Effects of processing on microstructure and properties of SLS Nylon 12

Abstract

There currently exists the requirement to improve reproducibility and mechanical properties of SLS Nylon parts for RRapid MManufacturing (RM). In order to achieve this, further fundamental research is needed and this paper addresses this need by investigating effects of potential sources of the lack of reproducibility (i.e. build procedure/parameters and powder blend) and reports effects in relation to crystal structure, microstructure, chemical structure (molecular weight) and mechanical properties.Different and γ p crystal forms were identified and related to the un-molten particle cores and the molten/crystallised regions of the microstructure. The melt point of the γ p form varied depending on processing conditions but the γ v remained principally constant. Observable differences were also present when comparing the microstructure of the parts. Molecular weight of parts was significantly higher than virgin powder but used powder (powder already held at elevated temperature) also showed an increase in molecular weight. This was related to improved elongation at break of parts built from the used powder, consistent with previous studies. Tensile strength showed some increase with parameters selected for improved strength but Young's modulus values were broadly similar.

Nanoclay/Polymer Composite Powders for Use in Laser Sintering Applications: Effects of Nanoclay Plasma Treatment

“…Although the DSC is commonly used to quantify the melting behavior of samples in both melt processing 1,24,25 and powder sintering, 5,7,14,26 we found that the melting temperatures obtained from the DSC did not result in fully melted powders in HSM (see Fig. 1).…”

“…7 The peak positions were just above 185°C with a variation <1°C. However, the melting temperature observed during HSM was different, revealing a much larger variation between neat PA12 and the two different composite powders, as shown in Fig.…”

“…5,6 Unlike other methods, LS, as an additive manufacturing technique, uses 3D CAD from a computer connected to the machine, to form three-dimensional parts in a layer-by-layer process. 7,8 In LS processing, laser power and powder bed temperature have to be carefully adjusted. The powder bed temperature is held below the powder melting temperature, 6 and is used to preheat the powder, whereas the laser is used to fuse polymer particles together.…”

“…Although many studies on LS have focused on thermoplastic polymers, particularly semi-crystalline thermoplastics, due to their low melting temperature such as polyamides (nylons), 7,8,10 few studies have been conducted on the reinforcement of polymers with nanofillers for LS in order to improve the mechanical properties of neat polymers by creating polymer nanocomposites. Polymers have been filled with different types of nanomaterials such as carbon nanotubes 11,12 or carbon nanofibers.…”

Application of layout optimization to the design of additively manufactured metallic components

“…Ti-6Al-4V also has a near perfectly plastic response (Rafi et al 2013), making it very suitable for use in conjunction with the suggested plastic optimization formulation (see Section 2.1). Polymer materials such as Nylon-12 can also be used but the material properties are very sensitive to process parameters and can be inconsistent between builds and machines (Vasquez et al 2011;Zarringhalam et al 2006).…”