1. Detailed explanation of carbon fiber hot press tank process

Um processo de fabrico avançado que utiliza um recipiente de pressão selado (tanque de prensagem a quente) para aplicar um ambiente controlável de alta temperatura, alta pressão e vácuo ao pré-impregnado de fibra de carbono (fibras de resina pré-impregnadas) colocado num molde, permitindo-lhe solidificar e formar peças compostas de elevado desempenho

2. Overview of Carbon Fiber Hot Pot Process

The hot press can process is the mainstream method for manufacturing high-performance, high-precision, and complex structured carbon fiber composite components. It achieves uniform heat distribution, high pressure (gas pressure), and vacuum negative pressure environment provided by the hot press tank

3. Characteristics of Hot Pot Process

High pressure and uniform pressure: High pressure gas (usually compressed air or nitrogen, with a pressure of several MPa or even higher) is evenly applied to the vacuum bag from all directions

The key to achieving high fiber volume content and low porosity is to achieve uniform compaction of the layer. Superior to vacuum bag pressing process relying solely on atmospheric pressure

Uniform heating: The hot air circulation or heater inside the hot press tank provides a highly uniform temperature field, ensuring synchronous curing of the entire component (especially large complex parts), reducing thermal stress deformation and internal stress

4. Process flow of carbon fiber hot press tank

1. Material Preparation

Pre impregnated material selection and cutting: Select the appropriate carbon fiber pre impregnated material (resin type, fiber type, surface density, layer direction) according to design requirements. Use automatic cutting machines or manual precision cutting to achieve the desired shape and angle

Preparation of auxiliary materials: Prepare corresponding sizes and types of vacuum bag film, breathable felt, release cloth, release film, sealing strip, vacuum joint, pressure-sensitive tape, etc

2. Mold Design and Preparation

Mold design: Consider the shape, dimensional accuracy, thermal expansion coefficient matching, stiffness, strength (to withstand high pressure), demolding method, heating efficiency, sealing, etc. of the workpiece. Common materials include steel, Invar (low expansion alloy), composite material molds, or silicone rubber soft molds

Mold cleaning and release agent coating: Thoroughly clean the surface of the mold to ensure that there is no grease or dust. Apply (spray or wipe) high-temperature release agent (such as wax or semi permanent release agent) evenly on the working surface of the mold to form an isolation layer

Sometimes use release cloth to lay on the surface of the mold

3. Lay up

Laying pre impregnated material: Accurately lay the cut pre impregnated material layers on the surface of the mold according to the designed laying sequence, angle, and position. Accurate alignment is required to avoid wrinkles, misalignment, and foreign objects from entering. Sometimes it is necessary to compact and exhaust between layers

Insertion placement: if necessary, place metal inserts, pre cured patches, connectors or core materials (honeycomb, foam, etc.)

4. Vacuum Bagging

This is a crucial and meticulous step

Sequential laying of auxiliary materials: Cover the surface of the layer in sequence

Release cloth: prevents resin from sticking to the breathable felt, ensuring the surface quality of the parts

Breathable felt/absorbent felt: provides channels for resin flow and gas exhaust. Absorbent felt is also used to absorb excess resin

Isolation film (such as FEP film): optional, prevents breathable felt/adhesive felt from sticking to the vacuum bag film

Vacuum bag film: covering the entire layer and mold edge, forming a closed space

Sealing: Use sealing tape to tightly adhere the vacuum bag film to the sealing edge of the mold, ensuring no air leakage

Connecting vacuum piping: Install a vacuum connection pipe at a suitable location (usually above the breathable felt) and connect the vacuum hose to the vacuum system of the hot press tank

Vacuum degree test: Vacuumize (generally required to reach at least -0.08 MPa or higher), check the sealing, ensure no leakage, and maintain pressure for a period of time. Vacuum degree is the key to ensuring compaction and exhaust

5. Hot press molding (curing cycle)

Push the packaged mold components into the hot press can, close the can door, and seal it

Vacuum pumping: Start the vacuum system, maintain and monitor the vacuum level

Pressurization: Fill the tank with compressed gas (air or inert gas such as nitrogen) and pressurize it to the target value according to the set program (usually in stages). Pressure is evenly transmitted to the workpiece through the vacuum bag

Heating: Start the heating system (hot air circulation or heater) and raise the temperature according to the precisely set temperature time curve (curing curve). The curve is determined by the curing kinetics of the resin system (including heating rate, insulation platform temperature and time, cooling rate, etc.)

Insulation curing: Maintain sufficient insulation time at the target curing temperature to ensure that the resin is fully crosslinked and cured. Pressure and vacuum are continuously maintained during this stage

Cooling: The program controls the cooling rate (usually slower) to avoid deformation or cracking of the parts due to thermal stress. Pressure and vacuum usually need to be maintained during the initial cooling stage, and can be gradually released later on

Pressure relief: After the temperature drops to a safe range, slowly release the pressure inside the tank

Out of the can: Open the can door and take out the mold components

6. Demolding and post-processing

Dismantling the vacuum bag system: Carefully remove the vacuum bag film and all auxiliary materials (release cloth, breathable felt, etc.)

Demolding: Using a mold designed demolding mechanism or tool, carefully separate the cured parts from the mold. Skills are needed to avoid damaging parts and molds

Edge trimming and machining: Remove burrs, glue flow, and process allowances. Perform necessary mechanical processing such as drilling, cutting, milling, etc. to achieve final dimensions and assembly requirements

Non destructive testing: using ultrasonic testing (UT), X-ray, impact testing and other methods to inspect whether there are defects such as delamination, pores, inclusions inside the workpiece

Surface treatment: cleaning, polishing (if necessary), preparing for subsequent painting or assembly

Final inspection and delivery: Conduct final inspections on dimensions, appearance, performance, etc., and deliver after passing the inspection

5. Advantages and disadvantages of carbon fiber hot pressing tank process

Vantagens

Extremely high quality of components: high fiber volume content (>60%), extremely low porosity (<1%), and optimal mechanical properties (strength, stiffness, fatigue performance)

Excellent surface quality: The contact mold surface (sticking surface) can achieve Class A or close to Class A surface smoothness

Excellent dimensional accuracy and stability: high mold accuracy, uniform curing pressure, uniform thermal field, good control of part size, and minimal deformation

Powerful ability to form complex structures: capable of manufacturing large, complex curved surfaces, variable thicknesses, reinforced ribs, sandwich structures, and other components that are difficult to form using other methods

High process maturity: Applied in aerospace and other fields for decades, the process is stable and reliable, with complete standards and specifications

Wide material selection: suitable for various high-performance resin matrices (epoxy, bismaleimide, polyimide, thermoplastic, etc.) and carbon fiber prepreg

Desvantagens

1. The equipment cost is extremely high: the investment in the large hot press tank itself and its supporting facilities (air compressor, vacuum system, cooling system, control system) is huge

2. High mold cost: molds that require high temperature and high pressure resistance, high precision, and low thermal expansion coefficient (such as Invar) are difficult to manufacture and have high costs

3. Huge energy consumption: Heating, pressurization, and vacuuming processes consume a very high amount of energy

4. Long process cycle: The entire process of preparation, laying, packaging, curing, cooling, and post-processing takes a long time (especially for curing large thick walled parts), resulting in relatively low production efficiency

5. High consumption and cost of auxiliary materials: The vacuum bag system material is a disposable consumable, with a large amount of usage and high cost

6. Complex operation and reliance on experience: The laying and packaging processes highly rely on skilled workers, and the formulation and optimization of curing process parameters also require profound professional knowledge

7. Size limitation: The size of the component is limited by the volume of the hot press can

8. Environmental challenge: Resins may release volatile organic compounds (VOCs) under high temperature and pressure, requiring treatment

6. Application fields of carbon fiber hot pressing tank technology; Future Development Trends

Domínio de aplicação

Aerospace (core field) aircraft main load-bearing structures (wings, fuselage panels, tail fins, beams, ribs), engine components (fan blades, casings), satellite structures, spacecraft components, unmanned aerial vehicle structures, etc

High end sports equipment: bicycle frames, tennis rackets, golf clubs, racing parts, rowing boats, high-performance skis/poles, etc

Automotive Industry (High Performance/Racing): F1 Racing Single Shell Body, Structural Components, Chassis Components, Prototype Parts of Body Covering Components for High Performance Sports Cars, etc

National defense and military industry: missile body, radar cover, unmanned aerial vehicle structure, armored vehicle components, etc

Industrial field: high-end medical equipment components (such as CT/MRI scanning bed plates, orthopedic instruments), robot arms, precision instrument structural components, high-end audio diaphragms, etc

New energy: wind turbine blades (some key parts), hydrogen cylinders, fuel cell components, etc

Resumo

The carbon fiber hot press can process is the gold standard for manufacturing the highest performance and highest quality composite material components, especially large and complex structural components

It achieves full compaction, low porosity, and precise controllable curing reaction of materials through the uniform high temperature, high pressure, and vacuum environment provided by the hot press tank, thereby endowing the parts with unparalleled mechanical properties and dimensional accuracy

However, its high equipment, mold, energy and material costs, as well as long process cycles, are the main obstacles to its widespread application

The core application areas of this process are concentrated in aerospace, high-end sports equipment, high-performance automobiles/racing cars, national defense and military industries, and other scenarios that require extremely strict performance and high added value