Carbon Fiber Composite Molding Process Characteristics and Process Flow
Molding process is a certain amount of prepreg into the metal mold cavity of the mold, the use of presses with a heat source to produce a certain temperature and pressure so that the prepreg in the mold cavity is softened by heat, pressure flow, full of flow, filled with the mold cavity molding and curing products of a process method.
Molding process is characterized by the need for heating in the molding process, the purpose of heating is to make the prepreg in the softening of the flow of resin, filling the mold cavity and accelerate the curing reaction of the resin matrix material. During the process of filling the mold cavity with prepreg, not only the resin matrix flows, but also the reinforcing material, and the resin matrix and reinforcing fibers fill all parts of the mold cavity at the same time.
Only the resin matrix viscosity is very large, the bond is very strong, in order to flow with the reinforcing fibers, so the molding process requires a greater molding pressure, which requires metal molds with high strength, high precision and corrosion resistance, and requires the use of special hot presses to control the temperature of the curing molding, pressure, holding time and other process parameters.
Molding method of high production efficiency, product size accuracy, surface finish, especially for the complex structure of the composite material products can generally be molded once, will not damage the performance of the composite material products. Its main shortcoming is that the mold design and manufacturing is more complex, the initial investment is larger. Although the molding process has the above shortcomings, the mold molding process still occupies an important position in the composite material molding process.
1、Preparation
Do a good job of prepreg, molding tooling molds, with the furnace test piece of supporting work, and clean up the mold in the last use of residual resin, debris, to keep the mold clean and smooth.
2、Cutting and laying of prepregs
Will be made into a product of carbon fiber raw materials ready, prepreg after passing the review, calculate the area of raw materials, materials, the number of sheets, the raw material layer by layer of incense added up, at the same time on the superposition of the material for the pre-pressure, pressed into the shape of a regular, the quality of a certain number of dense entities.
3、Molding and curing
Place the stacked raw materials into the mold, and at the same time in the internal plastic airbags, close the mold, the whole into the molding machine, the internal plastic airbags plus a certain constant pressure, constant temperature, set a constant time, so that its curing.
4、Cooling and demolding
After a period of time of pressure outside the mold first cold know for a period of time, and then open the mold, demolding outside the eye to clean up the tooling mold.
5、Processing molding
After demolding the product needs to be cleaned up, with a steel brush or copper brush to scrape off the residual plastic, and blowing with compressed air, the molded product is polished, so that the surface is smooth and clean.
6、Nondestructive testing and final inspection
Non-destructive testing and final inspection of the products are carried out according to the requirements of the design documents.
Analysis of technical points of prepreg molding process
Since the birth of carbon fiber composites, it has always been limited by the manufacturing cost and the impact of production beats, and has not been applied in large quantities. Decide the cost of carbon fiber production and beat is the molding process, carbon fiber composite material molding process there are many, such as RTM, VARI, hot press tanks, oven curing prepreg (OOA), etc., but there are two bottlenecks: 1, the molding cycle time is long; 2, the price is expensive (compared to metals and plastics). Prepreg CompressionMolding, as a kind of molding process, can realize batch production and reduce production cost, which is more and more widely used.
Prepreg molding process refers to the temperature, pressure, in a certain period of time will be prepreg spread into the pre-shaped body compression molding. The molding speed of this process is fast, the equipment requirements are simple, easy to operate, compared with the hot press tank, VARI and OOA process, the product is excellent in both surface apparent quality, good dimensional stability, the process is easy to control.
▲Pre-preg molding process flow chart
Four elements of the molding process
1. Temperature and uniformity: reflecting the degree of reaction between resin and curing agent and the uniformity of reaction position, mainly controlling the quality of molding surface and curing degree;
2. Pressure and uniformity: reflecting the air discharge and flow effect in the resin, controlling the molding surface quality and mechanical properties;
3. The length of curing time: reflecting the degree of curing, to ensure production efficiency;
4. Mold cavity thickness: reflecting the thickness of the product, according to the special characteristics of the carbon fiber material itself, design a reasonable cavity thickness.
Process applicability
Prepreg molding process can theoretically manufacture any structure of the product, product structure if too complex, such as inverted buckle, too much flange area, resulting in a substantial increase in the cost of molds and production difficulties, so for the structure of the particularly complex pieces of applicability is not strong, but we can be structural optimization or block design + bonding solutions to manufacture complex parts.
Related Technology
1. Multi-layer Cutting Technology: Multi-layer prepregs are cut at one time; prepregs with different angles are cut at one time to improve cutting efficiency.
2. Hot-in/hot-out technology: the mold is directly heated to the curing temperature, and the preform is put into the mold and pressed into shape, which shortens the molding time and reduces energy consumption.
3. Net-size molding technology: the preform is punched to net-size first, and then put into the net-size mold for curing, reducing the cutting process.
Process Difficulties
Difficulty in designing molds for complex structure products: If there are a lot of inverted buckles and negative corners in the products, it will make the molds more difficult to manufacture, and at the same time, after the molds are used for a long time, it will lead to the decrease of the precision of the positional coordination of the inserts. Therefore, when designing the product, try to avoid the inverted buckle or negative angle.
Note: the outer covering parts of the product surface quality requirements are very high, carbon fiber material parts of common problems are: product dew texture parts white spots; product messy texture problems; surface pinholes, lack of glue problems, and so on. To sum up the reasons, the curing agent in the prepreg is not uniformly mixed or the reaction is incomplete; the temperature of the mold is not uniform; the temperature and pressure are not in place; the mold design and processing are not in place; the molding process is not controlled; the mold release agent reacts, and so on.