Vacuum Forming of FRP Boats – Vacuum Induction Forming Process

 

 

The Vacuum Infusion Process (VIP) is to lay reinforcing materials (glass fiber, carbon fiber, sandwich materials, etc., which is different from the vacuum bag pressing process) on the mold, then lay the vacuum bag, and extract the air in the mold to form a negative pressure in the mold cavity.

 

The pressure generated by the vacuum is used to press the unsaturated resin into the fiber layer through the pre-laid pipeline, so that the resin can infiltrate the reinforcing material and fill the entire mold cavity. After the product is cured, the vacuum bag material is removed to obtain the desired product from the mold.

 

The vacuum infusion process uses a single-sided mold to establish a closed system. The basic principle of vacuum resin infusion molding is to inject the resin into the reinforcing material pre-laid on the mold with the help of vacuum drive, and use the diversion medium to form a high-flow penetration zone on the surface of the component, so that the resin quickly reaches the entire surface of the product. The impregnation is mainly achieved in the thickness direction.

 

Another form of this process is that the sandwich structure is slotted and perforated on the core material, and the reinforcing material is above or below the core material. The resin flows in the slots and holes at a faster speed than the flow in the diversion medium.

 

 

Figure: Vacuum Resin Infusion Molding Construction

 

The process flow of vacuum resin infusion molding is as follows:

 

Lay the reinforcing material according to the layer design (fixed with special spray glue);

 

Lay the demoulding cloth and guide cloth;

 

Arrange the guide pipe;

 

Vacuum and let the resin soak into the reinforcing material;

 

Curing;

 

Demolding.

 

 

 

Figure: Schematic Diagram of Vacuum Resin Infusion Molding Process

 

Advantages of Vacuum Resin Infusion Molding:

 

Excellent Product Performance.

Compared with manual lamination, the mechanical properties of the hull strength, stiffness, etc. of the vacuum resin infusion molding process can be improved by more than 30%.

 

No Bubbles, Stable Product Quality and Good Repeatability. The product quality is less affected by the construction personnel and the performance dispersion is small. The resin content can be controlled, and the minimum can be 35%~40%. The product fiber content is high, and the general fiber mass fraction is 60%~70%. The product porosity can be less than 5%, and there are fewer defects.

 

Improved Fatigue Resistance and Reduced Hull Weight. Due to the high fiber content, low porosity and good product performance of the product, especially the improvement of interlayer strength, the fatigue resistance of the product is greatly improved. Under the same mechanical performance requirements, the product weight can be reduced. The product has high strength and strong repeatability and can be used as a structural part.

 

Environmental Improvement. Vacuum resin infusion molding is a closed mold process. Volatile organic compounds are confined to the vacuum film. Only trace amounts of volatile compounds are emitted during vacuum pump exhaust (filterable) and resin stirring. The styrene concentration does not exceed 5ppm, which is far below the international standard value for volatile organic compounds. This has greatly improved the working environment of construction workers and expanded the range of materials used.

 

Good Product Integrity.

The vacuum resin infusion molding process can simultaneously mold the hull single plate and structural parts and their embedded parts and sandwich structures, thereby improving the integrity of the product. The molding efficiency is high, especially thick products can be molded in one go, and the product thickness is very uniform.

 

 

Disadvantages of Vacuum Resin Infusion Molding:

 

Lamination is difficult, and the preparation process takes a long time and is relatively complicated. The process requires correct lamination, laying of diversion media and diversion tubes, diversion cloth/net, and application of sealing strips for effective vacuum sealing. Any negligence will lead to construction failure. Therefore, for small-sized products, the molding time exceeds manual lamination molding, and some shapes cannot be used.

 

The production cost is high and more waste is generated. Auxiliary materials such as vacuum film, demoulding cloth, and guide net are all disposable, and the requirements for resin and reinforcement materials are also high, and some materials have to be imported. Although compared with manual lamination molding, the amount of resin used is reduced by 30%, the resin loss rate is less than 5%, and the labor is saved by more than 50%, the total production cost is generally higher than that of manual lamination molding.

 

The technical requirements for operators are high, and the process manufacturing has certain risks. Especially for large boats, once the resin introduction fails, the product is easy to be scrapped. Therefore, it is necessary to do a good job in preliminary research, strictly control the process and prepare effective remedial measures to ensure the success of molding.