Geometry-Based Design of a State-Dependent Process-Planning Space with Integrated Fixturing for 3 + 2-Axis Milling

Automated operation-sequence planning for 3 + 2-axis computer numerical control (CNC) milling remains challenging because material removal changes both feature accessibility and the surfaces available for fixturing. This paper introduces an explicit state-transition formulation for constructing a solver-independent planning space from evolving workpiece geometry. The workpiece state combines volumetric material occupancy, surface-state availability, and completed machining features; it determines geometry-induced precedence and the availability of surfaces for workpiece fixturing. These relations are integrated with admissible tools, predefined tool-access directions, and machining-related cost contributions before optimisation begins. An Evolving Ant Colony System (EACS) algorithm then searches the resulting candidate space. Evaluation uses a 24-part benchmark with 58 EACS runs and 1000 random admissible samples per part. Functional and geometric verification covers precedence construction, 573 fixturing situations, and model-internal clamping-placement comparison. Compared with random admissible sampling, EACS achieved lower mean objective values for all 24 parts, with complete observed distributional separation for 23 parts. This comparison does not establish superiority over alternative optimisation algorithms. Four experienced CAM practitioners additionally assessed the generated plans for technological plausibility. The results demonstrate how evolving geometry can be converted into explicit state-dependent admissibility conditions, while mechanical fixture validation and scalability remain open limitations.