Hybrid FFF-CNC Processing of PLA Fixtures with Gyroid Internal Structures

The study presents the results of experimental investigations into hybrid additive-subtractive manufacturing of lightweight PLA fixtures with gyroid internal structures. The proposed manufacturing approach combines FFF (Fused Filament Fabrication) printing with finish CNC milling in order to improve the dimensional accuracy, surface quality, and functional performance of polymer components intended for rapid tooling and functional prototyping applications. Test specimens with gyroid infill densities of 30% and 60% were manufactured from PLA material and subsequently subjected to finish milling under various cutting conditions. Particular attention was paid to the influence of cutting speed and feed per tooth on surface integrity, dimensional stability, and thermal effects occurring during machining. Maintaining the process temperature below the glass transition range of PLA (approximately 50 °C-60 °C) was identified as a critical factor for minimizing deformation and preserving geometric accuracy. The obtained results demonstrate that hybrid FFF-CNC processing enables the fabrication of lightweight yet sufficiently stiff fixtures characterized by improved surface roughness and high dimensional precision. The application of gyroid internal structures significantly reduces component mass while maintaining adequate mechanical rigidity. Moreover, the milled reference surfaces ensure precise positioning and repeatable geometric basing of cooperating machine and robotic assembly elements. The proposed hybrid manufacturing approach shows considerable potential for industrial implementation, particularly in the production of customized positioning fixtures, jigs, and functional tooling components used in automated assembly systems and rapid tooling applications.