Identifying and minimizing the root causes of paint defects occuring as a result of painting plastic parts

In this context, the product, process, and quality data from a company that paints clear-coated mirror caps for the automotive industry form the main material of this study. The data include the types and rates of defects identified from the arrival of injection-molded ABS parts at the paint shop to their dispatch to the warehouse. Data regarding defective part quantities were obtained through the company's ERP system. For the analysis of crater defects, defective parts were separated, the diameters of the craters were measured individually using a particle size gauge, and the number of craters per part was determined. To identify the root causes of defects, analyses were carried out through visual inspections, micron-level measurements, and Six Sigma methodologies. The experimental studies evaluated various parameters including primer thickness, paint thickness, clear coat thickness, primer viscosity, paint viscosity, clear coat viscosity, surface tension, and paint color. The experiments revealed that primer thickness and clear coat thickness had no significant effect on crater formation, whereas paint thickness was found to have a significant impact. Additionally, primer viscosity, paint viscosity, clear coat viscosity, and surface tension were determined to have no notable effect on crater defects. Further investigations revealed that oil accumulation had occurred in the compressor supplying air to the paint shop, and that this oil was contaminating the paint through the air lines, leading to crater formation.