Worker was helping 2 vendor mechanics disassemble tooling used to install a hard bar pin in a CAT D10R Dozer (Unit #6013). The tooling was ""bound,"" & each of the individuals began taking turns using a small sledge hammer to free the tooling. EE on his 2nd swing freed the tooling, but a piece of it (most likely a socket) hit him above his rt eyebrow requiring 12 stitches.