Use of rapid prototyping technology in complex plastic structures Part II. Impact of operating conditions on functional properties of polymer harmonic drives

摘要

The influence of operating conditions on physical and mechanical properties of tooth surface in the flexspline of a harmonic drive was investigated. 3D printed test models were made from poly(acrylonitrile-co-butadiene-co-styrene) (ABS) copolymer and from poly(lactic acid) (PLA) and subjected to the accelerated UV aging test and to bench tests. Measurements of hardness, Vicat softening point and atomic force microscopy (AFM) analysis were performed in order to determine the properties of the teeth surface in the gear wheels. Furthermore, the degree of degradation of the plastics was determined with IR spectroscopy. It was found, that the ambient conditions and exploitation of harmonic drives do not affect the value of softening point and hardness. On the other hand, the AFM analysis indicated that the sides of teeth were smoother as a result of their cooperation. The values of Ra parameter in the areas examined decreased from 110.0 to 54.6 nm and from 23.9 to 17.0 nm for the gear wheels made of ABS and PLA, respectively. Furthermore, the Derjaguin-Muller-Toporov modulus (DMT) of surfaces was also decreased from 10.0 to 3.0 GPa and from 4.5 to 2.2 GPa in the gear wheels made of ABS and PLA, respectively. The AFM imaging provide evidence for destructive effects of UV radiation and elevated humidity, confirmed by IR spectroscopy.