Rapid Resin Transfer Molding

 

RTM Molding Technology originated from the cold casting process in the 1950s, but the real RTM era is only about 20 years old. It was first developed in developed countries (the United States, Japan, Germany, etc.) and has been rapidly developed. In the past 20 years, RTM has been developing at a growth rate of more than 20%.

 

Domestic RTM technology started in the 1980s, but due to the lack of technology and equipment. The raw material supporting system is not perfect, and the process theory is immature, the domestic RTM process remains in the research and development state between hand lay-up and RTM process, and has not been able to form a large-scale. It was not until the 1990s that RTM rapid prototyping technology became mature and was applied to automotive panels, structural parts, and all-carbon fiber body.

 

RTM is one of the typical processes of LCM (liquid molding technology). The main principle is to lay fiber-reinforced materials or preforms designed according to the structural and performance requirements in the mold cavity, and then use RTM equipment to press low-viscosity resin into the mold cavity by giving the mold cavity a vacuum and low-pressure state, infiltrate the fiber, solidify and mold, and then demold to obtain composite products.

 

 

Figure 1 RTM Process Principle Diagram

 

The reason why RTM technology has developed rapidly in the past 20 years is that the RTM process has a series of advantages. It can quickly form large and complex components at one time. The surface of the resulting product is smooth and does not require much subsequent processing, which simplifies the work process and improves the work quality. And if it is prepared with a preform, it can achieve size control, strong designability, and realize automated or semi-automated production.

 

If you want to realize the automated production of RTM, the process is usually divided into several sub-processes (as shown in Figure 2), which mainly includes the preforming of fiber-reinforced materials, the pouring of resin, curing and post-processing. And each step can be operated independently, so that it can be constructed independently and increase work efficiency.

 

 

Figure 2 RTM Molding Process Flow

 

RTM Process Requirements for Resin

 

(1) The resin dedicated to the RTM process is liquid or solid at room temperature and can exist stably at room temperature. The chemical composition and properties of the resin will not change during storage.

 

(2) The resin system has an appropriate viscosity at the process temperature (approximately 0.2-0.8Pa•s within the working range). Too high viscosity will lead to difficulties in resin flow and fiber/resin impregnation; too low viscosity will lead to unstable resin flow and diffusion, forming pores.

 

(3) Sufficiently long gel time to meet the requirements of resin flow filling and fiber impregnation. At the same time, the low viscosity of the resin should be maintained for more than 40 minutes to form the low viscosity platform characteristics required by the RTM process resin.

 

(4) No volatile products are generated during the injection and curing process of the resin, and the resin should have good impregnation and adhesion to the reinforcement material.