Abstract
Background: Polyamide 6 (PA6) is a widely used engineering thermoplastic known for its excellent mechanical properties, thermal stability, and wear resistance. However, its semi-crystalline structure and low thermal conductivity present significant challenges during machining operations, particularly in achieving optimal surface finish. Surface roughness is a critical quality indicator that affects the functional performance, fatigue life, and aesthetic appearance of machined polymer components. Understanding the complex interactions between machining parameters and environmental conditions is essential for optimizing the turning process of PA6.
Objective: This comprehensive review investigates the influence of machining parameters—cutting velocity (Vc), feed rate (FR), and depth of cut (Dc)—and machining environments—dry (D), compressed air (A), and air-water mixture (A+W)—on the surface roughness (Ra) of Polyamide 6 during turning operations. The study aims to identify the most influential parameters, quantify their percentage contributions, and determine the optimal combination for achieving minimum surface roughness.
Methods: A systematic experimental approach was combined with statistical analysis using Taguchi Experiment Design (TED) and Analysis of Variance (ANOVA). Experiments were conducted on a CU-500 lathe using a carbide cutting tool (Mitsubishi CNMG 120408 UE6020) with a PCLNR 2525 M12 tool holder. PA6 samples of 40 mm diameter and 500 mm length were machined at three levels for each parameter: cutting velocity (125, 200, 250 m/min), feed rate (0.05, 0.1, 0.15 mm/rev), depth of cut (2, 4, 6 mm), and three machining environments. Surface roughness was measured using an SRT5000 roughness tester. The Taguchi L9 orthogonal array was employed to design experiments efficiently, and the signal-to-noise ratio (SNR) with "smaller-is-better" criterion was used for optimization. ANOVA quantified the percentage contribution of each parameter.
Results: The experimental results demonstrate that feed rate is the most dominant factor affecting surface roughness, contributing 61% of the total effect. Machining environment contributes 15%, depth of cut 13%, and cutting velocity 11%. Lower feed rates (0.05 mm/rev) consistently produced superior surface finishes (Ra = 1.2 μm), while higher feed rates (0.15 mm/rev) resulted in rougher surfaces (Ra = 2.5 μm). The air-water mixture environment significantly improved surface quality compared to dry and compressed air conditions due to enhanced cooling and lubrication effects. Lower cutting velocities (125-200 m/min) and shallower depths of cut (2 mm) also contributed to better surface finishes by reducing cutting forces, vibration, and thermal deformation. The optimal combination for minimum surface roughness was identified as: cutting velocity of 125 m/min, feed rate of 0.05 mm/rev, depth of cut of 2 mm, and air-water mixture environment, achieving a minimum Ra of 1.2 μm.
Conclusion: This comprehensive investigation establishes that feed rate is the primary control parameter for achieving high-quality surface finishes in PA6 turning operations. The air-water mixture environment provides significant improvements in surface quality through effective cooling and lubrication. The study provides manufacturers with evidence-based guidelines for selecting optimal machining parameters to enhance product quality, reduce costs, and extend tool life. The findings contribute to the broader understanding of polymer machining and offer a foundation for developing predictive models and process optimization strategies.
