Research On Surface Galling Behavior Of Auto Galvanized Deep Drawing Parts

Nowadays, the constantly growing demands of safety, corrosion resistance, energy conservation and eco-friendly of vehicles are motivated by the prosperous of automobile industries. Galvanized steel sheets are widely applied in motor industry for its good forming property, corrosion resistance and economy. Galvanized steels are composed of zinc coatings and steel substrates, diversities of mechanical properties are existed in two composition. Surface galling defects can be appeared easily in drawing processes such as coating pulverization and stripping etc. Based on the National Natural Science Foundation of China(51175445), the phenomenon of surface galling in deep drawing process at different diameters, blank holder force, procedures of galvanizing(DC54D+Z、DC54D+ZF、BUFDE+Z) were investigated. The mechanism and influence factors of galling were analyzed in this paper to offer a guidance to reduce the galling behavior on the galvanized steel sheets forming process.The basic structure, properties and forming procedures of galvanized steel sheet coatings are introduced in this paper. The main types, mechanisms of coating failure and damage force model are simply summarized. The stress–strain relationships between coating layers and matrix during deep drawing process are analyzed in detail. The stress relationships of flange area and straight wall of cylindrical parts are emphasized. The solid theoretical foundation was built for further finite element method analysis and physical experiments.Using FEM analysis software ANSYS/LS-DYNA, deep drawing processes of galvanized steel cylinder parts were simulated. The galling phenomenon of external surface of galvanized steel cylinder parts which were formed in deep drawing process is related to principal strain via simulations: Surface galling degree would be more serious if principal strain increased. Principal strain can be a data standard to measure the degree of surface galling. Influence of Blank holder force and sheet diameter was studied. Principal strain increases with the increase of blank holder force and sheet diameter and the surface galling degree of cylindrical deep drawing parts will be deteriorated.Deep drawing experiments of cylindrical parts for galvanized steel sheets were conducted by three factors and three levels orthogonal tests. It is indicated that the most severe galling phenomenon was appeared on the upper area of cylinder straight wall. Significant influence on the galling surface of galvanized steel sheet was conducted by sheet diameters in stamping process. Surface galling is getting more severe with the increasing diameters. Some influence on galling by blank holder force is unobvious. Different galling phenomenon is appeared by different craft of galvanized sheets: galling phenomenon on the surface of alloying hot dip galvanized steel sheets DC54D+ZF mainly are powdering and flaking. The failure of hot dip galvannealed steel sheets DC54D+Z mainly are scratching. The failure of electro-galvanizing steel sheets BUFED+Z mainly are ploughing and scratching.