Composite Material Molding Process-Vacuum Infusion Process

 

Definition of Vacuum Infusion Process

 

Vacuum Infusion Process (VIP) is a process in which a designed reinforcement preform is laid in the mold cavity, the air is extracted by a vacuum system, a negative pressure is formed in the mold cavity, and the resin is pressed into the fiber layer through the pre-laid pipe by the pressure generated by the vacuum. The resin completes the infiltration of the reinforcement preform during the flow filling process, and solidifies and forms a composite material component.

 

Characteristics of Vacuum Infusion Process

 

Advantages

 

Higher Quality Products: The resin infiltrates the glass fiber in a vacuum environment, and there are very few bubbles in the product compared with the traditional manufacturing process. No excess resin is left in the system, and the glass fiber content is high, up to 70% or even higher, and the resulting product is lighter and stronger.

 

Less Resin Loss: With the VIP process, the amount of resin can be accurately estimated, so that the resin loss is minimized and the cost is saved.

 

Uniform Distribution of Resin: The vacuum pressure is consistent in different parts, so the resin infiltration speed and content of the glass fiber tend to be consistent, which is critical for FRP parts with stable weight requirements.

 

Less Volatiles During the Production Process: The production process will not cause the resin to spill or drip, and there will be no large amount of odor. It can provide a clean, safe and friendly working environment to protect the physical and mental health of the operator.

 

Use a Single-Sided Mold: Only one side of the mold can be used to obtain a product with smooth and flat surfaces on both sides, which can better control the thickness of the product and save mold manufacturing costs and time.

 

Disadvantages

 

The Preparation Process Takes Too Long. Such as laying the diversion medium, diversion tube and vacuum tube, and effective sealing.

 

Generate More Process Waste. For example, vacuum bag film, diversion cloth, demoulding cloth and diversion tube cannot be reused.

 

Medium and High Temperature and Pressure Curing Technology is Difficult.

 

Raw Materials in Vacuum Infusion

 

The raw materials used in the vacuum infusion process are shown in Figure 1, including:

① Resin,

② Reinforcement material,

③ Sandwich material,

④ Release cloth,

⑤ Guide net,

⑥ Vacuum bag film,

⑦ Sealing tape,

⑧ Positioning spray glue,

⑨ Solenoid,

⑩ Guide tube

 

Resin

The vacuum infusion process has special requirements for resin viscosity, gel time, exothermic peak, wettability, etc. Commonly used resin types: epoxy resin, epoxy vinyl ester resin, unsaturated polyester resin.

 

The Technical Requirements of Resin Include:

 

① Low viscosity, fast infiltration of reinforcing materials. Mixture viscosity at operating temperature: less than 800mPa·s, in fact, generally 100-400mPa·s;

 

② Long application period (usually gel time GT >1h), gel time exceeds the resin infusion time, and the post-curing speed should be fast (△t should be short), which can be demoulded quickly and improve production efficiency;

 

③ The exothermic peak should be low to prevent the burning of thick parts and damage to the mold;

 

④ Excellent mechanical properties, especially strength and fatigue resistance.

 

The grades and applications of some resins suitable for vacuum infusion are shown in Table 1:

 

 

Reinforcement Materials

Reinforcement materials are classified by material: glass fiber, carbon fiber, etc.; classified by weaving method: uniaxial cloth, multiaxial cloth, three-dimensional fabric, woven cloth, etc.;

 

Technical Requirements for Reinforcement Materials:

 

① To meet the application performance requirements of the product, especially the mechanical performance requirements, a reasonable layer structure should be selected through material design. The second is corrosion resistance, moisture resistance, heat resistance, weather resistance, etc.;

 

② Good permeability and infiltration performance;

 

③ Easy to cut, such as satin cloth is easy to loosen when cutting;

 

④ The fabric has good compression resistance, and the permeability is less affected by external pressure;

 

⑤ The fiber is fixed by the stitching line, and the erosion resistance is excellent. Use thick fabrics as much as possible to reduce the “surge” phenomenon caused by too many layers.

 

⑥ The fabric slurry and adhesive should match the resin used.

 

Sandwich Materials

Generally, wood boards, Balsa wood, PVC foam, PUR foam, strong core felt, etc. are commonly used. Select appropriate sandwich materials according to the needs of the product.

 

Release Cloth

Generally, it is a high-strength polyester fiber plain cloth with tracer lines, which has been degreased and heat-set. The commonly used material is nylon 66. Its main function is to make the surface of the product flat and increase the shear force of the adhesive joint surface; it requires a dense structure, good draping, and loose bonding with the fiber layer. At the same time, it must have good permeability to the resin and will not affect the curing performance of the resin.

 

Guide Net

Generally, it is a polyethylene woven net with a good three-dimensional structure; its main function is to allow air to pass during vacuuming and resin to pass during infusion, thereby accelerating the running speed of the resin in the fiber. The flow net is required to have a certain thickness, low resistance to resin flow, and good draping.

 

Vacuum Bag Film

Generally, the material is copolymer, which has three categories: normal temperature, medium temperature, and high temperature; it mainly blocks air to prevent air from entering the fiber product during vacuuming.

 

Sealing Tape

The main function is to bond the vacuum bag film and the mold, blocking the connection between the outside air at the contact point and the air in the product.

 

Positioning Spray Glue

Mainly used to bond reinforcing materials, guide tubes, demoulding cloth and other materials to achieve positioning effect.

 

Solenoid

A spiral polyester tube, mainly used to be placed on the edge of the product, to assist in the conduction of air at the edge of the product when evacuating, and can also be used to guide resin.

 

Guide Tube

A pipe used to arrange the guide system, generally with an Ω-shaped cross-section, can also be replaced by a solenoid. The main function is to be the main pipeline of the guide system, responsible for the main direction of the resin in the entire guide system, and its layout determines the efficiency of the guide system.

 

Vacuum Induction Process Steps

The vacuum induction process operation steps are:

 

1. Spraying Release Agent
2. Making Gel Coat
3. Laying Reinforcement Material
4. Laying Demoulding Cloth
5. Laying Guide Net
6. Laying Resin Conduit and Fixing Silicone Nozzle
7. Laying Vacuum Bag
8. Connecting and Sealing the Guide Tube for Resin and Vacuum End
9. Vacuuming and Leak Detection
10. Injecting Resin, Maintaining Pressure and Curing
11. Removing Auxiliary Materials and Demoulding Products
12. Product Post-Processing