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Vacuum Infusion: A Comprehensive Guide to Composite Material Manufacturing

In the modern field of composite material manufacturing, vacuum infusion technology has become an important manufacturing process due to its efficiency, environmental friendliness, and ability to produce high-performance composite materials. This technique uses vacuum pressure to inject resin into dry fiber layers, not only optimizing the fiber-to-resin ratio but also significantly enhancing the mechanical properties of the materials. From aerospace to automotive manufacturing, from wind energy to marine engineering, vacuum infusion is widely applied and its unique process advantages make it excel in the production of complex parts.
This article will provide a detailed introduction to the principles of vacuum infusion, its process flow, material requirements, and the challenges and limitations it faces. Continue reading to learn more.

What Is Vacuum Infusion?

Vacuum infusion, also known as resin infusion, is a manufacturing process used to create composite materials that are strong and lightweight. This process involves using vacuum pressure to inject resin into a mold containing dry fiber layers. Vacuum infusion is a sophisticated composite material manufacturing technique that provides high-quality, strong, and lightweight parts with a clean, controllable process. It requires meticulous setup and monitoring but offers significant advantages in terms of part performance and environmental impact.

What Is the Principle of Vacuum Infusion?

The principle of vacuum infusion, also known as the Vacuum Infusion Process (VIP), utilizes vacuum pressure to inject resin into a mold’s dry fiber layers, thus creating composite materials. This process is distinctive because it uses atmospheric pressure to push resin into the mold cavity, rather than mechanical force or manual effort. Key factors influencing this process include the permeability of the laminate, the viscosity of the resin, and the pressure differential relative to atmospheric pressure.

What Is the Origin of Vacuum Infusion?

The Vacuum Infusion Process, also known as Crystic Vacuum Infusion (Crystic VI), originated in 1946 by Scott Bader in the United Kingdom. The development of this method aimed to optimize the fiber-to-resin ratio by using vacuum pressure to inject resin into the laminate, enhancing the mechanical performance of the produced composite materials.

What Is Another Term for Vacuum Infusion?

vacuum Bagging Film for Composites Infusion Process

Vacuum infusion is alternatively termed resin infusion. Additionally, it encompasses various abbreviations and names, such as:

  • Resin Transfer Molding (RTM)
  • Liquid Resin Injection (LRI)
  • Resin Film Infusion (RFI)
  • Resin Injection under Flexible Tooling (RIFT)
  • Controlled Atmospheric Pressure Resin Injection (CAPRI)
  • Double (Flexible) Bag Infusion
  • Closed Mold Molding
  • Liquid Composite Molding

What Is the Vacuum Infusion Process?

The Vacuum Infusion Process (VIP) is a technology for manufacturing composite materials that utilizes vacuum pressure to inject resin into a mold containing dry fiber layers. This process is unique in that it employs atmospheric pressure to drive resin into the mold cavity, instead of using mechanical force or manual manipulation. Here are the key steps and principles involved:

  1. Setup and Material Preparation: Dry fibers and core materials are laid into the mold. These materials include various types of fibers, such as glass or carbon fiber, and sometimes core materials to increase thickness and strength.
  2. Sealing: A vacuum bagging film is placed over the laid materials to seal the mold. This film ensures an effective vacuum is formed within the mold cavity.
  3. Vacuum Application: A vacuum pump is used to evacuate air from the mold cavity, creating a pressure differential. This pressure differential is crucial as it helps draw the resin into the fiber layers.
  4. Resin Injection: Once a complete vacuum is achieved, resin is introduced into the mold through strategically placed tubes. The vacuum pressure “pulls” the resin through the fibers, ensuring it permeates the entire layup.
  5. Curing: After the resin has fully impregnated the laminate, the inlet tubes are closed, allowing the resin to cure. Vacuum can be maintained during this stage to ensure no air re-enters the laminate.
  6. Demolding: After curing, the composite material part is removed from the mold. The vacuum bag material is also removed at this stage.

What Are the Different Types of Vacuum Infusion?

Different types of vacuum infusion include various methods and adjustments to the basic vacuum infusion process, each tailored for specific applications or improvements in composite material manufacturing. Here are the main types identified:

  1. Resin Transfer Molding (RTM): Typically involves injecting resin into a pair of clamped matching molds at pressures above atmospheric, but can also be a variant of vacuum infusion known as RTM Light.
  2. Liquid Resin Injection (LRI): This method primarily involves injecting resin into the laminate under controlled conditions.
  3. Modified Vacuum Infusion (MVI): Developed by Airbus, this technique adjusts the standard vacuum infusion process for specific aerospace applications.
  4. Resin Film Infusion (RFI): Involves placing a resin film within the mold, which is then melted and infused into the fibers under vacuum pressure.
  5. Resin Injection under Flexible Tooling (RIFT): Similar to standard vacuum infusion but uses a flexible mold to conform to the mold’s shape.
  6. Seemann Composite Resin Infusion Molding Process (SCRIMP): One of the earliest infusion process patents that helped standardize the method for industrial use.
  7. Vacuum-Assisted Resin Transfer Molding (VARTM): Similar to RTM but uses vacuum to assist in resin transfer, improving the fiber-to-resin ratio and reducing void content.
  8. Vacuum-Assisted Injection Molding (VAIM) and Vacuum-Assisted Process (VAP): These variations focus on optimizing vacuum levels and resin flow to enhance the quality of the final composite parts.
  9. Vacuum-Assisted Resin Injection (VARI) and Vacuum-Assisted Resin Injection Molding (VARIM): Similar to VARTM but may involve different setups or resin systems, particularly suited to specific manufacturing requirements.

What Is Vacuum Infusion Made Of?

Vacuum infusion consists of several key components that work together through a controlled process to manufacture composite materials. Here are the main materials and equipment used in vacuum infusion:

  1. Resins: Polyester, vinyl ester, and epoxy resins are commonly used in vacuum infusion. These resins are selected based on their properties, such as viscosity, which is crucial for ensuring smooth flow of the material during the infusion process.
  2. Fibers: Glass and carbon fibers are the most commonly used reinforcement materials in vacuum infusion. These fibers are chosen because of their good permeability, allowing the resin to pass well through the material gaps.
  3. Core Materials: For sandwich structures, materials like balsa wood or foam plastics can be used as the core of the laminate. These core materials may have resin channels to improve resin flowability.
  4. Flow Media: This is typically a plastic net added to the laminate to enhance resin flow and speed up the infusion process. It is removed after the part is demolded.
  5. Vacuum Bagging Film: This film is placed over the mold and dry materials to form a vacuum-sealable environment.
  6. Release Layers and Demolding Films: These materials are used to facilitate the removal of the vacuum bagging materials after the process is complete and improve the surface finish of the composite materials.
  7. Vacuum Pump: This is a critical piece of equipment that generates the vacuum needed to draw resin into the laminate. An oil-sealed single-stage rotary vane vacuum pump is commonly used.
  8. Tubing: Vinyl tubing is used because of its strength and ability to maintain shape under vacuum pressure. This tubing serves as a conduit for both vacuum and resin.
  9. Resin Catch Pot: Placed in the tubing to collect excess resin, which could otherwise reach and damage the vacuum pump.
  10. Sealant Tape, Manifolds, and Connectors: Used to ensure an airtight seal and manage material flow within the setup.

What Are the Key Features of Vacuum Infusion?

The main features of vacuum infusion include:

  1. High Fiber-to-Resin Ratio: Vacuum infusion allows precise control over the fiber-to-resin ratio, making parts stronger and lighter.
  2. Reduced Void Content: This process minimizes the presence of voids within the composite material, enhancing its overall strength and quality.
  3. Stable Resin Usage: Due to the controllability of the process, resin usage is very stable, helping to accurately predict material costs and mechanical performance of parts.
  4. Environmental Benefits: Compared to open molding processes, vacuum infusion is cleaner, as it reduces the emission of volatile organic compounds (VOCs).
  5. Complexity and Customization: The process is highly customizable and can produce large complex shapes that are difficult to achieve with other methods.
  6. Cost-Effectiveness: Although the setup and consumables may be relatively expensive, the lower mold costs and ability to produce high-quality parts make this process cost-effective for large parts.
  7. Time and Labor Intensive: Compared to simpler methods such as hand lay-up, vacuum infusion is more complex and time-consuming to set up. It requires careful planning and setup of vacuum and resin lines.
  8. Risk of Errors: Once the infusion process starts, it is difficult to correct errors, and even minor mistakes can lead to scrapping of parts. This makes the process somewhat risky, requiring careful monitoring and experience.

What Are the Applications of Vacuum Infusion?

Vacuum infusion is applied across various industries where producing large, lightweight, and high-strength composite parts is crucial. Here are its main applications:

  1. Aerospace Industry: Vacuum infusion is used to produce major structural components such as composite aircraft wings, struts, and other critical main structures. This method is favored for its ability to produce lightweight, high-load-bearing parts essential in aerospace applications.
  2. Marine Industry: In the maritime sector, vacuum infusion is particularly suited for manufacturing large parts like hulls and decks. The process can produce large complex-shaped products with excellent mechanical properties, making it an ideal choice for this industry.
  3. Wind Energy: The wind energy sector actively employs vacuum infusion to manufacture wind turbine blades. This process ensures high-quality production, which is crucial for blades as their length increases and they require excellent structural integrity.
  4. Automotive Industry: Although not explicitly mentioned in the materials, the automotive industry benefits from vacuum infusion technology, which can be used to manufacture structural components and panels requiring a high strength-to-weight ratio.
  5. Industrial Applications: Vacuum infusion is also used to mold large structural parts such as bridges, railway platforms, and other large industrial components. The process is valued for its high cost-effectiveness and the strength-to-weight ratio of the produced parts.

What Are the Limitations of Vacuum Infusion?

The limitations of vacuum infusion include several challenges and potential pitfalls that could impact the success and efficiency of the process. Here are the main limitations:

  1. Complex Setup and Risk of Errors: The setup for vacuum infusion is highly complex, requiring precise placement of vacuum and resin lines. Mistakes during setup can lead to catastrophic failures, such as resin pooling, insufficient saturation, or complete cessation of resin flow. Once infusion starts, these errors are difficult to correct, often leading to scrapped parts.
  2. Trial and Error Process: Vacuum infusion is often described as a trial and error process, especially for novices. It requires careful documentation and adjustment based on each attempt, which can be time-consuming and resource-intensive.
  3. High Startup Costs: The initial costs associated with vacuum infusion can be high, particularly due to the need for specialized equipment and materials. Therefore, this method is less suitable for small projects or businesses just starting with composite material manufacturing.
  4. Risk of Dry Spots and Pinholes: Incorrect setups or uneven resin flow can lead to dry spots where the resin does not fully permeate the fibers, or pinholes—small voids within the composite material. These defects weaken the final product.
  5. Limited Corrections During the Process: Once the vacuum infusion process starts, adjustments or corrections are very limited. This requires meticulous planning and flawless execution of the process from the start to avoid defects.
  6. Material and Process Limitations: The types of materials used, such as resins and fibers, must be compatible with the process. For example, the resin needs to have the right viscosity to ensure normal flow under vacuum conditions.
  7. Environmental Conditions: Factors like temperature and humidity can affect the performance of the vacuum infusion process, impacting resin viscosity and curing times. These need to be carefully controlled to ensure consistent results.

What Is the Best Resin for Vacuum Infusion?

Epoxy Resin: Highly recommended for use in vacuum infusion, especially when using high-performance fibers like carbon fiber and aramid. Epoxy resin has excellent mechanical properties, good heat resistance, and low shrinkage. It is known for producing sturdy, durable composite materials, suitable for a wide range of applications including aerospace and automotive parts.


Vacuum infusion is a powerful and versatile technique in the field of composite material manufacturing, offering numerous advantages such as high-quality parts, environmental benefits, and the ability to create complex shapes. However, its success depends on meticulous process control, careful material selection, and proper setup to mitigate its inherent risks and limitations.
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