Implementation method of low-pressure pouring process with mold capable of being reused

Abstract

The invention discloses an implementation method of a low-pressure pouring process with a reusable die, which adopts a double-layer composite structure die, and comprises a male die and a female die which can be opened and closed along a parting surface, and each of the male die and the female die consists of a flexible inner layer and a rigid outer layer. When a certain number of products are produced and the flexible inner layer is damaged, new flexible inner layers are respectively manufactured aiming at different products and are applied to the mold shell, so that one set of mold is shared. When the flexible inner layer is manufactured, firstly, a product prototype is processed according to a drawing, foamed cotton and the product prototype are sequentially pasted on the inner surface of a male die shell, a die is closed to form a cavity, and silica gel liquid is injected into the cavity to be cured into a female die silica gel layer; taking out the foamed cotton, cleaning the prototype, closing the mold, injecting silica gel liquid, and curing to form a convex mold silica gel layer. For similar products, only a new flexible inner layer needs to be manufactured and applied to the mold shell in the mold process, one set of mold can be shared, the generalization rate can be increased, the development cost and time can be reduced, and one set of mold shell can be used for production of multiple vehicle types and multiple parts.

Description

Technical Field

[0001] The present invention relates to the technical field of rapid and small-batch perfusion processes. Specifically, it is a method for implementing a low-pressure perfusion process with reusable molds. Background Art

[0002] With the widespread 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 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 perfusion process has significant advantages in the manufacture of large and complex plastic parts such as automotive bumpers, wheel covers, and inner door panels. However, the traditional low-pressure perfusion process requires complex vent holes to be arranged on the mold, and the number and position of the vent holes are different for different products. The mold must be customized for each product and cannot be universal. For example, as shown in Figure 1 Products 1 and 2 have similar sizes and envelopes, but there are significant differences in details, requiring different vent arrangements and unable to share the mold. It usually takes 5 - 7 days to make a set of molds for the low-pressure perfusion process. Such a long production cycle poses a challenge to providing rapid prototypes. Making molds consumes a large amount of man-hours and has a high cost. After completing the production task of the prototypes, the molds are left idle or scrapped, and the materials used for the molds cannot be recycled, which is a significant waste for the company and the environment. Therefore, it is of great practical significance to develop a new rapid prototyping process for large and complex plastic parts, which greatly shortens the mold production cycle, allows similar products to share the mold, and provides high-quality prototypes for new vehicle model development at a lower cost and faster speed. Summary of the Invention

[0003] Technical problems to be solved by the invention: The purpose of the present invention is to overcome the defects of the existing low-pressure perfusion process molds that need to be customized for each product, have a long production cycle, high cost, and the molds are left idle or scrapped after use and the materials cannot be recycled. A method for implementing a low-pressure perfusion process with reusable molds is provided. Based on the traditional low-pressure perfusion process, a vacuum-assisted system and a composite structure mold are combined to solve the above problems and further improve product quality, material utilization rate, formability, and environmental friendliness.

[0004] Technical solution: To achieve the above object, the technical solution provided by the present invention is: A method for implementing a low-pressure perfusion process with reusable molds, which uses a double-layer composite structure mold including a male mold and a female mold. The male mold and the female mold can be opened and closed along the parting surface. The characteristics are as follows: A variable-thickness silicone rubber seal ring with the same shape as the parting surface is arranged between the parting surfaces, and its thickness is adjusted according to the change of the parting surface gap. The lower surface of the silicone rubber seal ring is bonded to the parting surface of the female mold to form a sealing structure when closed with the parting surface of the male mold; both the male mold and the female mold are composed of a flexible inner layer and a rigid outer layer, and the rigid outer layer is the mold shell after removing the flexible inner layer.

[0005] The steps of casting different products on the same mold housing are as follows:

[0006] S1: Vacuum pumping: Before injection molding, vacuum pump the mold cavity to create a negative pressure environment, ensuring that the injected liquid resin material fully flows to all corners of the mold and avoiding the generation of air bubbles;

[0007] S2: Injection: After the product after injection molding is pressure-maintained and cured, take it out to form Product 1;

[0008] S3: Product replacement: Take out Product 1 and produce Product 2 in the same mold housing;

[0009] S4: Making the flexible inner layer of the female mold for Product 2: According to the drawing, process the prototype of Product 2, place the prototype in the mold to form a cavity between it and the female mold, inject silicone liquid, and after curing, form the flexible inner layer of the female mold;

[0010] S5: Making the flexible inner layer of the male mold for Product 2: A cavity is formed between the prototype and the male mold, inject silicone liquid, and after curing, form the flexible inner layer of the male mold;

[0011] S6: Producing Product 2: Apply the new flexible inner layer for Product 2 to the mold housing to realize the reuse of the same mold housing for the production of different products.

[0012] As a further improvement of the present invention, the mold housing includes a male mold housing and a female mold housing. The male mold housing and the female mold housing are respectively located outside the flexible inner layer of the male mold and the flexible inner layer of the female mold. The male mold housing successively includes a first rigid layer of the male mold and a second rigid layer of the male mold. The female mold housing successively includes a first rigid layer of the female mold and a second rigid layer of the female mold.

[0013] As a further improvement of the present invention, in step S4, the prototype is pasted on the foam, and then the foam is filled in the male mold housing. A cavity is formed between the prototype and the female mold housing, and silicone liquid is injected into this cavity and cured to form the flexible inner layer of the female mold;

[0014] As a further improvement of the present invention, in step S5, take out the foam in step S4, clean the prototype, a cavity is formed between the product prototype and the male mold housing, inject silicone liquid into this cavity, and after normal temperature curing, form the flexible inner layer of the male mold.

[0015] As a further improvement of the present invention, in the middle area of the lowest position of the first rigid layer of the male mold, a pouring hole is provided along the mold opening direction, which penetrates through the first rigid layer of the male mold and the second rigid layer of the male mold.

[0016] As a further improvement of the present invention, two exhaust holes are respectively arranged at both ends of the rigid layer of the punch along the mold opening direction, penetrating through the rigid layer of the punch and the rigid layer of the punch, namely the first exhaust hole and the second exhaust hole.

[0017] As a further improvement of the present invention, in step S4, the lower end of the perfusion hole is connected to the upper end of the first plastic rod, and the lower end of the first plastic rod is adhered to the surface of the lowest part of the product prototype; the lower ends of the first exhaust hole and the second exhaust hole are respectively connected to the second plastic rod and the third plastic rod, so that when the mold is closed, the cavity formed by the product prototype and the punch housing contains the first plastic rod, the second plastic rod and the third plastic rod extending from the perfusion hole, the first exhaust hole and the second exhaust hole.

[0018] As a further improvement of the present invention, after the curing of the punch silicone layer is completed, the mold is opened, and the first plastic rod, the second plastic rod and the third plastic rod are taken out, and the spaces left by these plastic rods are used to form complete perfusion holes and exhaust holes.

[0019] As a further improvement of the present invention, the method for manufacturing the variable-thickness silicone sealing ring is as follows:

[0020] S1: Clean the parting surface of the punch and apply a release agent, clean the parting surface of the die, and no release agent needs to be applied;

[0021] S2: Mix the silicone liquid, and after degassing, apply it evenly on the parting surface of the die;

[0022] S3: Move the punch downward to close the mold, so that all the gaps between the parting surfaces are filled with the silicone liquid, and clamp and cure for 2 hours;

[0023] S4: Trim the overflow glue and open the mold to check the quality of the sealing ring;

[0024] As a further improvement of the present invention, the mold is closed for vacuum degree detection, and the vacuum degree is between -0.08 and -0.1 MPa.

[0025] Beneficial effects: Adopting the technical solution provided by the present invention, compared with the prior art, the following beneficial effects are achieved:

[0026] 1. The mold can be reused, reducing costs and time: For similar products, only by making a new flexible inner layer and applying it to the mold housing can a set of molds be shared, greatly improving the generalization rate of the mold, reducing the project development cost, and shortening the development time. A set of mold housings can be shared by dozens of vehicle models and can produce hundreds or thousands of parts, while only dozens of rapid prototypes are needed for the development of new vehicle models, significantly saving costs and time.

[0027] 2. Improve product quality: After the mold is closed in the filling process, a negative pressure environment is created by a vacuum pump, enabling the liquid material to flow more smoothly, filling all corners of the mold, effectively avoiding the generation of bubbles, and improving the density and quality of the product.

[0028] 3. Solve the mold sealing problem: Traditional sealing methods have many drawbacks. This technology sets a variable-thickness silicone rubber sealing ring on the parting surface of the male mold and the female mold. The thickness of the sealing ring adjusts with the change of the parting surface gap, forms an integral body with the female mold, and closely fits the parting surface of the male mold when closed, playing a good sealing role. And as the mold deforms, only the sealing ring needs to be remade to put into production, which has the advantages of simple production, low cost, convenient use, and good sealing performance. Brief Description of the Drawings

[0029] Figure 1 It is a cross-sectional schematic diagram of plastic products 1 and 2;

[0030] Figure 2 It is a schematic diagram of the mold for producing plastic products using the low-pressure casting process;

[0031] Figure 3 It is a schematic diagram of the mold housing;

[0032] Figure 4 It is a schematic diagram of the mold for making the flexible inner layer of product 1;

[0033] Figure 5 It is a schematic diagram of the mold for making the flexible inner layer of product 2;

[0034] Figure 6 It is a schematic diagram of the side gap in the closed state of the mold;

[0035] Figure 7 It is a schematic diagram of the silicone rubber sealing ring;

[0036] Figure 8 It is a top view of the female mold.

[0037] Explanation of the reference numerals in the schematic diagrams:

[0038] 1. Product 1; 10. Punch; 101. Flexible inner layer of punch; 102. First rigid layer of punch; 103. Second rigid layer of punch; 20. Die; 201. Flexible inner layer of die; 202. First rigid layer of die; 203. Second rigid layer of die; 30. Parting surface; 120. Vent hole A; 130. Vent hole B; 11. Punch housing; 111. Silicone layer of punch; 21. Die housing; 211. Silicone layer of die; 30. Parting surface; 300. Pouring hole; 31. First extension line; 32. Second extension line; 301. First plastic rod; 311. First plastic rod; 321. Third plastic rod; 302. Fourth plastic rod; 312. Fifth plastic rod; 322. Sixth plastic rod; 121. Second silicone layer of punch; 221. Second silicone layer of die; 50. Silicone sealing ring; 41. Die parting surface; 51. Punch parting surface; 45. Gap. Detailed implementation mode

[0039] 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 modes.

[0040] 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. It 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.

[0041] In the description of the present invention, the meaning of "several" is one or more, the meaning of "multiple" is more than two, and understandings such as "greater than", "less than", "exceeding", etc. do not include the present number, and understandings such as "above", "below", "within", etc. include the present number. If the first and second are described only for the purpose of distinguishing technical features, they cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or the sequence relationship of the indicated technical features.

[0042] In the description of the present invention, unless otherwise clearly defined, words such as "set", "installed", "connected", 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.

[0043] The low-pressure casting process is to accurately measure two-component liquid materials (such as polyurethane, etc.) by a metering pump under a relatively low pressure (0.1 - 10 MPa), transport them to the mixing head for uniform mixing, and then inject them into a pre-prepared mold cavity, where a chemical reaction occurs and solidifies in the mold to obtain the required automotive exterior parts product.

[0044] Problems existing in the prior art are as Figure 1 shown, Figure 1 As shown in the figure, it is a schematic diagram of producing plastic products 1 and 2 by traditional low-pressure perfusion process. Due to the differences in the characteristics of products 1 and 2, the positions and quantities of the perfusion holes and exhaust holes of the two sets of molds are also different, resulting in that the two sets of molds cannot be shared and must be manufactured separately, increasing the mold manufacturing cost and time.

[0045] Therefore, the present invention provides a method for realizing a low-pressure perfusion process with reusable molds, as Figure 2 , the mold adopts a double-layer composite structure, including a punch 10 and a die 20. The punch 10 and the die 20 can be opened and closed along the parting surface 30. Along both sides of the parting surface 30, both the punch 10 and the die 20 are composed of a flexible inner layer and a rigid outer layer. Specifically, the punch 10 successively includes a punch flexible inner layer 101, a punch rigid layer 102 and a punch rigid layer 103; the die 20 successively includes a die flexible inner layer 201, a die rigid layer 202 and a die rigid layer 203. According to the shape and complexity of the product, generally a perfusion hole 300 is arranged at the lowest position of the product, and exhaust holes A120 and exhaust holes B130 are arranged at other corresponding positions.

[0046] The punch flexible inner layer 101 and the die flexible inner layer 201 are in direct contact with the perfusion plastic. Room temperature vulcanized silicone rubber (RTV) with a Shore hardness between A20 - A40 is selected, and the thickness is determined according to the complexity of the product and the difficulty of demolding. The flexible inner layer conforms to the shape of the product, and the thickness is appropriately increased in the areas with large curvature changes.

[0047] The rigid outer layer material of the mold adopts 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% - 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 process, a fatty amine curing agent needs to be matched and mixed according to the ratio of resin to curing agent of 4:1. Therefore, the epoxy resin used in the rigid material refers to the mixture containing the above-mentioned curing agent.

[0048] The punch rigid layer 102 and the die rigid layer 202 are mainly made of epoxy resin mixed with talcum powder, with a thickness of about 20 mm. The punch rigid layer 103 and the die rigid layer 203 are mainly made of epoxy resin mixed with river sand, with a thickness of about 30 mm. The average thickness of the entire rigid outer layer is about 50 mm, providing a firm support for the flexible inner layer and bearing the low-pressure perfusion pressure.

[0049] As Figure 3As shown, the composite rigid structure obtained after removing the flexible inner layer is the mold shell, which includes a punch shell 11 and a die shell 21. The punch shell 11 is mainly composed of a first punch rigid layer 102 and a second punch rigid layer 103, and the die shell 21 is mainly composed of a first die rigid layer 202 and a second die rigid layer 203. At the lowest position in the middle area of the first punch rigid layer 102, a pouring hole 300 penetrating through the first punch rigid layer 102 and the second punch rigid layer 103 is arranged along the mold opening direction; at both ends of the first punch rigid layer 102, two exhaust holes penetrating through the first punch rigid layer 102 and the second punch rigid layer 103 are respectively arranged along the mold opening direction, namely a first exhaust hole 310 and a second exhaust hole 320, which are used to discharge the residual gas in the cavity and can also be used as pouring holes. For a long and narrow mold, usually two exhaust holes are arranged on both sides of the punch, and for a larger mold, one exhaust hole is respectively arranged at the four corners of the punch.

[0050] After 25 - 30 parts are produced by low-pressure casting, the flexible inner layer is severely damaged and a new flexible inner layer needs to be remade. For similar products, such as Product 1 and Product 2, only a new flexible inner layer needs to be made for Product 1 or Product 2 respectively and applied to the mold shell, then the purpose of sharing a set of molds can be achieved.

[0051] Taking Product 1 as an example, as Figure 4 , the method for making the flexible inner layer of the mold is as follows:

[0052] Step 1: Make the flexible inner layer of the die:

[0053] S1. Make the product prototype:

[0054] According to the product design drawing, make Product 1 by high-precision 3D printing or CNC machining method;

[0055] S2. Install the product and the foam:

[0056] Use double-sided tape to conformally paste polyethylene foam with a thickness of 10 - 15 mm on the inner surface of the first punch rigid layer 102. Subsequently, use double-sided tape to paste Product 1 on the foam. Since the distance between Product 1 and the inner surface of the first punch rigid layer 102 is uneven, for local thin and void parts, the thickness of the foam needs to be appropriately increased to ensure that the foam fills the gap solidly;

[0057] S3. Pour silicone:

[0058] Close the mold shell to form a cavity between Product 1 and the inner surface of the die shell 21, and slowly pour the silicone liquid into the cavity from the first exhaust hole 310 or the second exhaust hole 320. During the pouring process, strictly control the pouring speed and flow rate to prevent bubbles from being generated until the highest point is filled;

[0059] S4. Silicone curing:

[0060] After pouring, place the mold in a normal temperature environment for curing. The specific curing time depends on the type of silicone and the ambient temperature, generally 8 - 16 hours.

[0061] S5. Forming the parting surface:

[0062] After the silicone layer 211 of the female mold is completely cured, cut the silicone at the first vent hole 310 and the second vent hole 320 to form the first extension line 31 of the parting surface 30.

[0063] Step 2. Manufacturing the flexible inner layer of the male mold:

[0064] S1. Mold opening and cleaning:

[0065] Open the mold along the parting surface 30, remove the foam between the product 1 and the male mold housing 11, and thoroughly clean the surface of the product 1.

[0066] S2. Installation of plastic rods:

[0067] Connect the upper end of the first plastic rod 301 with a diameter of 16 mm to the lower end of the pouring hole 300, and bond the lower end to the surface of the product 1 at approximately the lowest point; at the same time, connect the upper ends of the second plastic rod 311 and the third plastic rod 321 with diameters of 8 - 16 mm to the lower ends of the first vent hole 310 and the second vent hole 320 respectively, and bond the lower ends to the edge of the product 1.

[0068] S3. Spraying release agent:

[0069] Spray the release agent evenly on the surface of the parting surface 30 and these plastic rods, and then close the mold. At this time, a cavity is formed between the product 1 and the inner surface of the male mold housing 11, and the cavity contains the first plastic rod 301 extending the pouring hole 300, the second plastic rod 311 extending the first vent hole 310, and the third plastic rod 321 extending the second vent hole 320.

[0070] S4. Silicone pouring and curing:

[0071] Slowly pour the silicone liquid into the cavity from the first vent hole 310 or the second vent hole 320. During the pouring process, strictly control the pouring speed and flow rate to avoid generating bubbles until it is filled to the highest point. 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.

[0072] S5. Forming the pouring hole and vent holes:

[0073] After the curing of the silicone layer 111 is completed, the mold is opened, and the first plastic rod 301, the second plastic rod 311, and the third plastic rod 321 are taken out. The spaces left by these plastic rods form complete filling holes and vent holes.

[0074] When the project of Product 1 is completed, the flexible inner layer of the mold is removed, and the mold shell is reserved for subsequent projects. If the overall dimensions and envelope diagram of Product 2 have a difference within 30%, the mold shell can be reused. Only the flexible inner layer of Product 2 needs to be refilled according to the above method. For example, Figure 5 , according to Product 2, a new second male mold silicone layer 121 and a new second female mold silicone layer 221 are filled, a second extension line 32 of a new parting surface 30 is generated, a new filling hole extension channel is made with the fourth plastic rod 302, and new vent hole extension channels are made with the fifth plastic rod 312 and the sixth plastic rod 322, then it can be used to produce Product 2, achieving the sharing of a set of molds.

[0075] Since the service life of the mold shell is very long and it can produce hundreds or thousands of parts, generally only dozens of rapid prototypes are needed for the development of a new vehicle model. Therefore, a set of mold shells can be shared by dozens of vehicle models, greatly improving the generalization rate of the mold, reducing the project development cost, and shortening the development time.

[0076] In the above filling process, after the mold is closed, the mold cavity is evacuated by a vacuum pump to extract the air in the cavity, forming a negative pressure environment. Then, the liquid material to be filled is injected into the mold cavity under a lower pressure. Since the cavity is in a vacuum state, the material can flow more smoothly during the filling process, is easier to fill into every corner of the mold, can effectively avoid the generation of bubbles, and improve the density and quality of the product. By adopting this vacuum filling production method, there is no need to arrange complex vent holes, thus achieving the purpose of sharing the mold shell for similar products.

[0077] During the filling production process, the mold cavity needs to be evacuated to a vacuum state, and the sealing performance of the mold is crucial. To achieve a good sealing effect, the surface roughness of the mold mating surface needs to be strictly controlled between Ra0.8 - 1.6μm to reduce the risk of gas leakage. However, the surface roughness of the mold parting surface used in the current process is between Ra1.0 - 5.0μm, which is difficult to meet the sealing requirements. Moreover, during the mold manufacturing stage, the rigid layer will undergo shrinkage deformation to varying degrees due to various factors. After being put into use, the release of internal stress and the changes in environmental temperature and humidity will also cause the mold to deform, resulting in an imperfect fit of the parting surface. As Figure 6 is a side schematic diagram of the closed state of the mold. After closing the mold, the male mold parting surface 51 and the female mold parting surface 41 cannot be completely tightly fitted, there is a gap 45 between them, and the gap 45 is uneven. The gap in the contact area is 0, and the maximum gap in the non-contact area can reach about 1.0mm, far from meeting the sealing requirements, posing a challenge to the sealing performance of the mold.

[0078] Previously, the sealing was carried out by pasting tape around the parting surface. However, this method has many drawbacks: it not only affects production efficiency and increases the cost of consumables, but also the sealing effect is not ideal. The method of grinding and fitting the parting surface also has defects. It not only has a large workload and poor effect, but also is difficult to cope with the continuous deformation problems of the mold during use and due to seasonal changes. Conventional sealing rings are of regular and uniform thickness. Although they have a certain deformation ability, they cannot be applied to the mold parting surfaces with different gaps. The too-thin sealing ring cannot fill the large gap, resulting in sealing failure. While using a thicker sealing ring will raise the height of the punch, increase the space of the mold cavity, and the cast product will be too thick to be used.

[0079] To solve this technical problem, a variable-thickness silicone rubber sealing ring 50 is provided between the parting surfaces of the punch and the die, as Figure 8 shown in the top view of the die, which clearly presents the die parting surface 41. Matched with it is the punch parting surface 51. A silicone rubber sealing ring with the same shape as the parting surface and the thickness adjusted according to the gap of the parting surface is made between the two parting surfaces. As Figure 7 shown, the thickness of each point of the silicone rubber sealing ring 50 is equal to the mold gap 45 at the corresponding position. During mold manufacturing, the lower surface of the silicone rubber sealing ring 50 is bonded to the die parting surface 41 to form a tightly combined whole. When the punch and the die are closed, the punch parting surface 51 can perfectly fit with the silicone rubber sealing ring 50 to form a reliable sealing structure.

[0080] Considering that the sealing ring is thin in some areas and is easily damaged or even detached from the die, the requirements for the material of the sealing ring are strict. High-viscosity two-component room-temperature vulcanizing silicone rubber RTV-2 should be used, and the performance indicators are as follows: the viscosity requirement is 100000 - 120000 mPa·s to ensure good fluidity and adhesion during the bonding process; the Shore hardness requirement is 60A - 80A to ensure that the sealing ring has a certain strength and can adapt to the slight deformation of the parting surface; the tensile strength ≥ 4.25 MPa, the tear strength ≥ 18 N / m, the elongation rate ≥ 200%, and the shrinkage rate ≤ 0.1%. These performance parameters ensure the reliability and durability of the sealing ring under complex working conditions.

[0081] The specific manufacturing method of the silicone rubber sealing ring is as follows: First, place the mold stably on the operating table, and use a forklift to lift the punch 10 smoothly upward to separate it from the die 20. At this time, the punch parting surface 51 and the die parting surface 41 are completely exposed. Then, thoroughly clean the die parting surface 41, and then use an alkaline solution for deep cleaning to ensure that the parting surface is clean without impurities. Similarly, clean the punch parting surface 51 and apply a thin layer of silicone release agent on its surface to prepare for the subsequent demolding process.

[0082] Then, pour the selected silicone raw material and the curing agent into a stirring container in a ratio of 10:1, and stir thoroughly to mix evenly so that the two are completely fused. A large number of bubbles will be generated during the stirring process, and the mixed silicone liquid needs to be put into a vacuum degassing machine for degassing treatment. In a vacuum environment, the bubbles gradually escape, and the degassing time is controlled within 10 - 15 minutes until there are no obvious bubbles in the silicone liquid.

[0083] Apply the prepared silicone liquid evenly on the female die parting surface 41, and control the coating thickness to be about 0.5 mm. Then, slowly lower the male die 10 to accurately close it with the female die 20, and use a G-type clamp to lock the male die 10 and the female die 20 along the periphery of the mold. During this process, ensure that the position of the clamp and the locking force are consistent with the state during production. The gap between the parting surfaces is filled with the silicone liquid, and at the positions with a smaller gap, the silicone liquid will overflow to the outer wall of the mold due to extrusion.

[0084] Place the mold in a normal temperature environment for curing, and the curing time is about 2 hours. After curing, carefully cut off the overflowing silicone, remove the clamp, slowly open the mold, and check the surface quality of the sealing ring and its adhesion to the female die parting surface. After determining that the sealing ring has no defects, close the mold and lock it with a clamp, start the vacuum system, and use a vacuum pump to evacuate the air in the mold cavity, and at the same time check whether the vacuum degree in the cavity reaches -0.08 MPa to -0.1 MPa.

[0085] With the increase in the frequency of mold use and the change of seasons, the mold may continue to deform, resulting in a change in the gap between the parting surfaces. At this time, just peel off the old sealing ring from the female die, make a new sealing ring according to the latest state of the mold, and then it can be put into production. The variable-thickness sealing ring of the present invention has the advantages of simple production, low cost, convenient use, and good sealing performance.

[0086] The above schematically describes the present invention and its implementation manners, and this description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and design similar structural manners and embodiments without creative efforts without departing from the purpose of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. Method for realizing a low-pressure casting process with reusable molds, using a double-layer composite structure mold, including a male mold and a female mold, the male mold and the female mold can be opened and closed along the parting surface, characterized in that: A variable-thickness silicone rubber sealing ring with the same shape as the parting surface is arranged between the parting surfaces. Its thickness is adjusted according to the change of the parting surface gap. The lower surface of the silicone rubber sealing ring is adhered to the parting surface of the female mold, and a sealing structure is formed when it is closed with the parting surface of the male mold; both the male mold and the female mold are composed of a flexible inner layer and a rigid outer layer, and the rigid outer layer is the mold shell after removing the flexible inner layer. The steps of casting different products on the same mold shell are as follows: S1: Vacuum pumping: Before injection molding, vacuum pump the mold cavity to form a negative pressure environment to ensure that the injected liquid resin material fully flows to all corners of the mold and avoid the generation of bubbles. S2: Injection: After the product after injection molding is pressure-maintained and cured, take it out to form Product 1. S3: Product replacement: Take out Product 1 and produce Product 2 in the same mold shell. S4: Making the flexible inner layer of the female mold for Product 2: According to the drawing, process the prototype of Product 2, place the prototype in the mold to form a cavity between it and the female mold, inject silicone liquid, and after curing, form the flexible inner layer of the female mold. S5: Making the flexible inner layer of the male mold for Product 2: A cavity is formed between the prototype and the male mold, inject silicone liquid, and after curing, form the flexible inner layer of the male mold. S6: Producing Product 2: Apply the new flexible inner layer for Product 2 to the mold shell to realize the repeated use of the same mold shell for the production of different products.

2. The implementation method of the low-pressure casting process with reusable molds according to claim 1, characterized in that: The mold shell includes a male mold shell and a female mold shell. The male mold shell and the female mold shell are respectively located outside the flexible inner layer of the male mold and the flexible inner layer of the female mold. The male mold shell successively includes a first rigid layer of the male mold and a second rigid layer of the male mold, and the female mold shell successively includes a first rigid layer of the female mold and a second rigid layer of the female mold.

3. The implementation method of the low-pressure casting process with reusable molds according to claim 1, characterized in that: In step S4, the prototype is pasted on the foam, and then the foam is filled in the male mold shell. A cavity is formed between the prototype and the female mold shell, and silicone liquid is injected into this cavity and cured to form the flexible inner layer of the female mold.

4. The implementation method of the low-pressure casting process with reusable molds according to claim 1, characterized in that: In step S5, take out the foam in step S4, clean the prototype, a cavity is formed between the product prototype and the male mold shell, inject silicone liquid into this cavity, and after normal temperature curing, form the flexible inner layer of the male mold.

5. The implementation method of the low-pressure casting process with reusable molds according to claim 2, characterized in that: A pouring hole is arranged along the opening direction at the lowest position in the middle area of the first rigid layer of the male mold, penetrating through the first rigid layer of the male mold and the second rigid layer of the male mold.

6. The implementation method of the low-pressure casting process with reusable molds according to claim 2, characterized in that: Two exhaust holes are respectively arranged at both ends of the first rigid layer of the male mold along the opening direction, penetrating through the first rigid layer of the male mold and the second rigid layer of the male mold, which are the first exhaust hole and the second exhaust hole respectively.

7. The implementation method of the low-pressure casting process with reusable molds according to claim 3, characterized in that: In step S4, the lower end of the pouring hole is connected to the upper end of the first plastic rod, and the lower end of the first plastic rod is adhered to the surface of the lowest part of the product prototype; the lower ends of the first exhaust hole and the second exhaust hole are respectively connected to the second plastic rod and the third plastic rod. Thus, when the mold is closed, the cavity formed between the product prototype and the male mold shell contains the first plastic rod, the second plastic rod and the third plastic rod extending from the pouring hole, the first exhaust hole and the second exhaust hole.

8. The implementation method of the low-pressure casting process with reusable molds according to claim 7, characterized in that: After the flexible inner layer of the male mold is cured, open the mold and take out the first plastic rod, the second plastic rod and the third plastic rod. The spaces left by these plastic rods are used to form complete pouring holes and exhaust holes.

9. The implementation method of the low-pressure casting process with reusable molds according to claim 1, characterized in that: The manufacturing method of the variable-thickness silicone rubber sealing ring is as follows: S1: Clean the parting surface of the male mold and apply a release agent, clean the parting surface of the female mold, and no release agent needs to be applied. S2: Mix the silicone solution, and after degassing, apply it evenly on the parting surface of the female mold. S3: Lower the male mold, close the mold, so that all the gaps between the parting surfaces are filled with the silicone solution, clamp and cure for 2 hours. S4: Trim the overflow glue, open the mold and check the quality of the sealing ring.

10. The implementation method of the low-pressure casting process with reusable molds according to claim 9, characterized in that: Perform vacuum degree detection during mold closing, and the vacuum degree is between -0.08 and -0.1 MPa.

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