Mechanical properties of polyamide 12 manufactured by means of SLS: Influence of wall thickness and build direction

Abstract

The wall thickness and build direction of PA 12 parts manufactured via SLS are currently being investigated for applications requiring low weight and good mechanical properties (ultimate tensile strength, elongation at break, elastic modulus, and hardness). Current design guidelines for the SLS process include recommendations about the influence of build direction on the mechanical properties of the part; however, the recommended minimum wall thickness only considers the process's manufacturability, so this study aims to determine the wall thickness and build orientation conditions that present the slightest difference in mechanical properties, considering different conditions such as vertical, horizontal, and transverse build directions and wall thicknesses of 2.0, 2.5 and 3.0 mm. Statistical differences were found between build direction, ultimate tensile stress, and elongation at break and hardness. It was observed that the significant differences in the direction of impression were between the vertical direction vs the transverse and horizontal directions. The differences were between the values of 2.0 mm vs 2.5 and 3.0 mm for the wall thickness. The mechanical properties between these last two thicknesses do not present significant differences, so it is suggested that parts manufactured with PA 12 by SLS with thicknesses of 2.5 mm could have the same tensile mechanical properties as those of 3.0 mm. The horizontal and transverse directions with a 2.5 -3.0 mm thickness showed the highest mechanical properties with an ultimate tensile stress of ≈43 MPa, a modulus of elasticity of 2.2 GPa, an elongation at break of 16-18% and a hardness of ≈75 Shore D.

Innovative Approaches to 3D Printing of PA12 Forearm Orthoses: A Comprehensive Analysis of Mechanical Properties and Production Efficiency

“…Lammens [99] obtained slightly higher σt values (45.0-49.4 MPa), while Calignano [51] obtained significantly lower σt values (34.8-38.3 MPa). Analogous strength tests in three orientations for the MJF method are presented in the literature [47,100,102]. Tensile strength values of 36.5-44.5 MPa, similar to those obtained by us, were obtained by Mehdipour [47].…”

“…Increasing the bonding energy makes the model properties more isotropic [76]. In our study, as in the publications [47,100,103], the lowest strength was not associated with samples printed in Z orientation, i.e., in the direction of tensile force.…”

“…tensile elongation is due to the significantly higher elongation of the specimens 3D printed in X and Y orientation. Similar tensile strength tests of SLS samples, but printed only in three orientations (X, Y, Z) on EOS devices, were carried out by the authors of publications [47,[99][100][101], among others. The tensile strength values we obtained of 41-45 MPa are similar to those presented by [47,100,101].…”

“…Similar tensile strength tests of SLS samples, but printed only in three orientations (X, Y, Z) on EOS devices, were carried out by the authors of publications [47,[99][100][101], among others. The tensile strength values we obtained of 41-45 MPa are similar to those presented by [47,100,101]. Lammens [99] obtained slightly higher σt values (45.0-49.4 MPa), while Calignano [51] obtained significantly lower σt values (34.8-38.3 MPa).…”

Characterization and Simulation of Shear-Induced Damage in Selective-Laser-Sintered Polyamide 12

“…In order to utilise the full potential of SLS PA12, a thorough understanding of the material properties under a wide range of loading conditions is essential. In recent years, studies have been conducted on the material behaviour of SLS PA12 under both quasi-static and cyclic loading [ 14 , 15 , 16 , 17 , 18 ]. Due to the lack of comprehensive standards in the field of AM, the procurement and interpretation of material data remain difficult [ 19 ].…”