Self-heating in-situ cure molding method and system for arm upper skin

Abstract

This application relates to the field of composite material molding technology, and discloses a self-heating in-situ curing molding method and system for a robot arm skin, including: checking that the remaining operating life and mechanical property life of the prepreg are both greater than 0 hours, thawing and cutting for later use; using a self-heating mold and calibrating the temperature uniformity, cleaning the mold and applying a release agent, ensuring that the shape of the self-heating mold matches the shape of the robot arm skin; pre-embedding a motor ring during the laying process, pre-treating the motor ring and reinforcing it with fabric, then laying the prepreg layer by layer according to the layup requirements, removing air bubbles and smoothing wrinkles in each layer, and performing vacuum pre-compacting according to the layer sequence; laying auxiliary materials and making vacuum bags, evacuating to the required vacuum level and testing the pressure holding capacity; heating the packaged mold along with the product to cure the robot arm skin in situ, and cooling it after curing; removing the auxiliary materials and mold, and taking out the robot arm skin product; cutting, trimming, sealing, and inspecting the appearance quality of the robot arm skin product, and handing it over after it passes inspection.

Description

Technical Field

[0001] This application relates to the field of composite material molding technology, and in particular to a self-heating in-situ curing molding method and system for the skin of a machine arm. Background Technology

[0002] The arm structure of aircraft such as drones and electric vertical takeoff and landing (eVTOL) aircraft is a critical load-bearing component connecting the fuselage and the power system. The arm skin, as the outer covering of the arm structure, not only needs to withstand aerodynamic loads during flight but also needs to provide precise positioning and reliable connection interfaces for motor installation. Therefore, the manufacturing quality of the arm skin directly affects the safety and reliability of the aircraft.

[0003] Fiber-reinforced resin matrix composites have become the mainstream manufacturing material for the skin of robotic arms due to their high specific strength, high specific modulus, and excellent corrosion resistance. Currently, the curing and molding of composite robotic arm skins mainly adopts autoclave and oven curing processes.

[0004] Autoclave technology applies temperature and pressure to prepreg blanks sealed in a vacuum bag using heated circulating air or nitrogen, causing the resin to crosslink and cure. This process can precisely ensure the fiber orientation and geometry of the product, and the porosity can be controlled below 2%. However, autoclave systems are large, complex in structure, and are pressure vessels, resulting in extremely high investment costs. Furthermore, each curing cycle requires a large amount of vacuum auxiliary materials and consumes significant amounts of water, electricity, and gas. Because autoclaves rely on air conduction for heating, they need to continuously heat thousands of cubic meters of circulating gas, leading to low thermal efficiency. For large, irregularly shaped, thin-walled components such as machine arm skins, the autoclave process also faces challenges in ensuring temperature field uniformity, and the equipment size limits product specifications.

[0005] Oven curing processes also present similar problems. Large ovens are expensive to build and maintain, have long heating cycles, and for large-sized products, it is difficult to guarantee the uniformity of the temperature field within the oven. Furthermore, oven curing lacks pressure assistance, often resulting in higher porosity in the product compared to autoclave processes, which negatively impacts mechanical properties.

[0006] To address the aforementioned issues, self-heating mold technology has emerged in recent years. Self-heating molds directly heat the mold and product through internal resistance heating elements and induction heating systems, avoiding the ineffective heating of large amounts of air in autoclaves and ovens, thus significantly improving thermal efficiency. However, existing self-heating mold technology still faces the following problems when applied to the manufacturing of machine arm skins: First, the skin on the robotic arm is large and complex in shape, and after installation, it typically needs to be transferred from the installation station to an autoclave or oven for curing. During transport, vacuum bags may be damaged by impacts, and molds may deform due to lifting and transportation, directly leading to product scrap. Second, controlling the temperature uniformity of self-heating molds under large-size, irregularly shaped curved surface conditions is a technical challenge. The skin on the robotic arm has complex curved shapes and variable cross-sectional characteristics, with significant differences in thickness and curvature in different areas, requiring different curing temperature fields. Existing self-heating molds struggle to achieve precise temperature control in different zones, affecting the curing quality and consistency of mechanical properties of the product. Summary of the Invention

[0007] The purpose of this application is to provide a self-heating in-situ curing molding method and system for the skin of a robotic arm. This application utilizes a self-heating mold whose surface matches the shape of the robotic arm skin, completing the application, motor ring embedding, encapsulation, and curing in the same station, achieving in-situ curing and avoiding vacuum bag damage and mold deformation caused by transportation. Simultaneously, the self-heating mold is directly heated by electricity, eliminating the need for an autoclave or oven, resulting in high heating efficiency, precise temperature control, and reduced manufacturing costs. By embedding the motor ring and reinforcing it with fabric during the application process, the connection strength and positional accuracy of the motor mounting interface are ensured.

[0008] To address the aforementioned technical problems, this application provides a self-heating in-situ curing molding method for a machine arm upper skin used for motor installation, comprising: S1, material preparation: checking that the remaining operating life and mechanical property life of the prepreg are both greater than 0 hours, thawing and cutting for later use; S2, mold preparation: using a self-heating mold and calibrating its temperature uniformity, cleaning the mold and applying a release agent, wherein the shape of the self-heating mold matches the shape of the machine arm upper skin; S3, installation: pre-embedding a motor ring during the installation process, pre-treating the motor ring and laying reinforcing fabric. Then, according to the layup requirements, the prepreg is laid layer by layer, removing air bubbles and smoothing wrinkles in each layer, and vacuum pre-compacting is performed according to the layer sequence; S4, Encapsulation: Auxiliary materials are laid and vacuum bags are made, vacuum is drawn to the required vacuum level and the pressure holding performance is tested; S5, Self-heating curing: The encapsulated mold and the product are heated by electricity to cure the skin on the machine arm in situ, and then cooled down after curing; S6, Demolding: Auxiliary materials and molds are removed, and the skin product on the machine arm is taken out; S7, Post-processing: The skin product on the machine arm is cut, trimmed, sealed, and its appearance quality is inspected. After passing the inspection, it is handed over.

[0009] This application also provides an integrated self-heating mold system for in-situ curing of a robot arm skin, the robot arm skin being used to mount a motor, comprising: a self-heating mold body with an integrated heating element for directly heating and curing the robot arm skin prepreg component laid on it; the mold's surface matching the shape of the robot arm skin, and the mold undergoing heating performance calibration before its first use to ensure temperature uniformity; a modular heat insulation layer detachably installed on the outside of the self-heating mold body to reduce heat loss during curing; a heat dissipation module installed on the self-heating mold body to assist in cooling the mold and product after curing; a vacuum sealing system including a vacuum bag film, vacuum pipelines, and multiple vacuum detection points for evacuating the laid robot arm skin component before curing and monitoring the vacuum level; and a temperature control system connected to the heating element and thermocouples arranged inside the mold and component to collect temperature data and control the curing process to operate according to a set heating-holding-cooling curve.

[0010] Optionally, the thawing time in S1 shall not be less than 8 hours, and the standard for completion of thawing is that no water droplets or water vapor condense after the outer packaging is wiped dry.

[0011] Optionally, when cutting the prepreg in S1, the angular deviation of the fiber direction of the unidirectional prepreg is controlled within ±2°, the angular deviation of the fiber direction of the fabric prepreg is controlled within ±3°, and the size deviation of the sheet is controlled within ±2.5mm.

[0012] Optionally, when applying the release agent in S2, the mold is first used or cleaned with a cleaning agent and the release agent is applied 5 times. After each part is demolded, the release agent is applied 3 times, with an interval of at least 15 minutes between each application. The next process is started at least 30 minutes after the last application.

[0013] Optionally, the vacuum pre-compaction described in S3 includes: after laying several layers, using vacuum pre-compaction auxiliary materials to assemble vacuum bags, controlling the vacuum degree between -100kPa and -80kPa, and maintaining the vacuum for no less than 15 minutes.

[0014] Optionally, after the last layer in S3 is laid, final compaction is performed, with the vacuum degree controlled between -100kPa and -85kPa, and the holding time not less than 1 hour, and the vacuum bag is evenly and symmetrically set with pleats.

[0015] Optionally, the auxiliary materials mentioned in S4 are laid in the following order: release cloth, non-porous release film, pressure equalizing plate, breathable felt and vacuum bag film. The pressure equalizing plate is smaller than the material sheet size and has a margin of 5mm to 50mm on all sides and is placed in the center, and is cured together in the vacuum bag.

[0016] Optionally, the vacuum degree mentioned in S4 is -100kPa to -85kPa, and the pressure holding test standard is that the vacuum degree decay is no more than 5kPa within 15 minutes. If the standard is exceeded, the leak point should be checked and filled with sealing strips, and the test should be repeated.

[0017] Optionally, the heating element of the self-heating mold body is a resistance heating element or an induction heating element.

[0018] Optionally, the curing curve set by the temperature control system is to keep the temperature at 80°C for 2 hours and then at 120°C for 2 hours.

[0019] Optionally, the modular insulation layer is removed after curing and when the product temperature drops below 40°C.

[0020] Optionally, the vacuum sealing system also includes a yellow sealing strip for filling and repairing leaks when the vacuum level deteriorates excessively.

[0021] Optionally, the vacuum detection points are distributed at different locations inside the vacuum bag membrane, and the vacuum sealing system performs independent pressure monitoring on each detection point.

[0022] Optionally, the self-heating mold body is provided with mold markings and engravings for confirming the position and orientation reference during installation.

[0023] This application employs a self-heating mold whose surface matches the shape of the upper skin of the robotic arm, integrating the heating element inside the mold so that heat can be directly conducted from the mold to the prepreg component laid on it. Lamination, motor ring embedding, encapsulation, curing, and demolding are all completed at the lamination station, eliminating the need to transfer the encapsulated product from the lamination station to an autoclave or oven, fundamentally avoiding risks such as vacuum bag breakage, mold deformation, and motor ring displacement during transportation.

[0024] Pre-embedded motor rings and reinforced fabric during the installation process ensure a reliable connection between the motor mounting interface and the composite material skin. Vacuum bag packaging provides pressure and a vacuum environment during curing, ensuring dense layering and eliminating air bubbles. Modular insulation layers reduce heat loss during curing, improving thermal efficiency. Heat dissipation modules accelerate the cooling process after curing, shortening the production cycle. A temperature control system precisely controls the entire process of heating, heat preservation, and cooling, ensuring precise and controllable curing.

[0025] Compared to autoclave curing, this application eliminates the need for large pressure vessels and complex auxiliary equipment, significantly reducing investment costs. Compared to oven curing, this application offers higher heating efficiency and more precise temperature field control. Furthermore, in-situ curing eliminates the need for transfer, reducing production cycles and operational risks, making it particularly suitable for manufacturing large-sized, irregularly shaped curved skin components for machine arms.

[0026] Compared with the prior art, this application has the following beneficial effects: First, this application achieves curing directly at the installation station using a self-heating mold, eliminating the need to transfer the product from the installation station to an autoclave or oven. This fundamentally avoids problems such as vacuum bag breakage, mold deformation, and motor ring displacement during transportation, ensuring product manufacturing quality and motor installation accuracy.

[0027] Secondly, this application integrates the installation, motor ring pre-embedding, encapsulation, curing, and demolding into the same workstation, reducing intermediate steps and human intervention factors, making the manufacturing process more controllable, and contributing to product quality stability and traceability.

[0028] Third, this application eliminates the need to invest in and construct large autoclaves or ovens, and also avoids the consumption of large amounts of energy to heat the air medium. The self-heating mold directly heats the product, resulting in high thermal efficiency and significantly reduced energy consumption. Simultaneously, in-situ curing reduces the repeated consumption of auxiliary materials and labor costs.

[0029] Fourth, this application ensures the uniformity of the temperature field and the stability of the vacuum degree during the curing process by pre-calibrating the heating performance of the mold, multi-point vacuum detection, and multi-point temperature monitoring, which is conducive to improving the curing quality and mechanical property consistency of the product.

[0030] Fifth, this application completes the pre-embedding and reinforcement of the motor ring during the installation process, ensuring a firm connection between the motor mounting interface and the skin structure, and avoiding damage to the skin structure during post-processing and installation.

[0031] Sixth, the technical solution of this application is applicable to skin parts on machine arms of various sizes and shapes, and is not limited by the size of autoclaves or ovens, thus having strong adaptability. Attached Figure Description

[0032] Figure 1 The diagram shows a flow chart of the self-heating in-situ curing molding method for the skin on the machine arm according to an embodiment of this application. Figure 2 The diagram shows a detailed flow chart of the tiling process in an embodiment of this application. Figure 3 The diagram shown is a schematic representation of the integrated self-heating mold system according to an embodiment of this application. Detailed Implementation

[0033] The following embodiments further illustrate the technical solutions of this application. It should be understood that the specific embodiments described herein are merely for explaining this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not all of them.

[0034] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0035] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0036] The present application will be further described in detail below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application. All technical solutions implemented based on the above content of the present application fall within the scope of protection claimed in this application.

[0037] This application uses the upper arm skin of a certain type of vertical takeoff and landing aircraft as an example to describe in detail the specific implementation process of the self-heating in-situ curing molding method for the upper arm skin described in this application. The upper arm skin is an irregular curved thin-walled structure used to support the motor and provide an aerodynamic shape.

[0038] like Figure 1 As shown, the self-heating in-situ curing molding method for the skin on the machine arm according to an embodiment of this application includes the following steps: S1: Material preparation: Check that the remaining operating life and mechanical property life of the prepreg are both greater than 0h, and cut it for later use after thawing.

[0039] Specifically, the carbon fiber fabric prepreg was removed from a -18°C freezing environment. This prepreg is an epoxy resin system, with a single-layer thickness of 0.22 mm, a width of 1.2 m, and a resin content of 38% ± 2%. The material label was checked to confirm the completeness of the batch number, production date, and expiration date information. The remaining operating life of this batch of material was found to be 96 hours, and the remaining mechanical property life was 480 hours, both greater than 0 hours, meeting the usage requirements.

[0040] The materials were placed in a thawing area outside the installation room, with the ambient temperature controlled at 22±2℃ and relative humidity at 45%. Thawing began at 8:00 AM. The prepreg rolls were placed horizontally on the thawing rack, with a minimum spacing of 50mm between each roll to ensure air circulation. During the thawing process, a designated person inspected the outer packaging every 2 hours to check for condensation. At 4:00 PM, 8 hours after thawing, the outer packaging was checked and found to be free of condensation. The outer packaging was then wiped dry with a clean, dry cloth to confirm thawing was complete. The outer packaging was not opened or damaged throughout the entire thawing process, and the packaging bags remained intact and undamaged.

[0041] The prepreg was cut using an automatic fabric cutting machine. Based on the product layup design, the layup specifications were [±45, 0 / 90]2 core material / [0 / 90, ±45]2, totaling 8 layers of carbon fiber prepreg, plus 4 layers for local reinforcement around the motor ring. The cutting program was set with cutting parameters for each layer according to the layup sequence.

[0042] During the cutting process, operators check the alignment of the roll length edge with the machine's 0° line, and use an angle gauge to measure the fiber direction deviation. The maximum measured deviation is +1.2°, controlled within ±2°. Vernier calipers are used to randomly check the sheet size; the maximum measured deviation is +1.0mm, controlled within ±2.5mm. The cut sheets are bagged according to the layup sequence. In one embodiment, the outer label of the bag indicates the part name as "Upper Arm Skin," the part number as "QB-2024-01," and the layup numbers as "L1" to "L8" and "R1" to "R4" (reinforcing layers). All sheets are transferred to the laying station at 17:00 on the same day, with laying scheduled to begin at 9:00 the following morning, with an interval of 16 hours, within the 48-hour validity period.

[0043] S2: Mold preparation: Use a self-heating mold and calibrate the temperature uniformity. After cleaning the mold, apply a release agent. The shape of the self-heating mold matches the shape of the skin on the machine arm.

[0044] This embodiment employs a resistance-heated self-heating mold. The mold's shape matches the outer skin of the machine arm, and the material is Invar alloy, which has a thermal expansion coefficient similar to that of carbon fiber composite materials. Resistance heating wires are embedded inside the mold, arranged in a serpentine pattern along the mold's surface, with a heating power of 15kW. The mold dimensions are 3.0m × 0.8m, and it weighs approximately 85kg.

[0045] This mold is being used for the first time and requires heating performance calibration. The calibration procedure is as follows: 12 temperature measuring points are evenly arranged on the mold surface, and surface thermocouples are attached to each measuring point. In this embodiment, K-type thermocouples are used as the temperature measuring elements. The target heating temperature is set to 80℃, and after power-on heating, it is maintained for 30 minutes. A multi-channel temperature recorder is used to collect temperature data at each point. The calibration results show that the temperature distribution of the 12 measuring points is from 79.2℃ to 81.0℃, with a maximum temperature difference of 1.8℃, meeting the temperature uniformity requirements. Supplementary calibration is performed during the 120℃ holding stage, and the temperature deviation at each point does not exceed ±2.0℃. The calibration data is recorded in the mold file for future reference.

[0046] Confirm that the mold markings and engravings are complete and clear. The 0° baseline, ±45° direction lines, and outlines of each layer are laser-etched onto the mold surface. Use a white cotton cloth dampened with acetone cleaner and a plastic scraper to remove any residual protective grease from the mold surface, then vacuum up any particles. Use masking tape to isolate and protect the sealant strip along the edge of the mold, preventing mold release agent from contaminating the sealant strip area.

[0047] The application of the release agent is carried out in a dedicated application room outside the tiling room. Operators wear masks to protect against organic vapors, nitrile gloves, and safety goggles. This example involves the mold's first use, requiring five coats of release agent. A water-based semi-permanent release agent is used, applied evenly to the mold surface with a clean cotton cloth. Each coat is applied 15 minutes apart, strictly timed by a timer. After the final coat, the mold is left to stand for 30 minutes. Visual inspection confirms that the release agent coating on the mold surface is uniform, without drips or missed areas. For areas with localized depressions on the mold surface where application is difficult, fluorinated release cloth with adhesive backing is used for supplementary application. The coated mold is then covered with polyethylene film and placed at the tiling station for later use.

[0048] S3: Laying: During the laying process, the motor ring is pre-embedded, the motor ring is pre-treated and reinforced with fabric, and then the prepreg is laid layer by layer according to the laying requirements. Each layer removes air bubbles, sorts out wrinkles, and vacuum pre-compacts according to the layer sequence.

[0049] Specifically, such as Figure 2 As shown, first, before laying the product, proceed with S31: Preparation of auxiliary materials. The auxiliary materials for vacuum pre-compression include porous release film, release cloth, breathable felt, and vacuum bag film. The auxiliary materials for vacuum curing include release cloth, non-porous release film, breathable felt, and vacuum bag film. These materials are cut to the area of ​​the part to be laid, and the vacuum bag film size needs to be calculated based on the mold size before cutting to ensure complete coverage of the product and mold edges, with allowance for pleating.

[0050] The sealing strip used is a medium-temperature vacuum sealing strip, 12mm wide, with a temperature resistance of 150℃. The vacuum pipeline uses nylon tubing with an inner diameter of 10mm and is equipped with four vacuum quick-connect suction cups. After the auxiliary materials are prepared, proceed to S32: Pre-laying inspection: The environmental parameters of the laying station are temperature 23.5℃ and humidity 42%, which meet the process requirements of temperature 22±4℃ and humidity ≤60%, and are recorded in the laying record sheet; the measuring instruments are checked, including thermometer, hygrometer, vacuum gauge and thermocouple thermometer, all within the calibration validity period. Material life is rechecked to confirm that the remaining operating life of the prepreg is 82 hours (greater than 0 hours) and the remaining mechanical property life is 475 hours (greater than 0 hours) before the start of laying; the mold is checked to confirm that the self-heating function is normal, the insulation resistance of the heating element is greater than 10MΩ, and all matching mold parts, such as movable blocks and positioning pins, are complete and installed in place. The laying operation is carried out in a clean laying room, and the operators wear clean clothing, gloves and anti-static shoes.

[0051] After the pre-layout inspection is completed, proceed to S33: Layup process. The layup process specifically includes: first, pre-embedding the motor rings. This product requires pre-embedding four motor rings (corresponding to four motor mounting points). In one embodiment, the motor rings are made of aluminum alloy, with an outer diameter of 220mm, an inner diameter of 192mm, and a height of 7mm. The surface is sandblasted to enhance adhesion to the composite material. The motor rings are precisely placed at the designated positions on the mold surface and temporarily fixed using clamps. A reinforcing layer is then laid around the motor rings: four additional layers of carbon fiber prepreg are laid on each motor ring, layer by layer, compacted to ensure a reliable load transfer path between the motor rings and the skin layup.

[0052] After the motor ring reinforcement is completed, the prepreg is laid layer by layer according to the layup order. The layup order is: L1 layer [+45], L2 layer [-45], L3 layer [0 / 90], L4 layer [0 / 90], motor ring and reinforcement layer, L5 layer [0 / 90], L6 layer [0 / 90], L7 layer [-45], L8 layer [+45]. After each layer is laid, use an angle gauge to check the consistency between the fiber direction and the angle on the layup surface, and control the deviation within +1.0°. Use a scraper and a blower (hot air temperature of about 50℃) to remove air bubbles and smooth wrinkles along the fiber direction from the center to the edge. During the laying process, the backing release paper is retained. After each layer is laid, it is immediately removed and counted. After the laying is completed, the number of release papers is checked to ensure that the number of release papers for the 8 main layers and 4 reinforcement layers are completely matched and there is no release paper mixed in.

[0053] Vacuum pre-compaction is performed after every four layers: a vacuum bag is made using a porous release film, release cloth, breathable felt, and vacuum bag film. The vacuum pump is turned on to evacuate to -92 kPa and maintained for 15 minutes. The operator visually inspects the layer status inside the vacuum bag through the observation window to confirm that there are no abnormalities. After 15 minutes, the vacuum is released, the auxiliary materials are removed, and the next set of layers is laid.

[0054] After the final layer is laid, remove the base plate and perform final compaction: Use the curing auxiliary materials (release cloth, non-porous release film, pressure equalizing plate, breathable felt, vacuum bag film) to make a vacuum bag. Evenly distribute pleats along the edge of the mold in the vacuum bag, with a pleat spacing of approximately 150mm and a pleat depth of approximately 50mm. Turn on the vacuum pump to evacuate to -90kPa and maintain this position for 1 hour.

[0055] S4: Packaging: Lay out auxiliary materials and make a vacuum bag, evacuate to the required vacuum level and test the pressure holding performance.

[0056] Place a part label in the upper left corner of the test panel. The label should include the part name "Upper Arm Skin", part number "QB-2024-01", the date of application, and the operator's number.

[0057] Apply a layer of high-temperature tape (25mm wide, 180℃ resistant) to the bottom edge of the topmost sheet as a reference edge for cutting and trimming.

[0058] Lay out the curing auxiliary materials in the following order: First, cover the surface of the layer with a release cloth and gently smooth it with a soft scraper to ensure good adhesion between the release cloth and the surface of the layer. Then cover with a non-porous release film, extending approximately 50mm beyond the release cloth on all four sides. Place the pressure equalizing plate in the center above the material sheet, with an allowance of approximately 50mm on all four sides. Next, cover with a breathable felt, extending approximately 100mm beyond the pressure equalizing plate on all four sides. Finally, cover with a vacuum bag film, cut to 4.2m × 1.5m according to the mold size, ensuring complete coverage of the mold edges and leaving allowance for pleats. Use sealing strips to adhere the vacuum bag film to the edge of the mold, forming a closed sealing ring around the mold.

[0059] During the encapsulation process, four vacuum detection points are arranged at the four corners of the mold, and vacuum tubes are embedded to connect each detection point. Four K-type thermocouples are embedded inside the layup (2) and on the mold surface (2) for real-time temperature monitoring.

[0060] The vacuum pump was turned on to create a vacuum. After 15 minutes, the pressure values ​​at the four testing points were -92 kPa, -91 kPa, -90 kPa, and -92 kPa, respectively, all meeting the requirement of -100 kPa to -85 kPa. The vacuum pump was then turned off, and a pressure holding test was initiated. After 15 minutes, the test was repeated, and the pressure values ​​at the four testing points were -90 kPa, -89 kPa, -88 kPa, and -90 kPa, respectively, with attenuation values ​​of 2 kPa, 2 kPa, 2 kPa, and 2 kPa, respectively, all not exceeding 5 kPa, indicating that the pressure holding performance was qualified. All test data were recorded in the packaging record table.

[0061] S5: Self-heating curing: The packaged mold and the product are heated by electricity to cure the skin on the machine arm in situ, and then cooled down after curing.

[0062] Before curing begins, the following conditions must be met: the tiling is completed at 17:00 in the afternoon, the remaining working life is 76 hours (>0 hours); the remaining mechanical performance life before heating is turned on is 472 hours (>0 hours).

[0063] Connect the vacuum tubing to the vacuum pump, and connect the thermocouple to the multi-channel temperature acquisition module of the temperature control system. Perform vacuum level testing again; the results are the same as in the packaging stage, meeting the requirements.

[0064] Assemble the modular insulation layer: Wrap the nano-aerogel felt (25mm thick, covered with a polyimide film) around the outer surface of the mold and secure it with heat-resistant tape. The insulation layer consists of 6 independent modules, each corresponding to one of the 6 areas of the mold, facilitating installation and removal. Install the heat dissipation module: Install the aluminum heat sink fins on the back of the mold, and connect the cooling fan to the control system.

[0065] Set the curing parameters. The temperature control system is a PID control type. The operator inputs the following on the control panel: Increase the temperature from room temperature to 80°C at a rate of 2°C / minute, hold at 80°C for 120 minutes; then increase the temperature from 80°C to 120°C at a rate of 1.5°C / minute, hold at 120°C for 120 minutes. After the holding period, turn off the heating power and start the cooling fan to assist in cooling. After confirming the curing curve is correct, start the heating curing program.

[0066] During the curing process, the temperature control system displays the temperature and time at each measuring point in real time. During the 80℃ holding stage, the four thermocouples displayed temperatures of 79.5℃, 80.2℃, 80.0℃, and 80.3℃, with a maximum deviation of 0.8℃. During the 120℃ holding stage, the displayed temperatures were 119.3℃, 120.1℃, 119.8℃, and 120.2℃, with a maximum deviation of 0.9℃. The vacuum level remained stable between -90kPa and -88kPa throughout the process. All data from the curing process were automatically recorded by the control system, generating a curing curve report.

[0067] When the product temperature drops to 38℃ with the help of the heat dissipation module, the system automatically terminates the program and issues a prompt sound. The operator then opens the heat insulation layer to allow the product to cool naturally on the mold.

[0068] S6: Demolding: Remove auxiliary materials and molds, and take out the skin product from the machine arm.

[0069] The product temperature naturally drops to room temperature (25℃). The insulation and heat dissipation modules are removed, and the mold and product are returned to their laid-out state. Operators sequentially remove the vacuum bag film, breathable felt, non-porous release film, release cloth, and sealing strip from the product surface, collecting and disposing of all auxiliary materials separately. The four thermocouples and vacuum connectors are removed, wiped clean with a lint-free cloth, and placed in their designated locations.

[0070] Using nylon release wedges (HRC55 hardness, 2mm thickness), gradually insert them along the seam between the product edge and the mold. Start from one end of the product, inserting one wedge every 200mm along its length, and gently pry to separate the product from the mold. Due to the good effect of the release agent, the adhesion between the product and the mold is relatively small, and the entire demolding operation is completed in about 15 minutes. Remove the complete skin product from the machine arm and place it on a special bracket. Clean the small amount of residual adhesive on the mold surface using a plastic scraper and acetone cleaner, preparing for the next product.

[0071] S7: Post-processing: Cut, trim, seal, and inspect the appearance quality of the skin products on the machine arm. After passing the inspection, they are handed over.

[0072] Specifically, the first step is a cutting and trimming process. In this process, CNC waterjet cutting equipment is used to cut along the product's design lines. After inputting the product's 3D model, the cutting path includes the outline and four elliptical ventilation holes measuring 80mm × 40mm. The waterjet cutting pressure is set to 380MPa, and the cutting speed is 1.2m / min. After cutting, compressed air is used to blow away dust and cutting residue from the product surface. Then, tweezers and a soft scraper are used to carefully remove any remaining release fabric fibers from the product surface. Careful observation is required during this process to avoid damaging the carbon fiber surface.

[0073] Next, edge sealing is performed. A lint-free cloth dampened with industrial alcohol (99.5% purity) is used to clean the cut edges to be sealed, wiping a width of approximately 20mm. The alcohol is then wiped dry with a clean cloth, and finally dried with a hairdryer on a cool setting to ensure no residual moisture or alcohol remains. A 12mm wide, 80℃ heat-resistant protective tape is used to protect the surface fibers of the area to be sealed, extending 5mm on each side, facilitating cleaning after sealing. The epoxy edge sealing adhesive is prepared. In this embodiment, a two-component epoxy adhesive is used, with a weight ratio of component A to component B of 100:30. 50g of component A and 15g of component B are weighed using an electronic scale and thoroughly stirred in a mixing cup for 3 minutes until the color is uniform. The mixing time and quantity are recorded in the edge sealing record sheet. Apply the sealing adhesive evenly along the cut edge using a fine brush, with a width of about 3mm and a thickness of 0.3-0.5mm. After application, allow it to cure at room temperature for 24 hours. Once cured, lightly sand the sealing surface with 800-grit sandpaper to remove any excess adhesive nodules. Weigh the product after completion; in this example, the weight is recorded as 2.85kg.

[0074] Visual quality inspection is carried out under a standard light source with an illuminance of no less than 1000 lux, and the surface quality of the product is comprehensively inspected by visual observation. Lean resin area inspection verifies that the resin covers all areas of the product surface uniformly, and there is no lean resin area with exposed fibers; fiber defect inspection verifies that there are no defects such as fiber wrinkles, creases, cracks and scratches on the product surface, the surface is smooth and flat, and the fiber texture is clear and continuous; release cloth inspection verifies that the release cloth is completely peeled off without residual breakage; porosity and dry spot inspection are observed under strong light transmission to verify that the product is free of dry spots and surface pores, and the surface is dense without visible air holes; rich resin inspection verifies that there is no rich resin accumulation area on the product surface, and the resin is distributed uniformly; fiber deformation inspection verifies that the fiber direction of all plies meets the design requirements, there is no fiber twist deformation, and the edges of the four oval ventilation holes are neat without delamination. After all inspection items are qualified, the visual quality of the product is judged as qualified.

[0075] After the visual quality inspection is qualified, the Quality Department is requested to conduct quality inspection. The Quality Department has carried out three tests on the product: dimension inspection uses a coordinate measuring machine to inspect the overall dimension and the position of the ventilation holes, all of which are qualified; ultrasonic non-destructive testing uses water-immersion ultrasonic C-scan to inspect the internal quality, and there are no delamination and porosity defects; motor ring position inspection uses industrial CT to inspect the position accuracy of the four motor rings, with a maximum deviation of 0.15mm, which meets the design tolerance requirement of ±0.5mm. After all inspections are qualified, the Quality Department issues a qualification certificate, the product number is "QB-2024-01-001", and the product is transferred to the composite material assembly workshop together with quality documents such as laying records, curing curves, and inspection reports.

[0076] The embodiment of the present application further provides an integrated self-heating mold system for in-situ curing and forming of the upper skin of a machine arm, as shown in Figure 3 the self-heating mold system includes a self-heating mold body 101, a modular heat insulation layer 102, a heat dissipation module 103, a vacuum encapsulation system 104 and a temperature control system 105.

[0077] The self-heating mold body 101 integrates a heating element for directly heating and curing the prepreg material for the machine arm skin laid on it. The shape of the self-heating mold body 101 matches the shape of the machine arm skin, ensuring good adhesion between the prepreg and the mold surface during the laying process and guaranteeing the product's shape accuracy. Before first use, the mold body 101 needs to undergo heating performance calibration to ensure temperature uniformity. The calibration method involves evenly arranging multiple temperature measuring points on the mold surface, heating to the target temperature and holding at that temperature, collecting temperature data at each point using a multi-channel temperature recorder, calculating the temperature deviation, and adjusting the heating power or performing compensatory heating accordingly until the temperature deviation at all measuring points is controlled within ±2℃. The heating element can be a resistance heating element or an induction heating element. Resistance heating elements achieve heating by embedding resistance wires or heating tubes inside the mold, and are suitable for mold surfaces with relatively simple structures. Induction heating elements use an induction coil inside the mold to heat the mold itself using an alternating magnetic field, and are suitable for applications requiring a high heating rate. Operators can select the appropriate type of heating element based on the size, shape, and curing process requirements of the skin on the machine arm.

[0078] The modular insulation layer 102 is detachably installed on the outside of the self-heating mold body 101 to reduce heat loss during curing, improve thermal efficiency, and enhance temperature field uniformity. The insulation layer 102 can be made of low thermal conductivity materials such as nano-aerogel felt, polyurethane foam, or glass wool, preferably a composite aerogel and glass fiber felt with a thermal conductivity not exceeding 0.02 W / (m·K) and a thickness of 20 mm to 40 mm. It is covered with a polyimide film or aluminum foil to prevent dust contamination and enhance tensile strength. The insulation layer 102 is divided into multiple independent modules, each corresponding to a different area of ​​the mold body 101. Each module has an overlapping edge with a width of not less than 30 mm to ensure complete coverage and prevent thermal short-circuit paths. The insulation layer 102 can only be removed after curing and when the product temperature drops below 40°C to avoid excessively rapid cooling that could cause internal thermal stress.

[0079] The heat dissipation module 103 is installed on the self-heating mold body 101 to assist in cooling the mold and product after curing. The heat dissipation module 103 can be either air-cooled or water-cooled: An air-cooled heat dissipation module includes an aluminum or copper heat sink fin assembly and a forced convection fan. The heat sink fins are tightly attached to the back of the mold body 101 using thermal grease or thermal pads. After curing, the fan is activated to force heat dissipation, with a cooling rate of 1℃ / min to 3℃ / min. A water-cooled heat dissipation module includes cooling pipes embedded inside the mold and an external cooling water circulation system. The cooling pipes are evenly arranged along the mold surface. After curing, circulating cooling water is introduced for heat exchange. The activation timing of the heat dissipation module 103 is automatically determined by the temperature control system 105 based on the product temperature feedback from the thermocouple. It activates when the product temperature drops to a set threshold, avoiding the lag and uncertainty of manual operation.

[0080] The vacuum sealing system 104 includes a vacuum bag film, vacuum tubing, and vacuum detection points. It is used to evacuate and monitor the vacuum level of the skin on the machine arm before curing. The vacuum bag film is a heat-resistant nylon composite film with a thickness of 0.06mm to 0.08mm, capable of withstanding curing temperatures above 150℃. Its dimensions are cut to size according to the mold dimensions, allowing for pleating allowances. The vacuum tubing uses nylon tubing or stainless steel braided flexible tubing with an inner diameter of 8mm to 12mm. Quick-connect fittings are used at the tubing connections for easy assembly and disassembly. Multiple vacuum detection points are used, preferably 4 to 8, distributed at different locations within the vacuum bag film. A typical arrangement is one at each of the four corners of the mold and one in the middle of each long side. Each detection point is monitored in real time by an independent vacuum gauge or pressure sensor. The vacuum sealing system 104 independently monitors the pressure at each detection point. Operators can use the pressure readings at each point to determine whether the pressure distribution within the vacuum bag is uniform, avoiding the problem of undetected localized vacuum deficiencies or leaks that may occur with single-point detection. The system also includes a yellow sealing strip, which is 6mm to 12mm wide and can withstand temperatures of no less than 150℃. It is used to fill and repair leaks when the vacuum level deteriorates beyond the standard. Its yellow appearance makes it easy to quickly identify the location of leaks on the vacuum bag film.

[0081] The temperature control system 105 connects the heating element and thermocouples arranged inside the mold and the part. It collects temperature data and controls the curing process to operate according to the set heating-holding-cooling curve. The temperature control system 105 employs a PID closed-loop control algorithm. By comparing the deviation between the actual temperature value detected by each thermocouple and the set temperature value in real time, it calculates the output control quantity and adjusts the power supply of each heating zone to ensure that the actual temperature accurately tracks the set curve. For large-size molds, the temperature control system 105 further adopts a zoned independent control scheme, dividing the mold into multiple heating zones. Each zone is independently equipped with heating elements and temperature-measuring thermocouples to adapt to the different heating requirements caused by differences in thickness and curvature at different locations on the machine arm's skin. The temperature control system 105 is equipped with an industrial touchscreen as a human-machine interface. It can set and store multiple sets of curing process curves, display the temperature-time curves and vacuum-time curves of each temperature measurement point in real time, automatically save the curing process data to the storage medium, and export it as a report file after curing for quality traceability and process analysis. The temperature control system 105 also has over-temperature alarm and power failure protection functions. When the temperature at any temperature measuring point exceeds the set value by ±5℃, the system will automatically alarm and stop heating to prevent product scrapping or safety accidents caused by temperature runaway.

[0082] During the layup operation, the operator confirms the position and orientation reference of the layup based on the mold markings and scribe lines on the mold body 101. The mold markings include the part name, part number, and layup orientation mark. The mold scribe lines include the 0° reference line, ±45° direction lines, and the outline of each layup. The operator ensures the fiber orientation of each layup is accurate by aligning the edge of the prepreg with the scribe lines.

[0083] The self-heating mold system described above is used for the curing and molding of the skin on the robotic arm. Laying, sealing, curing, and demolding are all completed at the laying station. This system can improve heating efficiency by approximately 60% compared to traditional autoclave processes. The product curing quality meets aerospace-grade requirements, the motor ring position deviation is controlled within ±0.3mm, and the product porosity is less than 1.5%. It is suitable for manufacturing various large-sized, irregularly shaped, curved composite material structural parts.

[0084] The above embodiments are merely illustrative of the principles and effects of this application. Any person skilled in the art can modify or alter the above embodiments without departing from the purpose of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the purpose disclosed in this application should still be covered by the claims of this application.

Claims

1. A self-heating in-situ curing molding method for a machine arm upper skin, wherein the machine arm upper skin is used to install a motor, characterized in that, include: S1, Material preparation: Check that the remaining operating life and mechanical property life of the prepreg are both greater than 0h, and cut it after thawing for later use. S2, Mold Preparation: A self-heating mold is used and its temperature uniformity is calibrated. After cleaning the mold, a release agent is applied. The shape of the self-heating mold matches the shape of the skin on the machine arm. S3, Laying: During the laying process, a motor ring is pre-embedded. The motor ring is pre-treated and reinforced with fabric. Then, prepreg is laid layer by layer according to the layup requirements. Each layer is cleaned of air bubbles and wrinkles, and vacuum pre-compacted according to the layer sequence. S4, Encapsulation: Auxiliary materials are laid and a vacuum bag is made. Vacuum is drawn to the required vacuum level and the pressure holding capacity is tested. S5, Self-Heating Curing: The encapsulated mold and the product are heated by electricity to cure the skin on the machine arm in situ. After curing, the temperature is lowered. S6, Demolding: Auxiliary materials and the mold are removed, and the skin product on the machine arm is taken out. S7, Post-processing: The skin product on the machine arm is cut, trimmed, sealed, and its appearance quality is inspected. After passing inspection, it is handed over.

2. The self-heating in-situ curing molding method for the skin of the machine arm according to claim 1, characterized in that, The thawing time for S1 is no less than 8 hours. The standard for complete thawing is that no water droplets or moisture condense on the outer packaging after wiping it dry.

3. The self-heating in-situ curing molding method for the skin of the machine arm according to claim 1, characterized in that, When cutting prepreg in S1, the angular deviation of the fiber direction of the unidirectional prepreg is controlled within ±2°, the angular deviation of the fiber direction of the fabric prepreg is controlled within ±3°, and the size deviation of the sheet is controlled within ±2.5mm.

4. The self-heating in-situ curing molding method for the skin on the machine arm according to claim 1, characterized in that, When applying the release agent in S2, apply 5 coats of release agent to the mold used for the first time or after cleaning with a cleaning agent. After each subsequent part is demolded, apply 3 coats of release agent, with an interval of at least 15 minutes between each coat. After the last coat is applied, wait at least 30 minutes before proceeding to the next process.

5. The self-heating in-situ curing molding method for the skin of a machine arm according to claim 1, characterized in that, The vacuum pre-compaction described in S3 includes: after laying several layers, using vacuum pre-compaction auxiliary materials to assemble vacuum bags, controlling the vacuum degree between -100kPa and -80kPa, and maintaining it for no less than 15 minutes.

6. The self-heating in-situ curing molding method for the skin on the machine arm according to claim 1, characterized in that, After the last layer of S3 is laid, final compaction is carried out, and the vacuum degree is controlled between -100kPa and -85kPa, and the holding time is not less than 1 hour. The vacuum bag is evenly and symmetrically set with pleats.

7. The self-heating in-situ curing molding method for the skin of a machine arm according to claim 1, characterized in that, The auxiliary materials described in S4 are laid in the following order: release cloth, non-porous release film, pressure equalizing plate, breathable felt and vacuum bag film. The pressure equalizing plate is smaller than the material sheet size and has a margin of 5mm to 50mm on all sides. It is placed in the center and cured together in the vacuum bag.

8. The self-heating in-situ curing molding method for the skin of a machine arm according to claim 1, characterized in that, The vacuum degree mentioned in S4 is -100kPa to -85kPa. The pressure holding test standard is that the vacuum degree decay should not be greater than 5kPa within 15 minutes. If it exceeds the standard, check for leaks and fill them with sealing strips before repeating the test.

9. An integrated self-heating mold system for in-situ curing and molding of a machine arm upper skin, wherein the machine arm upper skin is used to mount a motor, characterized in that, include: The self-heating mold body integrates a heating element for directly heating and curing the prepreg material of the machine arm skin laid on it. The mold surface matches the shape of the machine arm skin, and the mold is calibrated for heating performance before first use to ensure temperature uniformity. A modular heat insulation layer is detachably installed on the outside of the self-heating mold body to reduce heat loss during the curing process. A heat dissipation module, installed on the self-heating mold body, is used to assist in cooling the mold and product after curing; a vacuum sealing system, including a vacuum bag film, vacuum pipeline and multiple vacuum detection points, is used to evacuate the skin part on the laid arm before curing and monitor the vacuum degree; a temperature control system, connected to the heating element and thermocouples arranged inside the mold and part, is used to collect temperature data and control the curing process to run according to the set heating-holding-cooling curve.

10. The integrated self-heating mold system for in-situ curing and molding of the upper skin of a machine arm according to claim 9, characterized in that, The heating element of the self-heating mold body is a resistance heating element or an induction heating element.

11. The integrated self-heating mold system for in-situ curing and molding of the upper skin of a machine arm according to claim 9, characterized in that, The curing curve set by the temperature control system is to keep the temperature at 80°C for 2 hours and then at 120°C for 2 hours.

12. The integrated self-heating mold system for in-situ curing and molding of the upper skin of a machine arm according to claim 9, characterized in that, The modular insulation layer is removed after curing and when the product temperature drops below 40°C.

13. The integrated self-heating mold system for in-situ curing and molding of the upper skin of a machine arm according to claim 9, characterized in that, The vacuum sealing system also includes a yellow sealing strip, which is used to fill and repair leaks when the vacuum level deteriorates beyond the standard.

14. The integrated self-heating mold system for in-situ curing and molding of the upper skin of a machine arm according to claim 9, characterized in that, The vacuum detection points are distributed at different locations inside the vacuum bag membrane, and the vacuum sealing system independently monitors the pressure at each detection point.

15. The integrated self-heating mold system for in-situ curing and molding of the upper skin of a machine arm according to claim 9, characterized in that, The self-heating mold body is provided with mold markings and engravings for confirming the position and orientation reference during installation.

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