Brief Introduction of 1. HP-RTM Process

HP-RTM(High PressureResinTransfer Molding) is the abbreviation of high pressure resin transfer molding process. It is an advanced molding technology. It refers to the use of high-pressure pressure to mix and inject resin into a vacuum-tight mold that is pre-laid with fiber-reinforced materials and pre-set inserts. The resin flow is filled, impregnated, cured and demoulded. The molding process to obtain high-performance, high-precision composite products. With the advantages of high efficiency, energy saving and environmental protection, it has been widely used in automobile, aerospace, electronics and other fields.

The process is shown in Figure 1:

Fig.1 Schematic diagram of HP-PTM process

2. HP-RTM process characteristics

HP-RTM include preform processing, resin injection, pressing processes, and trimming processes. Compared with the traditional RTM process, the HP-RTM process increases the pressing process after injection, reduces the difficulty of resin injection filling, improves the impregnation quality of the preform, and shortens the molding cycle. Specific process characteristics are as follows:

(1) filling mold fast. The resin quickly fills the mold cavity, the infiltration effect is good, the bubbles are significantly reduced, the porosity is reduced, and the low viscosity resin greatly improves the injection speed of the resin and shortens the molding process cycle.

(2) high active resin. The curing reaction rate of the resin is improved, and the curing cycle of the resin is shortened. The use of high-activity fast-curing resin system, and the use of high-efficiency high-pressure mixing, injection equipment, so that the resin matrix mixing uniformity is better, while molding requires high temperature environment, greatly improving the curing reaction rate of the resin, shorten the production cycle, process stability and high repeatability,

(3) Use internal release agent and self-cleaning system to improve the cleaning efficiency of the equipment. The self-cleaning technology of the injection mixing head is used, and the internal release agent component is added to the raw materials, which effectively improves the cleaning efficiency of the equipment. At the same time, the surface effect of the parts is excellent, and the thickness and shape deviation are small. Achieve low-cost, short-cycle (high-volume), high-quality production.

(4) the use of rapid vacuum technology in the mold. It reduces the pore content in the parts and improves the performance of the parts. Effectively reduce the pore content in the parts, improve the fiber impregnation efficiency, improve the fiber and resin interface binding ability, improve the quality of the product.

(5) Vacuum pumping is combined with the compression molding process after injection. The process difficulty of the parts is reduced and the quality of the resin impregnated reinforcement material is improved. The design difficulty of glue injection port and exhaust port in RTM process is reduced, and the flow filling ability of resin and the impregnation quality of resin to fiber are improved.

(6) the use of double rigid closed mold, while the use of large tonnage hydraulic press pressure. The thickness of the product and the three-dimensional shape size deviation is low. In order to ensure the sealing effect of the mold, the double rigid closed mold is used, and the large-tonnage hydraulic press is used to pressurize, which improves the clamping force of the molding process and effectively reduces the thickness and shape deviation of the parts.

(7) The product has excellent surface performance and quality. The use of in-mold spraying technology and high-finish molds makes the parts obtain high-precision apparent quality in a very short time.

(8) It has high process stability and repeatability. The use of gap injection and compression technology after injection greatly improves the filling flow capacity of the resin, effectively reduces the probability of process defects, and has a high process repeatability.

3. key process technology

1. Predetermined technology for fiber-reinforced materials

Fiber preforming technology mainly includes: textile, knitting and weaving preforms; stitch-bonded preforms; chopped fiber injection preforms; hot-pressed preforms, etc. Among them, hot-pressing shaping technology is the most widely used, in which the shaping agent is the basic guarantee, and the fiber preform mold and pressing process technology are the key to fiber shaping. For the HP-RTM process, the structure of the parts is relatively simple, therefore, the shaping mold is also relatively simple, the key lies in how to design and control the program, control the shaping mold and pressure tooling effective, orderly pressure shaping.

2. High precision resin metering, mixing and injection technology

The mixing and injection of resin in HP-RTM process mainly includes two systems: resin main material and in-mold spraying resin. The key to its control lies in high-precision resin metering system, fast and uniform mixing technology and self-cleaning technology of mixing equipment. HP-RTM the main resin material needs to be accurately measured at high temperature and high pressure, high-precision metering pump equipment is required. Uniform resin mixing and self-cleaning requires the design of efficient, self-cleaning, multiple mixing heads.

3. Design of Temperature Field Uniformity and Sealing of Forming Die

In the HP-RTM process, the uniformity of the mold temperature field not only determines and affects the flow and filling performance of the resin in the mold cavity, but also has a great influence on the wetting performance of the fiber, as well as the overall performance of the composite material and the internal stress of the product. Therefore, it is necessary to use the method of medium heating combined with efficient and reasonable circulating oil circuit design. The tightness of the molding die directly determines the resin flow filling pattern and the emptying capacity of the molding process, which is a key link affecting the performance of the product. It is necessary to design the position, mode and quantity of sealing rings according to the product. At the same time, it is necessary to solve the sealing problems of mold fit clearance, ejection system, vacuum pumping system and other positions to ensure that no air leakage occurs during the resin filling process to ensure the performance of the parts.

4. High Precision Hydraulic Press and Its Control Technology

In the HP-RTM process, the clamping gap control of the filling process of the resin and the pressure control of the pressing link all need to be guaranteed by the high-efficiency and high-precision hydraulic press system. At the same time, it is necessary to provide timely control technology according to the needs of the glue injection process and the pressing process to ensure the continuity of the molding process.