Experimental Investigation of the Formability of Organic Coated Steel Sheet Metal

Application of the coating to material in a flat condition has economical, technological and ecological advantages. As the material is subsequently formed into shape not only the base material needs to withstand this process but the coating as well. Development of forming tools for coated metals is mainly concerned with the prediction of performance of the base material and does not analyse the condition of the coating. However, during the forming process, major surface damage can occur when the coated sheet is bent and unbent around the die geometry. To reduce surface damage of coatings, proper control of the parameters during forming and a detail study of the surface conditions is required. This research is conducted on metallically and organically coated sheet material which is commonly used for structural applications. The crack density of the coating is analysed during a deep drawing process and a forming limit diagram is obtained from the biaxial straining of the prepainted steel samples. The results show that cracks initiate from within the organic coating and are linked to the strain in the base material.