Development and accuracy assessment of a PMMA 3D diamond model using region-based adaptive machining (RBAM) and FDM-based fabrication

Manufacturing engineering is a combination of science and art; in modern manufacturing, additive and subtractive manufacturing are predominant. Both approaches have their pros and cons, but model-building accuracy is an influential factor in reducing post-processing in both cases. Model build accuracy is influenced by cusp height (δ); it represents the deviation between the actual surface of the CAD model and the stepped surface created in the layered part during manufacturing. The present work deals with building a diamond, and its analytical analysis reveals variation in cusp height (δ). A diamond with 12 facets at the top and 19 facets at the bottom, width 40 mm, and height 39 mm was generated with a uniform layer height Z = 0.25 mm, and the result showed a cusp height δ = 0.135 mm in both the traditional negative and positive tolerance models. To improve geometric accuracy, a hybrid manufacturing methodology that combines additive and subtractive principles was proposed, employing an innovative Region-Based Adaptive Machining (RBAM) approach. The RBAM strategy enables fabrication of complex geometries on a 2.5D CNC machine using a simple Z-level machining strategy. The developed approach significantly reduced the cusp height to δ = 0.0074 mm. Experimental validation of the RBAM approach was performed using CAD/CAM software, a 2.5D CNC machine, and PMMA sheets fabricated layer-by-layer in 5 stages, with a constant Z step-over of 0.25 mm. The dimensional accuracy of the RBAM-fabricated and FDM-printed models was evaluated using a 3D laser scanning system. The scanning results demonstrated that the RBAM-fabricated model achieved a volume ratio of 1.017 and a volumetric error of 1.731%, comparable to the FDM-fabricated model, which achieved a volume ratio of 1.602 and a volumetric error of 1.602%. The proposed RBAM approach enables the fabrication of complex prototypes while overcoming the limitations of printable materials in additive manufacturing and the build volume constraints of CNC machining and 3D printing systems.