Large-size sand mold 3D printing method

Abstract

The invention discloses a large-size sand mold 3D printing method, and relates to the technical field of additive manufacturing, a small-layering-thickness selective laser sintering process is adopted in the area close to the surface of a sand mold, a large-layering-thickness jet bonding process is adopted in other areas, and relative to all small-layering-thickness selective laser sintering, the large-layering-thickness jet bonding process is adopted. Compared with a whole large-layering-thickness jet bonding technology, the sand mold surface has higher forming precision, and the contradiction between the large-size sand mold 3D printing forming efficiency and forming precision is effectively solved. In addition, the invention further provides a follow-up powder spreading device applied to the large-size sand mold 3D printing method, during sand spreading, the deflection angles of the two sand outlets are accurately adjusted through a servo motor, the opening degrees of the two sand outlets are accurately adjusted through a push-pull electromagnet, and therefore the sand spreading thickness is automatically adjusted.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and specifically relates to a method for 3D printing large-sized sand molds. Background Art

[0002] 3D printing sand molds eliminates the need for production molds, greatly reducing R & D costs; enables flexible production, improving R & D efficiency; is suitable for small and medium batch manufacturing; and is widely used in fields such as aerospace, industrial machinery, ship pumps and valves, and automobiles.

[0003] There are mainly two 3D printing sand mold technologies on the market: Selective Laser Sintering (SLS) and Binder Jetting. Selective Laser Sintering has high precision, but slow forming speed and high cost, and is suitable for precision parts. Binder Jetting has a fast forming speed and low cost, but poor precision, and is suitable for large-sized sand molds.

[0004] For the 3D printing of large-sized sand molds with high precision requirements, using Selective Laser Sintering, although the precision can meet the requirements, the cost is high and the forming time is long, while the Binder Jetting technology cannot meet the precision requirements. If the advantages of Selective Laser Sintering and Binder Jetting technologies can be combined into one to achieve high-efficiency, high-precision, and low-cost 3D printing of large-sized sand molds has always been the pursued goal.

[0005] Therefore, it is necessary to provide a new method for 3D printing large-sized sand molds. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for 3D printing large-sized sand molds to solve the above-mentioned defects in the prior art.

[0007] A method for 3D printing large-sized sand molds includes the following steps:

[0008] S1: Stratify and slice the large-sized sand mold to be formed. Adopt a small-thickness stratification printing strategy in the area near the sand mold surface, and adopt a large-thickness stratification printing strategy in the remaining areas;

[0009] S2: Selectively lay a layer of small-thickness coated sand on the edge area of each layer cross-section, and then use the Selective Laser Sintering process to sinter the sand-laying area, so that the coated sand in this area forms the surface of the sand mold. Then repeat the process of selectively laying coated sand and Selective Laser Sintering in the formed surface area until the small-thickness stratification of multiple accumulated sand mold surface areas reaches the large-thickness stratification of the remaining areas;

[0010] S3: Use a sand suction device to suck out the unsintered coated sand in the internal area of the formed part;

[0011] S4: Spread sand in the remaining areas of each layer's cross-section, and then adopt the spray bonding process. Use a nozzle to spray the adhesive inside the formed part, so that the sand in this area adheres to form the interior of the sand mold.

[0012] S5: Repeat steps S2 - S4 until the entire sand mold printing is completed.

[0013] S6: Clean the loose sand grains and perform curing treatment on the printed large-sized sand mold.

[0014] Preferably, in S1, the layer thickness of the small-thickness layer is 0.1 - 0.3 mm, and the layer thickness of the large-thickness layer is 0.4 - 1.2 mm.

[0015] Preferably, in S1, the layer thickness of the large-thickness layer is an integer multiple of the layer thickness of the small-thickness layer.

[0016] Preferably, in S2, the selectively coated resin-bonded sand area is the area 1 - 2 mm outward and 5 - 10 mm inward along the contour line.

[0017] Preferably, in S2, the selective laser sintering area is the contour line and the area 4 - 8 mm inward.

[0018] Preferably, in S2, the selective laser sintering is carried out by using a dual-laser beam sintering process. The first laser beam performs pre-sintering, and the second laser beam performs re-sintering.

[0019] A follow-up powder spreading device applied to a large-sized sand mold 3D printing method, including a mounting plate 10, a sand box 12, a servo motor 13 and a push-pull electromagnet 18. The mounting plate 10 is of an L-shaped structure and has a circular mounting opening 10a in the center of its bottom. The sand box 12 is of a funnel-shaped structure and is rotatably connected to the mounting opening 10a through a thrust bearing 11. The sand box 12 is partitioned into a first sand storage bin 121 and a second sand storage bin 122 by a partition plate 120 disposed in the center of its interior, and corresponding sand outlets 121a and 122a are provided at its bottom. The servo motor 13 is vertically mounted at the bottom of the mounting plate 10, and a first gear 14 is key-connected to its output end. A toothed ring 17 is coaxially fixed to the top of the sand box 12, and the toothed ring 17 meshes with the first gear 14. A pair of push-pull electromagnets 18 are provided and symmetrically distributed left and right. The push-pull electromagnets 18 are horizontally mounted on the side of the sand box 12 through a fixing plate 19, and a baffle plate 20 is connected to its telescopic end. The baffle plates 20 on the left and right sides are respectively slidably connected to the sand outlets 121a and 122.

[0020] Preferably, the mounting plate 10 is screw-connected to the end of the robotic arm through mounting holes 10b circularly arrayed on its side.

[0021] Preferably, a pair of second gears 16 are symmetrically engaged on the left and right sides of the gear ring 17, and the second gears 16 are rotatably connected to the bottom of the mounting plate 10 through the mounting shafts 15.

[0022] Preferably, a pair of vibration motors 21 are symmetrically installed on the left and right sides of the sand box 12.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The large-size sand mold 3D printing method provided by the present invention adopts the selective laser sintering process with a small layer thickness in the area near the surface of the sand mold, and the jet bonding process with a large layer thickness in the remaining areas. Compared with the selective laser sintering with all small layer thicknesses, it has higher forming efficiency and lower cost. Compared with the jet bonding process with all large layer thicknesses, the sand mold surface has higher forming accuracy, effectively solving the contradiction between the forming efficiency and forming accuracy of large-size sand mold 3D printing. In addition, the double-laser beam selective laser sintering process is adopted, and the surface porosity of the formed part is effectively reduced through pre-sintering and re-sintering, realizing high-efficiency, high-precision and low-cost forming of large-size sand mold 3D printing.

[0025] 2. When the follow-up powder spreading device applied to the large-size sand mold 3D printing method provided by the present invention spreads sand, the whole follow-up powder spreading device is driven by a robotic arm to move spatially along the set motion trajectory; the sand box is driven to rotate by a servo motor, so as to ensure that the length direction of the sand outlet is always perpendicular to the powder spreading contour line; by controlling the on-off current and the current magnitude of the push-pull electromagnet, the position of the baffle plate at the sand outlet can be controlled, so as to realize the opening and closing of the sand outlet and adjust the width of the sand outlet. The larger the current, the more the baffle plate moves outward, the larger the width of the sand outlet, the more sand powder flows out in the same time, and the thicker the sand powder laid. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of a sand mold formed based on the 3D printing method in the present invention.

[0027] Figure 2 It is a schematic structural diagram of the double-laser beam sintering process mentioned in the present invention.

[0028] Figure 3 It is a three-dimensional view of the whole follow-up powder spreading device in the present invention.

[0029] Figure 4 It is a front view of the whole follow-up powder spreading device in the present invention.

[0030] Figure 5 It is a side view of the whole follow-up powder spreading device in the present invention.

[0031] Figure 6 It is a three-dimensional view of the mounting plate in the follow-up powder spreading device.

[0032] Figure 7 It is a three-dimensional view of the sand box in the follow-up powder laying device.

[0033] Among them:

[0034] 10 - mounting plate; 10a - mounting opening; 10b - mounting hole; 11 - thrust bearing; 12 - sand box; 120 - partition plate; 121 - first sand storage bin; 121a - first sand outlet; 122 - second sand storage bin; 122a - second sand outlet; 13 - servo motor; 14 - first gear; 15 - mounting shaft; 16 - second gear; 17 - gear ring; 18 - push-pull electromagnet; 19 - fixing plate; 20 - sand baffle; 21 - vibration motor. Specific embodiments

[0035] To make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0036] Embodiment 1

[0037] As Figures 1 to 2 shown, a large-size sand mold 3D printing method includes the following steps:

[0038] S1: Stratify and slice the large-size sand mold to be formed, adopt a small-thickness stratification printing strategy in the area near the surface of the sand mold, and adopt a large-thickness stratification printing strategy in the remaining areas;

[0039] S2: Selectively lay a layer of small-thickness coated sand on the edge area of each layer cross-section, and then use the selective laser sintering process to sinter the laid sand area, so that the coated sand in this area forms the surface of the sand mold, and then repeat the process of selectively laying coated sand and selective laser sintering in the formed surface area until the small-thickness stratification of multiple accumulated sand mold surface areas reaches a large-thickness stratification of the remaining areas;

[0040] S3: Use a sand suction device to suck out the unsintered coated sand in the internal area of the formed part;

[0041] S4: Lay sand in the remaining areas of each layer cross-section, and then adopt the injection bonding process, use a nozzle to spray the adhesive in the internal area of the formed part, so that the sand in this area is bonded to form the inside of the sand mold;

[0042] S5: Repeat S2 to S4 until the entire sand mold printing is completed;

[0043] S6: Clean the loose sand grains and perform a curing treatment on the printed large-size sand mold.

[0044] In this embodiment, in S1, the layer thickness of the small-thickness layer is 0.1 - 0.3 mm, and the layer thickness of the large-thickness layer is 0.4 - 1.2 mm.

[0045] In this embodiment, in S1, the layer thickness of the large-thickness layer is an integer multiple of the layer thickness of the small-thickness layer.

[0046] In this embodiment, in S2, the selectively coated resin sand area is the area 1 - 2 mm outward and 5 - 10 mm inward along the contour line.

[0047] In this embodiment, in S2, the selective laser sintering area is the contour line and the area 4 - 8 mm inward.

[0048] In this embodiment, in S2, the selective laser sintering is carried out by a dual-laser beam sintering process. The first laser beam performs pre-sintering, and the second laser beam performs re-sintering. By pre-sintering and re-sintering, the surface porosity of the formed part is effectively reduced, and high-efficiency, high-precision, and low-cost forming of large-sized sand molds by 3D printing is achieved.

[0049] This method for 3D printing large-sized sand molds:

[0050] The selective laser sintering process with a small layer thickness is used in the area near the surface of the sand mold, and the jet bonding process with a large layer thickness is used in the remaining areas. Compared with all selective laser sintering with a small layer thickness, it has higher forming efficiency and lower cost. Compared with all jet bonding with a large layer thickness, the sand mold surface has higher forming precision, effectively solving the contradiction between the forming efficiency and forming precision of 3D printing of large-sized sand molds.

[0051] Embodiment 2

[0052] As Figures 3 to 7As shown in the figure, a follow-up powder spreading device applied to a large-size sand mold 3D printing method includes a mounting plate 10, a sand box 12, a servo motor 13 and a push-pull electromagnet 18. The mounting plate 10 is of an L-shaped structure and has a circular mounting opening 10a in the center of its bottom. The sand box 12 is of a funnel-shaped structure and is rotatably connected to the mounting opening 10a through a thrust bearing 11. The sand box 12 is partitioned into a first sand storage bin 121 and a second sand storage bin 122 by a partition plate 120 disposed in the center thereof, and corresponding sand discharge openings 121a and 122a are provided at the bottom thereof. The servo motor 13 is vertically mounted at the bottom of the mounting plate 10, and a first gear 14 is key-connected to the output end thereof. A gear ring 17 is coaxially fixed to the top of the sand box 12, and the gear ring 17 meshes with the first gear 14. A pair of push-pull electromagnets 18 are provided and symmetrically distributed left and right. The push-pull electromagnets 18 are horizontally mounted on the side of the sand box 12 through a fixing plate 19, and a sand baffle 20 is connected to the telescopic end thereof. The sand baffles 20 on the left and right sides are respectively slidably connected to the sand discharge openings 121a and 122. The selective laser sintering sand powder is stored in the first sand storage bin 121, and the sand powder for jet bonding is stored in the second sand storage bin 122. The deflection angles of the two sand discharge openings are accurately adjusted by the servo motor 13, and the opening degrees of the two sand discharge openings are accurately adjusted by the push-pull electromagnets 18.

[0053] In this embodiment, the mounting plate 10 is screwed to the end of the robotic arm through mounting holes 10b circularly arrayed on its side. By adding the above structure, the entire follow-up powder spreading device can be screwed to the end of the robotic arm.

[0054] In this embodiment, a pair of second gears 16 are symmetrically meshed on the left and right sides of the gear ring 17, and the second gears 16 are rotatably connected to the bottom of the mounting plate 10 through mounting shafts 15. By adding the above structure, the force on the gear ring 17 can be made more uniform.

[0055] In this embodiment, a pair of vibration motors 21 are symmetrically mounted on the left and right sides of the sand box 12. The vibration generated by the vibration motors 21 can help the sand powder in the sand storage bin to smoothly pass through the corresponding sand discharge openings.

[0056] The working principle of this follow-up powder spreading device applied to the large-size sand mold 3D printing method:

[0057] When spreading sand, the entire servo powder spreading device is driven by a robotic arm to move spatially along a set motion trajectory; the sand box 12 is driven to rotate by a servo motor 13, so as to ensure that the length direction of the sand outlet is always perpendicular to the powder spreading contour line; by controlling the energization and de-energization of the push-pull electromagnet 18 and the magnitude of the current, the position of the baffle plate 20 at the sand outlet can be controlled, thereby realizing the opening and closing of the sand outlet and adjusting the width of the sand outlet. The greater the current, the more the baffle plate 20 moves outward, the greater the width of the sand outlet, the more sand powder flows out in the same time, and the thicker the spread sand powder is.

[0058] Therefore, the above-disclosed embodiments are illustrative in all respects and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. A method for 3D printing of large-sized sand molds, characterized in that, It includes the following steps: S1: Perform layer slicing on the large-sized sand mold to be formed. Adopt a small-thickness layer printing strategy in the area close to the surface of the sand mold, and adopt a large-thickness layer printing strategy in the remaining areas; S2: Selectively lay a layer of small-thickness coated sand on the edge area of each layer cross-section, and then use the selective laser sintering process to sinter the sand-laying area, so that the coated sand in this area forms the surface of the sand mold. Then repeat the process of selectively laying coated sand and selective laser sintering in the formed surface area until the small-thickness layers in multiple accumulated sand mold surface areas reach a large-thickness layer in the remaining areas; S3: Use a sand suction device to suck out the unsintered coated sand in the internal area of the formed part; S4: Lay sand in the remaining areas of each layer cross-section, and then adopt the injection bonding process. Use a nozzle to spray the adhesive on the internal area of the formed part to bond the sand in this area to form the interior of the sand mold; S5: Repeat S2 to S4 until the entire sand mold is printed; S6: Clean the loose sand grains and perform curing treatment on the printed large-sized sand mold.

2. The method for 3D printing a large-sized sand mold according to claim 1, wherein, In S1, the layer thickness of the small-thickness layer is 0.1 - 0.3 mm, and the layer thickness of the large-thickness layer is 0.4 - 1.2 mm.

3. A method for 3D printing of large-sized sand molds according to claim 2, characterized in that, In S1, the layer thickness of the large-thickness layer is an integer multiple of the layer thickness of the small-thickness layer.

4. A method for large-scale sand mold 3D printing according to claim 1, characterized in that, In S2, the area of selectively laying coated sand is the area 1 - 2 mm outward and 5 - 10 mm inward along the contour line.

5. A method for 3D printing of large-sized sand molds according to claim 1, characterized in that, In S2, the area of selective laser sintering is the contour line and the area 4 - 8 mm inward.

6. A method for large-scale sand mold 3D printing according to claim 1, characterized in that, In S2, the selective laser sintering is carried out by adopting a double-laser beam sintering process. The first laser beam performs pre-sintering, and the second laser beam performs re-sintering.

7. A follow-up powder spreading device applied to the large-size sand mold 3D printing method according to any one of claims 1-6, characterized in that, It includes a mounting plate (10), a sand box (12), a servo motor (13) and a push-pull electromagnet (18). The mounting plate (10) is of an L-shaped structure and is provided with a circular mounting opening (10a) in the center of its bottom. The sand box (12) is of a funnel-shaped structure and is rotatably connected to the mounting opening (10a) through a thrust bearing (11). The sand box (12) is separated into a first sand storage bin (121) and a second sand storage bin (122) by a partition plate (120) arranged in the center of it, and corresponding sand outlets (121a) and (122a) are provided at its bottom. The servo motor (13) is vertically mounted at the bottom of the mounting plate (10), and a first gear (14) is key-connected to its output end. A gear ring (17) is coaxially fixed at the top of the sand box (12), and the gear ring (17) meshes with the first gear (14). A pair of push-pull electromagnets (18) are provided and are symmetrically distributed left and right. The push-pull electromagnets (18) are horizontally mounted on the side of the sand box (12) through a fixing plate (19), and a sand blocking plate (20) is connected to its telescopic end. The sand blocking plates (20) on the left and right sides are respectively slidably connected to the sand outlets (121a) and (122).

8. A follow-up powder spreading device according to claim 7, characterized in that, The mounting plate (10) is screw-connected to the end of the robotic arm through mounting holes (10b) arranged in a circular array on its side.

9. The follow-up powder spreading device according to claim 7, wherein, On the left and right sides of the ring gear (17), a pair of second gears (16) are symmetrically engaged. The second gears (16) are rotatably connected to the bottom of the mounting plate (10) through mounting shafts (15).

10. The follow-up powder spreading device according to claim 7, characterized in that, On the left and right sides of the sand box (12), a pair of vibration motors (21) are symmetrically installed.

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