Effect and characterization of different methods on pattern formation on polymer optical mold surfaces of automobile lighting products

In the field of automotive lighting, headlight and rear combination lamp units enable vehicles to be seen by other vehicles in traffic and to illuminate the direction in which the vehicle is traveling. With this feature, the products are very important in terms of driving safety. Optical regulations are considered during product development processes. Optical regulation regulates the colour, position on the vehicle, light intensity, and distribution of each function. Optical expectations are followed by life requirements and product quality. Most of the parts consist of plastic components produced by injection moulding, PCBs, and LED lighting elements. Reflective properties can be achieved by subjecting plastic parts to aluminium metallization using the PVD method. When the sub-parts are arranged inside the body, the final products are obtained by welding body with external lens that can transmit light. These products are required to perform at high and low temperatures (- 40 °C and + 85 °C), harsh vibration conditions and wet environments. Customer expectations in automotive lighting technology are increasing day by day. Therefore, functional features are followed by style. These products have become the most important iconic element that reveals the style and identity of the vehicles. So many different optical concepts are used in product development processes to meet these expectations. In automotive lighting products, which are a stylistic element of vehicles and an important component in terms of safety, the distribution of light homogeneously across a surface and the absence of illumination gradients on this surface is called optical homogeneity. Customers' expectations for optical homogeneity are quite high. Optical homogeneity can be achieved with diffusive materials as well as surface roughness applications. Diffusive materials contain light-scattering polymer particles, and when light rays fall on these particles, they scatter and disperse. These particles may contain high molecular weight PMMA or may consist of micro- or nano-sized dispersed polystyrene materials. This dispersion in the light rays ensures that the illumination has a homogeneous appearance. The homogeneity level is checked in optical analysis software in the industry. However, most of the time, these homogeneity levels cannot be achieved in real parts coming out of injection moulds. This may be caused by the patterned surface in the mould not being transferred to the part at the same level, the surface topography being different, or the pattern in the mould having an insufficient depth profile. Pattern creation can be achieved by methods such as Electrical Discharge Machining (EDM), LASER, chemical etching, or sandblasting. However, the extent to which the pattern in the mould affects the part and the differences between these methods have not been revealed analytically. For this reason, in this study, the effects of patterns at different roughness levels created by EDM and chemical etching methods on product topography and optical performance at different distances were investigated. In addition, it is aimed to increase the accuracy of the optical analysis software by providing analysis of unknown points with analytical data with these outputs. As a result of these findings, it is aimed to reduce the cost of poor quality by contributing to product development processes and to establish standards for these applications.