CREATING AN EDGE FLANGE ON A CURVED SHEETMETAL PART

Hi Guys,

Need some help with creating an edge flange on a curved sheetmental part. The attached parts shows what I am trying to do but I created this flange with a sweep feature and when I flatten the sheetmetal part, it dissapears. I tried unfloding the part and them trying to create an edge flange but SW will not allow me to. Can someone please help!

SolidworksSheet Metal