A method for integrally forming a composite material box body with improved vacuum stability

Abstract

This invention relates to a method for integral molding of composite material box bodies using a vacuum-resistant material (VARI) process to improve vacuum stability. The method includes the following steps: mold preparation; outer skin laying; steel frame fixing; mold closing; core material laying; inner skin laying; vacuum-assisted material laying; vacuum leak detection; resin injection; box body curing; blank demolding; and blank trimming. Specifically, the vacuum-assisted material laying includes: laying of release cloth and flow guide net; layout of spiral tubes and injection ports; laying of the first vacuum bag mold; fabrication of the auxiliary vacuum-guided cavity membrane; cavity membrane laying; laying of the second vacuum bag membrane; and installation of the injection tube. This invention can effectively control the vacuum level during the integral molding process of large composite material box body blanks using a VARI process, improve resin flow and permeability, avoid poor resin wetting in localized corner areas, and is suitable for the promotion and application of integral molding of similar large composite material box bodies using a VARI process.

Description

Technical Field

[0001] This invention relates to the field of composite material box molding process, and more particularly to a method for integral molding of composite material boxes using VARI co-curing to improve vacuum stability. Background Technology

[0002] VARI (Vacuum Assisted Resin Infusion) co-curing integral molding technology is a low-cost, high-density molding process for large composite skin + steel frame sandwich structures. The molding process is characterized by the use of resin flow and penetration under vacuum pressure after the upper and lower molds are closed, to impregnate fibers and fabrics, completing vacuum resin introduction and co-curing integral molding, forming an integrated skin box blank. This achieves dual protection of the airtightness of the integral composite inner and outer skin structure, and enhances the overall load-bearing strength of the steel frame. It can be extended to the manufacture of large composite material packaging boxes.

[0003] In recent years, the VARI split molding method has been widely used for the molding of large composite material boxes. That is, after the box blank is formed by a semi-enclosed mold, it is fixed by screw (welding) + adhesive assembly.

[0004] The prior art patent document CN 113510944A proposes a VARI molding resin flow channel structure and resin impregnation method for large-size reinforced wall panels. The complex large-size reinforced wall panel preform is divided into several small and simple unit bodies. Valves are used to control the opening and closing of the glue injection and dispensing branches to achieve function switching, ensuring that the resin impregnation of each unit is carried out in succession, shortening the resin flow distance, and reducing the non-uniformity of the resin flow direction thickness and internal quality of the reinforced wall panel.

[0005] The prior art patent document CN 114055819A proposes a packaging box skin, a preparation method, and a packaging box, which designs a packaging box skin structure layup method to achieve higher interface strength.

[0006] The prior art patent document CN 105501685A discloses an ultra-large composite material pressurized packaging box, which reduces strain and avoids breakage or damage from the perspective of structural strength. The structure includes a lid and body, a core layer material vacuum-formed as a single unit, and inner and outer composite felt reinforcement composite materials.

[0007] The existing patent document CN 216685716U discloses a high-strength, lightweight composite material packaging box. The box body is integrally molded from fiber composite material, and both the box body and the door adopt a foam sandwich structure. The structural design has high strength and excellent environmental adaptability and impact resistance.

[0008] The prior art patent document CN 113135002A discloses a carbon fiber composite packaging box and its manufacturing method, which is designed with a skin layup method and uses EPS foam layer for cushioning and shock absorption layer, and is formed by compression molding.

[0009] The aforementioned patent CN 113510944A addresses improvements to the prefabricated large-size reinforced wall panel and resin flow channel structure, enhancing the resin wetting effect during the VARI molding process. However, it does not involve methods to improve resin flow and permeability by increasing the vacuum stability during the resin injection process.

[0010] The aforementioned patents CN 114055819A, CN 105501685A, and CN 216685716U only address the structural design of the packaging box and do not propose specific molding methods.

[0011] The aforementioned patent CN 113135002A addresses the design of the packaging box skin layer structure and proposes the use of compression molding, but does not involve the VARI integral molding process. Summary of the Invention

[0012] To address the aforementioned problems, this invention provides a VARI co-curing integral molding process for large composite material boxes that improves the vacuum stability during resin infusion.

[0013] The technical solution adopted in this invention is as follows:

[0014] A method for integral molding of a composite material box for improving vacuum stability (VARI) includes the following steps:

[0015] The inner surfaces of the upper and lower box forming molds are covered with fiber fabric of outer skin;

[0016] A steel frame is placed inside the cavities of the upper and lower box forming molds;

[0017] The upper box forming mold and the lower box forming mold are joined together;

[0018] The core material is laid on the steel frame placed inside the upper and lower box forming molds after the mold is closed;

[0019] After the mold is closed, the inner cavity surfaces of the upper and lower box forming molds are covered with fiber fabric of inner skin.

[0020] Vacuum-assisted materials are laid in the inner cavities of the upper and lower box forming molds after the molds are closed.

[0021] The process involves sequentially performing vacuum leak detection, resin injection, box curing, demolding of the blank, and trimming of the blank to obtain the composite material box.

[0022] Furthermore, mold preparation is performed before laying the outer skin, the mold preparation including:

[0023] Prepare the box forming molds, including the upper box forming mold and the lower box forming mold;

[0024] Clean the mold of any remaining foreign objects and glue residue, and carefully clean the inner surface of the mold. Blow the mold clean with an air gun, and finally wipe the tooling cavity with acetone to make its surface smooth, free of oil stains, impurities, and glue particles.

[0025] Spray gel coat resin on the surface of the mold cavity to facilitate demolding and let it cure.

[0026] Furthermore, the steel frame is located between the outer skin and the inner skin of the composite material, serving as the internal skeleton of the composite material; the steel frame is made of steel with U-shaped grooves, and the steel frame joints are welded and fixed.

[0027] Furthermore, the core material being laid includes:

[0028] The U-shaped groove of the steel frame is filled with foam boards of appropriate size, and the inner cavity of the box is laid with light wood boards of appropriate thickness to form a flat surface, so as to facilitate the laying of the inner skin.

[0029] Furthermore, the laying of the vacuum-assisted material includes:

[0030] Release cloth and flow guide net laying: Loosely lay the release cloth on the surface of the composite skin, and fix it locally with shaping adhesive. Lay the flow guide net on the surface of the release cloth, with the flow guide net pattern consistent with the direction of the flow guide net. Fix the flow guide net with sealing tape.

[0031] Spiral tube and injection port layout: The spiral tubes are distributed circumferentially inside the mold cavity of the box body, and additional spiral tubes are appropriately added at irregular positions at the bottom of the box body; the spiral tubes are fixed to the guide net with sealing tape, and the resin is guided to the guide net through the spiral tubes;

[0032] First vacuum bag film laying: The first vacuum bag film is made into a shape similar to a woven bag according to the envelope size of the box mold. The bag opening is glued to the sealing strip that is pre-attached to the skirt of the mold port, so that the vacuum bag film and the box mold form a sealed space. Several vacuum discharge ports are arranged on the skirt of the mold port and connected to the vacuum tube, and connected to the connector of valve No. 1 of the vacuum pump.

[0033] Fabrication of the auxiliary vacuum guide cavity membrane: The length of the auxiliary vacuum guide cavity membrane is determined based on half the length of the inner cavity of the box mold; the auxiliary vacuum guide cavity membrane includes a plastic connector, a breathable felt, a release cloth, a vacuum bag film, and sealing tape to seal the boundary. First, the vacuum bag film is cut according to the specified size to wrap the release cloth, and the sides are sealed with sealing tape. The head of the cavity membrane is glued with a plastic connector to form a vacuum port, wherein the part of the connector extending into the vacuum bag film is wrapped with a breathable felt;

[0034] Cavity membrane placement: Fix the head of the cavity membrane to the corresponding surface of the skirt at the mold port. Connect one end of the cavity membrane vacuum port to the plastic connector and the other end to the vacuum tube. Connect the vacuum tube to the No. 2 valve connector of the vacuum pump. At the middle of the length of the first vacuum bag membrane placed in the mold, cut a notch of the same width as the cavity membrane. Connect the tail of the cavity membrane to the notch and seal it to form an auxiliary channel for assisting in vacuuming.

[0035] The second vacuum bag film is laid out: the auxiliary vacuum guide cavity membrane is located between the second vacuum bag film and the first vacuum bag film. The second vacuum port of the second vacuum bag film is fixed at the skirt position of the mold port, connected to the vacuum tube, and connected to the valve connector No. 3 of the vacuum pump;

[0036] Installation of injection tubes: Several injection ports distributed inside the mold cavity of the box body penetrate the first vacuum bag film and the second vacuum bag film, are sealed and fixed with sealing tape, and are connected to the injection tubes.

[0037] Furthermore, the interlayer overlap of the release fabric is no more than 100mm, and the edge of the release fabric should extend about 200mm beyond the composite skin; the interlayer overlap of the flow guide net is 50-100mm; the circumferential spacing of the spiral tube is 40-60mm; and the width of the auxiliary vacuum flow guide cavity membrane is 30cm.

[0038] Furthermore, the vacuum leak detection includes:

[0039] Select one glue injection tube extending from the bottom and top of the inner cavity of the box, and connect them to the interfaces of pressure gauges 1 and 2 respectively. Temporarily seal the interfaces of the remaining glue injection tubes with sealing tape.

[0040] Connect valve 1 of the vacuum pump to the first vacuum port, valve 2 to the diaphragm vacuum port, and valve 3 to the second vacuum port. Operate the vacuum pump, open valves 1 and 2, and close valve 3 to compact the first vacuum bag membrane at all corners, reinforcing ribs, and surfaces of the chamber. The vacuum pressure value should not be lower than -0.09MPa, and the pressure holding time should not be less than 20 minutes.

[0041] After the pressure holding time ends, check the readings of pressure gauges 1 and 2 for leak detection. If the values ​​are not lower than -0.09MPa and the readings of the two pressure gauges are consistent and stable, it is determined that the vacuum level in the bottom area of ​​the chamber can be effectively improved by the auxiliary vacuum evacuation and diversion membrane, so that the overall vacuum level of the chamber is stable and controllable and there is no leakage.

[0042] Further, the resin injection includes:

[0043] Place the resin in the dispensing tank, disconnect the dispensing tube of the pressure gauge, seal it with sealing tape, operate the vacuum pump to open valves 1 and 2, and close valve 3. Set the vacuum pressure value to be no less than -0.09MPa.

[0044] During the resin introduction process, the injection ports are numbered sequentially from the bottom of the tank upwards, from 1 to N. First, the seal at the interface of the first injection port is opened, and the injection port is placed in the injection tank to begin injection. The wetting of the injection port area is observed. The injection time for each injection port is determined according to the size of the tank. When the third injection port begins injection, the first injection port is sealed, and so on.

[0045] Further, the curing of the enclosure includes:

[0046] After the resin injection is completed, seal all the injection ports. At this time, operate the vacuum pump to open valve No. 3 and close valves No. 1 and No. 2. During the resin curing period, the second vacuum bag film will be vacuumed to produce a compaction effect, which will prevent the first vacuum bag film from collapsing due to pressure drop during the curing process, thereby improving the consistency of fiber volume content in various parts of the box blank.

[0047] The present invention also provides a composite material box body formed according to the above method.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] This invention addresses the problem of significant vacuum drop and poor sealing during the vacuum resin introduction process, particularly in the distal area of ​​the vacuum outlet and at local corners. It adds an auxiliary vacuum guiding membrane to create a secondary vacuum negative pressure effect in the middle of the chamber, improving the vacuum stability during resin infusion and allowing for controllable fiber volume content in the molded chamber blank. Practical verification has shown reliable results, making it suitable for composite material molding of similar products.

[0050] This invention is based on the VARI integral molding of composite material box body. An auxiliary vacuuming process is added during the vacuum resin introduction process, and double vacuum bag film is laid to ensure that the vacuum degree in each area inside the box is consistent, which can improve the resin flow and wetting effect. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of a composite material box structure provided in an embodiment of the present invention.

[0052] Figure 2 This is a schematic cross-sectional view of a composite material box structure provided in an embodiment of the present invention.

[0053] Figure 3 This is a flowchart of the VARI integral molding process for composite material boxes provided in an embodiment of the present invention.

[0054] Figure 4 This is a schematic diagram of the placement of auxiliary materials for vacuuming the box provided in an embodiment of the present invention.

[0055] Figure 5 This is a schematic diagram of the auxiliary vacuum guiding cavity membrane provided in an embodiment of the present invention.

[0056] Figure 6 This is a physical image of the auxiliary vacuum diversion cavity membrane laid out according to an embodiment of the present invention.

[0057] In the diagram: 1-Composite material box body; 2-Schematic diagram of longitudinal symmetrical cross-section of box body molding; 3-Breathable felt; 4-Second vacuum bag film; 5-Auxiliary vacuum diversion cavity film; 51-Plastic joint; 52-Breathable felt; 53-Release cloth; 54-Vacuum bag film; 55-Sealing tape sealing boundary; 6-First vacuum bag film; 7-Drainage net; 8-Release cloth; 9-Breathable felt; 10-Sealing tape sealing point; 11-Second vacuum port; 12-Cavity film vacuum port; 13-First vacuum port; 14-Box body mold (partial diagram after mold closing); 15-Composite skin + sandwich structure (partial diagram); 16-Injection port. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0059] An embodiment of the present invention provides a composite material box structure, such as Figure 1 As shown, Figure 2 This is a cross-sectional schematic diagram of the composite material box structure.

[0060] This invention proposes a VARI co-curing integral molding process for composite material boxes to improve vacuum stability. The specific steps are as follows: Figure 3As shown, steps one through twelve are VARI co-curing integral molding, and the detailed process (1) through (7) of step seven is the vacuuming auxiliary material laying process.

[0061] Step 1: Mold Preparation. The box forming mold of this invention includes an upper box forming mold and a lower box forming mold. Preferably, before production, the box mold is inspected. Any remaining foreign matter or glue residue on the mold is first cleaned with a copper flat chisel, then the inner surface of the mold is carefully cleaned with a clean cotton cloth, then the mold is blown clean with an air gun, and finally the tooling cavity is wiped with acetone to make its surface smooth, free of oil stains, impurities, and glue protrusions. If local damage or breakage of the mold is found after demolding, the mold should be repaired or repaired in a timely manner according to the degree of damage. Preferably, a clean cotton cloth is used to wipe the mold cavity with a release agent, using a rotating or cross-shaped method to ensure that the entire mold cavity is wiped thoroughly. Preferably, a gel coat resin is sprayed onto the surface of the mold cavity to facilitate demolding. The gel coat thickness is controlled to be 0.4–0.6 mm. After the gel coat is applied, it is allowed to cure at a curing temperature of 15–35°C for at least 30 minutes.

[0062] Step Two: Outer Skin Laying. Preferably, before mold closing, appropriately sized fiber fabric is laid onto the inner surfaces of the upper and lower box-shaped mold cavities according to specifications, and a small amount of setting adhesive can be used for fixation. Preferably, the fiber fabric should be laid out along the length of the mold as a whole. When laying on a flat surface, overlaps should be minimized, paying particular attention to corners to avoid excessively thick layers. Fiber layers at corners or other irregular shapes should be appropriately broken to avoid bridging. Preferably, the overlap between fiber layers is 30-50mm, and gradual overlap treatment should be used in localized areas to avoid bridging.

[0063] Step 3: Steel Frame Fixing. The steel frame is located between the outer and inner skins of the composite material, serving as the internal skeleton of the composite material and improving its strength. Preferably, the steel frame is placed at the position required by the box molding mold. The steel frame is made of steel with U-shaped grooves, and the steel frame joints (where the steel overlaps) are welded and fixed using carbon dioxide gas shielded welding.

[0064] Step 4: Mold Assembly. Clean the flanges of the upper and lower box-shaped molds, and apply an appropriate amount of silicone sealant evenly around the flanges. After the upper and lower box-shaped molds are joined, fasten them with screws, and complete the welding of the steel frame at the joint surface.

[0065] Step 5: Laying the sandwich material. Preferably, foam boards of suitable size are used to fill the U-shaped channels of the steel frame, and a small amount of sizing adhesive can be sprayed on for fixation. Then, balsamic wood boards of suitable thickness are laid out to conform to the shape of the inner cavity of the box, forming a flat surface to facilitate the laying of the inner skin. The foam boards and balsamic wood boards are combined together as the sandwich material.

[0066] Step Six: Inner Sheet Laying. Preferably, appropriately sized fiber fabrics are laid out according to specifications onto the inner surface of the molded box after molding, and a small amount of setting adhesive can be used for fixation. The fabric is laid out as a single sheet along the length of the mold to minimize overlap.

[0067] Step 7: Laying out vacuum-assisted materials. This includes the following sub-processes:

[0068] (1) Laying of release fabric and flow guide net. Preferably, such as... Figure 4 As shown, the release fabric 8 is loosely laid on the surface of the composite skin 15 and locally fixed with adhesive. The overlap between layers should not exceed 100mm. The release fabric 8 can be wrinkled but not taut, and the edge of the release fabric 8 should extend about 200mm beyond the composite skin. The flow guide net 7 is laid entirely on the surface of the release fabric 8, with an overlap of 50-100mm. The flow guide net pattern should be consistent with the direction of the adhesive flow. The flow guide net points are fixed with sealing tape.

[0069] (2) Layout of Spiral Tubes and Injection Ports. Preferably, the spiral tubes are distributed circumferentially within the mold cavity of the housing, with circumferential intervals of 40-60mm, and additional spiral tubes are appropriately added at irregular positions on the bottom of the housing. The spiral tube is a spirally wound plastic tube used to improve resin flowability and prevent resin buildup. Sealing tape is used to fix the spiral tubes to the flow guide net, and the resin flows through the spiral tubes to the flow guide net. Preferably, an injection port is symmetrically arranged at the center line of each circumferential spiral tube, connecting to the injection tube for bidirectional resin injection.

[0070] (3) Laying the first vacuum bag film. Preferably, the first vacuum bag film 6 is made into a shape similar to a woven bag according to the envelope size of the box mold. The bag opening is glued to the sealing strip that is pre-attached to the skirt of the mold port, so that the vacuum bag film and the box mold form a sealed space. Several vacuum outlets are arranged on the skirt of the mold port and connected to vacuum tubes, and connected to the connector of valve No. 1 of the vacuum pump.

[0071] (4) Fabrication of the auxiliary vacuum diversion cavity membrane. For large boxes, during the vacuum resin introduction process, a significant decrease in vacuum level and poor sealing effect are prone to occur in the distal area of ​​the second vacuum port 10 and at local corners. Therefore, this invention adds the laying of the auxiliary vacuum diversion cavity membrane 5 to improve the vacuum stability during the resin pouring process. Preferably, the length of the cavity membrane is determined based on half the length of the inner cavity of the box mold, and the width of the cavity membrane is about 30cm. The structure of the cavity membrane is as follows: Figure 5 As shown, first cut the vacuum bag film 54 to the specified dimensions to wrap the release cloth 53, and then seal the sides with sealing tape. Figure 5 The sealing tape seals the boundary 55 of the cavity membrane, and the head of the cavity membrane is bonded with a plastic connector 51 to form a vacuum port. The part of the connector extending into the vacuum bag membrane 54 needs to be wrapped with a breathable felt 52 to prevent the cavity membrane from being scratched during the vacuuming process.

[0072] (5) Laying the cavity membrane. Preferably, the head of the cavity membrane is fixed to the corresponding surface of the skirt at the mold port. One end of the cavity membrane vacuum port 12 is connected to the plastic connector 51, and the other end is connected to the vacuum tube, which is connected to the valve connector No. 2 of the vacuum pump. At the middle position of the first vacuum bag membrane 6 laid in the mold of the box, a notch of the same width as the cavity membrane is cut. The tail of the cavity membrane is connected to the notch and sealed to form an auxiliary channel for auxiliary vacuuming. Auxiliary vacuum guiding cavity membranes are arranged on each side of the inner cavity of the box, or auxiliary vacuum guiding cavity membranes can be arranged on 3 of the 4 sides of the inner cavity. The vacuum ports of the cavity membranes are all connected to the valve connector No. 2 of the vacuum pump through the vacuum tube.

[0073] (6) Laying the second vacuum bag film. For example... Figure 4 As shown, the auxiliary vacuum guiding cavity membrane 5 is located between the second vacuum bag membrane 4 and the first vacuum bag membrane 6. The second vacuum bag membrane is laid in the same way as the first, with a breathable felt appropriately covering a local area between the two vacuum bag membranes to improve the vacuum compaction effect of the second vacuum bag membrane. Preferably, the second vacuum port 11 is fixed at the skirt position of the mold port, connected to the vacuum tube, and connected to the valve connector No. 3 of the vacuum pump.

[0074] (7) Installation of the injection tube. Preferably, the injection ports distributed in the inner cavity of the box mold penetrate the first and second vacuum bag films, are sealed and fixed with sealing tape, and are connected to the injection tube.

[0075] Step 8: Vacuuming and Leak Detection. Preferably, select one injection tube extending from the bottom and top of the inner cavity of the chamber, and connect them to the interfaces of pressure gauges 1 and 2 respectively. Temporarily seal the interfaces of the remaining injection tubes with sealing tape. Preferably, operate the vacuum pump, open valves 1 and 2, and close valve 3 (Note: Valve 1 is connected to the first vacuum port 13; valve 2 is connected to the cavity membrane vacuum port 12; valve 3 is connected to the second vacuum port 13), and compact the first vacuum bag membrane at all corners, reinforcing ribs, and surfaces of the chamber. The vacuum pressure value should not be lower than -0.09 MPa, and the pressure holding time should not be less than 20 minutes. After the pressure holding time, check the readings of pressure gauges 1 and 2 for leak detection. If both values ​​are not lower than -0.09 MPa, and the readings of the two pressure gauges are consistent and stable, it can be determined that the vacuum degree in the bottom area of ​​the inner cavity of the chamber has been effectively improved by the auxiliary vacuuming and guiding the cavity membrane, resulting in controllable overall vacuum stability of the inner cavity of the chamber and no leakage.

[0076] Step Nine: Resin Injection. Preferably, the mold is placed vertically 14 times and secured using an elevated platform. Using room-temperature curing resin, the prepared resin is placed in the injection tank. The injection tube interface of the pressure gauge is disconnected and sealed with sealing tape. The vacuum pump is operated to open valves 1 and 2 and close valve 3. The vacuum pressure is set to no less than -0.09 MPa. During resin introduction, the injection ports are numbered sequentially from the bottom of the mold upwards, from 1 to N (parameters are set appropriately according to the mold length). First, the sealing at the first injection tube interface is opened, and the mold is placed in the injection tank. Injection begins, and the resin wetting of each injection port area is observed. The injection time for each injection port is determined according to the mold size. Based on practical experience, when injection begins at the third injection port, the first injection port should be sealed, and so on. To avoid excessively long injection time, which could lead to gelation before the resin is fully impregnated, the injection time should be determined reasonably based on the resin gelation time.

[0077] Step 10: Cabinet Curing. Preferably, after resin injection is completed, all injection ports are sealed. At this time, the vacuum pump is operated to open valve 3 and close valves 1 and 2. During resin curing, the second vacuum bag film is used to create a compaction effect, preventing the first vacuum bag film from collapsing due to pressure loss during the curing process. This can improve the consistency of fiber volume content in various parts of the cabinet blank. Preferably, the room temperature curing time for the cabinet is not less than 24 hours.

[0078] Step 11: Demolding the blank. After the box blank has cured, remove the vacuum bag film, injection tube, flow guide net, and release cloth, etc. Using the matching tools, remove the connecting screws of the upper and lower box molds, and drive wedge blocks into the molds from both symmetrical ends at the center to loosen and release the product from the mold. After demolding, the box blank needs to be placed in a 60℃ oven for curing for 4-6 hours.

[0079] Step 12: Finishing the blank. The flange at the end of the box blank is a boundary area where resin may not be fully injected, resulting in "dry spots". The finishing process requires cutting and grinding the flange excess, and polishing any uneven areas on the surface.

[0080] In one specific embodiment of the present invention, a VARI co-curing integral molding process for a large glass fiber / epoxy vinyl ester composite box is provided, such as... Figure 3 As shown; to improve the vacuum stability during resin injection, this invention provides a method for laying auxiliary materials for vacuum evacuation of the container, such as... Figure 4 As shown, it includes: a first vacuum bag membrane 6, a second vacuum bag membrane 4, an auxiliary vacuum guiding cavity membrane 5, a second vacuum port 11, and a cavity membrane vacuum port 12.

[0081] The process flow method includes the following steps:

[0082] Step 1: Mold Preparation. Before production, carefully inspect and wipe the mold to ensure its surface is smooth, free of oil stains, impurities, and protruding glue particles. Spray the prepared gelcoat resin onto the surface of the mold cavity, controlling the gelcoat coating thickness to 0.4–0.6 mm. After the gelcoat coating is applied, allow it to cure at a temperature of 15–35℃ for at least 30 minutes.

[0083] Step Two: Outer Skin Laying. Before mold closing, lay the five layers of fiberglass woven fabric, which have been cut, along the length of the mold onto the inner surface of the upper and lower box forming molds. At corners or other irregular shapes, the fiber layers should be appropriately broken to avoid bridging. The overlap between fiber layers should be 30-50mm. To avoid bridging in localized areas, use gradual overlap treatment as needed, and fix with a small amount of setting adhesive.

[0084] Step 3: Steel Frame Fixing. Place the steel frame in the mounting slots within the upper and lower box-shaped mold cavities, ensuring it fully fits the mold cavity to prevent any gaps. The steel frame joints are welded and fixed using CO2 gas shielded welding.

[0085] Step 4: Mold Assembly. Clean the flanges of the upper and lower box molds thoroughly, and apply an appropriate amount of silicone sealant evenly around the flanges and each screw mounting hole. Secure the upper and lower box molds together with screws, and weld the steel frame at the joint surface.

[0086] Step 5: Laying the core material. Fill the U-shaped groove of the steel frame with PVC foam board of appropriate size, and apply a small amount of setting adhesive for fixation. Then, lay a 3 / 8-inch thick layer of balsa wood material to conform to the shape of the inner cavity of the box.

[0087] Step Six: Inner Liner Covering. The five layers of fiberglass woven fabric, after being cut, are laid sequentially along the length of the mold onto the inner surface of the box mold after it is closed, and fixed with a small amount of setting adhesive.

[0088] Step 7: Vacuuming and auxiliary material placement. Detailed steps:

[0089] (1) Laying of release cloth and flow guide net. Loosely lay the release cloth 7 on the surface of the composite skin 15, and fix it locally with setting adhesive. The overlap between layers should not exceed 100mm. The release cloth can be wrinkled but not taut. The edge of the release cloth should extend about 200mm beyond the composite skin. The flow guide net 7 is laid on the surface of the release cloth 8, with an overlap between layers of 50-100mm. The flow guide net pattern should be consistent with the direction of the flow guide. Use sealing tape to fix the flow guide net at the points.

[0090] (2) Layout of spiral tubes and injection ports. The spiral tubes are distributed circumferentially within the mold cavity of the box body, with a circumferential interval of 50mm. Spiral tubes are appropriately added at irregular positions at the bottom of the box body. The spiral tubes are fixed to the guide net using sealing tape. An injection port 16 is symmetrically arranged at the center line of each circumferential spiral tube, which is connected to the injection tube for bidirectional injection.

[0091] (3) Laying the first vacuum bag film. The vacuum bag film is made into a shape similar to a woven bag according to the envelope size of the box mold. The bag opening is glued to the sealing strip that is pre-attached to the skirt of the mold port, so that the first vacuum bag film 6 and the box mold 14 form a sealed space. The first vacuum port 13 is arranged on each of the four sides of the skirt of the mold port, and connected to the vacuum tube and connected to the valve connector of vacuum pump 1.

[0092] (4) Fabrication of the auxiliary vacuum guide cavity membrane. The length of the cavity membrane 5 is set at 250cm based on half the length of the inner cavity of the box mold, and the width of the cavity membrane is 30cm. First, the vacuum bag membrane 54 is cut according to the specified size and wrapped with the release cloth 53. The sides are sealed with sealing tape to form the sealing tape sealing boundary 55. The head of the cavity membrane 5 is glued with a plastic connector 51 to form a vacuum port. The part of the connector extending into the vacuum bag membrane needs to be wrapped with a breathable felt 52.

[0093] (5) Laying the cavity membrane. Fix the head of the cavity membrane to the corresponding surface of the skirt at the mold port. Connect the vacuum port 12 of the cavity membrane to the vacuum tube, and connect the vacuum tube to the valve connector of vacuum pump No. 2. At the middle position of the first vacuum bag membrane 6 laid in the mold of the box, cut a notch of the same width as the cavity membrane. Seal the tail of the cavity membrane with the notch to form an auxiliary channel. Arrange auxiliary vacuum guiding cavity membranes 5 on each side of the inner cavity of the box. The vacuum port 12 of the cavity membrane is connected to the valve connector of vacuum pump No. 2 through the vacuum tube. Figure 6 This is a photograph of the actual membrane placement in the auxiliary vacuum diversion cavity of this embodiment.

[0094] (6) Laying the second vacuum bag film. The second vacuum bag film 4 is laid in the same way as the first, except that a breathable felt 3 is appropriately covered in a local area between the two films. The second vacuum port 11 is fixed at the skirt position of the mold port, connected to the vacuum tube, and connected to the valve connector of the vacuum pump 3.

[0095] (7) Installation of injection tubes. Several injection ports 16 distributed in the inner cavity of the box mold penetrate the first and second vacuum bag films, are sealed and fixed with sealing tape, and are connected to the injection tubes respectively.

[0096] Step 8: Vacuuming and Leak Detection. Select one injection tube each extending from the bottom and top of the chamber's inner cavity and connect them to the interfaces of pressure gauges 1 and 2, respectively. Temporarily seal the interfaces of the remaining injection tubes with sealing tape. Operate the vacuum pump, open valves 1 and 2, and close valve 3. The vacuum pressure should be -0.095 MPa, and the pressure holding time should be 20 minutes. After the pressure holding time is completed, check the readings of pressure gauges 1 and 2 for leak detection. If both readings are -0.095 MPa and the readings of the two gauges are consistent and stable, it can be determined that the overall vacuum stability of the inner cavity of the chamber is controllable and there is no leakage.

[0097] Step Nine: Resin Injection. Place the mold vertically, securing it with an elevated platform. Place the prepared vinyl epoxy resin into the injection tank. Seal the injection tube interface (where the pressure gauge was removed) with sealing tape. Operate the vacuum pump, opening valves 1 and 2, and closing valve 3. Set the vacuum pressure to -0.095 MPa. During resin introduction, number the injection ports sequentially from the bottom of the mold upwards, from 1 to 10. First, open the seal at the interface of injection port 1, place it in the injection tank, and begin injection, observing the resin wetting at each injection port. Based on the mold dimensions, determine an injection time of approximately 10 minutes per injection port. Based on practical experience, when injection begins at the 3rd injection port, seal the 1st injection port, and so on. The total resin injection time was 1 hour and 45 minutes.

[0098] Step 10: Chamber Curing. After the resin injection is complete, seal all injection ports. At this time, operate the vacuum pump to open valve 3 and close valves 1 and 2. During the resin curing period, the second vacuum bag film will create a compaction effect. The chamber will cure at room temperature for 24 hours.

[0099] Step 11: Demolding the blank. After the box blank has cured, remove the vacuum bag film, injection tube, flow guide net, and release cloth, etc. Remove the connecting screws of the upper and lower box molds, and drive wedge blocks into the molds from both symmetrical ends at the center to loosen and release the product from the mold. After demolding, the box blank needs to be placed in a 60℃ oven for 4 hours to cure.

[0100] Step 12: Finishing the blank. Cut and grind the flange allowance at the ends of the box blank, and polish any uneven areas on the surface.

[0101] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A method for integral molding of a composite material box for improving vacuum stability, characterized in that, Includes the following steps: The inner surfaces of the upper and lower box forming molds are covered with fiber fabric of outer skin; A steel frame is placed inside the cavities of the upper and lower box forming molds; The upper box forming mold and the lower box forming mold are joined together; The core material is laid on the steel frame placed inside the upper and lower box forming molds after the mold is closed; After the mold is closed, the inner cavity surfaces of the upper and lower box forming molds are covered with fiber fabric of inner skin. Vacuum-assisted materials are laid in the inner cavities of the upper and lower box forming molds after the molds are closed. The process involves sequentially performing vacuum leak detection, resin injection, box curing, demolding of the blank, and trimming of the blank to obtain the composite material box. The steel frame is located between the outer and inner skins of the composite material, serving as the internal skeleton of the composite material; the steel frame is made of steel with U-shaped grooves, and the steel frame joints are welded and fixed. The process of laying the core material includes: filling the U-shaped groove of the steel frame with foam board of appropriate size, and laying balsa wood of appropriate thickness in the inner cavity of the box to form a flat surface, so as to facilitate the laying of the inner skin; The laying of vacuum-assisted materials includes: Release cloth and flow guide net laying: Loosely lay the release cloth on the surface of the composite skin, and fix it locally with shaping adhesive. Lay the flow guide net on the surface of the release cloth, with the flow guide net pattern consistent with the direction of the flow guide net. Fix the flow guide net with sealing tape. Spiral tube and injection port layout: The spiral tubes are distributed circumferentially inside the mold cavity of the box body, and additional spiral tubes are appropriately added at irregular positions at the bottom of the box body; the spiral tubes are fixed to the guide net with sealing tape, and the resin is guided to the guide net through the spiral tubes; First vacuum bag film laying: The first vacuum bag film is made into a shape similar to a woven bag according to the envelope size of the box mold. The bag opening is glued to the sealing strip that is pre-attached to the skirt of the mold port, so that the vacuum bag film and the box mold form a sealed space. Several vacuum discharge ports are arranged on the skirt of the mold port and connected to the vacuum tube, and connected to the connector of valve No. 1 of the vacuum pump. Fabrication of the auxiliary vacuum guide cavity membrane: The length of the auxiliary vacuum guide cavity membrane is determined based on half the length of the inner cavity of the box mold; the auxiliary vacuum guide cavity membrane includes a plastic connector, a breathable felt, a release cloth, a vacuum bag film, and sealing tape to seal the boundary. First, the vacuum bag film is cut according to the specified size to wrap the release cloth, and the sides are sealed with sealing tape. The head of the cavity membrane is glued with a plastic connector to form a vacuum port, wherein the part of the connector extending into the vacuum bag film is wrapped with a breathable felt; Cavity membrane placement: Fix the head of the cavity membrane to the corresponding surface of the skirt at the mold port. Connect one end of the cavity membrane vacuum port to the plastic connector and the other end to the vacuum tube. Connect the vacuum tube to the No. 2 valve connector of the vacuum pump. At the middle of the length of the first vacuum bag membrane placed in the mold, cut a notch of the same width as the cavity membrane. Connect the tail of the cavity membrane to the notch and seal it to form an auxiliary channel for assisting in vacuuming. The second vacuum bag film is laid: the auxiliary vacuum guide cavity film is located between the second vacuum bag film and the first vacuum bag film. The second vacuum port of the second vacuum bag film is fixed at the skirt position of the mold port, connected to the vacuum tube, and connected to the valve connector No. 3 of the vacuum pump. Installation of injection tubes: Several injection ports distributed inside the mold cavity of the box body penetrate the first vacuum bag film and the second vacuum bag film, are sealed and fixed with sealing tape, and are connected to the injection tubes.

2. The method according to claim 1, characterized in that, Mold preparation is performed before the outer skin is laid, and the mold preparation includes: Prepare the box forming molds, including the upper box forming mold and the lower box forming mold; Clean the mold of any remaining foreign objects and glue residue, and carefully clean the inner surface of the mold. Blow the mold clean with an air gun, and finally wipe the tooling cavity with acetone to make its surface smooth, free of oil stains, impurities, and glue particles. Spray gel coat resin on the surface of the mold cavity to facilitate demolding and let it cure.

3. The method according to claim 1, characterized in that, The interlayer overlap of the release cloth is no more than 100mm, and the edge of the release cloth should extend about 200mm beyond the composite skin; the interlayer overlap of the flow guide net is 50-100mm; the circumferential spacing of the spiral tube is 40-60mm; and the width of the auxiliary vacuum flow guide cavity membrane is 30cm.

4. The method according to claim 1, characterized in that, The vacuum leak detection includes: Select one glue injection tube extending from the bottom and top of the inner cavity of the box, and connect them to the interfaces of pressure gauges 1 and 2 respectively. Temporarily seal the interfaces of the remaining glue injection tubes with sealing tape. Connect valve 1 of the vacuum pump to the first vacuum port, valve 2 to the diaphragm vacuum port, and valve 3 to the second vacuum port. Operate the vacuum pump, open valves 1 and 2, and close valve 3 to compact the first vacuum bag membrane at all corners, reinforcing ribs, and surfaces of the chamber. The vacuum pressure value should not be lower than -0.09MPa, and the pressure holding time should not be less than 20 minutes. After the pressure holding time ends, check the readings of pressure gauges 1 and 2 for leak detection. If the values ​​are not lower than -0.09MPa and the readings of the two pressure gauges are consistent and stable, it is determined that the vacuum level in the bottom area of ​​the chamber can be effectively improved by the auxiliary vacuum evacuation and diversion membrane, so that the overall vacuum level of the chamber is stable and controllable and there is no leakage.

5. The method according to claim 4, characterized in that, The resin injection includes: Place the resin in the dispensing tank, disconnect the dispensing tube of the pressure gauge, seal it with sealing tape, operate the vacuum pump to open valves 1 and 2, and close valve 3. Set the vacuum pressure value to be no less than -0.09MPa. During the resin introduction process, the injection ports are numbered sequentially from the bottom of the tank upwards, from 1 to N. First, the seal at the interface of the first injection port is opened, and the injection port is placed in the injection tank to begin injection. The wetting of the injection port area is observed. The injection time for each injection port is determined according to the size of the tank. When the third injection port begins injection, the first injection port is sealed, and so on.

6. The method according to claim 5, characterized in that, The curing of the enclosure includes: After the resin injection is completed, seal all the injection ports. At this time, operate the vacuum pump to open valve No. 3 and close valves No. 1 and No.

2. During the resin curing period, the second vacuum bag film will be vacuumed to produce a compaction effect, which will prevent the first vacuum bag film from collapsing due to pressure drop during the curing process, thereby improving the consistency of fiber volume content in various parts of the box blank.

7. A composite material box formed by the method according to any one of claims 1 to 6.

Images