MECHANISTIC FORCE MODELING FOR MILLING OF CARBON FIBER-REINFORCED THERMOPLASTIC LAMINATES

Carbon fiber-reinforced thermoplastic composites (CFRTPs) are increasingly utilized across various sectors including transportation, automotive, mass transit, marine, aerospace, military, and construction due to their superior impact toughness, cost-effectiveness, ease of recyclability, and flexibility of design relative to conventional thermoset composites. The global emphasis on reducing the carbon footprint and promoting sustainable manufacturing practices has further expanded CFRTP applications. Despite the near-net-shape production of CFRTPs via processes like compression and injection molding, secondary machining such as milling, drilling, and turning remains essential for achieving precise dimensions and tight geometric tolerance. While extensive research exists on the drilling and milling of thermoset composites, studies focused on the milling of CFRTPs are limited. This study proposes a mechanistic cutting force model for milling compression-molded carbon fiber-reinforced polyamide 6 (CF/PA6) laminates. This model is based on experimentally collected cutting force data from down-milling using a diamond-like coated end mill. A time domain simulation is performed to validate the force model. The objective is to investigate the relationship between the tool wear and the cutting force coefficients for the milling force model. The results indicate a linear increase in the normal, axial and edge force coefficient with the volume of material removed (VMR). The tangential cutting force coefficients exhibit stability in their values. Tool wear, quantified by flank wear width (FWW), is analysed to correlate the growth of cutting force coefficients with wear progression. A maximum FWW value of 0.12 mm was observed across the experiments, remaining below the selected end-of-life criterion of 0.2 mm. Surface quality is evaluated using scanning electron microscopy (SEM) to assess surface defects like delamination, fiber pull-out, or matrix smearing on the machined surface. The simulated are in good agreement with the measured values validating the developed predictive force model.