Abstract: A formed sheet metal structure is manufactured from a sheet metal workpiece (1, 101). A main anvil tool (10, 110) constrains the first surface (3, 103) of the sheet metal workpiece. The workpiece is bent to form a first basal region (50, 150) and a second basal region (60, 160) with a bend (56, 156) between them. A first auxiliary forming tool (30) deforms first and second sidewall portions (51, 61, 151, 161) with respect to the first and second basal regions (50, 60, 150, 160) thereby to form a first fold region (55, 165) in the sheet metal workpiece (1, 101) between the first sidewall portion (51, 151) and the second sidewall portion (61, 161). Progressively sliding the first auxiliary forming tool (30) along the first fold region (55, 165) causes shear material transfer in the first fold region (55, 165) to further deform the first fold region (55, 165).