Composite structure mold for low-pressure pouring process of large complex plastic part and manufacturing method of composite structure mold

Abstract

The composite structure mold for the low-pressure pouring process of the large complex plastic part is composed of a male mold and a female mold, the male mold and the female mold can be opened and closed along a preset parting line, and a mold cavity is defined when the male mold and the female mold are closed. A flexible inner layer which is consistent with the outline and easy to strip is attached to the inner wall of the cavity and comprises a male die flexible inner layer and a female die flexible inner layer. When the mold is closed, a specific space is formed between the two flexible inner layers and is used for curing and forming pouring plastic. Besides, a multi-layer rigid outer layer structure is further arranged outside the flexible inner layer, a first rigid layer and a second rigid layer are sequentially arranged on the two sides of the parting line and the outer side of the flexible inner layer from inside to outside, and the first rigid layer and the second rigid layer form a multi-layer stable protection system together with the flexible inner layer so as to provide support and bear low-pressure pouring pressure. The invention further discloses a manufacturing method of the composite structure mold, and the purpose of rapidly providing high-quality samples for new cars at low cost is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of rapid prototyping and small batch manufacturing. Specifically, it relates to a composite structure mold for the low-pressure casting process of large and complex plastic parts and a manufacturing method thereof. Background Art

[0002] With the wide application of plastic products in various industries, the demand for large and complex plastic parts is increasing day by day. Especially in the automotive industry, multiple new vehicle models are launched every year, and a large number of rapid prototypes are required during the development stage. As an efficient and low-cost molding process, the low-pressure casting process has significant advantages in the manufacturing of large and complex plastic parts such as automotive bumpers, wheel covers, and inner door panels. However, traditional single-material molds, such as fully rigid molds, are difficult to accurately replicate the fine structures of complex plastic parts and are prone to damage the plastic parts during the demolding process; while fully soft molds can better fit the product shape, but they cannot withstand large pressures during the casting process and are prone to deformation, resulting in difficulty in ensuring the dimensional accuracy of the product. Although some composite molds combine hard and soft materials, namely a silicone inner layer and a resin outer layer, their structural design and manufacturing methods are only suitable for small and simple-shaped parts and cannot manufacture large and complex molds. Therefore, it is of great practical significance to develop a new type of composite structure mold for the low-pressure casting process of large and complex plastic parts, which can quickly provide high-quality prototypes for the development of new vehicle models at low cost. Summary of the Invention

[0003] Technical problems to be solved by the invention: The purpose of the present invention is to overcome the difficulty of single-material molds in balancing accuracy and demolding protection in the above-mentioned prior art, and the difficulty of composite molds in adapting to the low-pressure casting requirements of large and complex parts, and to provide a composite structure mold for the low-pressure casting process of large and complex plastic parts and a manufacturing method thereof.

[0004] Technical solution: To achieve the above purpose, the technical solution provided by the present invention is: A composite structure mold for the low-pressure casting process of large and complex plastic parts, including a male mold and a female mold, and the male mold and the female mold can perform opening and closing actions along a preset parting line; in the closed state, a cavity for forming a product is enclosed between the male mold and the female mold; a flexible inner layer that is consistent with the contour of the cavity inner wall and is easy to peel off is attached along the inner wall of the cavity, and this flexible inner layer is specifically a male mold flexible inner layer located on the inner wall of the male mold and a female mold flexible inner layer located on the inner wall of the female mold;

[0005] In the mold closed state, a specific space dedicated to casting plastic is formed between the male mold flexible inner layer and the female mold flexible inner layer, and the plastic to be cast solidifies in this specific space to form the required product;

[0006] Outside the flexible inner layer, there are multiple layers of rigid outer layer structures for providing stable support and withstanding low-pressure perfusion pressure. They are arranged on both sides of the parting line, outside the flexible inner layer, and include a first rigid layer and a second rigid layer arranged in sequence from inside to outside, which together with the flexible inner layer form a multi-level stable protection system.

[0007] As a further improvement of this composite structure mold, the first rigid layer includes a first convex mold rigid layer arranged outside the flexible inner layer of the convex mold, and a first concave mold rigid layer arranged outside the flexible inner layer of the concave mold;

[0008] The second rigid layer includes a second convex mold rigid layer arranged outside the first convex mold rigid layer, and a second concave mold rigid layer arranged outside the first concave mold rigid layer.

[0009] As a further improvement of this composite structure mold, the flexible inner layer is made of room temperature vulcanized silicone rubber with a Shore hardness between A20 - A40 and a thickness of 10 - 15 mm; the flexible inner layer is capable of accurately replicating the shape and details of the product.

[0010] As a further improvement of this composite structure mold, the rigid outer layer is a resin-based composite material formed by a low-viscosity bisphenol A epoxy resin and an aliphatic amine curing agent, which is a mixture mixed with different proportions of fillers.

[0011] As a further improvement of this composite structure mold, the filler of the first rigid layer is a mixture of talcum powder - river sand in a ratio of 1:1, with an average thickness of 20 mm. The tensile bond strength between this layer and the silicone rubber is 1 - 4 MPa, the shear bond strength is 0.5 - 3 MPa, and the surface roughness of the parting surface is controlled at Ra2 - 5 μm.

[0012] As a further improvement of this composite structure mold, the filler of the second rigid layer is a mixture of talcum powder - river sand in a ratio of 1:2, with an average thickness of 30 mm.

[0013] As a further improvement of this composite structure mold, a low-pressure perfusion hole is provided at the lowest position of the product prototype, and multiple product vent holes are provided on both sides of the low-pressure perfusion hole according to the shape and complexity of the product; silicone rubber vent holes are also provided on the flexible inner layer, specifically, a convex mold silicone rubber vent hole and a concave mold silicone rubber vent hole that extend from the flexible inner layer of the convex mold and the flexible inner layer of the concave mold to the outside of the mold respectively.

[0014] The present invention also provides a manufacturing method for a composite structure mold used in the low-pressure perfusion process of large and complex plastic parts, including the following steps:

[0015] I. Product prototype manufacturing

[0016] S1. Prototyping: According to the design drawings, use high-precision 3D printing or CNC machining technology to produce a product prototype, requiring a smooth and flawless surface, and the dimensional accuracy is controlled within ±0.1 mm;

[0017] S2. Surface treatment of complex structures: Perform polishing, grinding and other treatments on the complex structure prototype to ensure good adhesion of the flexible inner layer and accurately replicate the surface features;

[0018] II. Production of wooden brackets: Use wooden strips to make multiple wooden brackets for supporting the product prototype along the surface of the product prototype;

[0019] III. Production of the rigid outer layer of the female mold

[0020] S1. Laying of foamed cotton: Lay a layer of foamed cotton with a thickness of 10 - 15 mm along the outer surface of the product prototype, and lay 2 - 3 layers at complex positions or structural voids;

[0021] S2. Arrangement of exhaust holes for female mold silicone: Glue one end of the female mold plastic tube to the foamed cotton to form the exhaust holes for the female mold silicone;

[0022] S3. Production of the first rigid layer of the female mold: Evenly apply a mixture of resin - talcum powder - river sand with a ratio of 1:2:2 on the foamed cotton, with a thickness of 15 - 20 mm, and initially cure and form;

[0023] S4. Production of the frame structure of the female mold: Lay and weld an equilateral angle iron mesh on the first rigid layer of the female mold, and then weld square iron pipes on it to form the frame structure of the female mold;

[0024] S5. Production of the second rigid layer of the female mold: Lay a mixture of resin - talcum powder - river sand with a ratio of 3:4:8 on the first rigid layer of the female mold and the mesh angle iron, with a total thickness of 50 mm, and cure at room temperature for 8 - 12 hours;

[0025] IV. Production of the rigid outer layer of the male mold

[0026] S1. Inversion and cleaning of the female mold: Invert the female mold, remove the wooden brackets, and clean the surface of the product prototype;

[0027] S2. Laying and fixing of foamed cotton: Lay a layer of polyethylene foamed cotton with a thickness of 10 - 15 mm on the upper surface of the product prototype, and lay 2 - 3 layers at complex positions or structural voids;

[0028] S3. Arrangement of exhaust holes for male mold silicone: Glue one end of the male mold plastic tube to the foamed cotton to form the exhaust holes 120 for the male mold silicone;

[0029] S4. Arrangement of low-pressure perfusion holes: Bond a plastic bottle at the lowest part of the product prototype to form low-pressure perfusion holes;

[0030] S5. Vent hole arrangement: At the highest part of the product prototype and on the complex structure, bond plastic bottles to form vent holes;

[0031] S6. Silicone casting hole arrangement: At both ends of the foam cotton, bond plastic bottles to form silicone casting holes;

[0032] S7. Making the first rigid layer of the male mold: Apply the mixed resin - talcum powder - river sand with a ratio of 1:2:2 on the foam cotton, with a thickness of 15 - 20 mm, and preliminarily cure it;

[0033] S8. Making the frame structure of the male mold: Lay and weld the equal - angle iron mesh on the first rigid layer of the male mold, and then weld square iron pipes on it to form the male mold frame structure 104;

[0034] S9. Making the second rigid layer of the male mold: Lay the mixed resin - talcum powder - river sand with a ratio of 3:4:8 on the first rigid layer of the male mold and the mesh - shaped angle iron, with a thickness of 50 mm, and cure it at room temperature for 8 - 12 hours;

[0035] V. Making the flexible inner layer of the female mold

[0036] S1. Mixing and degassing of silicone rubber raw materials: Mix silicone rubber raw materials and curing agent, and degas them under vacuum for 10 - 15 minutes;

[0037] S2. Casting and curing: Remove the foam cotton in the female mold, clean the product prototype, cut the bottom of the plastic bottle, close the mold, pour silicone rubber until it is full, and cure it at room temperature for 8 - 16 hours;

[0038] VI. Making the flexible inner layer of the male mold

[0039] S1. Preliminary preparation: Remove the foam cotton in the male mold, clean the prototype, cut off the protruding part of the prototype fixing rod, and clean the surface of the prototype;

[0040] S2. Arranging slender plastic rods: Cut the bottoms of the plastic bottles where the low - pressure perfusion holes, the first vent holes, and the second vent holes are located, and arrange slender plastic rods in them and fix them;

[0041] S3. Casting and curing: Close the mold, pour silicone liquid until it is full, and cure it at room temperature for 8 - 16 hours;

[0042] VII. Making the cavity and pouring and exhaust holes: After the flexible inner layers of the female mold and the male mold are made, open the mold to take out the product prototype to form a cavity, take out the plastic rods at the low - pressure perfusion holes, the first vent holes, and the second vent holes, and the mold making is completed.

[0043] As a further improvement to the above - mentioned manufacturing method, in the making of the rigid outer layer of the female mold, according to the shape or complexity of the product, arrange female mold plastic pipes or female mold barbed angle irons at multiple places; in the making of the rigid outer layer of the male mold, according to the shape or complexity of the product, arrange male mold plastic pipes or male mold barbed angle irons at multiple places.

[0044] As a further improvement to the above manufacturing method, during the production of the rigid outer layer of the punch, the embedding positions and quantities of the prototype fixing rods are determined according to the shape and complexity of the product, so as to effectively fix the product prototype when casting the flexible inner layer of the die.

[0045] Beneficial effects:

[0046] 1. Achieving high-precision replication: The silicone material of the flexible inner layer can accurately replicate the complex shapes and fine surface features of large and complex plastic parts, with high product replication accuracy, meeting the strict requirements for product appearance and dimensional accuracy.

[0047] 2. Good demolding performance: The flexibility of the silicone inner layer makes the demolding process smoother, reducing the risk of product damage due to uneven stress during demolding and improving the product qualification rate.

[0048] 3. High stability and strength: The double-layer design of the rigid outer layer combined with the reticulated angle iron reinforcement structure provides strong rigid support for the mold, enabling the mold to withstand the pressure during the low-pressure casting process and frequent mold opening and closing operations, and extending the service life of the mold.

[0049] 4. Optimization of material properties and costs: Low-viscosity resins are selected to increase low-cost fillers. The talcum powder in the first rigid layer enhances dimensional stability, surface smoothness, and adhesion to the silicone layer. The river sand in the second rigid layer enhances rigidity and toughness, and the material cost is optimized due to reasonable material selection.

[0050] 5. Efficient exhaust: The reasonably designed exhaust system can effectively discharge the air in the cavity, avoiding defects such as air holes and material shortages in the product, and improving production efficiency and product quality.

[0051] 6. Reliable and environmentally friendly interlayer bonding: The good adhesion between the soft inner silicone layer and the inner layer of the rigid outer layer is enhanced through a mechanical mechanism, ensuring that there will be no delamination or peeling during use, guaranteeing the stable operation of the mold, and avoiding potential hazards brought by the use of silane coupling agents.

[0052] 7. Long service life: Generally, after producing 25 - 30 parts, the damaged silicone inner layer can be relatively easily peeled off. Just pour a new silicone layer to continue production, and it can be recycled many times to produce hundreds of parts. Description of the drawings

[0053] Figure 1 It is a schematic diagram of the overall structure of the composite structure mold of the present invention.

[0054] Figure 2 It is the process of making a wooden support to support the prototype and laying polyethylene foam.

[0055] Figure 3The process of manufacturing the rigid outer layer of the female mold.

[0056] Figure 4 The process of removing the wooden support.

[0057] Figure 5 The process of manufacturing the rigid outer layer of the male mold.

[0058] Figure 6 The process of manufacturing the rigid-flexible inner layer of the female mold.

[0059] Figure 7 The process of manufacturing the rigid-flexible inner layer of the male mold.

[0060] Explanation of the reference numerals in the schematic diagram:

[0061] 1. Product prototype; 10. Wooden support; 21. Polyethylene foam on the outer side of the prototype; 11. Polyethylene foam on the inner side of the prototype;

[0062] 100. Male mold; 300. Parting line; 101. Flexible inner layer of the male mold; 102. First rigid layer of the male mold; 103. Second rigid layer of the male mold; 104. Frame structure of the male mold; 110. Low-pressure injection hole; 111. First exhaust hole; 112. Second exhaust hole; 113. First silicone casting hole; 114. Second silicone casting hole; 120. Silicone exhaust hole of the male mold; 130. Hook angle iron of the male mold; 140. Prototype fixing rod;

[0063] 200. Female mold; 201. Flexible inner layer of the female mold; 202. First rigid layer of the female mold; 203. Second rigid layer of the female mold; 204. Frame structure of the female mold; 220. Silicone exhaust hole of the female mold; 230. Hook angle iron of the female mold. Detailed implementation manners

[0064] To further understand the content of the present invention, the present invention will be described in detail in combination with the accompanying drawings and specific implementation manners.

[0065] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0066] In the description of the present invention, "several" means one or more, "multiple" means more than two, and understandings such as "greater than", "less than", "exceeding", etc. do not include the present number, while understandings such as "above", "below", "within", etc. include the present number. If there is a description of "first" and "second", it is only for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0067] In the description of the present invention, unless otherwise clearly defined, words such as "arrangement", "installation", "connection", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0068] Such as Figure 1 , a composite structure mold for the low-pressure casting process of large and complex plastic parts, includes a male mold 100 and a female mold 200, and the male mold 100 and the female mold 200 can perform opening and closing actions along a preset parting line 300; when closed, a specific cavity for forming a product is enclosed between the male mold 100 and the female mold 200. On the inner wall where the cavity is located, a flexible inner layer that fits tightly with the cavity contour is disposed, specifically, a male mold flexible inner layer 101 and a female mold flexible inner layer 201 respectively located on the inner walls of the male mold 100 and the female mold 200. When the male mold and the female mold are closed, a specific space for casting plastic is formed between these two flexible inner layers, and this space is connected to a low-pressure casting hole 110. During the casting process, the casting plastic is injected into this specific space through the low-pressure casting hole 110 and solidifies and forms between the male mold flexible inner layer 101 and the female mold flexible inner layer 201 to form the required plastic product.

[0069] In order to improve the rigidity and compressive resistance of the mold and effectively ensure the dimensional accuracy and stability of the mold during the manufacturing process and use process, on both sides of the parting line 300, a rigid outer layer structure is disposed outside the flexible inner layer. The rigid outer layer structure includes a rigid first layer and a rigid second layer arranged in sequence from the inside to the outside, and together with the flexible inner layer, forms a multi-level stable protection system.

[0070] Among them, the rigid first layer includes a male mold rigid first layer 102 and a female mold rigid first layer 202 that closely adhere to the outside of the male mold flexible inner layer 101 and the female mold flexible inner layer 201; the rigid second layer is located on the outermost side of the entire structure, that is, it is composed of a male mold rigid second layer 103 and a female mold rigid second layer 203 respectively disposed outside the male mold rigid first layer 102 and the female mold rigid first layer 202. These two rigid layers cooperate with each other and act synergistically to provide stable support for the flexible inner layer and bear the low-pressure casting pressure, ensuring the stable operation of the mold and the reliable forming of the product.

[0071] The flexible inner layer is made of room temperature vulcanizing silicone rubber (RTV), with a Shore hardness between A20 and A40. The specific thickness is determined according to the complexity of the product and the difficulty of demolding. Usually, the thickness is set at 10-15 mm. In areas where the product has a large curvature change, to ensure that the flexible inner layer can better conform to the shape of the product, the thickness will be appropriately increased. The flexible inner layer has good flexibility, elasticity, tear resistance and chemical stability, and can accurately replicate the shape and details of the product. Even if the product contains complex structures such as undercuts, it is convenient for demolding. In addition, the flexible inner layer has good bonding performance with the subsequent rigid layer, which can effectively prevent the two from falling off during use and ensure the overall stability of the mold.

[0072] The rigid outer layer is made of a resin-based composite material, which is composed of epoxy resin mixed with talcum powder and river sand. Since the curing shrinkage rate of pure epoxy resin is relatively high, usually between 2% and 8%, in order to reduce the shrinkage rate, improve the rigidity and compressive resistance of the mold, and ensure the dimensional accuracy and stability of the mold during the manufacturing process and use, a certain amount of filler needs to be added.

[0073] In terms of material selection, a low-viscosity bisphenol A epoxy resin, such as E-51 epoxy resin, is selected. Its viscosity at 25°C is approximately between 20000 and 40000 mPa·s, and it is paired with an aliphatic amine curing agent. The resin and the curing agent are mixed in a ratio of 4:1. This ratio has a high reaction activity at room temperature and a fast curing speed. The resins used in the rigid outer layer below are all resin-based composite materials containing curing agents.

[0074] In terms of fillers, talcum powder and river sand with a mesh size of 80-100 are selected and mixed according to the weight ratio of the filler (powder-sand mixture) to the resin (containing curing agent) of approximately 4:1. The high filling ratio inhibits the curing shrinkage rate through mechanisms such as steric hindrance effect, thermal conductivity improvement, and rigid modulus matching, reducing it to 0.2%-0.5%. The mechanical properties of the fully cured rigid outer layer are high rigidity (elastic modulus 10-15 GPa), medium strength (tensile strength 20-30 MPa), and low toughness (impact toughness 2.0-3.5 KJ / m2), which are suitable for scenarios with high requirements for compressive strength in low-pressure casting. The price of river sand and talcum powder is much lower than that of epoxy resin. Using such a high filling method also greatly reduces the manufacturing cost of the mold.

[0075] The rigid outer layer is further divided into two-layer structure. The first rigid layer requires a low surface roughness to improve the mold clamping sealing performance, and at the same time, it also requires better adhesion to the silicone rubber of the flexible inner layer. It is completely filled with talcum powder, which can well meet the requirements of roughness and adhesion. However, talcum powder particles usually have a flaky or layered structure, relatively small particle size and regular shape. This flaky structure will cause cracks to easily spread along the talcum powder lamellar direction when the material is subjected to external forces, thus showing greater brittleness. To solve this problem, a certain proportion of river sand needs to be filled. River sand has a larger particle size and irregular shape. When the material is subjected to external forces, it can play a role in supporting and dispersing stress, helping to improve the toughness of the material and reduce brittleness. Through a large number of experimental studies, it is determined that the filler of the first rigid layer is a mixture of talcum powder and river sand in a ratio of 1:1, with an average thickness of about 20 mm. The tensile adhesion strength between this layer and the silicone rubber is 1 - 4 MPa, and the shear adhesion strength is 0.5 - 3 MPa. The surface roughness of the parting surface is controlled at Ra 2 - 5 μm.

[0076] For the outermost second rigid layer, a filler with a higher river sand content is selected. This not only further reduces the brittleness of the mold but also effectively reduces costs (river sand is more widely sourced and cheaper than talcum powder). After comprehensively comparing various performance indicators, it is determined that the second rigid layer uses a mixture of talcum powder and river sand in a ratio of 1:2 as the resin filler, with an average thickness of about 30 mm. The average thickness of the rigid outer layer composed of the first rigid layer and the second rigid layer is about 50 mm. The two rigid layers work together to provide stable and reliable support for the flexible inner layer.

[0077] During the filling process, at the lowest position of the product, usually only one low-pressure filling hole 110 needs to be set. On both sides of the low-pressure filling hole 110, multiple product vent holes can be set according to the shape and complexity of the product, such as the first vent hole 111 set at the highest part of the product and the second vent hole 112 set at the complex part of the product; on both ends of the convex die flexible inner layer 101, a first silicone rubber pouring hole 113 and a second silicone rubber pouring hole 114 are respectively set.

[0078] To enable the flexible inner layer to fully combine with the first rigid layer, increase the adhesion force, and avoid the flexible inner layer from falling off during product demolding in the low-pressure filling production process, silicone rubber vent holes are also set on the flexible inner layer. Specifically, it is composed of a convex die silicone rubber vent hole 120 and a concave die silicone rubber vent hole 220 that respectively extend from the convex die flexible inner layer 101 and the concave die flexible inner layer 201 to the outside of the mold. These two types of silicone rubber vent holes can be arranged in multiple places according to needs.

[0079] In addition, in order to solve the technical problem that the flexible inner layer of silicone rubber in large flat molds is relatively weakly bonded to the rigid layer, the male mold barb angle iron 130 and the female mold barb angle iron 230 can be pre-embedded in the rigid layer of the male mold 100 and the female mold 200. One end of the barb angle iron hooks the flexible inner layer of silicone rubber, and the other end is embedded in the rigid layer. The barb angle iron can be pre-embedded in multiple places as needed to help hook the flexible inner layer of silicone rubber and prevent it from falling off. This is to use the mechanical bite mechanism to enhance the bonding force between the flexible inner layer of silicone rubber and the rigid outer layer. Compared with the use of chemicals such as silane coupling agents that are irritating and toxic, this method is more advantageous. Although silane coupling agents can enhance adhesion, the siloxy group at one end of the molecule can undergo a condensation reaction with the hydroxyl group on the surface of the silicone rubber to form a stable silicon-oxygen bond, and the amino and other organic functional groups at the other end will chemically react or physically entangle with the functional groups in the epoxy resin. This chemical bonding and strong interaction make the silicone rubber tightly connected to the rigid outer layer, making it very difficult to peel off. In addition, there will be silicone and coupling agent residues on the surface of the rigid layer, which is not conducive to the production of a new silicone layer.

[0080] The present invention makes full use of the mechanical bite mechanism to enhance the bonding force between the flexible inner layer and the rigid outer layer of the silicone rubber, instead of using chemicals such as silane coupling agents that are irritating and toxic, to avoid harm to the environment and personnel. Low-pressure perfusion produces 25-30 pieces, and the inner layer of the silicone rubber is severely damaged and needs to be remade. The silicone layer that uses a mechanical mechanism to enhance the bonding force is easier to peel off, and the surface of the rigid layer is also relatively clean, which is conducive to making a new silicone layer.

[0081] In order to further strengthen the mold structure and facilitate the disassembly and transportation of the mold, a frame structure is set in the key connection areas between the rigid first layer and the rigid second layer, such as the edges, corners and large flat areas of the mold. For the punch, specifically, the equilateral angle irons are laid in a mesh on the rigid first layer 101 of the punch, and are tightly connected to form a solid mesh structure by welding. Subsequently, the square iron pipes are further welded on the mesh structure composed of the equilateral angle irons to form a frame structure. This structure composed of the mesh angle irons and the square iron pipes is defined as the punch frame structure 104. Correspondingly, the die part is also provided with a die frame structure 204. The frame structure has high strength and good structural stability, and can effectively enhance the overall rigidity of the mold. After the resin and filler are fully cured, the mesh angle irons and the frame structure are firmly fixed on the rigid layer to ensure that they can work together with the rigid outer layer during the low-pressure infusion process to jointly withstand external pressure, effectively improve the bearing capacity of the mold, reduce the deformation of the mold, and ensure the high precision requirements of the product size.

[0082] A method for manufacturing a composite structure mold for a low-pressure infusion process of large and complex plastic parts comprises the following steps:

[0083] 1. Product Prototyping

[0084] S1. Produce a prototype according to the design drawing: According to the design drawing of the large and complex plastic part, use methods such as high-precision 3D printing or CNC machining to produce product prototype 1, requiring that the surface of product prototype 1 is smooth and free of defects, and the dimensional accuracy is strictly controlled within ±0.1 mm.

[0085] S2. Surface treatment of complex structures: For products with complex curved surfaces or fine structures, perform fine post-treatment such as surface polishing and grinding on product prototype 1 to ensure good adhesion of the subsequent flexible inner layer and accurately replicate its surface features.

[0086] II. Manufacture of wooden brackets

[0087] As Figure 2 shown, use wooden strips to make wooden bracket 10 that supports product prototype 1 along the surface of product prototype 1. Place product prototype 1 on wooden bracket 1, ensuring that product prototype 1 is fully supported by wooden bracket 10 to effectively resist deformation caused by its own weight. Wooden bracket 10 and product prototype 1 are bonded with glue to prevent deformation during subsequent manufacturing processes.

[0088] III. Manufacture of the rigid outer layer of the female mold

[0089] S1. Laying of foamed cotton: As Figure 2 shown, lay 1 layer of polyethylene foamed cotton 21 with a thickness of 10 - 15 mm along the outer surface of product prototype 1 to make it conform to the outer surface of product prototype 1. At complex positions or local voids of the product structure, lay 2 or 3 layers, and use double-sided tape to bond between product prototype 1 and the foamed cotton and between multiple layers of foamed cotton.

[0090] S2. Arrangement of exhaust holes for female mold silicone: As Figure 3 shown, bond one end of the female mold plastic tube to the foamed cotton, and the vertical channel where the female mold plastic tube is located forms exhaust hole 220 for the female mold silicone.

[0091] S3. Arrangement of female mold barbed angle irons: Bury the horizontal limb and part of the vertical limb of female mold barbed angle iron 230 into the foamed cotton.

[0092] According to the shape and complexity of the product, it may be necessary to arrange such female mold plastic tubes and female mold barbed angle irons 230 in multiple places.

[0093] S4. Manufacture of the first layer of the rigid female mold

[0094] (1) Material preparation: Prepare a resin-based composite material, mix bisphenol A epoxy resin and aliphatic amine curing agent in a ratio of 4:1, stir evenly, weigh, and then add 2 times the weight of 80 - 100 mesh talcum powder and 2 times the weight of 80 - 100 mesh river sand, and stir evenly again.

[0095] (2) Smearing and curing: Evenly smear the mixture of resin - talcum powder - river sand with a ratio of 1:2:2 on the outer side polyethylene foam 21 of the prototype, with the smearing thickness reaching 15 - 20 mm. Let it stand for about 2 hours for preliminary curing to form a rigid layer 202.

[0096] S5. Production of the concave die frame structure

[0097] Lay the equal - angle iron in a mesh pattern on the rigid layer 202 of the concave die, and weld the angle iron using the arc - welding process to form a firm mesh structure. Subsequently, weld square iron pipes on the mesh - shaped angle iron to form an integral concave die frame structure 204.

[0098] S6. Production of the second rigid layer of the concave die

[0099] Mix the mixture of resin - talcum powder - river sand according to the ratio of 3:4:8. The increased content of river sand helps to further improve toughness and reduce costs. After stirring evenly, lay it on the rigid layer 202 of the concave die and the mesh - shaped angle iron, with an average thickness of 30 - 35 mm, ensuring that the total thickness of the first rigid layer and the second rigid layer of the concave die reaches 50 mm. Then, cure it naturally at room temperature, and the curing time is generally 8 - 12 hours.

[0100] IV. Production of the rigid outer layer of the convex die

[0101] S1. Inversion and cleaning of the concave die: As Figure 4 , invert the concave die made in the third step, remove the wooden support 10, and clean the inner surface of the product prototype 1.

[0102] S2. Laying and fixing of the foam: As Figure 5 , lay 1 layer of prototype inner - side polyethylene foam 11 with a thickness of 10 - 15 mm along the inner surface of the product prototype 1, making it fit the inner surface of the product prototype. At the complex positions of the product structure and local voids, it may be necessary to increase the thickness of the foam, laying 2 or 3 layers. Use double - sided tape to bond between the product prototype and the foam as well as between multiple layers of foam.

[0103] S3. Arrangement of the convex - die silicone exhaust holes: Glue one end of the convex - die plastic pipe to the foam, and the vertical channels formed by the body of the convex - die plastic pipe constitute the convex - die silicone exhaust holes 120.

[0104] S4. Arrangement of the convex - die barb angle iron and the prototype fixing rod: Bury the horizontal limb and part of the vertical limb of the convex - die barb angle iron 130 into the foam, take a prototype fixing rod 140, and pass one end of it through the foam and glue it to the surface of the product prototype 1.

[0105] Depending on the shape and complexity of the product, it may be necessary to arrange such punch plastic tubes, punch barb angle irons 130, and prototype fixing rods 140 in multiple places, or it may not be necessary at all.

[0106] S5. Low-pressure perfusion hole arrangement: Bond the bottom end of a perfusion plastic bottle used for perfusion to the lowest position of the product prototype 1. The vertical channel formed by the bottle body of the perfusion plastic bottle constitutes the low-pressure perfusion hole 110.

[0107] S6. Vent hole arrangement: Bond the bottom ends of multiple plastic bottles to the highest part and complex structures of the product prototype 1. The vertical channels formed by these plastic bottles constitute the vent holes during the perfusion process, such as the first vent hole 111 and the second vent hole 112.

[0108] S7. Silicone casting hole arrangement: Bond the bottom ends of two plastic bottles to the ends on both sides of the polyethylene foam 11 inside the prototype respectively. The vertical channels formed by these two plastic bottles constitute the first silicone casting hole 113 and the second silicone casting hole 114 respectively.

[0109] S8. Production of the first rigid layer of the punch

[0110] Evenly apply a mixture of resin-talc powder-sand with a ratio of 1:2:2 on the foam. The application thickness reaches 15 - 20 mm, and let it stand for about 2 hours for preliminary curing to form the first rigid layer of the punch.

[0111] S9. Production of the punch frame structure

[0112] Lay the equal-angle iron in a mesh pattern on the first rigid layer 102 of the punch. Use the arc welding process to weld the angle iron to form a strong mesh structure. Then weld square iron pipes on the mesh angle iron to form an integral punch frame structure 104.

[0113] S10. Production of the second rigid layer of the punch

[0114] Lay a mixture of resin-talc powder-sand with a ratio of 3:4:8 on the first rigid layer 102 of the punch and the mesh angle iron. The average thickness is 30 - 35 mm to ensure that the total thickness of the rigid layer of the punch reaches 50 mm. Then cure it naturally at room temperature, and the curing time is generally 8 - 12 hours.

[0115] At this time, the prototype fixing rod 140 on the punch is embedded in the rigid outer layer of the punch. One end of the prototype fixing rod 140 extending into the mold cavity is glued to the surface of the product prototype 1, which plays a role in fixing the product prototype 1 when pouring the flexible inner layer 201 of the die. Such prototype fixing rods can be embedded in multiple places on the rigid outer layer of the punch as needed, while the rigid outer layer of the die does not need to be set, because only when pouring the flexible inner layer 201 of the die, the product prototype 1 is in a suspended state and requires additional fixing measures, and when pouring the flexible inner layer 101 of the punch, the product prototype 1 has been firmly fixed by the flexible inner layer 201 of the die and does not require additional fixing support. When pouring the flexible inner layer 101 of the punch, the part of the prototype fixing rod 140 extending out of the rigid layer needs to be cut off.

[0116] V. Fabrication of the Flexible Inner Layer of the Die

[0117] S1. Mixing and Degassing of Silicone Rubber Raw Materials: Mix the selected silicone rubber raw materials and curing agent in a stirring container in accordance with the specified ratio (generally 10:1 - 15:1, and the specific ratio is determined according to the silicone product instructions) and stir well to ensure uniform distribution of the two. A large number of bubbles will be generated during the stirring process. Put the mixed silicone liquid into a vacuum degassing machine for degassing treatment. In a vacuum environment, the bubbles gradually escape, and the degassing time is generally 10 - 15 minutes until there are no obvious bubbles in the silicone liquid.

[0118] S2. Pouring and Curing: Open the upper and lower molds and remove Figure 5 the polyethylene foam 21 on the outside of the prototype as shown. Clean the surface of the product prototype 1, cut open the bottoms of the plastic bottles at the first and second silicone pouring holes 113 and 114, and then close the mold. At this time, inside the die, a cavity is formed between the rigid layer 202 of the die and the product prototype 1. Lock the upper and lower molds with G-clamps, and slowly pour the degassed silicone liquid into the die cavity from the first silicone pouring hole 113 and the second silicone pouring hole 114. Control the pouring speed and flow rate during the pouring process to avoid generating new bubbles until the highest point is filled, ensuring that the silicone rubber fills every corner of the cavity, as Figure 6 shown. After pouring, place the mold in a normal temperature environment for curing. The curing time depends on the type of silicone and the ambient temperature, generally 8 - 16 hours.

[0119] VI. Fabrication of the Flexible Inner Layer of the Punch

[0120] S1. Preliminary Preparation: After the flexible inner layer 201 of the die is fabricated, open the upper and lower molds. Remove as Figure 6The inner polyethylene foam cotton 11 of the shown prototype is cleaned on the surface of the prototype; the part of the prototype fixing rod 140 extending out of the first layer of the punch is cut off; the bottom of the plastic bottle where the low-pressure perfusion hole 110 is located is cut open, and a slender plastic rod is arranged along the central axis of the bottle, and its bottom end contacts the product prototype 1 and is fixed with glue; the bottoms of the plastic bottles where the first exhaust hole 111 and the second exhaust hole 112 are located are cut open, and slender plastic rods are arranged along the central axis of the bottle, and the bottom ends contact the product prototype 1 and are fixed with glue.

[0121] S2. Pouring and curing: Close the mold. Inside the punch, a cavity is formed between the first layer of the punch rigidity 102 and the product prototype 1. Lock the upper and lower molds with G-clamps, and slowly pour the degassed silicone liquid into this cavity from the first silicone pouring hole 113 or the second silicone pouring hole 114. During the pouring process, control the pouring speed and flow rate to avoid generating new bubbles until it is filled up to the highest point, ensuring that the silicone rubber liquid fills every corner of the cavity, and the plastic bottles at the low-pressure perfusion hole 110, the first exhaust hole 111, and the second exhaust hole 112 are also filled with silicone, as Figure 7 shown. After pouring is completed, place the mold in a normal temperature environment for curing. The curing time depends on the type of silicone and the ambient temperature, generally 8 - 16 hours. If it is necessary to accelerate the curing speed, the mold can be placed in an oven and heated and cured at a temperature of 50 - 70 °C, but it is necessary to pay attention to controlling the temperature and time to prevent the silicone from aging or its performance from degrading due to overheating.

[0122] VII. Cavity and pouring and exhaust hole manufacturing

[0123] After the flexible inner layers of the female mold and the male mold are manufactured, open the mold and carefully take out the prototype, and a cavity is formed inside the mold. Take out the plastic rods at the low-pressure perfusion hole 110, the first exhaust hole 111, and the second exhaust hole 112, and the corresponding low-pressure perfusion holes and exhaust holes are formed. The mold manufacturing is completed and delivered for production.

[0124] The above schematically describes the present invention and its implementation manners. This description is not restrictive, and what is shown in the drawings is only one of the implementation manners of the present invention. The actual structure is not limited to this. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural manners and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A composite structure mold for the low-pressure casting process of large and complex plastic parts, characterized in that: It includes a punch and a die, and the punch and the die can perform opening and closing actions along a preset parting line; in the closed state, a cavity for forming a product is enclosed between the punch and the die; a flexible inner layer that is consistent with its contour and is easy to peel off is attached to the inner wall of the cavity. Specifically, the flexible inner layer includes a punch flexible inner layer located on the inner wall of the punch and a die flexible inner layer located on the inner wall of the die. In the mold closing state, a specific space dedicated to pouring plastic is formed between the punch flexible inner layer and the die flexible inner layer, and the required product can be formed by curing the poured plastic in this specific space. Outside the flexible inner layer, there is also a multi-level rigid outer layer structure for providing stable support and withstanding low-pressure pouring pressure. It is arranged on both sides of the parting line and outside the flexible inner layer, including a rigid layer 1 and a rigid layer 2 arranged in sequence from the inside to the outside, which together with the flexible inner layer form a multi-level stable protection system.

2. The composite structure mold for the low-pressure casting process of large and complex plastic parts according to claim 1, wherein: The rigid layer 1 includes a punch rigid layer 1 arranged outside the punch flexible inner layer and a die rigid layer 1 arranged outside the die flexible inner layer. The rigid layer 2 includes a punch rigid layer 2 arranged outside the punch rigid layer 1 and a die rigid layer 2 arranged outside the die rigid layer 1.

3. The composite structure mold for the low-pressure casting process of large and complex plastic parts according to claim 1, characterized in that: The flexible inner layer is made of room temperature vulcanized silicone rubber, with a Shore hardness between A20 - A40 and a thickness of 10 - 15 mm; the flexible inner layer has the ability to accurately replicate the shape and details of the product.

4. The composite structure mold for the low-pressure casting process of large and complex plastic parts according to claim 2, characterized in that: The rigid outer layer is a resin-based composite material formed by a low-viscosity bisphenol A epoxy resin and an aliphatic amine curing agent, and is a mixture mixed with different proportions of fillers.

5. The composite structure mold for the low-pressure casting process of large and complex plastic parts according to claim 4, characterized in that: The filler of the rigid layer 1 is a mixture of talcum powder - river sand in a ratio of 1:1, with an average thickness of 20 mm. The tensile bond strength between this layer and the silicone rubber is 1 - 4 MPa, and the shear bond strength is 0.5 - 3 MPa. The surface roughness of the parting surface is controlled at Ra2 - 5 μm.

6. The composite structure mold for the low-pressure casting process of large and complex plastic parts according to claim 4, wherein: The filler of the rigid layer 2 is a mixture of talcum powder - river sand in a ratio of 1:2, with an average thickness of 30 mm.

7. The composite structure mold for the low-pressure casting process of large and complex plastic parts according to claim 1, characterized in that: A low-pressure pouring hole is set at the lowest position of the product prototype, and on both sides of the low-pressure pouring hole, multiple product vent holes are set according to the shape and complexity of the product; silicone rubber vent holes are also set on the flexible inner layer, specifically, a punch silicone rubber vent hole and a die silicone rubber vent hole that extend from the punch flexible inner layer and the die flexible inner layer to the outside of the mold respectively.

8. The manufacturing method of the composite structure mold for the low-pressure pouring process of large and complex plastic parts as shown in claims 1 - 7 includes the following steps: I. Product prototype manufacturing S1. Prototype manufacturing: According to the design drawings, use high-precision 3D printing or CNC machining technology to manufacture the product prototype, requiring a smooth and flawless surface, and the dimensional accuracy is controlled within ±0.1 mm. S2. Surface treatment of complex structures: Perform polishing, grinding and other treatments on the complex structure prototype to ensure good adhesion of the flexible inner layer and accurately replicate the surface features. II. Wooden support manufacturing: Use wooden strips to make multiple wooden supports for supporting the product prototype along the surface of the product prototype. III. Manufacturing of the die rigid outer layer S1. Foam cotton laying: Lay a layer of foam cotton with a thickness of 10 - 15 mm along the outer surface of the product prototype, and lay 2 - 3 layers at complex positions or structural voids; S2. Arrangement of exhaust holes for female mold silicone: Stick one end of the female mold plastic tube on the foam cotton to form the exhaust holes for the female mold silicone; S3. Fabrication of the first rigid layer of the female mold: Evenly apply the mixed resin - talcum powder - river sand with a ratio of 1:2:2 on the foam cotton, with a thickness of 15 - 20 mm, and preliminarily cure and form; S4. Fabrication of the female mold frame structure: Lay and weld the equal - angle iron mesh on the first rigid layer of the female mold, and then weld square iron pipes on it to form the female mold frame structure; S5. Fabrication of the second rigid layer of the female mold: Lay the mixed resin - talcum powder - river sand with a ratio of 3:4:8 on the first rigid layer of the female mold and the mesh angle iron, with a total thickness of 50 mm, and cure at room temperature for 8 - 12 hours; IV. Fabrication of the rigid outer layer of the male mold S1. Inversion and cleaning of the female mold: Invert the female mold, remove the wooden support, and clean the surface of the product prototype; S2. Laying and fixing of foam cotton: Lay a layer of polyethylene foam cotton with a thickness of 10 - 15 mm along the upper surface of the product prototype, and lay 2 - 3 layers at complex positions or structural voids; S3. Arrangement of exhaust holes for male mold silicone: Stick one end of the male mold plastic tube on the foam cotton to form the exhaust holes 120 for the male mold silicone; S4. Arrangement of low - pressure perfusion holes: Bond a plastic bottle at the lowest part of the product prototype to form the low - pressure perfusion holes; S5. Arrangement of exhaust holes: Bond plastic bottles at the highest part and complex structures of the product prototype to form the exhaust holes; S6. Arrangement of silicone casting holes: Bond plastic bottles at both ends of the foam cotton to form the silicone casting holes; S7. Fabrication of the first rigid layer of the male mold: Apply the mixed resin - talcum powder - river sand with a ratio of 1:2:2 on the foam cotton, with a thickness of 15 - 20 mm, and preliminarily cure; S8. Fabrication of the male mold frame structure: Lay and weld the equal - angle iron mesh on the first rigid layer of the male mold, and then weld square iron pipes on it to form the male mold frame structure 104; S9. Fabrication of the second rigid layer of the male mold: Lay the mixed resin - talcum powder - river sand with a ratio of 3:4:8 on the first rigid layer of the male mold and the mesh angle iron, with a thickness of 50 mm, and cure at room temperature for 8 - 12 hours; V. Fabrication of the flexible inner layer of the female mold S1. Mixing and degassing of silicone rubber raw materials: Mix the silicone rubber raw materials and the curing agent, and degas in vacuum for 10 - 15 minutes; S2. Casting and curing: Remove the foam cotton inside the female mold, clean the product prototype, cut the bottom of the plastic bottle, close the mold, pour silicone rubber until full, and cure at room temperature for 8 - 16 hours; VI. Fabrication of the flexible inner layer of the male mold S1. Preliminary preparation: Remove the foam cotton inside the male mold, clean the prototype, cut off the protruding part of the prototype fixing rod, and clean the surface of the prototype; S2. Arrangement of slender plastic rods: Cut the bottom of the plastic bottles where the low - pressure perfusion holes, the first exhaust holes, and the second exhaust holes are located, and arrange slender plastic rods inside and fix them; S3. Casting and curing: Close the mold, pour silicone rubber liquid until full, and cure at room temperature for 8 - 16 hours; VII. Cavity and gating system manufacturing: After the flexible inner layers of the female die and male die are manufactured, open the mold to remove the product prototype to form a cavity, and take out the plastic rods at the low-pressure casting holes, the first vent holes, and the second vent holes. The mold manufacturing is completed.

9. The manufacturing method of the composite structure mold for the low-pressure casting process of large and complex plastic parts according to claim 8, characterized in that: During the manufacturing of the rigid outer layer of the female die, according to the shape or complexity of the product, arrange female die plastic tubes or female die barbs at multiple locations; during the manufacturing of the rigid outer layer of the male die, according to the shape or complexity of the product, arrange male die plastic tubes or male die barbs at multiple locations.

10. The manufacturing method of the composite structure mold for the low-pressure casting process of large and complex plastic parts according to claim 8, characterized in that: During the manufacturing of the rigid outer layer of the male die, the embedding positions and quantities of the prototype fixing rods are determined according to the shape and complexity of the product to effectively fix the product prototype when casting the flexible inner layer of the female die.

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