Brief Introduction of Carbon Fiber Parts Molding Process
According to the latest research report released by market research and consulting service provider Fact.MR, during the forecast period of 2021-2031, the global carbon fiber market will enter a remarkable expansion period, and the compound annual growth rate of the market size during the forecast period will be More than 8%, the global carbon fiber market is expected to reach 9 billion US dollars by 2031. Aerospace and defense applications are still the largest areas of carbon fiber sales and are expected to account for nearly 60% of total sales.
Among many composite materials, carbon fiber composite materials are representative of composite materials with superior performance. Their high elastic modulus and high strength mechanical properties have made them widely used in many fields. As the production process matures and cost control, Carbon fiber composite materials have gradually entered the daily necessities of the general public from aerospace and defense.
There are many ways to form customized carbon fiber products, such as molding, hand lay-up, and autoclave. Among them, the molding process is a relatively common one, which means that the carbon fiber pre-preg is laminated and compacted and placed in a metal mold, and then subjected to high temperature and high pressure molding. The advantages of the molding process include high production efficiency, suitable for automated production; high product accuracy , high efficiency; Compared with the autoclave process, the production efficiency is higher, and the mass production of carbon fiber products can be carried out.
Compression molding is a suitable molding method for thermoset and thermoplastic materials. The technological process is as follows: firstly, the carbon fiber prepreg blank is preheated and softened, and then the carbon fiber prepreg blank is put into the mold cavity to close the mold. The mold is heated and solidified to form, cooled to open the mold, and the carbon fiber composite product is obtained after de-molding. The molding effect of compression molding is better, and the product size accuracy is higher. However, this molding method also has limitations. For example, the design and manufacture of molds are more complicated, the initial investment in equipment such as presses is relatively high, and the size of the product is limited by the scale of the equipment, so the compression molding process is generally only suitable for medium and For mass production of small products, for large-scale carbon fiber products, you can choose the autoclave molding process. However, if precision machining of molds can be achieved, and hydraulic presses with larger tables and temperature control in segments can be selected, the compression molding process can also achieve the production of auto parts, large mechanical parts and other products.
The compression molding of carbon fiber board is the result of temperature, pressure and time. During the research process, the researchers found that the pre-compaction process, heating rate and pressure actually have a great influence on the performance of the carbon fiber board.
1, Pre-compaction process: A common pressing process is to heat and press the product after it is placed in the mold. At this time, a small amount of glue overflow will be produced. However, in the actual layup, air must be mixed between each layer of prepreg. During the heating and pressurization process, the resin cannot be completely discharged due to the excessive viscosity. Future recommends that the mold be placed in the press. Pressure is applied to exhaust the air between the prepreg layers to reduce the porosity.
2, Heating rate: During compression molding, the upper and lower molds of the hot press are electrically heated for high temperature curing. The difference from the autoclave is that the hot press is heated in an open environment, and its heating control is also not heated. Constant like a pressure tank. The temperature is low and the temperature is higher, and the temperature is higher, and the temperature is slow. If the carbon fiber board is thicker, the heating speed is too fast, resulting in inconsistent resin fluidity between the inner and outer resins, and the interlayer shear strength is reduced. Therefore, in the molding process, in order to better control the heating rate, the heating power can be changed, or the thickness of the kraft paper can be increased between the mold and the heating plate to promote the equalization of the heating rate.
3, Pressing timing: Pressing timing is also very critical to the carbon fiber molding process. Too early pressurization will cause the resin to flow out from the overflow tank too much, causing the resin content to be too low and the interlayer shear strength to decrease. When the pressure is too late, the resin has gelled and initially solidified. Not only the thickness is difficult to guarantee, but the bending strength of the carbon fiber board is reduced. In actual use, it is necessary to determine the timing of pressing according to the thermosetting properties of the resin and the specifications and thickness of the carbon fiber board.