Investigation on the mass finishing of 17-4PH steel produced via binder jetting for orthopedic surgical applications

Binder Jetting is an innovative Additive Manufacturing process that was employed to produce 17-4PH steel components for orthopedic surgery applications, starting from pre-alloyed powders. Poor surface finishing of as-printed components often requires post-processing to comply with biomedical requirements. Mass finishing is a widely applied technology to lower roughness by means of mechanical abrasion. This study optimized a centrifugal disk machine mass finishing process for 17-4PH components produced by Binder Jetting. Surface printing orientation, abrasive paste composition, and precipitation hardening thermal treatment effects were investigated. Sample morphology was characterized by optical and scanning electron microscopy, roughness was measured by contact and confocal profilometry, material removal rate was estimated by mass loss measurements, and surface chemical composition was investigated by energy-dispersive X-ray spectroscopy. SiC, Al2O3, and SiO2 containing abrasive pastes effectively reduced roughness across all printing orientations. Abrasive smoothening effectiveness was correlated with the material removal rate. SiC-based paste resulted in the highest roughness reduction, reaching an average Ra of 0.62 +/- 0.25 mu m after 4 h of treatment. Traces of mass finishing abrasive pastes were observed on the polished surfaces, not precluding biomedical compatibility for orthopedic surgical applications. Upon precipitation hardening treatment, Vickers hardness increased by 42%. As a consequence, the material removal rate and roughness reduction were slowed down. Experimental results indicated that performing the mass finishing process before thermal aging allows roughness requirements to be met in a shorter time.