Hybrid Manufacturing Technology Integrating Pellet Extrusion Forming and Milling for High Precision and Surface Quality

Abstract

The application of pellet extrusion forming in aerospace and medical is limited due to challenges such as unstable forming quality, low manufacturing precision, and poor surface quality. To address these issues, this study proposes a hybrid manufacturing technology integrating pellet extrusion with milling. This approach combines the rapid forming and complex structure fabrication capabilities of additive manufacturing with the precision machining strengths of subtractive manufacturing, enabling high-precision and high-surface-quality fabrication of complex components. To improve internal forming quality and reduce defects like stringing and overflow in cavities, an innovative retraction strategy with pre-retraction buffering was developed. Orthogonal experiments and Taguchi analysis identified optimal retraction parameters, while simulations revealed the critical influence of filling speed on overflow quality, enabling parameter optimization. Experimental results show a significant reduction in the relative error of circular hole diameters, from 4.45% to 0.35%. To further enhance mechanical properties and surface quality, the impact of alternating additive and subtractive processes on tensile performance and surface roughness was systematically analyzed. Results demonstrate that process switching significantly reduces tensile strength at bonding interfaces, with hybrid components achieving only 37.7% of the tensile strength of purely additively manufactured parts. By optimizing extrusion speed, layer height, and introducing ironing, interfacial bonding performance improved by 164.8% compared with conventional methods. Surface roughness was found to depend heavily on milling allowance and extrusion path spacing, achieving optimal roughness when the final surface aligns with the middle of the deposited filament. Surface quality was also maximized when milling direction aligned with extrusion paths. The proposed hybrid pellet extrusion and milling process significantly improves internal quality, dimensional accuracy, and surface quality of thermoplastic particle components, expanding its potential applications in industrial fields.