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A systematic study was conducted to evaluate the effects of solid film lubricant (SFL) coating weights on the frictional properties of sheet steels used in stamping plants. Samples of cold rolled, hot-dipped galvanized, electrogalvanized, and galvannealed sheet steels were coated from 0.11 to 3.22 gm/m2 (10 to 300 mg/ft2) with a SFL. Static and dynamic friction coefficients and percent elongation changes, as a function of SFL coating weights, were determined with a sliding friction apparatus. Changes in surface morphology as a function of SFL coating weight, after sliding friction testing, were ascertained by profilometry and scanning electron microscopy. The obtained results were related to and shown to be consistent with friction mechanisms postulated by current friction theory. The effect of low friction on sliding velocity was examined with a sliding draw bead apparatus.

The concept of forming prepainted steel products directly, as an alternative to post-painting formed parts, is economically very attractive. Significant paint burnishing, scoring, and flaking may occur when prepainted steel is subjected to conventional stamping plant forming operations. Results obtained on laboratory friction and forming test equipment show that prepainted steel products coated with solid lubricant films display improved lubricity and formability and exhibit anti-burnishing, -scoring, and -flaking tendencies. These test results successfully predicted field performance of prepainted sheet steel products coated with a solid lubricant: formability was improved and surface damage reduced under actual press line stamping conditions. These improvements have been attributed to a solid lubricious material separating the tool-paint interface.