Patent ID: 8070406

Claim:
A method for forming a joint in at least one high strength sheet steel having a UTS in the range 200 to 1400 MPa using a self-piercing rivet comprising the steps of: positioning the sheet material over a die; providing a rivet having a substantially cylindrical shank, a head, and a central axis, the shank having a central blind bore and an annular piercing end spaced from said head, the ratio of the difference between the outside and inside diameters of the shank in the region around the bore to the outside diameter of the shank is in the range 0.47 to 0.52, the ratio of the effective length of the rivet to the depth of the bore is in the range 1.56 to 2.4:1:, the annular piercing end of the rivet having a first portion that is radially outboard of a second portion, the second portion being a conical taper intermediate the first portion and the bore, the first portion being generally disposed such that it is inclined at an angle of between 0Â° and 10Â° to the perpendicular to the central axis; positioning a rivet over the sheet material at a position opposite the die; using a punch to set the rivet and force it into the sheet material such that it pierces the upper surface thereof and such that the shank deforms outwardly to interlock with the material but without penetration to the die side of the material.