One-Click Access To Learn About HP-RTM Process

 

1. Process Definition

HP-RTM (High Pressure Resin Transfer Molding) is the abbreviation of high pressure resin transfer molding process. It refers to the process of using high pressure to mix resins and inject them into a vacuum-tight mold pre-laid with fiber reinforcement materials and pre-set inserts, and then obtain the molding process of composite materials through resin flow filling, impregnation, curing and demolding. The process is shown in Figure 1:

 

Figure 1 Schematic diagram of HP-RTM process principle

 

2、 HP-RTM

2. HP-RTM Process Evolution

 

RTM (Resin Transfer Molding) process originated from the MARCO method in 1940. The Macro method is quite simple, which is to vacuum the mold cavity to drive the resin impregnation process. The US Navy contractor used this method to develop a large fiberglass reinforced plastic hull.

 

In the 1950s, it was called the RTM process. This process can produce double-sided smooth products. The injection pressure of the resin is moderate, which is superior to the hand lay-up process, so it has been developed. From the 1950s to the 1970s, the initial RTM had low cost but high technical requirements, especially high requirements for raw materials and molds, so it developed slowly.

 

It was not until 1985 that the second-generation RTM processing method, which aims to shorten the molding cycle, improve surface smoothness and quality stability, was made public, which made RTM have obvious advantages in terms of raw materials and product strength. In the 1990s, the RTM molding process and its theoretical research reached a climax. Many European and American companies invested heavily in the development of RTM technology and opened vocational schools to train RTM professionals.

 

Entering the 21st century, with the improvement of my country’s chemical industry and machinery manufacturing level, as well as the improvement of market application technology level, my country’s RTM process technology for composite materials has also ushered in a new development period, not only in the technical level, but also in the production scale and automation level. Great progress has been made.

 

In comparison, the RTM process technology has obvious advantages, and its characteristics are mainly reflected in: strong flexibility in mold manufacturing and material selection; can manufacture parts with good surface quality and high dimensional accuracy, especially large parts; easy to achieve local reinforcement, and embedded parts can be pre-placed; fiber content can reach up to 60%, and fillers can be added to the resin to reduce costs and improve performance; closed mold molding, low styrene emissions, which is beneficial to environmental protection; low-pressure injection, generally ≤0.4MPa, fiberglass molds, aluminum molds, etc. can be used, and the mold cost is low; the product porosity is low, generally less than 1%.

 

Limitations: suitable for a certain batch of products, economic scale products are 500~2000 pieces; mold design and manufacturing are somewhat difficult; resin flow and impregnation control are difficult, resulting in increased process complexity and uncontrollability.

 

Compared with other molding processes, composite RTM molding technology has obvious advantages of high performance and low cost. Especially in the face of the current rapid development and huge potential of the automotive composite material market demand, how to improve composite material molding technology to better adapt to market demand has become one of the focuses of researchers.

 

Domestic and foreign researchers have also carried out a lot of fruitful research, making RTM technology more mature and forming a complete material, process and theoretical system. And a series of new RTM molding technologies have been developed based on RTM process technology. The main ones are: VARTM (Vacuum Assisted Resin Transfer Molding), Light-RTM (Light-Resin Transfer Molding), SCRIMP (Seemann Composites Resin Infusion Manufacturing Process), MI-RTM (Multiple Insert Tooling Resin Transfer Molding), HP-RTM (High Pressure Resin Transfer Molding), HP-CRTM (High Pressure Compression Resin Transfer Molding), etc.

 

Compared with the conventional RTM process, the VARTM process technology uses vacuum pressure as the power, and adopts a single-sided rigid mold and a vacuum bag to form the mold cavity of the product, making the mold lighter; the role of vacuum helps the resin to impregnate the fiber, making the fiber impregnation more fully; at the same time, the vacuum also plays a role in removing the air in the fiber bundle, thereby reducing the formation of microscopic voids and obtaining products with lower void ratios; the role of vacuum makes the product fiber content higher and the mechanical properties of the produced components better.

 

Based on the VARTM process technology, the Light-RTM process uses a semi-rigid mold and a rigid mold to form the mold cavity of the product, and adopts vacuum sealing technology. The molding mold can be used repeatedly, which greatly reduces the mold cost and the manufacturing cost of the product; at the same time, the use of a ring-like channel to inject glue from all sides of the mold, and the collection cup aggregate technology, greatly improves the flow and filling of the resin, and improves production efficiency.

 

The SCRIMP process uses a carefully set resin distribution system to make the resin glue quickly flow and fill in the length direction first, and then slowly infiltrate in the thickness direction under vacuum pressure, which greatly improves the impregnation effect, reduces the occurrence of defects, and makes the molded parts have good consistency and repeatability. It also overcomes the shortcomings of VARTM in the production of large-scale flat and curved laminated structures and reinforced special-shaped components, such as slow fiber impregnation speed and long molding cycle. Especially in the field of large-scale product production, this technology has unique technical advantages.

 

MI-RTM process technology consists of multiple insert molds and mold cavity support systems. It mainly decomposes and moves out of the mold cavity to complete the multiple processes that were originally concentrated in the mold cavity in the traditional RTM process. This greatly reduces the molding time and fully utilizes the effectiveness of RTM equipment, thereby reducing the mold manufacturing cost and providing a low-risk and low-cost method for mass manufacturing of RTM products.

 

The multi-station medium and high pressure RTM molding process technology that has emerged in recent years is also based on this concept. In the relatively time-consuming fiber laying link of the molding cycle, multiple fiber laying stations are set up, and the products are injected and molded in sequence or alternately with a single fixed mold, which greatly shortens the fiber laying time, improves production efficiency and equipment utilization, and has reduced the cost of parts.

 

HP-RTM is a new RTM process technology introduced in recent years to cope with the mass production of high-performance thermosetting composite parts. It uses preforms, steel molds, vacuum-assisted exhaust, high-pressure mixed injection, and resin impregnation and curing of fibers under high pressure to achieve low-cost, short-cycle (large-scale), and high-quality production.

 

Compared with traditional RTM, the HP-RTM process has the following advantages: First, fast mold filling and good impregnation effect, which significantly reduces bubbles and porosity; second, the use of highly active resins shortens the production cycle, and the process stability and repeatability are high; third, the use of internal release agents and self-cleaning systems, the surface effect of the parts is excellent, and the thickness and shape deviations are small. It can achieve low-cost, short-cycle (large-scale), and high-quality production.

 

The HP-CRTM process technology increases the gap in the sealed mold cavity before resin injection in the HP-RTM process technology, thereby increasing the resin injection channel. After the injection is completed, the mold is completely closed under high pressure, and the resin system flows to fill the mold with the closing pressure. The molding pressure is relatively low, which avoids the impulse of the fibers, increases the permeability and flow distance of the resin, increases the impregnation speed of the fibers, effectively avoids the generation of dry fibers, and shortens the molding cycle of the parts.

 

3. Process Flow

(1) Upstream Process

 

(2) Pressing Process

 

(3) Downstream Process

4. Process Analysis

The HP-RTM process technology is introduced by taking the HP-RTM automated production line (as shown in Figure 2) jointly developed by Dieffenbacher and KraussMaffei of Germany as an example. The specific process is as follows:

 

Figure 2 HP-RTM automated production line developed by Dieffenbacher and KraussMaffei

 

As can be seen from the HP-RTM automated production line in Figure 2, the HP-RTM automated production line is mainly composed of a preform processing center, preform handling, RTM injection system, metering control system, and a part processing center. The fiber preform processing center is shown in Figure 3.

 

Figure 3 Fiber preform preparation and processing center

 

 1) Upstream Process

① Fiber unwinding and cutting

Figure 4 Automatic cutting of carbon fiber plies

 

First, fix the roll of carbon fiber fabric on the rotating shaft of the automatic cutting machine, input the preform cutting pattern into the automatic cutting, and optimize the cutting pattern; unfold the carbon fiber fabric roll, start the cutting machine, and automatically cut the preform ply pattern, as shown in Figure 4. The cut fiber ply is sucked up by the suction cup of the robot arm and transferred to the next process equipment, as shown in Figures 5 and 6.

 

Figure 5 The robotic arm absorbs and transfers the cut fiber fabric

Figure 6 The robot arm suction cup absorbs and cuts the fiber fabric

 

② Figure 6 The robot arm suction cup absorbs and cuts the fiber fabric

Figure 7 Spraying of pre-setting agent for fiber fabric

 

The cut fiber fabric is transferred to the pre-setting agent spraying equipment, and the spraying equipment is started to spray the pre-setting adhesive evenly on the surface of the fiber fabric. The fiber fabric needs to be moved during spraying so that the pre-setting agent can be evenly sprayed on the surface of the fiber fabric, as shown in Figure 7.

 

③ Positioning And Stacking Of Fiber Layers

The carbon fiber fabric coated with the fiber pre-setting agent is transferred to the fabric stacking equipment, and the fiber fabric is positioned and stacked in sequence according to the designed fiber layer structure of the workpiece, and laid flat on the fabric stacking conveyor belt. As shown in Figure 8.

 

Figure 8 Positioning, stacking and laying of fiber layers

 

④ Fiber Laying

Use the fabric stacking conveyor to transfer the stacked fiber fabric to the fiber preforming equipment, as shown in Figure 9; when transferring the fiber fabric, the conveyor belt’s moving speed and position must be precisely controlled to prevent the fiber fabric from moving or dislocating during the laying process, which would affect the performance of the product.

 

Figure 9 Transfer and laying of fiber layer structure

 

⑤ Pre-forming of Fiber Fabric

Evenly lay the fiber fabric layer in the preforming mold. First, press down the pressure head in the center of the preform to compact the fiber layer structure. Then press down the pressure head of the preform mold from the center to the outside in sequence. When pressing down, try to reduce the shrinkage of the fiber as much as possible to affect the performance of the product. As shown in Figure 10. Under the heat and pressure of the preforming mold, the fiber preform is shaped.

 

Figure 10 Hot pressing preforming of fiber preform

 

⑥ Cutting of Preform

The preheated and prepressed carbon fiber reinforcement is transferred into the preform cutting mold and covered with a cutting sample mold. Based on the cutting sample mold, the robot arm cuts along the edge of the sample mold to remove excess carbon fiber and obtain a fiber preform corresponding to the size of the injection mold cavity. The cutting process is shown in Figures 11 and 12.

 

Figure 11 Cutting and trimming of fiber preform

Figure 12 The fiber preform and its cutting mold after trimming

 

(2) Pressing process

① Placing the preform

Stack the brackets for placing the preforms neatly in sequence, and use a robot arm with a suction cup to suck up the fiber preforms. Transfer the preforms to the opened RTM molding mold, close the RTM injection mold, and lock the RTM molding mold with a locking mechanism. As shown in Figures 13, 14, and 15.

 

Figure 13 Fiber preform fixing bracket, robot arm, and suction cup

Figure 14 Fiber preform transferred into RTM molding mold

Figure 15 Closure of RTM injection mold

 

② Resin Transfer Injection Process

Under the condition that the injection mold cavity is always sealed, the mold is evacuated, and the mold clearance of the mold is increased by using the rebound performance of the double rubber sealing ring, as shown in the figure; and the liquid low-viscosity resin is injected from the bottom center of the mold into the high-temperature (mold temperature ≥ 150℃) sealed injection mold under the action of the high-pressure injection machine.

 

The proportion of each component material (main resin, curing agent, internal release agent, etc.) in the resin system is accurately measured and controlled by a high-precision high-temperature injection machine, and enters the mixing head of the injection machine under the action of a high-pressure metering pump, and is mixed at high pressure in the mixing head, and the mixed resin is quickly injected into the high-temperature mold cavity.

 

Figure 16 Closing gap of the mold during the HP-RTM main resin injection process

Figure 17 HP-RTM resin vacuum injection process

 

After the injection is completed, the mold is completely closed. During the closing process, the mold further squeezes the injected resin to fill and infiltrate the carbon fiber reinforced material, and then quickly solidifies under high temperature and high pressure.

 

Figure 18 When the injection is finished, the mold is closed and the resin is squeezed out

 

③ In-mold Spraying Technology

After the HP-RTM resin is cured, the mold gap is controlled again, and low-viscosity mold surface resin is injected from the reserved side holes and flow channels, and the mold is completely closed again, the gel coat resin is squeezed to fill the mold as much as possible, and a uniform resin film is sprayed on the surface of the product.

 

Figure 19 In-mold spraying process during HP-RTM process

 

④ Demolding And Mold Cleaning

After the gel coat resin is cured, open the hydraulic press from slow to fast, use the mechanical arm and its adsorption device to adsorb and fix the workpiece, open the ejection mechanism to eject the workpiece, and make the ejected workpiece tightly adsorbed on the suction cup of the mechanical arm. At the same time, clean the resin flash remaining in the mold.

 

Figure 20 The part wrapped in the upper mold when the mold is opened

Figure 21 Adsorption and ejection of the workpiece

 

⑤ Cooling And Shaping Of The Workpiece

After demolding, the molded workpiece, which is still in a high temperature state, is transferred to the cooling and shaping tooling using a robotic arm and a suction cup, and the workpiece is tightly adsorbed on the cooling and shaping tooling using a vacuum, and the workpiece is quickly cooled to room temperature through the cooling and shaping tooling.

 

Figure 22: The workpiece is transferred to the cooling and shaping tooling

Figure 23 Cooling and shaping tooling and molded parts

 

⑥ Applying Release Agent

After the part is demolded, use a brush, air pump, air nozzle, etc. to clean the mold, remove the residual resin and fiber in the mold, and wipe the mold clean. Apply the release agent evenly on the surface of the mold and prepare for the next cycle of production.

 

(3) Downstream Process

① Trimming the contour of the part

The cooled and shaped composite sample is transferred to the machining center. In order to ensure the machining accuracy of the part, the part is directly moved to the machining tooling, and the manipulator and machining tool are used to trim the excess flash and process edges of the part.

 

Figure 24 Composite material machining center

Figure 25 Composite material machining tools and tool holders

Figure 26 Machining trimming of composite parts

 

② Processing Of The Connection Structure Of The Workpiece And Dimensional Inspection

After the trimming process is completed, the connection and matching structure of the workpiece, such as the positioning hole and the flatness of the matching surface, needs to be machined. During the processing, the cutting tool needs to be replaced according to the situation to ensure the processing accuracy of the workpiece. After the machining is completed, the inspection tool needs to be replaced to check the dimensional tolerance of the workpiece. After the inspection is completed, the composite material workpiece that meets the use requirements is obtained. As shown in Figures 27 and 28.

 

Figure 27 Machining of connection holes in composite parts

Figure 28 Dimensional accuracy inspection of composite parts

 

5. Process Characteristics

HP-RTM includes preforming, resin injection, pressing and finishing processes. Compared with the traditional RTM process, the HP-RTM process adds a pressing process after injection, reduces the difficulty of resin injection filling, improves the impregnation quality of preforms, and shortens the molding cycle. The specific process characteristics are as follows:

① The resin quickly fills the mold cavity. The larger mold gap and higher injection pressure (1.0-15.0MPa), as well as the low viscosity resin, greatly improve the injection speed of the resin and shorten the molding process cycle (3-5min).

② The curing reaction rate of the resin is improved and the curing cycle of the resin is shortened. The high-activity fast-curing resin system is adopted, and the high-efficiency high-pressure mixing and injection equipment are used to make the resin matrix mixing uniformity better. At the same time, a high-temperature environment is required during molding, which greatly improves the curing reaction rate of the resin.

③ Use internal release agent and self-cleaning system. 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.

④ The pore content in the part is reduced and the performance of the part is improved. The use of in-mold rapid vacuuming technology effectively reduces the porosity content in the parts, improves the impregnation efficiency of the fiber, improves the interface bonding ability of the fiber and the resin, and improves the quality of the product.

⑤ Reduces the process difficulty of the parts and improves the quality of the resin impregnated reinforcement. The combination of vacuuming and compression molding after injection reduces the difficulty of designing the injection port and exhaust port of the RTM process, improves the flow filling ability of the resin, and the impregnation quality of the resin on the fiber.

⑥ The thickness and three-dimensional shape size deviation of the product are low. In order to ensure the sealing effect of the mold, a double-rigid surface closed mold is used, and a large-tonnage hydraulic press is used for pressurization, 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 enables the parts to obtain high-precision surface quality in a very short time.

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

 

6. Key Process Technologies

 

(1) Pre-forming technology for fiber-reinforced materials

Fiber pre-forming technology mainly includes: textile, knitting and woven preforms; stitching preforms; chopped fiber spray preforms; hot pressing preforms, etc. Among them, hot pressing setting technology is the most widely used. In this technology, the setting agent is the basic guarantee, and the fiber preforming mold and pressing process technology are the key to fiber setting.

For the HP-RTM process, the structure of the product is relatively simple, so the setting mold is also relatively simple. The key lies in how to control the setting mold and pressurizing tooling to effectively and orderly pressurize and set by designing and controlling the program.

 

(2) High-precision resin metering, mixing and injection technology

The mixing and injection of HP-RTM process resin mainly includes: two systems: resin main material and in-mold spraying resin. The key to its control lies in high-precision resin metering system, rapid and uniform mixing technology and mixing equipment self-cleaning technology.

The HP-RTM process resin main material needs to be accurately metered under high temperature and high pressure, which requires high-precision metering pump equipment. Uniform mixing and self-cleaning of resins require the design of efficient, self-cleaning, and multiple mixing heads.

 

(3) Design of uniformity and sealing of the molding mold temperature field

During the HP-RTM process, the uniformity of the molding mold temperature field not only determines and affects the flow filling performance of the resin in the mold cavity, but also has a great influence on the fiber wetting performance, as well as the overall performance of the composite material and the internal stress of the product. Therefore, it is necessary to adopt a medium heating method combined with an efficient and reasonable circulation oil circuit design.

 

The sealing of the molding mold directly determines the resin flow filling characteristics 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, method and number of the sealing ring according to the product design. At the same time, it is necessary to solve the sealing problems of the mold matching gap, ejection system, vacuum system and other positions to ensure that there is no leakage during the resin filling process to ensure the performance of the product.

 

(4) High-precision hydraulic press and its control technology

 

During the HP-RTM process, the mold gap control during the resin filling process and the pressure control during the pressing process require an efficient and high-precision hydraulic press system to ensure. At the same time, it is necessary to provide timely control technology according to the needs of the injection process and the pressing process to ensure the continuity of the molding process.

 

With the advancement of carbon fiber preparation and processing technology, the price of carbon fiber has dropped significantly, and the automobile industry, which has high expectations for carbon fiber, has seen hope. The advent of the German BMW pure electric vehicles I3 and I8 has attracted the attention of composite material research to the extensive use of HP-RTM process technology in I3 and I8. According to a report from BMW, as shown in Figure 29, among the 34 carbon fiber composite parts of the Life module structure of the i3 car body, 13 of them are made by HP-RTM process, 2 are made by foam sandwich RTM process, and the remaining 19 are made by molding process. There are also 14 parts made by RTM process on the I8 car, as shown in Figure 30. BMW’s latest 7 series sedan uses 4 composite molding process technologies in the 16 composite materials of the body, as shown in Figure 31.

Figure 29 Distribution of composite materials in the body structure of the BMW I3 sedan

Figure 30 Distribution of composite materials in the body structure of the BMW I8 sedan

Figure 31 Distribution of composite materials in the body structure of the BMW 7 Series sedan

 

In the past two years, researchers of composite materials at home and abroad have been unprecedentedly active in the research and development of HP-RTM process technology, its raw materials and supporting equipment. A series of research progress has also been achieved, which are specifically manifested as follows:

 

(1) Resin Matrix

The requirements for the resin matrix used in the HP-RTM process are mainly reflected in: “one long” refers to the appropriately long gel time of the resin; “one fast” refers to the fast curing speed of the resin; “two highs” refers to the high defoaming and high wettability of the resin; “four lows” refers to the low viscosity, low volatility, low curing shrinkage and low exothermic peak of the resin.

At present, the relatively mature resin matrix preparation technology for HP-RTM process is mainly in the hands of international chemical giants, among which the representative ones are:

Huntsman’s two resin systems produced on a large scale include: Araldite® LY 3585/Aradur® 3475, Araldite® LY 3585/Hardener XB 3458 (largely used in the body structure of I3). These two resin systems can be used in both HP-RTM process and WCM (Wet Compression Molding) process. The molding temperatures of the two resins are 115℃ and 100℃ respectively, and the process cycles are: 3 minutes and 30 seconds and 6 minutes and 15 seconds respectively.

The injection time of DOW Chemical Company’s VORAFORCE 5300/ VORAFORCE 5300 IMR resin system is 15-60s, and the curing time is 30-120s.

The EP TRAC 06000/ EK TRAC 06130 resin system developed by Hexion has a molding temperature of 120°C and a mold molding time of 93s.

The curing time of Loctite MAX3 matrix resin produced by Henkel is 5.5min and is used to produce the roof of the car.

The molding cycle of Epikote 05475/ Epikure 05500/ Heloxy 112 resin system produced by Momentive is 2 minutes and 15 seconds at 130°C, and the glass transition temperature of the resin matrix is ​​110°C.

BASF has developed a new epoxy resin system Baxxodur System 2202 resin system specifically for the HP-RTM process of structural parts. The resin has an injection time of only 45 seconds at 120°C, and has excellent fiber impregnation effect, and can be cured within 2.5 minutes.

Domestic: Shanghai Huibai New Materials Co., Ltd. produces three resin systems: RA-8930A/B, RA-8931A/B, and RA-8920A/B. The gel time at 120°C is 34s, 33s, and 18s respectively.

The EpoTech®4330A/B resin system produced by Guangdong Bohui New Materials Technology Co., Ltd. can achieve rapid curing and molding at 130°C/1min or 120°C/3min. The EpoTech®4330A/4331B resin system can now be rapidly cured and molded at 140°C/2min or 120°C/5min.

 

(2) Molding Equipment

At present, the HP-RTM process equipment technology is relatively mature and mainly in the hands of international mechanical processing equipment manufacturing giants, among which the representative ones are:

The high-pressure resin transfer molding process (HP-RTM) automated production line jointly developed by Dieffenbacher and KraussMaffei of Germany. The specific division of labor between the two companies is shown in Figure 32; the fiber preforming equipment and pressing molding equipment for the HP-RTM production line developed by Dieffenbacher are shown in Figures 33 and 34; the injection molding machine and mixing head for the HP-RTM process designed and developed by KraussMaffei are shown in Figures 35 and 36.

Figure 32 Specific division of labor of HP-RTM production lines of Dieffenbacher and KraussMaffei

Figure 33 Fiber preforming equipment provided by Tiefenbach

Figure 34 High-pressure pressing equipment provided by Tiefenbach

Figure 35 RTM glue injection machine provided by KraussMaffei HP-RTM

 

Figure 36 Special mixing head provided by KraussMaffei HP-RTM

 

ENGEL and Hennecke jointly developed an automated production line for high-pressure resin transfer molding. The principle of the designed production line is shown in Figure 37, and Figure 38 is a physical picture of the production line; the HP-RTM glue injection machine and its mixing head developed by Hennecke are shown in Figures 39 and 40.

Figure 37 Schematic diagram of the HP-RTM production line developed by Engel and Hennecke、

Figure 38 Engel and Hennecke develop HP-RTM production line

Figure 39 Hennecke develops HP-RTM glue injection machine

Figure 40 Hennecke develops mixing head for HP-RTM injection machine

 

Cannon of Italy independently designed and developed a complete HP-RTM production line as shown in Figures 41-45.

Figure 41 HP-RTM production line designed and developed by Kanglong Company 1

Figure 42 HP-RTM fiber preforming production line designed by Kanglong

Figure 43 HP-RTM fiber preforming production line developed by Kanglong

Figure 44 HP-RTM special glue injection machine developed by Kanglong

Figure 45 HP-RTM special mixing head designed and developed by Kanglong Company

 

Germany’s Schuler Group and Germany’s FRIMO Group also jointly developed an HP-RTM production line, the designed production line is shown in Figure 46; the special hydraulic press developed by Schuler is shown in Figure 47.

Figure 46 HP-RTM production line designed by German Schuler Group and German Fulimo Group

Figure 47 HP-RTM hydraulic press produced by Schuler, Germany

 

Domestic research has also been conducted on HP-RTM process molding equipment. However, due to the high requirements for equipment R&D investment, it is difficult for a single equipment manufacturer to support the development of the entire production line in terms of funds and technical reserves. There is also a lack of effective communication and cooperation mechanisms between large enterprises. Therefore, so far, except for the two HP-RTM production lines introduced from abroad by Kangde Composite Materials Co., Ltd., there is no independently developed HP-RTM production line.

 

The single equipment developed in China mainly includes: Shanghai Yueke Composite Materials Co., Ltd. developed a HP-RTM special injection machine, and Zhejiang Youpu Mould Co., Ltd. developed a rapid prototyping double-station RTM press and molding mold, as shown in Figure 48.

Figure 48 Dual-station RTM press and molding mold developed by Zhejiang Youpu Mould Co., Ltd.

 

 (3) Application Development Direction and Trend

The composite materials prepared by HP-RTM have the characteristics and advantages of high strength modulus, low porosity, excellent surface performance, and high production efficiency. The products currently developed are mainly used for various automotive parts with high load-bearing functions. The composite materials products currently produced by HP-RTM process mainly include:

 

The car roof produced by Italy’s Conlon Group for the BMW M3 sedan, as shown in Figure 49. The BMW i3 body Life module body structure jointly developed by BMW and SGL and manufactured by HP-RTM process, as shown in Figure 50. The side roof reinforcement plate and the middle cross beam structure of the BMW 7 series sedan are all made by HP-RTM process, as shown in Figure 51. The composite leaf spring produced by Benteler-SGL using Henkel’s Loctite resin matrix using HP-RTM can reduce the weight by 65%, as shown in Figure 52; Benteler-SGL uses HP-RTM process to produce composite vehicle struts, as shown in Figure 53. KraussMaffei uses Henkel Loctite Max3 resin to produce a car roof,

 

as shown in Figure 54. Tiefenbach produces HP-RTM composite trunk lining,

 

as shown in Figure 55. Shanghai Huibai New Materials Co., Ltd. uses RA-8920A/B to produce a car roof, as shown in Figure 56.

Figure 49 BMW M3 sedan HP-RTM roof

Figure 50 I3 sedan body jointly developed by BMW and SGL

Figure 51 HP-RTM side roof reinforcement for BMW 7 Series sedan

Figure 52 Composite leaf spring produced by Benteler-SGL using HP-RTM、

Figure 53 Composite vehicle support rod produced by Benteler-SGL using HP-RTM process

Figure 54 Car roof produced using Henkel Loctite Max3 resin

Figure 55 HP-RTM composite trunk lining produced by Tiefenbach

Figure 56 Automobile roof produced by Shanghai Huibai New Materials Co., Ltd. using RA-8920A/B

It is not difficult to see from the application and development of HP-RTM process products that the products currently developed are mainly concentrated in the field of composite structural parts with high strength requirements. Moreover, since the HP-RTM process equipment system includes not only a fiber preforming system, but also requires a fast hydraulic system, an efficient self-cleaning mixed injection system, a high-sealing mold system, a computer control system, etc., the equipment system is complicated and the manufacturing technology is difficult, which greatly increases the manufacturing cost of composite parts. Although this process technology meets the production rhythm requirements of automotive products, its high manufacturing cost is still a certain distance from the low cost required by the automotive industry. Therefore, it is difficult to promote and apply it.

 

In summary, the problems that must be solved for the further promotion and application of HP-RTM process technology mainly include:

① Design and manufacturing technology capabilities of high-efficiency and low-cost manufacturing equipment;

② Research and development of high-performance, low-viscosity, and fast-curing resin systems;

③ Collaborative development mechanisms and cooperation models of industry-related enterprises;

④ Actively explore and develop new application markets.