Purpose: This paper aims to investigate the processability by selective laser melting (SLM) of materials of potential interest for innovative biodegradable implants, pure Fe and pure Zn. The processability of these materials is evaluated with a more established counterpart in permanent implants, stainless steel. In particular, the processing conditions were studied to reduce porosity due to incomplete fusion of the powder. Design/methodology/approach: In the first phase of the experiments, SLM of AISI 316L was studied through design of experiments method. The study was used to identify the significant parameters in the experimental range and estimate the fluence ranges for pure Fe and pure Zn using the lumped heat capacity model. In the second phase, SLM of pure Fe and pure Zn were studied using estimated fluence ranges. In the final phase, best conditions were characterized for mechanical properties. Findings: The results showed that complete melting of AISI 316L and pure Fe could be readily achieved, whereas laser melting generated a foam-like porous structure in Zn samples. The mechanical properties of laser melt implant materials were compared to as-cast and rolled counterparts. Laser melted AISI 316L showed superior mechanical performance compared to as-cast and rolled material, whereas Fe showed mechanical performance similar to rolled mild steel. Despite 12 per cent apparent porosity, laser melted Zn exhibited superior mechanical properties compared to as-cast and wrought material because of reduced grain size. Originality/value: The paper provides key processing knowledge on the SLM processability of new biodegradable metals, namely, pure Fe, which has been studied sparingly, and pure Zn, on which no previous work is available. The results prefigure the production of new biodegradable metallic implants with superior mechanical properties compared to their polymeric counterparts and with improved degradation rates compared to magnesium alloys, the reference material for biodegradable metals.

Melt pool monitoring in selective laser melting (SLM) is a key challenge to enhance the understanding of the basic process physics as well as the in-situ identification of drifts. The main issues are related to the molten pool’s fast dynamics and small spatial extent, which require high performance monitoring systems in terms of temporal and spatial resolution, often resulting in unmanageable data rates. Furthermore, the broadband thermal emission from the process can be viewed in different spectral ranges depending on the sensor and optical system employed. Accordingly, a wide range of sensing configurations is possible. The choice of monitoring parameters is crucial to achieve a solution capable of describing process dynamics with industrial applicability in terms of data transport and analysis. This work discusses the design of a coaxial monitoring module to assess melt pool dynamics in SLM using temporal and spatial cues related to the process physics. Restrictions regarding data management were considered to ensure a future inline process control. The system was tested with an external illuminator to reveal the actual melt pool geometry employing an acquisition rate of 1200 fps, 4.3mm x 4.3mm field of view and 14 μm/pixel spatial resolution. The process emission in visible (640 nm) and near-infrared regions (850-1000 nm) was also acquired and the band choice discussed. The proposed solution captured successfully the melting conditions from both a spatial and temporal viewpoint. The monitoring system depicted the melt pool shape variations when processing different geometries using both modulated and continuous wave laser emission.