CHARACTERIZATION OF ADHESIVE STRENGTH OF PHOSPHATE COATINGS IN COLD METAL-FORMING

A rest method is proposed to characterize adhesive strength of phospha te coatings based on the various deformation patterns at the tool-work piece interface. The deformation patterns were induced by tools of dif ferent surface geometrical profiles, i.e., flat surface, sinusoidal su rface, saw-tooth surface and multi-surface profiles, in a localized ro d drawing technique. With change in the tool geometry, three deformati on regimes were observed, i.e., full film lubrication regime, mired re gime, and seizure regimes, which were categorized by the level of fric tion coefficient attained, and the degree of galling observed on the s urface of the drawn specimens. The full film lubrication regimes were noticed when flat dies were used. In this case, the friction coefficie nt was maintained at nearly mu = 0.065, irrespective of the change in the surface roughness of the tools and reduction. With sinusoidal surf ace and other non-flat dies, mi-red regime and seizure regimes were ob served, and the friction coefficient varied from mu = 0.1 to 0.3. To c omplement the friction data, surface analysis of the tool-workpiece in terface was also conducted. The frictional range of mu = 0.065 to 0.3 obtained in this study, therefore, provides for a manageable character ization of phosphate coatings for cold metal forming of objects with i ntricate shapes.