Search Results

The use of adhesives for bonding thinner galvanized steel automotive body parts is increasing. Associated with the use of adhesives is adhesive bond durability. Adhesive bond durability can be improved by chemically modifying the surface of galvanized steel. Five surface modifiers, each representing a different chemical class, were found to enhance adhesive bond durability of galvanized steel to an epoxy adhesive as demonstrated by environmental unstressed and stressed adhesively bonded lap shear durability tests. The observed durability improvements are attributed to interfacial chemistry changes resulting from surface modification that occurs between the adhesive and adherend.

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.

Comparative studies have been made on the tribological behavior of liquid and solid lubricants on bare and coated sheet steel products using laboratory friction and forming equipment. Friction or wear tendencies were quantitatively assessed in terms of static and dynamic friction coefficients, percent elongation, surface morphology changes, and chatter. The effect of the temperature and solid film lubricant hardness on friction and wear was examined. The phenomenon of chatter was recorded from an accelerometer attached to the test die. Significant improvements in friction reduction and anti-galling and anti-chatter tendencies were observed on sheet steel products coated with solid lubricant films. A greater degree of formability, prior to failure, was demonstrated by the LDH test on samples coated with solid lubricant films.

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.