Sheet metal coining method utilizing bilateral coin punching

A method of coining a metal part, the method comprising:

• positioning the metal part between an upper die and a lower die, an upper punch being positioned within the upper die, a lower punch being positioned within the lower die;
• and
• a punching step including punching an upper surface of the metal part with the upper punch to cause an upper portion of the metal part to deform into a concave surface of the upper die, and punching a lower surface of the metal part with the lower punch to cause a lower portion of the metal part to deform into a concave surface of the lower die,
• the punching step, after completion, resulting in an indentation in the upper surface of the metal part and an indentation in the lower surface of the metal part,
• the metal part including a side edge extending from the upper surface to the lower surface, the upper surface and the side edge defining an upper corner of the metal part, the lower surface and the side edge defining a lower corner of the metal part,
• the upper portion of the metal part deformed into the concave surface of the upper die during the punching step including the upper corner of the metal part,
• the lower portion of the metal part deformed into the concave surface of the lower die during the punching step including the lower corner of the metal part,
• during the punching step:
• the concave surface of the upper die contacts the upper corner of the metal part as the upper punch begins to penetrate into the upper surface of the metal part, and
• the concave surface of the lower die contacts the lower corner of the metal part as the lower punch begins to penetrate into the lower surface of the metal part.