2 FABRICATION PROCESSES The mixture of reinforcement/resin does not really become a composite material until the last phase of the fabrication,that is,when the matrix is hardened.After this phase,it would be impossible to modify the material,as in the way one would like to modify the structure of a metal alloy using heat treatment,for example. In the case of polymer matrix composites,this has to be polymerized,for example, polyester resin.During the solidification process,it passes from the liquid state to the solid state by copolymerization with a monomer that is mixed with the resin The phenomenon leads to hardening.This can be done using either a chemical (accelerator)or heat.The following pages will describe the principal processes for the formation of composite parts. 2.1 MOLDING PROCESSES The flow chart in Figure 2.1 shows the steps found in all molding processes. Forming by molding processes varies depending on the nature of the part,the number of parts,and the cost.The mold material can be made of metal,polymer, wood,or plaster. 2.1.1 Contact Molding Contact molding(see Figure 2.2)is open molding (there is only one mold,either male or female).The layers of fibers impregnated with resin (and accelerator)are placed on the mold.Compaction is done using a roller to squeeze out the air pockets.The duration for resin setting varies,depending on the amount of accel- erator,from a few minutes to a few hours.One can also obtain parts of large dimensions at the rate of about 2 to 4 parts per day per mold. 2.1.2 Compression Molding With compression molding (see Figure 2.3).the countermold will close the mold after the impregnated reinforcements have been placed on the mold.The whole assembly is placed in a press that can apply a pressure of 1 to 2 bars.The polymerization takes place either at ambient temperature or higher. The process is good for average volume production:one can obtain several dozen parts a day (up to 200 with heating).This has application for automotive and aerospace parts. 2003 by CRC Press LLC2 FABRICATION PROCESSES The mixture of reinforcement/resin does not really become a composite material until the last phase of the fabrication, that is, when the matrix is hardened. After this phase, it would be impossible to modify the material, as in the way one would like to modify the structure of a metal alloy using heat treatment, for example. In the case of polymer matrix composites, this has to be polymerized, for example, polyester resin. During the solidification process, it passes from the liquid state to the solid state by copolymerization with a monomer that is mixed with the resin. The phenomenon leads to hardening. This can be done using either a chemical (accelerator) or heat. The following pages will describe the principal processes for the formation of composite parts. 2.1 MOLDING PROCESSES The flow chart in Figure 2.1 shows the steps found in all molding processes. Forming by molding processes varies depending on the nature of the part, the number of parts, and the cost. The mold material can be made of metal, polymer, wood, or plaster. 2.1.1 Contact Molding Contact molding (see Figure 2.2) is open molding (there is only one mold, either male or female). The layers of fibers impregnated with resin (and accelerator) are placed on the mold. Compaction is done using a roller to squeeze out the air pockets. The duration for resin setting varies, depending on the amount of accel￾erator, from a few minutes to a few hours. One can also obtain parts of large dimensions at the rate of about 2 to 4 parts per day per mold. 2.1.2 Compression Molding With compression molding (see Figure 2.3), the countermold will close the mold after the impregnated reinforcements have been placed on the mold. The whole assembly is placed in a press that can apply a pressure of 1 to 2 bars. The polymerization takes place either at ambient temperature or higher. The process is good for average volume production: one can obtain several dozen parts a day (up to 200 with heating). This has application for automotive and aerospace parts. TX846_Frame_C02 Page 17 Monday, November 18, 2002 10:40 AM © 2003 by CRC Press LLC