Investigating mechanical anisotropy and end-of-vector effect in laser-sintered nylon parts

Abstract

DOI: 10.1243/09544054JEM537Abstract: A study investigating the effects of part-build orientation in the laser sintering process is presented. The investigation uses tensile, flexural, and compression testing methods to assess the changes in the mechanical properties of laser-sintered nylon-12 parts. The test parts were built in the x, y, and z orientations with the x axis parallel to the direction of the laser scanning, the y axis perpendicular to the direction laser of scanning, and the z axis in the direction of powder layers. The results from the tests show that the build orientation of the parts has an effect on the mechanical properties produced. The tensile tests show a maximum difference of 16 per cent and 11.2 per cent in strength and modulus respectively for parts built in the x, y, and z axes. The flexural tests show a 9.4 per cent and 7 per cent maximum difference in strength and modulus respectively for the parts produced in the x, y, and z axes. For the compressive tests, there is a 3.4 per cent and 13.4 per cent maximum difference in strength and modulus respectively for the parts produced in the x, y, and z axes. A statistical analysis of the results obtained highlights the presence of anisotropy in tensile and compression parts owing to their build orientation in the laser sintering machine. The test parts built in the x axis orientation showed the highest strength and modulus values while the parts built in the z axis orientation showed poor strength and modulus values. However, this is not the case for the flexural test parts, which show the highest strength and modulus values are from those built in the y axis orientation. Analysis has shown that this is due to the end-of-vector effect, which is most prominent in the y axis orientation. This effect should always be considered during laser sintering, when mechanical integrity is vital.

Effect of infra‐red power level on the sintering behaviour in the high speed sintering process

“…b a b a This would help to explain the existence of a maximum achievable thermal penetration depth within the process. This can also be related to SLS research 18 which shows that sintering occurs to a lesser degree in the z direction than in the x and y directions, indicating that less thermal energy is transferred in the z direction.…”

Glass bead filled Polyetherketone (PEK) composite by High Temperature Laser Sintering (HT-LS)

“…Nylon, a wellresearched and optimised polymeric material for laser sintering showed a difference of 16% in tensile strength in the X, Y and Z axes. [28] Previous study on laser sintered HP3 PEK showed a significantly higher difference in tensile strength amongst the three directions [29] (approx. 50%), which could the result of the higher processing temperatures and therefore higher thermal gradients between layers in Z axis.…”

“…They also introduced the terminology of "degree of particle melt (DPM)" when discussing the layering effect similar to the one noticed here. Ajoku et al, [28] explained clearly the bonding mechanisms and temperature differences that take place between vectors and layers and led to the layered structure. The neck growth is significantly smaller in Z direction than X and Y axes.…”

What triggers a microcrack in printed engineering parts produced by selective laser sintering on the first place?

“…The manufacturing process builds up parts layer by layer, so the bonding between layers, warping/curling effects which come into play and the interaction between layers impact heavily on the resulting mechanical strength. A variety of studies have been performed investigating the anisotropy of SLS parts, where [18] took standard process parameters and built tensile bars in the x,y and z orientations. The samples were subjected to flexural and compressive tests to determine the degree of anisotropy [19] printed nylon PA12 tensile bars again across the x,y and z directions, but this time using both new and aged powder.…”