It is the objective of this research to validate the origins of hesitation lines and other related surface defects by characterizing and analyzing aesthetics and mechanical performance of samples with induced oscillating flow in injection molding. These results will be utilized to verify the validity of two hypotheses.; The first hypothesis is that these defects are the result of shear stress variances, while the second hypothesis relates hesitation effects to changes in melt temperature. The purpose of this thesis is to verify that the cause of hesitation defects is due to one or both of these sources.; The results and analysis indicated that the main contributor of hesitation effects for polyamide is solidification of the melt front resulting from changes in oscillation time. Formation of surface distortions evident in the poly-carbonate was more difficult to confirm, but the most influential processing parameter was determined to be flow rate indicating hesitation marks occur due to variations in shear stress. However, the influence of melt and mold temperature was also shown to play a role for the polycarbonate as well.
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