Processes of Autoclave Production Method
What are the processes of the autoclave production method for composite parts? The curing process of the autoclave and the technical points for each stage are explained as follows:
1. Temperature Increasing Stage
It is essential to set a reasonable heating rate, i.e. considering the time and speed for increasing temperature. For large parts, the heating should be slow to ensure uniform heating of the entire part. 2 ℃/min is the commonly used heating rate. At this stage, vacuum pressure is mainly used, and a certain amount of pressure can be applied depending on the situation.
2. Temperature Maintaining Stage - Glue suction stage
This is a stage of keeping the temperature at certain degree in order to let the resin the flow thoroughly. For temperature and duration time of this stage vary for different kinds of resin matrix. The purpose of this stage is to let resin melt and impregnate the fiber completely removing volatile matters. Resin would then gradually solidified to gel stage. The forming pressure at this stage is 1/3 to 1/2 of the total pressure, allowing some resin to flow out to ensure that the final resin content of the product meets the design requirements.
3. Continual temperature increasing stage
At this stage, the resin matrix has become semi cured, and the solvent and low molecular weight volatile matter are fully discharged, elevating the temperature to the curing temperature. The curing aversion of thermosetting resin is exothermic reaction. During the curing process, there is heat release. If the heating rate is too fast, the curing reaction speed will be accelerated rapidly, and a large amount of heat will be released in a concentrated manner, which will lead to local burning of materials. This phenomenon is called explosion polymerization which must be avoided.
4. Temperature and Pressure Keeping Stage
The resin matrix further solidifies at this stage which full pressure is required to ensure that the resin is fully compacted between layers during the further solidification process. The stage from full pressure to the end is called the pressurising stage. The time from the point reaching the curing temperature until the completion of whole autoclave process is called constant temperature time.
The temperature, pressure, and constant temperature time are important process parameters in the forming process, and must be strictly controlled according to the formula of the resin matrix used.
5. Cooling stage
At this stage, the pressurized level is maintain and the autoclave is cooled by free air or forced air.
The pressure then is relieved and the product can be taken out. If the cooling time is too short, it is easy to cause warping, cracking and other phenomena in the product. If the cooling time is too long, it will not significantly help the product quality, but it will prolong the production cycle.
This stage, also known as the post-processing stage, refers to the high-temperature cured parts that can be maintained at a lower temperature for a period of time to eliminate the internal stress generated by high-temperature curing and prevent deformation of the parts after unloading and demolding.
In summary, the various process parameters during the curing process of the autoclave should be determined based on the characteristics of the resin matrix used. During the molding process, strict control of various process parameters is necessary to obtain high-quality products.
Complex shapes, larger sizes, and high-quality products can be obtained by using only one female or male mold.
Autoclave is still widely used to manufacture high-end composite materials, but the equipment investment is large and the operation cost is high. In order to reduce manufacturing costs and improve production efficiency, a new molding technology has been developed, which is the co-curing integrated molding technology is developed.
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