The effect of process conditions on mechanical properties of laser-sintered nylon

Purpose - The purpose of this paper is to measure the effect of process conditions on mechanical properties of laser-sintered nylon 12 (Duraform (R)) and to determine the range of conditions that provide consistent mechanical performance for additive manufacturing. Design/methodology/approach - Tensile test specimens were fabricated over a range of well-characterized process conditions including laser power, laser speed, scan spacing, layer thickness, build orientation, and build position. Tensile modulus, yield strength, ultimate tensile strength and elongation-at-fracture were measured and related to process parameters. Findings - Tensile properties are strongly related to the amount of energy deposited during scanning. Strength and modulus approach their maximum values as the energy deposited exceeds the amount needed to fully melt the applied powder. Elongation-at-fracture does not reach its maximum until higher energy-melt ratio. Performance of blends with reused powder matches that of virgin powder when blend composition is adjusted to a standard melt-flow index. The volumetric energy density and the energy-melt ratio are useful for correlating mechanical properties with multiple process parameters and material thermal properties. Originality/value - This work presents the most extensive data to date on mechanical properties of nylon 12 (Duraform (R)) as they relate to the full range of process parameters. These data show that mechanical performance correlates strongly with the volume energy density. In contrast to the area energy density (a.k.a. Andrews Number), this volumetric parameter includes the effect of varying layer thickness and can be related directly to the melting characteristics of the polymer material. Within the parameter range studied, this relationship allows adjustment of one scan parameter for improved speed or dimensional accuracy while ensuring good strength by an offsetting adjustment of another parameter. Such trade-offs will be important in future manufacturing applications of the laser sintering process. Understanding the energy-melt ratio provides insight into the relationship between scan conditions and the physics of powder melting and sintering, and offers a methodology to relate results at other bed temperatures and with other polymer powders.