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<p>This study presents a post-processing framework for verifying and modifying numerical control (NC) data to enhance geometric form accuracy in ball-end milling of free-form surfaces. During three-axis CNC machining, geometric form errors, specifically chord errors along the feed direction and scallop errors along the step-over direction, significantly impact surface quality. We developed mathematical models to predict these errors at the G01 block basis, enabling identification of problematic NC data that exceed machining tolerances or cause surface damage through overcuts. The proposed verification method analyzes each NC block by modeling scallop curves as continuous combinations of spheres and cylinders, representing the ball-end mill’s swept volume without approximation. Based on verification results, our modification algorithm classifies chord errors into seven distinct cases according to surface form and cutting characteristics, applying targeted corrections to eliminate overcuts while maintaining machining tolerances. For scallop error reduction, we present adaptive algorithms tailored to iso-scallop and iso-planar tool path planning methods, the latter employing an iterative optimization to redistribute step-overs across the entire surface. Validation through simulations and machining experiments demonstrated substantial reduction in maximum form errors and complete elimination of all overcuts. The approach addresses limitations of commercial CAM software, which often generates NC data that fail to meet specified tolerances despite defined constraints, thereby improving machined surface quality without substantially increasing machining time in a post-CAM step.</p>

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NC data verification and modification to improve form accuracy of machined surfaces in ball-end milling

  • 期刊论文

  • 发表日期：

    2026年3月12日

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  • Jeongmo Kang,
  • Sungchul Jee

摘要

This study presents a post-processing framework for verifying and modifying numerical control (NC) data to enhance geometric form accuracy in ball-end milling of free-form surfaces. During three-axis CNC machining, geometric form errors, specifically chord errors along the feed direction and scallop errors along the step-over direction, significantly impact surface quality. We developed mathematical models to predict these errors at the G01 block basis, enabling identification of problematic NC data that exceed machining tolerances or cause surface damage through overcuts. The proposed verification method analyzes each NC block by modeling scallop curves as continuous combinations of spheres and cylinders, representing the ball-end mill’s swept volume without approximation. Based on verification results, our modification algorithm classifies chord errors into seven distinct cases according to surface form and cutting characteristics, applying targeted corrections to eliminate overcuts while maintaining machining tolerances. For scallop error reduction, we present adaptive algorithms tailored to iso-scallop and iso-planar tool path planning methods, the latter employing an iterative optimization to redistribute step-overs across the entire surface. Validation through simulations and machining experiments demonstrated substantial reduction in maximum form errors and complete elimination of all overcuts. The approach addresses limitations of commercial CAM software, which often generates NC data that fail to meet specified tolerances despite defined constraints, thereby improving machined surface quality without substantially increasing machining time in a post-CAM step.