On the reduction of the gloss property of organic coated sheet metal after forming

Organic coated sheet metals (OCSM) are widely used in many industrial applications such as the automobile industry or in electrical appliances because of their high corrosion resistance and satisfaction of ecological requirements. However, original functions of the very thin coating layer in OCSM products may change during forming, which leads to a reduction of the product’s quality. This paper deals with the reduction of the gloss property of OCSM products. To this end, first a forming limit diagram (FLD) and a fracture limit diagram of the coating layer (FLDC) of OCSM are established by using Nakajima tests. Subsequently, the Nakajima tests are performed at a predefined strain in order to evaluate the change of the gloss property depending on the strain states. The loss of gloss as a function of plastic strain is used as a reference. For the verification of this reference, deep-drawing tests are carried out and the change of the gloss property on the surface is analyzed. The obtained results are in good agreement with the reference, so it can be applied for process design to predict the gloss reduction of OCSM products.