To address the limited understanding of chip formation mechanisms in precision turning of D6AC hardened steel using polycrystalline cubic boron nitride (PCBN) tools, this study conducts an orthogonal experimental analysis of chip free-surface and cross-sectional morphologies, and quantitatively evaluates the influence of cutting parameters on chip morphology characterization indices. The results indicate that serrated chip formation in D6AC hardened steel primarily follows an adiabatic shear mechanism, and chip morphology is mainly governed by chip heat capacity, with the nominal undeformed chip cross-sectional area (AD) playing a significant regulatory role. When AD ≤ 0.1 mm2 and f is small, chips remain continuous and smooth; at larger f, chips exhibit weak serration. For AD > 0.01 mm2, chips display pronounced serration, with Gs ranging from 0.23 to 0.43. At the critical AD of 0.01 mm2, a smaller f (0.05 mm/rev) produces smooth chips, whereas a larger f (0.1 mm/rev) produces serrated chips. Within the investigated parameter range, the influence of cutting parameters on serration frequency Gs, deformation coefficient ξ, and shear angle φ follows the order: f (55.53%–62.52%) > ap (17.27%–25.86%) > vc (0.11%–3.45%), while the influence order on serration frequency fc is: f (47.75%) > vc (36.46%) > ap (4.28%). For smooth continuous chips, a smaller deformation coefficient ξ and larger shear angle φ are preferred, with the optimal combination of process parameters being vc = 150 m/min, ap = 0.1 mm, and f = 0.05 mm/rev. This study systematically elucidates the chip formation mechanism in high-speed precision turning of D6AC hardened steel with PCBN tools, proposes AD as a key parameter for chip morphology control, and provides recommendations for process parameter optimization based on the Taguchi method. The findings offer a theoretical basis and data support for hard turning of similar high-hardness, high-strength, low-thermal-conductivity materials, and serve as a reference for quantitative investigations of chip morphology and process parameter optimization.

Chip formation in precision turning of D6AC hardened steel with polycrystalline cubic boron nitride tools

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发表日期：

2026年7月30日

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Yihan Liu,
Shutao Huang,
Ruyu Li,
Xiaoliang Yang,
Zhonghan Cui,
Haicheng Shi,
Zhong Zhuang,
Jinzhou Cui

摘要

To address the limited understanding of chip formation mechanisms in precision turning of D6AC hardened steel using polycrystalline cubic boron nitride (PCBN) tools, this study conducts an orthogonal experimental analysis of chip free-surface and cross-sectional morphologies, and quantitatively evaluates the influence of cutting parameters on chip morphology characterization indices. The results indicate that serrated chip formation in D6AC hardened steel primarily follows an adiabatic shear mechanism, and chip morphology is mainly governed by chip heat capacity, with the nominal undeformed chip cross-sectional area (A_D) playing a significant regulatory role. When A_D ≤ 0.1 mm² and f is small, chips remain continuous and smooth; at larger f, chips exhibit weak serration. For A_D > 0.01 mm², chips display pronounced serration, with Gs ranging from 0.23 to 0.43. At the critical A_D of 0.01 mm², a smaller f (0.05 mm/rev) produces smooth chips, whereas a larger f (0.1 mm/rev) produces serrated chips. Within the investigated parameter range, the influence of cutting parameters on serration frequency Gs, deformation coefficient ξ, and shear angle φ follows the order: f (55.53%–62.52%) > a_p (17.27%–25.86%) > v_c (0.11%–3.45%), while the influence order on serration frequency f_c is: f (47.75%) > v_c (36.46%) > a_p (4.28%). For smooth continuous chips, a smaller deformation coefficient ξ and larger shear angle φ are preferred, with the optimal combination of process parameters being v_c = 150 m/min, a_p = 0.1 mm, and f = 0.05 mm/rev. This study systematically elucidates the chip formation mechanism in high-speed precision turning of D6AC hardened steel with PCBN tools, proposes A_D as a key parameter for chip morphology control, and provides recommendations for process parameter optimization based on the Taguchi method. The findings offer a theoretical basis and data support for hard turning of similar high-hardness, high-strength, low-thermal-conductivity materials, and serve as a reference for quantitative investigations of chip morphology and process parameter optimization.