Method for joining together two or several overlying sheet formed members (1, 2), at which an essentially coaxial arrangement of a punch (4), a die (3), with a die cavity (9), and an anvil (5) are caused to cooperate by means of their coaxial relative movements, comprising the following steps: (a) said overlaying sheet formed members (1, 2) are placed between the punch (4) and the die (3); (b) said punch (4) is caused to carry out a first relative movement in a first direction coaxially towards said die (3); (c) an essentially cylindrical core portion (6) of the punch (4) is caused to coact with the die cavity (9) to form during the movement in the direction of the die cavity (9) by means of drawing of said sheet formed members (1, 2), a cup-shaped or protruding portion (10) having a side wall portion and a bottom wall portion (12); (d) said anvil (5) is caused to carry out a movement relative to said die in a second direction and is caused to be locked in a predetermined position relative to the die; (e) said punch (4) is caused to carry out a second relative movement in said first direction coaxially towards said die (3), and by means of forces between said punch (4) and said anvil (5) compress said bottom wall portion whereby there is formed a laterally enlarged shape which mechanically interlocks the sheet formed members (1, 2) and whereby said punch is provided, around the rear end of said core portion (6), with a lateral extension (8) which during said step c is caused to deform and displace material from the area around the opening (11) of the cup-shaped or protruding portion (10) mainly in the upper sheet formed member (1) axially in the direction of the die (3).