Manufacturing and Analysis of Overmolded Hybrid Fiber Polyamide 6 Composite

Currently, fiber-reinforced thermoplastic composites are widely applied in structural applications. It has great potential to replace metal structures and provides advantages in weight reduction. In this study, the pretensioned unidirectional carbon fiber was overmolded by Polyamide 6 contained 30%wt of glass fibers (PA 6-30GF). Process parameters such as injection pressure, melting temperature, duration of carbon fiber cryogenic treatment, and fiber pretension were optimized to maximize the flexural strength, impact strength, and interlaminar properties of the hybrid composite. The relationship between factors and responses was analyzed using Box-Behnken design (BBD) from response surface methodology (RSM) and analysis of variance (ANOVA). Three levels were assigned for each factor. There were 27 experimental trials carried out, and a significant regression for the coefficient between the factors was derived. The BBD and ANOVA analysis demonstrate that the predicted values from the model are in satisfactory correlation with the experimental results. The optimum responses found were achieved by setting the following injection molding parameters: melting temperature of 278 °C and injection pressure of 122 bar. Carbon fiber, as a unidirectional reinforcement, should be immersed in liquid nitrogen for 10 min and mounted on the mold in a pretensioned state with a force of 100 N. The combination of these parameters can produce an optimum flexural strength of 248.6 Mpa, impact strength of 173.4 kJ/m² and an ILSS of 30.4 Mpa.