridging of the premixed sand when the resin viscosity is high, thus preventing normal sand dropping; the sand surface is leveled by vibration compaction, which reduces the bonding mechanism of molding sand while compacting each layer of molding sand, thereby improving the overall strength of the sand mold.

[0031] Furthermore, in step 7, the resin curing method uses UV LED ultraviolet light to irradiate the photosensitive resin, which promotes the polymerization and cross-linking of the resin in the projection area, forming a network structure between the sand particles. This reduces the impact on accuracy caused by nozzle spraying and improves the precision forming effect. The resin exposure time of each layer in the projection area is 30-60 seconds, which is about 35% more efficient than traditional 3D printing sand molds.

[0032] The beneficial effects of this invention are:

[0033] (1) Replacing the printhead with a light projection avoids a series of problems caused by uneven ink spraying and splashing, effectively improving the accuracy of the sand mold.

[0034] (2) UV curing technology consumes less energy, hardly produces any side reactions, has lower production costs, is more energy-efficient, greatly shortens the printing time, saves labor costs, and improves production efficiency.

[0035] (3) The photosensitive resin absorbs ultraviolet light from DLP irradiation for curing, so the energy consumed is small. The cross-linking polymerization reaction of the photosensitive resin only occurs in the projection area, and the waste sand can be reused, which is conducive to green and sustainable development. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of a digital optical projection sand mold printing device according to an embodiment of the present invention;

[0037] Figure 2 This is a cross-sectional view (AA) of a digital optical projection sand mold printing device according to an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the digital projection mechanism described in an embodiment of the present invention;

[0039] Figure 4 This is a top view of the structure of a digital optical projection sand mold printing device according to an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of the vacuum sand-filling box described in an embodiment of the present invention;

[0041] Figure 6 A schematic diagram of the integrated vibration compaction and sand-laying mechanism described in this embodiment of the invention;

[0042] Figure 7 This is a BB cross-sectional view of the integrated vibration compaction sand-laying mechanism described in an embodiment of the present invention;

[0043] Figure Descriptions: 1-Vacuum sand feeding box; 2-Digital light projection mechanism; 3-Base; 4-Integrated vibration compaction sand spreading mechanism; 5-Protective panel support frame; 6-Printing platform; 7-Lifting guide column; 8-Fixed connecting plate; 9-Servo motor a; 10-Electric telescopic rod; 11-Spherical hinge; 12-Projection equipment; 13-Support rod; 14-Fixed support; 15-Screw propeller; 16-Ball screw mechanism; 17-Vacuum sand suction hopper; 18-Servo motor b; 19-Cylinder; 20-Sand storage tank switch plate; 21-Sand quantity monitoring window; 22-Double roller extrusion discharge trough; 23-Vibration compaction mechanism; 24-Servo motor c; 25-Vibration compaction plate; 26-Double extrusion rollers. Detailed Implementation

[0044] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0045] like Figure 1 , 2 As shown in Figures 4 and 5, the embodiment of the present invention provides a digital light projection sand mold printing device, which includes: an integrated vibration compaction sand spreading mechanism 4, a ball screw mechanism 16, a vacuum sand feeding box 1, a machine base 3, a protective panel support frame 5, a digital light projection mechanism 2, and a printing lifting platform.

[0046] In the vacuum sand feeding box 1, the vacuum sand suction hopper 17 has a built-in air switch valve to control the sand from the hopper into the sand storage tank. The sand storage tank has a built-in screw propeller 15, and the servo motor b18 controls the screw propeller 15 to evenly spread the sand in the sand storage tank. The sand storage amount can be observed through the sand quantity monitoring window 21. Cylinders 19 are installed on both sides of the sand storage tank. The cylinders 19 control the opening of the sand storage tank switch plate 20 to drop sand into the double roller extrusion discharge trough 22. In the integrated vibration compaction sand spreading mechanism 4, the double roller extrusion discharge trough 22 and the vibration compaction mechanism 23 are connected by a fixed plate. The sand surface can be flattened and compacted at the same time as sand spreading to improve the performance of the sand mold. The digital light projection mechanism 2 realizes the movement of the projection screen through the mechanical motion module. After sand spreading, the sand surface is light-projected and the resin is cured in the designated projection area. The printing platform 6 is lowered to a certain layer thickness by the lifting guide column 7. Through layer-by-layer sand spreading and layer-by-layer irradiation, the sand mold is accurately and efficiently formed.

[0047] like Figure 6 , 7 As shown, the integrated vibratory compaction sand-spreading mechanism 4 consists of a double-roller extrusion discharge trough 22 and a vibratory compaction mechanism 23. The double-roller extrusion discharge trough 22 is equipped with double rollers 26 for extruding and discharging the sand. The gap and rotation speed of the two rollers are adjusted according to the required discharge volume to achieve quantitative sand spreading. The double-roller extrusion discharge trough is moved by a movable slide connected to a ball screw mechanism 16. The movement is achieved based on the required 900cm diameter of each printed surface. 3 Quartz sand, the two rollers are 40cm long and 3cm in diameter, the gap between the two rollers is adjusted to 3mm and the rotation speed is adjusted to 90r / min; the vibration compaction mechanism consists of a vibration compaction plate 25, a servo motor c24, a cam and a small lifting guide column, which is connected to the double roller extrusion discharge trough through a fixed plate, and moves together with the sand spreading mechanism on the slide rail, compacting and flattening the sand surface while spreading sand, thereby improving the sand spreading and printing efficiency.

[0048] like Figure 3 As shown, the digital light projection mechanism 2 consists of a mechanical motion module and a projection device 12, which is connected to the protective panel support frame 6 via a fixed connecting plate 8, replacing the traditional 3D sand mold printing nozzle. The projection area of ​​the projection device 12 should be able to fully cover the printing platform 6. Different wavelength light sources can be replaced for irradiation according to the actual curing requirements. The projection screen is moved parallel to the printing platform 6 via a mechanical structure to project the two-dimensional image required for the current layer. The light source used by the projection device 12 is a UV LED, and the wavelength range of the replaceable light source is 280-380nm. The mechanical motion module consists of a servo motor a9, an electric telescopic rod 10, a ball hinge 11, a support rod 13, and a fixed support 14. The support rod plays a fixed support role. When moving the projection device 12, the servo motor a9 controls the upper electric telescopic rod 10 and the ball hinge 11 to lower the projection screen, and the lower ball hinge moves accordingly until the projection screen is parallel to the printing platform.

[0049] In addition, this embodiment also provides a digital optical projection sand mold printing method.

[0050] According to the requirements of ordinary casting molds, 270 / 300 mesh quartz sand can be selected. The viscosity of photosensitive resin is adjusted to 25 MPa·s. During sand mixing, 6.5 wt.% resin can be added to the original sand to premix the molding sand particles. The three-dimensional geometric model of the sand mold is designed and layered and sliced ​​to obtain the two-dimensional slice information of each layer. The layer thickness is set to 0.25 mm, and a certain layer thickness of molding sand is pre-laid to prevent adhesion to the printing platform. Quartz sand particles and 6.5 wt.% photosensitive resin binder are put into the sand mixer and uniformly stirred to obtain premixed molding sand particles with binder. The premixed molding sand particles with binder are discharged into the sand storage tank through the vacuum sand suction hopper 17. The sand storage tank has a built-in screw propeller 15 to uniformly load the premixed sand into the double roller extruder. Inside the discharge trough, the sand loading process is completed; the integrated vibratory compaction sand-laying mechanism 4 moves from left to right via the ball screw mechanism 16, pressing the pre-mixed binder-laden molding sand particles onto the printing platform through two rollers; the compaction mechanism follows the sand-laying mechanism, patting and flattening the pre-mixed curing agent-laden molding sand particles on the printing platform to complete one layer of sand-laying process; the digital light projection mechanism 2 moves above the printing platform via a mechanical structure to project the current layer's two-dimensional image, exposing the current layer's resin for 50 seconds to catalyze the reaction and promote resin curing; the current layer's irradiation stops, the printing platform descends by one layer thickness, and layer-by-layer sand-laying and exposure printing continues until the sand mold is prepared; the sand mold is removed, waste sand is recycled, and post-processing is performed as needed.

[0051] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims

1. A green forming device for sand mold printing based on digital light projection, comprising a base (3), characterized in that, The base (3) is equipped with an integrated vibration compaction sand spreading mechanism (4), a vacuum sand feeding box (1), a protective panel support frame (5), a digital light projection mechanism (2), and a printing lifting platform; the vacuum sand feeding box (1) is equipped with a sand storage tank, and the inside of the sand storage tank is equipped with a screw propeller (15); the top of the sand storage tank is equipped with a vacuum sand suction hopper (17), wherein the vacuum sand suction hopper (17) has a built-in air switch valve, the servo motor b (18) is connected to one end of the screw propeller (15), and cylinders (19) are installed on both sides of the sand storage tank. The cylinders (19) control the opening of the sand storage tank switch plate (20) to drop sand to the double roller extrusion discharge trough (22); the integrated vibration compaction sand spreading machine The structure (4) includes a double-roller extrusion discharge trough (22) and a compaction mechanism (23); the double-roller extrusion discharge trough (22) and the vibration compaction mechanism (23) are connected by a fixed plate; the digital light projection mechanism (2) consists of a mechanical motion module and a projection device (12), which is connected to the protective panel support frame (5) by a fixed connecting plate (8). The projection area of ​​the projection device (12) should be able to fully cover the printing platform (6). The projection device (12) changes to a light source of different wavelengths according to the actual curing requirements for irradiation. The projection screen is moved parallel to the printing platform (6) through a mechanical structure and the required two-dimensional image of the current layer is projected; the light source used by the projection device (12) is UV. The LED is replaceable and has a wavelength range of 280-380nm. The mechanical motion module consists of a servo motor a (9), an electric telescopic rod (10), a ball hinge (11), a support rod (13), and a fixed support (14). When the projection device (12) is moved, the servo motor a (9) controls the upper electric telescopic rod (10) and the ball hinge (11) to lower the projection screen, and the lower ball hinge moves accordingly until the projection screen is parallel to the printing platform.

2. The green forming device for sand mold printing based on digital light projection according to claim 1, characterized in that: The side of the vacuum sand box (1) is provided with several sand quantity monitoring windows (21).

3. The green forming device for sand mold printing based on digital light projection according to claim 1, characterized in that: The digital light projection mechanism (2) moves the projection device (12) through a mechanical motion module, and after spreading sand, it performs light projection and resin curing on the sand surface in the designated projection area.

4. The green forming device for sand mold printing based on digital light projection according to claim 1, characterized in that: The bottom of the printing platform (6) is lowered by a certain layer thickness through the lifting guide column (7), and after layer by layer of sand is laid and layer by layer of irradiation, the sand mold is accurately and efficiently formed.

5. The green forming device for sand mold printing based on digital light projection according to claim 1, characterized in that, The double roller extrusion discharge trough (22) is equipped with double rollers (26) for extrusion discharge. The double roller extrusion discharge trough (22) is connected to the ball screw mechanism (16) below the double roller extrusion discharge trough (22) to achieve movement. The vibration compaction mechanism consists of a vibration compaction plate (25), a servo motor c (24), a cam and a small lifting guide column. It is connected to the double roller extrusion discharge trough (22) through a fixed plate and moves together with the sand spreading mechanism on the slide rail. While spreading sand, it compacts and flattens the sand surface.

6. A method for green sand molding based on digital light projection, according to any one of claims 1-5, of a sand molding green forming apparatus based on digital light projection, characterized in that, The method includes the following steps: Step 1: Select molding sand, binder, and their mixing formula according to the casting requirements; Step 2: Design the three-dimensional geometric model of the sand mold and perform layered slicing to obtain the two-dimensional slice information of each layer; Set the layer thickness to 0.1-0.6mm and pre-lay a certain layer of molding sand to prevent it from sticking to the printing platform; Step 3: Add the proportioned raw sand particles and the corresponding amount of 2-8 wt.% photosensitive resin binder to the sand mixer and stir evenly to obtain premixed molding sand particles with binder. Step 4: The premixed molding sand particles are fed into the sand storage tank through the vacuum sand suction hopper (17); the sand storage tank has a built-in screw propeller (15) to uniformly load the premixed sand into the double roller extrusion discharge trough, and the sand loading process is completed; Step 5: The integrated vibration compaction sand spreading mechanism (4) moves from left to right through the ball screw mechanism (16) to press the pre-mixed molding sand particles of the sand spreading mechanism onto the printing platform (6) by two rollers. Step 6: The compaction mechanism moves behind the sand spreading mechanism and pats the premixed molding sand particles with curing agent onto the printing platform (6) to flatten them and complete the sand spreading process. Step 7: The digital light projection mechanism (2) moves parallel to the printing platform (6) through a mechanical structure to project the current layer two-dimensional image, and exposes the current layer resin for 30-60 seconds to catalyze the reaction and promote resin curing; Step 8: Stop the current layer irradiation and lower the printing platform by one layer thickness; Step 9: Repeat steps 5 to 8, exposing and printing layer by layer until the sand mold is prepared; Step 10: Remove the sand mold, recycle the waste sand, and post-process the sand mold as needed.

7. A green forming method for sand mold printing based on digital light projection according to claim 6, characterized in that, Step 1 involves selecting molding sand, binder, and their mixing formula. The types of molding sand selected include quartz sand, magnesium olivine sand, and zircon sand. The mesh size of the molding sand ranges from 140 to 600 mesh. The viscosity range of the photosensitive resin binder is 20 to 300 MPa·s. The mixing formula of the molding sand and binder can be adjusted according to the printing requirements.

8. A green forming method for sand mold printing based on digital light projection according to claim 6, characterized in that, Steps 5 and 6 involve sand spreading using a double-roller extrusion method to quantitatively discharge the sand, saving raw materials and preventing severe bridging of the premixed sand when the resin viscosity is high, which would prevent normal sand discharge. The sand surface is leveled by vibration compaction, which reduces the sand bonding mechanism and compacts each layer of sand, thereby improving the overall strength of the sand mold.

9. A green forming method for sand mold printing based on digital light projection according to claim 6, characterized in that, Step 7 uses a resin curing method that employs UV LED ultraviolet light to irradiate photosensitive resin, causing the resin in the projection area to polymerize and cross-link, forming a network structure between the sand particles. This reduces the impact on accuracy caused by inkjet splashing from the printing nozzle and improves the precision forming effect. The resin exposure time for each layer in the projection area is 30-60 seconds.

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