The effect of lubricants on deep drawability of zinc‐coated steel sheets

Abstract

The effect of lubricants on deep drawability was studied for two types of zinc-coated steel sheets on a high-speed deep-drawing machine. The drawability of galvannealed steel sheet, GA, at low speeds is significantly improved by friction modifiers, due to reduction in frictional forces around the die radius. I n contrast to the results for GA, double layered steel, GAE, which has an Fe-rich alloy coating on the top, and is superior to GA in terms of drawability, is insensitive to changes in the additives. This is mainly because the hardness of the upper coating layer of GAE decreases frictional resistance through a decline in the boundary contact area. Abstract Keywordsdeep drawing, alloy-coated steel, double layered steel, zinccoated steel, friction modifiers, viscositySince the mid 1970s, various types of zinc-coated steel have been developed for automotive bodies in place of cold rolled steel to improve corrosion resistance. The main corrosionresistant materials used are hot-dip galvannealed steels, whose coating weight has increased from 20 g/m2 t o 60 g/m2 in accordance with the requirement for a high level of anticorrosion. Recently, double layered steel with an electrogalvanised Fe-rich alloy coating has been used for the outer panels of automobiles owing to excellent spot weldability and paintability. As the coating weight has increased, however, zinc-coated steels have been liable to exhibit fracture during the drawing process because of insufficient lubricity between the coating layer and the tool when conventional rust preventive oils are In order to improve the drawability of zinc-coated steels, rust preventive oils with high lubricity are required.

Enhanced lubricity of zinc phosphate coating by stearic acid

“…However, this coating is not effective to reduce the friction when galvanised steel is subject to metal‐working process such as deep drawing for forming into complex shapes . In this case, lubricants such as oils, emulsions, or colloids are often sprayed, rolled, or dripped onto the substrate to reduce the friction and to prevent the galling between the substrate and the shaping tools . Some dry lubricants are also available today to enhance the formability of coated steel sheet .…”

“…3 In this case, lubricants such as oils, emulsions, or colloids are often sprayed, rolled, or dripped onto the substrate to reduce the friction and to prevent the galling between the substrate and the shaping tools. 4 Some dry lubricants are also available today to enhance the formability of coated steel sheet. [5][6][7][8][9][10] They can operate at a wider range of surface texture specifications of steels and are helpful to reduce oil waste and improve surface finish.…”

Tribo-Characteristics of Stainless Steel Sheets in Iterative Processes of Sheet Metal Forming

“…Many tribological studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14] have been carried out on the press formability of different sheet metals using various friction tests including deep drawing, draw-bead, U-bending, belt friction and flat die types. These friction tests are useful for simulating the tribological phenomena for only some passes in press forming.…”