Formability of an anti-fingerprint clear coating on satin stainless steel sheet metal

Since several years the application of stainless steel sheet metal with anti-fingerprint coating increases in the household appliance industry. These imperceptible clear coatings improve the cleaning characteristics. In essence, they reduce the adhesion and visibility of fingerprints on satin stainless steel surfaces. The thickness of these coatings amounts to a few micrometers. They are applied by the stainless steel manufacturer in a coil coating process. The curing procedure by ultraviolet radiation and the nanoparticle reinforced coating system cause a high hardness and a good scratch resistance. The final painted sheets are further processed e.g. to covering parts. The final processor does not spend any effort on varnishing or curing on-site. During forming operations a damage of the clear coating in the form of crack formation and delamination can be observed. This paper deals with experimental analyses for the identification and quantification of the deformation-induced damages to the coating considering different states of stress. On the basis of the results a coating-specific forming limit curve is defined, that can be used in forming simulations to forecast the occurrence of inacceptable coating damages. The validation of the forming limit curve of the coating is demonstrated in an exemplary comparison of a finite-element-method simulation and the coating damages of a real drawn part.