Method of forming a riveted joint
According to a first aspect of the invention there as provided a method of forming a riveted joint comprising a UHSS layer and a non-UHSS layer using a self-piercing rivet comprising a head and a shank, an outer diameter of a top of the shank being greater than an outer diameter of a bottom of the shank before insertion of the rivet, the method comprising pushing the self-piercing rivet into the UHSS layer such that the lower portion of the shank flares outwards and cuts a slug from the UHSS, and pushing the flared shank of the self-piercing rivet and the slug into the non-UHSS layer such that the non-UHSS layer deforms into a die recess and flows around an outer surface of the flared shank.
1. A method of forming a riveted joint comprising a UHSS layer and a non-UHSS layer, using a self-piercing rivet comprising a head and a shank, the shank comprising a lower shank portion, and an upper shank portion, a recess extending at least part way into the lower shank portion, wherein an outer diameter of the upper shank portion is greater than an outer diameter of the lower shank portion, the method comprising:
pushing the self-piercing rivet into the UHSS layer such that the lower portion of the shank flares outwardly and cuts a slug from the UHSS layer; and
pushing the self-piercing rivet and slug into the non-UHSS layer such the lower portion of the shank cuts a slug from the non-UHSS layer;
wherein a die receives the slugs from the UHSS and non-UHSS layers, and wherein the die promotes flow of the non-UHSS layer around an outer surface of the lower shank portion;
wherein the upper portion of the shank comes into contact with the UHSS layer around a circumference of the shank.
2. The method of claim 1 , wherein the die comprises an annular ridge which extends around an outer edge of a die recess of the die, wherein optionally the annular ridge includes a tapered face which is generally directed towards the rivet.
3. The method of claim 1 , wherein the die comprises an annular ridge which extends around a cylindrical opening, the cylindrical opening defining a diameter which is between 0.5 mm and 1 mm greater than the outer diameter of the lower shank portion.