Investigation Of Surface Damage Behavior In Deep Drawing Of Galvanized Steel

With the rapid development of the automobile industry and the requirementfor safety, energy conservation, environmental protection and anti-corrosiongetting more and more concerned, galvanized steel are getting widely used in theautomotive industry. However, due to the differences in mechanical properties ofthe substrate and coating, coating damages such as powdering, flaking andcracking may occurs during the plastic deformation process produces, meanwhile,surface scratches and galling phenomenon would happens. The surface damagephenomenon has become an important factor in inhibiting application ofgalvanized steel stamping in automotive parts. Based on the National NaturalScience Foundation of China (51175445), surface damage phenomena of the hotdip galvanized steel (DC53D+Z) and hot dip galvannealed steel (DC53D+ZF)during stamping is studied in this paper, generation mechanisms and influencingfactors are analysised to reduce or eliminate the surface damage behavior ofgalvanized steel stamping.The damage mechanism and damage mechanical model of the zin coatingunder tension or compression stress are introduced and the stress analysis ofcylinder deep drawing process of galvanized steel are taken to study the impact ofthe processing parameters to the surface damage behavior of galvanized steelstamping, such as the die radius, the friction coefficient between the die and thesheet and the blank holder force.A deep drawing experimental device is designed to study the surface damagemechanisms and influencing factors of the galvanized steel stamping. Experimentalresults indicate that scratching and ironing signs are the two main types of surfacedamage in the forming of hot-dip galvanized steel, cracking and scratching are twomain types of surface damage for hot-dip galvannealed steels. The region near themouth of the straight wall is the place where the most serious surface damageoccurs.The die radius has a significant impact on surface damage of galvanizedsteel stamping,the ironing signs of the galvanized coating and cracking of thegalvannealed coating getting obvious with the decreases of die radius. Ironingsigns which perpendicular to the drawing direction of the galvanized coating areobvious and flaking of the galvannealed coating on the fillet and the outside of the straight wall could be observed when the die fillet radius is3mm.The finite element software ANSYS/LS-DYNA is imported in this study bythe establishment of finite element model based on interface combined of cylinderdrawing of galvanized sheet. Simulation results show that the distribution of themax principal strain which along the drawing direction and the min principal strainwhich perpendicular to the drawing direction associated with the surface damageof the drawing part, the greater of the max principal strain or the smaller of themin principal strain, the more severe of the surface damage phenomena. With thedecrease of die radius or the increase of friction coefficient and blank holderforce,the max principal strain of the coating increases, which resulting in moresevere of surface damage phenomenon. the coating damage mechanism andmechanical model under uniaxial tension or compression stress can be applied toanalysis the surface damage behavior as the complex stress state drawing part.