Among the current materials, composite materials are widely used due to their light weight and high strength. The manufacturing process for composite materials is also constantly improving and innovating. From the initial hand lay-up, to mechanized spraying, pultrusion, molding, etc., to the current vacuum introduction process, the process related to vacuum introduction is resin transfer molding (RTM), vacuum assisted RTM (VARTM), Vacuum bag pressure, SCRIMP, SRIM (Structural Reaction Molding), RTI (resin film infusion). But there are some differences, many of which have been introduced in the article, so I won't go into details here.
1. Vacuum infusion process (VIP)
Vacuum infusion process, abbreviated as VIP, reinforced material on the mold (glass
Glass fiber, carbon fiber, sandwich material, etc., different from the vacuum bag process), then vacuum bag, and extract the air in the system, forming a negative pressure in the mold cavity, using the pressure generated by the vacuum to pass the unsaturated resin through The laid pipe is pressed into the fiber layer, and the resin is immersed and the reinforcing material finally fills the entire mold. After the product is cured, the vacuum bag material is removed, and the desired product is obtained from the mold. The VIP uses a single-sided mold (just like a normal hand lay-up and spray mold) to create a closed system. The vacuum introduction process has been published for a long time, and the process was patented in 1950. However, it has not been developed until recently. Since this process is introduced from abroad, there are various names in the naming, vacuum introduction, vacuum infusion, vacuum injection, and the like.
2. Theory
The vacuum introduction process can be widely applied and has its theoretical basis. This is Darcy’s Law t = l 2h/(2 kDP )
t is the import time and is determined by four parameters.

The viscosity of the h-resin can be seen from the formula, the lower the viscosity of the resin used, the shorter the introduction time required, and therefore the viscosity of the resin used for vacuum introduction is generally not too high. This allows the resin to quickly fill the entire mold.
l-Injection length, which refers to the distance between the resin feed port and the discharge port, and the distance required is also long.

DP-pressure difference, the greater the difference between the pressure in the system and the pressure outside the system, the greater the driving force for the resin, and the faster the resin flow rate, of course, the shorter the introduction time.

k = permeability, refers to the parameters of glass fiber, sandwich material and other infiltration of resin. A large k value indicates that the wetting is good, like a multi-directional felt is more than a gingham cloth, and the chopped strand mat is easily infiltrated by a resin. Therefore, in order to make the resin easily fill the system under the condition that the reinforcing material is compacted, some guiding grooves are generally artificially set, for example, punching holes in the sandwich foam.
3. Advantage
In a typical hand lay-up, the reinforcing material is placed in a mold and manually infiltrated with a brush, roller or other means. Another improved method is to use a vacuum bag to suck excess resin from the laminate during hand lay-up. This increased fiberglass content results in higher strength and lighter weight, and VIP offers many advantages over traditional processes.
Take the hand paste, vacuum bag and vacuum introduction as an example. Vacuum introduction has obvious advantages in mechanical properties.

 
This shows the advantages of vacuum introduction.
a Higher quality product: The resin infiltrates the glass fiber in a vacuum environment, and there are few bubbles in the product compared to the conventional manufacturing process. There is no excess resin left in the system, and the glass fiber content is high, which can reach 70% or even higher. The resulting article is lighter in weight and higher in strength. The batch and batch are also very stable.

b Less resin loss: With the VIP process, the amount of resin can be accurately budgeted, and it is difficult to control the hand lay-up or spray process due to the variability of the operator. VIP can minimize resin loss and, more importantly, save costs.

c Resin distribution is uniform: For a product, the pressure generated by different parts of the vacuum is consistent, so the resin infiltration rate and content of the glass fiber tend to be consistent. This is critical for weight-reliable FRP parts.
d Process is less volatile: there are no brushes or rollers in the production process, and it will not cause the splash or dripping of the resin, and there will be no large amount of odor. So it provides a clean, safe and friendly working environment that protects the operator's physical and mental health.

e Use single-sided mold: Only one side of the mold can be used to obtain smooth and smooth products on both sides, which can better control the thickness of the product. Save mold manufacturing costs and time.

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