**Comparison Between Vacuum Infusion Process And Hand Lay-Up Process**

Hand lay-up is an open-mold process with significant advantages, including great flexibility in mold shape changes, low mold costs, strong adaptability, market-recognized product performance, and low investment. This makes it particularly suitable for small companies. However, this process also presents several issues, such as excessive emissions of volatile organic compounds (VOCs), significant health risks to operators, high staff turnover, material limitations, lower product performance, high resin consumption and waste, and, most notably, inconsistent product quality. The ratio of fiberglass to resin, part thickness, lamination speed, and uniformity all depend on the operator's skill, requiring a high level of technical expertise, experience, and competence. The resin content in hand lay-up products generally ranges from 50% to 70%. The VOC emissions of this open-mold process exceed 500 PPM, and styrene volatilization reaches 35%–45% of the amount used, while regulations in various countries set limits at 50–100 PPM. Currently, most foreign manufacturers have switched to dicyclopentadiene (DCPD) or other low-styrene emission resins. However, as a monomer, styrene still lacks an effective substitute.

The vacuum resin infusion process is a low-cost manufacturing technique that has been developed over the past 20 years, particularly suitable for producing large-scale products. Its advantages are as follows:

(1) Excellent product performance and high yield rate. Under the same raw material conditions, components formed using the vacuum resin infusion process exhibit 30%–50% higher strength, stiffness, and other physical properties compared to hand lay-up components. Once the process is stabilized, the yield rate can reach nearly 100%.

(2) Stable product quality and high repeatability.
Product quality is less affected by the operator, ensuring a high degree of consistency within and between components. The fiber content is pre-placed in the mold before resin infusion according to specified amounts, resulting in a relatively constant resin ratio, typically between 30%–45%. This significantly enhances the uniformity and repeatability of the product compared to the hand lay-up process while also reducing defects.

(3) Improved fatigue resistance and reduced structural weight.
With a high fiber content, low porosity, and superior mechanical properties—particularly enhanced interlaminar strength—the vacuum infusion process significantly improves fatigue resistance. For the same strength or stiffness requirements, products made using this process can achieve weight reduction in structural applications.

(4) Environmentally friendly.
As a closed-mold process, vacuum resin infusion confines volatile organic compounds (VOCs) and hazardous air pollutants within the vacuum bag. Only minimal emissions occur during vacuum pump exhaust (which can be filtered) and when opening resin containers. VOC emissions remain below the 5 PPM standard, greatly improving the working environment for operators, stabilizing the workforce, and expanding the range of applicable materials.

(5) Enhanced structural integrity.
The vacuum resin infusion process enables the simultaneous molding of stiffeners, sandwich structures, and embedded components, enhancing overall product integrity. This makes it particularly suitable for manufacturing large structures such as wind turbine nacelle covers, boat hulls, and superstructures.

(6) Reduced raw material consumption and labor costs.
Compared to hand lay-up, resin usage is reduced by 30% for the same laminate structure, with minimal waste and a resin loss rate of less than 5%. The process also significantly improves labor productivity, cutting labor costs by over 50%. This is especially beneficial for molding large, complex geometries with sandwich and stiffened structures, offering substantial savings in both materials and labor. For instance, in the production of vertical rudders for the aerospace industry, the use of fasteners is reduced by 365 pieces, lowering costs by 75% compared to traditional methods, while maintaining the same weight and achieving superior performance.

(7) High dimensional accuracy.
Products manufactured using the vacuum resin infusion process exhibit superior dimensional accuracy (thickness) compared to hand lay-up products. Under the same lay-up conditions, the thickness of vacuum-infused products is typically two-thirds that of hand lay-up products. Thickness deviation is about ±10%, whereas hand lay-up typically results in ±20% deviation. Additionally, the surface smoothness of vacuum-infused products is superior. For example, the inner wall of nacelle covers produced with this process is smooth, with a naturally formed resin-rich layer on the surface, eliminating the need for an additional gel coat. This reduces labor and material costs associated with sanding and painting.

Disadvantages of the Vacuum Resin Infusion Process:

(1) Longer and more complex preparation process.
The process requires precise lay-up, proper placement of flow media and infusion channels, and effective vacuum sealing. As a result, for small-sized products, the processing time can actually exceed that of the hand lay-up method.

(2) Higher production costs and material waste.
Auxiliary materials such as vacuum bag film, flow media, release fabric, and infusion tubes are typically single-use, many of which still rely on imports, making the production cost higher than that of hand lay-up. However, as product size increases, this cost difference decreases. With the increasing availability of domestically produced auxiliary materials, the cost gap is narrowing. The development of reusable auxiliary materials is also a key focus for future advancements in this process.

(3) Process-related risks.
For large and complex structures, any failure during resin infusion may lead to product rejection. Therefore, thorough preliminary research, strict process control, and effective contingency measures are essential to ensure the success of the process.