Effects of environmental conditions, aging, and build orientations on the mechanical properties of ASTM type I specimens manufactured via stereolithography

Purpose - The purpose of this paper is to investigate the effects of aging, pre-conditioning, and build orientation on the mechanical properties of test samples fabricated using stereolithography (SL) and a commercially available resin. Design/methodology/approach - American Society for Testing and Materials (ASTM) Standard 0638 Type I specimens were manufactured in a Viper si2 SL system using WaterShed (TM) 11120 resin. The specimens were manufactured in two different build setups, designed to fit batches of 18 or 24 specimens with different build orientations. The specimens were randomly tested in tension, and a design of experiments (DOE) was used to determine the effect of aging (4, 30 or 120 days), pre-conditioning (ambient, desiccant, or ASTM recommended conditioning), and build orientation (flat, on an edge, or vertical) on the ultimate tensile stress (UTS) and elastic modulus (E) of SL fabricated samples. Additionally, the fractured samples were imaged using scanning electron microscopy (SEM) to characterize the fractured surfaces. Findings - Results showed that aging, pre-conditioning, and build orientation each had an effect on the mechanical properties of the SL samples. In general, the samples aged at the shortest time frame (4 days) and the samples preconditioned according to ASTM recommendations had the lowest values of UTS. Regarding the effect of build orientation, the specimens built flat (with layers oriented along the thickness of the sample) had the lowest UTS and E values and the mechanical properties were statistically different from those built vertically or on an edge. The specimens built in the vertical orientation (with layers oriented along the length of the sample) had the highest values of UTS and E, yet the mechanical properties of the samples built on an edge (with layers oriented along the width of the sample) were not statistically different from the samples built vertically. SEM images of the fractured specimens showed fracture surfaces typical of polymers with a mirror zone and changes in surface texture from smooth to coarse. Research limitations/implications - The research was limited to a single commercially available resin. Through a statistical DOE approach, statistically significant differences in mechanical properties of SL fabricated samples were found as functions of aging, pre-conditioning, and build orientation. These results can assist the ASTM F42 Committee with developing test standards specific to SL and the additive manufacturing community. Originality/value - The statistical analyses presented here can help identify and classify the effects of fabrication, storage, and conditioning parameters on mechanical properties for SL fabricated parts. Understanding how the mechanical properties of SL resins are affected by different parameters can help improve the use of SL for a variety of applications including direct manufacturing of end-use products.