A novel sink mark model for high gloss injection molded parts - Correlation of deflectometric and topographic measurements

This paper introduces a mathematical model which approximates the topographic shape of punctiform sink marks to a Gaussian-bell-like function. Such a model enables the description of sink mark shapes with few parameters, and the calculation of features which can be used to describe the visibility of the sink marks. The topography of test series of sink marks on black high-gloss plastic parts was measured with a chromatic coding confocal microscope. The obtained data was fitted to the model which enables calculation of a sink mark's amplitude and volume. These two parameters are proposed to feature a sink mark's intensity. The results were compared to deflectometric measurements of the sink marks. Despite the fact that the two measurement methods are based on different principles, the results show high correlation. Especially, the behavior of sink mark volumes agreed well with the behavior of sink mark intensity which was measured using deflectometry. Therefore, the model also represents a viable option for the calibration of deflectometric applications. Additionally, the model can be used in future to simulate sink mark properties such as visual perceptibility.