Influence of energy density on polyamide 12 processed by SLS: from physical and mechanical properties to microstructural and crystallization evolution

Abstract

Purpose This paper aims to provide a detailed study on influence of the laser energy density on mechanical, surface and dimensional properties of polyamide 12 (PA12) parts produced by selective laser sintering (SLS), providing the microstructural and crystallization evolution of the samples produced at different energy densities. Design/methodology/approach Making use of a space filling design of experiments, a wide range of laser sintering parameters is covered. Surface morphology is assessed by means of profile measurements and scanning electron microscopy (SEM) images. Mechanical testing, SEM, X-ray diffraction (XRD), differential scanning calorimeter (DSC) and infrared spectroscopy (FTIR) were used to assess the influence of energy density on structural and mechanical properties. Findings Results show a high dependency of the properties on the laser energy density and also a compromise existing between laser exposure parameters and desired properties of laser sintered parts. Surface roughness could be associated to overlap degree when using higher scan line spacing values and lower laser speeds improved surface roughness when high scan line spacing is used. Higher mechanical properties were found at higher energy density levels, but excessively high energy density decreased mechanical properties. A transition from brittle to ductile fracture with increasing energy density could be clearly observed by mechanical analysis and SEM. XRD and DSC measurements show a decrease on the crystal fraction with increasing energy densities, which corroborated the plastic behavior observed, and FTIR measurements revealed polymer degradation through chain scission might occur at too high energy densities. Originality/value Valuable guidelines are given regarding energy density optimization for SLS of PA12 considering not only quality criteria but also microstructure characteristics. Surface properties are studied based on the concept of degree of overlap between laser scanning lines. For the first time, crystallization behavior of SLS PA12 parts produced at different energy levels was studied by means of XRD measurements. Polymer degradation of SLS PA12 parts was evaluated with FTIR, which is a non-destructive and easy test to be conducted.

Influence of Atmospheric Conditions on Mechanical Properties of Polyamide with Different Content of Recycled Material in Selective Laser Sintering

“…Tensile strength and tensile modulus were highest when using only the original material, whereas the values of mixed and recycled material did not differ. According to Czelusniak et al [21], with the optimal processing parameters when applying 50:50% mixed polyamide, a tensile strength of 45 MPa could be obtained, which roughly corresponds to these results. By applying the original material and drying, the strength can be increased to 50 MPa and more.…”

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

“…[23] The presence of peak representing γ phase and absence of α phase confirmed by the XRD can be attributed to rapid α to γ transformation, which occurs near the melting temperature as confirmed by previous studies. [1,[23][24][25] Attributing melting peaks in the temperature ranges (185-187 C), which are comparable to values found in this study, with the presence of γ form of PA 12 has been reported in previous studies. [23][24] The onset melting temperature (T m[onset] ), peak melting temperature (T m ), melting enthalpy (ΔH m ), onset crystallization temperature (T c[onset] ), peak crystallization temperature (T c ), and crystallization enthalpy (ΔH c ) for all the powder samples, which were obtained from their first heating and cooling curves are presented in Table 2.…”

Preparation of Porous Ceramic Building Decoration Materials by Foaming Method and Research on Nanomechanical Properties

“…Czelusniak and Amorim. [ 11 ] used α -Al 2 O 3 as raw material, gum arabic as dispersant, and organic foams with different pore sizes as templates. After sintering at 1200°C/2 h by the organic foam impregnation method, porous alumina with a porosity of up to 93% was prepared.…”