Laser Sintering offers manufacturers freedom of design, which enables creating parts with complex geometries. However, very little investigation has been made into the effects of geometry on mechanical properties of the parts. In the present study, Laser Sintered Nylon 12 parts with different section-thickness are subjected to displacement-controlled tension-tension and force-controlled fully-reversed fatigue loading to investigate the effect of geometry on their fatigue behaviour. Sectionthickness of the parts is shown to have no significant influence on the fatigue behaviour under tension-only loading. However, fatigue life of parts under fullyreversed loading is shown to increase with section thickness.

Powder bed fusion (PBF) is an additive manufacturing (AM) technique which offers efficient part-production, light-weighting, and the ability to create complex geometries. However, during a build cycle, multiple aging and degradation processes occur which may affect the reusability of the Polyamide 12 (PA-12) powder. Limited understanding of these phenomena can result in discarding re-usable powder unnecessarily, or the production of parts with insufficient properties, both of which lead to significant amounts of waste. This paper examines the thermal, chemical, and mechanical characteristics of PA-12 via an oven storage experiment that simulates multi jet fusion (MJF) conditions. Changes in the properties of PA-12 powder during oven storage showed two separate, time-dependent trends. Initially, differential scanning calorimetry showed a 4.2 °C increase in melting temperature (Tm) and a rise in crystallinity (Xc). This suggests that secondary crystallisation is occurring instead of, or in addition to, the more commonly reported further polycondensation process. However, with extended storage time, there were substantial reductions in Tm and Xc, whilst an 11.6 °C decrease in crystallisation temperature was observed. Fourier transform infrared spectroscopy, a technique rarely used in PBF literature, shows an increased presence of imide bonds—a key marker of thermo-oxidative degradation. Discolouration of samples, an 81% reduction in strength and severe material embrittlement provided further evidence that thermo-oxidative degradation becomes the dominant process following extended storage times beyond 100 h. An additional pre-drying experiment showed how moisture present within PA-12 can also accelerate degradation via hydrolysis.

Abstract

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Additive manufacturing (AM) of Inconel 718, IN718, is increasingly being used for the manufacture of complex geometry parts for high temperature applications. However, the low surface integrity and build resolution of as-built AM IN718 parts demands post processing such as machining. This paper reviews the machining of AM IN718 to understand the effect of anisotropic behaviour of the AM part and the hardening post AM treatment on the machinability of the latter. A better understanding on the cutting parameters and machining performance measures such as cutting forces, tool wear, chip morphology and surface integrity of workpiece led to the development of a workplan for future investigation.