PURPOSE: To attach a trim-ring simply and surely in the process to attach metallic trim-ring to the circumference of a synthetic resin wheel cover by using dies of ring contour consisting with straight line and hook portions.

CONSTITUTION: For the forming of dies, a thick wall cylindrical die holder 2 is installed on the lower base plate 1 of the press and a calking die 3 consisting of the section of straight portion 4 and hook formed portion 5 is formed to the upper inner side, and a free sliding die 6 is also installed to the inner circumference. On the other hand, a punch 10 is attached to the feely sliding upper die base 8 through a punch holder 9, and the die 11 which coincide with the section of the trim-ring is formed to the periphery of the under surface. Now, the trim- ring 13 is attached to the wheel cover 12, ad setting the external flange 13a to the calking die 3, then the punch 10 and die 6 are lowered, and form the external flange 13a to the form 13b which coincides with the hooked portion 5.