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Original Date: 07/23/1996
Revision Date: 01/18/2007
Best Practice : Paint First Run Yields
Nascote ensured high-quality first run yields on its plastic injection molded parts through the development of and compliance to documented processes. Because its plastic injection molded parts used substrates with inherent painting problems, first run yields were a high priority. Nascote’s customer required that fascias be painted separately from the automobile; consequently, color match and quality of the applied finishes were also critical. Nascote formed four teams of experts to address these industry problems. The teams are comprised of paint process engineers, technicians, and suppliers.
Part preparation was the first issue of the team’s focus. While electrostatic painting was normal for these plastic- injection molded products, some substrates were non-conductive such as Xenoy. However, once the part was sprayed it became conductive, attracting contaminates to the wet surface. Nascote developed a process of rinsing the part with ionized water to remove any charge, then applying an adhesion promoter to ensure bonding of the basecoats. After spraying this adhesion promoter to a thickness of 2-4 mils, the fascia could then continue with the standard procedure. This method proved successful, but incurred an additional cost; however, through Design of Experiments (DOE), Nascote determined that by applying the adhesion promoter, the basecoat paint usage was reduced by 50%. Instead of the previous 10 pieces per gallon of basecoat, 20 pieces per gallon could be produced by using the adhesion promoter. When compared to the cost of basecoat paint, $150 per gallon, the additional costs of the adhesion promoter were offset. This innovative approach received customer approval.
Painted surface contamination was another issue, as application of materials made the parts tacky. Two personnel from Nascote’s painting department were assigned full-time responsibility to identify and catalogue contaminates (Figure 2-1), allowing process engineers to address specific entry of each contaminate. This approach helped Nascote achieve an 86-90% average for first run yields. The results highlighted the benefit of Nascote’s approach to document and adhere to strict guidelines in achieving high-quality first run paint yields on its plastic injection molded parts.
Figure 2-1. Buick Product Line Contamination for June 1996
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