Effects of LM-PAEK film thickness and processing parameters on interfacial remelting and lap-shear strength of overmolded CF/PEEK joints

Injection overmolding of short carbon fiber reinforced PEEK onto continuous carbon fiber reinforced PEEK (cCF/PEEK) laminates is promising for lightweight composite structures. However, the high melting temperature of PEEK often leads to insufficient interfacial remelting due to limited thermal input during overmolding, resulting in weak interfacial bonding. To address this issue, a low-melting polyaryletherketone (LM-PAEK) film is introduced as an interlayer between the laminate and the overmolded part. This study investigates the effects of LM-PAEK film thickness and key processing parameters on the interfacial microstructure and lap-shear strength of the overmolded joints. The results show that the LM-PAEK film enables preferential interfacial remelting due to its lower melting point, establishing a robust dual-interface bonding structure. As the LM-PAEK film thickness increases, resin-rich regions become more pronounced, while continuous fiber dispersion decrease, reducing the reinforcing effect of the continuous fibers and the interfacial strength. Among the investigated conditions, the sample with a 0.15 mm LM-PAEK film showed the best performance, achieving the highest interfacial strength of 39.15 ± 2.35 MPa, compared to 14.31 ± 2.79 MPa for the sample without film. Regarding processing parameters, higher insert preheating and melt temperatures enhance interfacial fusion and promote hybrid failure, while injection velocity exhibits the highest strength at 50 mm/s. Overall, the LM-PAEK film with controlled film thickness and processing conditions provides a robust strategy for strengthening overmolded PEEK joints, delivering superior mechanical performance and processing flexibility.