The perceived quality of car interior that customers can experience is closely related to the five human senses, including visual, auditory and tactile senses. Normally, they influence human perception collectively. This study was conducted with the purpose of optimizing perceived wood surface quality without use of real material. We focused on how to implement luxurious and realistic features for wooden interior parts. When evaluating the touch perception for interior surfaces, hardness and roughness can be used as tactile indices. And for visual perception, density and fineness of pattern can be used as visual indices. However, generally, these tactile and visual indices are closely related with each other. So when we try to develop both luxurious and realistic wooden surfaces, we need quantitative indices which can be easily transformed to manufacturing-related factors. In this paper, we discuss how to quantify the tactile and visual values into manufacturing factors and how we optimize those with statistical methods to have luxurious and realistic surface at the same time. Among many manufacturing methods of wooden surfaces, we chose the multi-layer pad printing method because it could provide us much freedom of design compared to insert film or curl fit method with lower cost. In this process, several layers of pad printing need on pattern engraved substrate. However, this method requires numerous iterations to implement realistic surface appearance. So we make several samples according to some extracted factors related to these processes to have different ranges of wood surface feeling visually and tactilely. We made several images of a real wood grain patterns to be engraved on mold to find best combination with printed layers. And we generated several contrast combinations with reduced number of printed layers of wood grain on the injected substrates. We could obtain the preferred range of both visual and tactile factors from statistical analysis of customer survey results. We have conducted surveys for domestic and European customers, and we found there were slight differences in perception of real wood depending on the region and culture. We conducted the same survey and analysis about perception of luxurious wood surface. In this study, we tried to implement the most preferred wood grain pattern in terms of visual and tactile senses by quantifying and optimizing process-related factors of the multi-layer pad printing method. Additionally, we could save cost by reducing iterated processes and integrating several coating processes without any loss of perceived quality.

Mr. Sung Sik Choi, Senior Research Engineer, Hyundai Motor Company