Correlation of reuse extent with degradation degree of PA 12 powder during laser powder bed fusion and mechanical behavior of sintered parts

Abstract

The development of an effective powder utilization is key to maximizing the potential of polyamide 12 (PA 12) for commercial laser‐based powder bed fusion of polymers (PBF‐LB/P). This requires an extensive study of relationships between the powder reuse extent, macroscopic properties of the powder, and mechanical properties of sintered parts. This work investigates the effects of the extent of PA 12 powder reuse during PBF‐LB/P on the powder's degradation degree and mechanical properties of the sintered parts. Powder reuse extent was expressed in terms of cumulative build time while degradation degree was assessed in terms of deviations in the properties of the reused powders from those of virgin powder. Increase in the powder reuse extent led to increased thickness of crystallite, melting temperature, and sintering window of the powder while the crystallization temperature, crystallinity degree, and melt flow rate decreased with increased reuse extent. The mechanical strength and modulus of the sintered parts initially decreased with an increase in number of build cycles to reach a minimum at the sixth build cycle, after which it increased. This study is a step further towards achieving an efficient PA 12 powder management and a systematic control of quality of sintered parts.

The Effect of Powder Re-Use on the Coalescence Behaviour and Isothermal Crystallisation Kinetics of Polyamide 12 within Powder Bed Fusion

“…This could contribute to the anisotropic behaviour often observed in LS parts, whereby vertically orientated samples have the weakest tensile strength and are the most brittle [ 53 , 56 ]. Overall, un-molten particles and reduced melt flow rate cause reduced material coalescence, resulting in surface defects (orange peel) [ 34 ] and increased porosity [ 32 , 35 , 57 ] within parts fabricated from re-used powder. Increased porosity reduces part strength and induces embrittlement [ 32 , 36 ], which could render LS parts un-fit for purpose, particularly in critical end-use applications.…”

“…As LS occurs under atmospheric pressure, coalescence is particularly important because particle viscosity and surface tension become the driving force for complete consolidation and compaction of the powder layer [ 34 ]. Therefore, reductions in material coalescence can hinder the surface finish of LS parts [ 34 ] and cause increased part porosity, which often results in embrittlement of fabricated components [ 32 , 35 , 36 ]. However, there have been no previous investigations into the effect of powder re-use, aging, and virgin refresh rates on the isothermal crystallisation kinetics of PA-12 powder.…”

Recovery of residual polyamide (PA12) from polymer powder bed fusion additive manufacturing process through a binder jetting process

“…Commonly, PA12 recycled is mixed with 30%-50% of virgin powder to refresh the properties (Gomes et al, 2022a;Wegner et al, 2014). However, even after refreshing an aging powder, the mechanical (Gomes et al, 2022b;Guo et al, 2023;Lopes et al, 2021;Mwania et al, 2020;Yao et al, 2020) and thermal properties (Alo et al, 2023a;He et al, 2022;Mwania et al, 2020;Wudy and Drummer, 2019;Yang et al, 2021) are affected, while the average particle size does not change significantly (Al Amin et al, 2022;Arbelaez Ríos et al, 2021).…”