The man is welding the iron.
The guy melted the hard metal
Just because iron is being welded does not imply that iron was the hard metal that was melted.
exists e1 x1 x2.(n_iron(x2) & n_man(x1) & Theme(e1,x2) & Actor(e1,x1) & v_weld(e1))
exists e1 s1 x1 x2.(n_metal(x2) & a_hard(s1) & Theme(s1,x2) & n_guy(x1) & Theme(e1,x2) & Actor(e1,x1) & v_melt(e1))