With a slight modification it comes out
In[121]:= Clear[Bk]
Bk = {{{0, 0}, {62, 61}, 1}, {{0, 0}, {60, 50},
2}, {{0, 50}, {60, 100}, 2}, {{60, 50}, {120, 100}, 2}};
Clear[graficar]
graficar[bk_List] :=
Module[{placas = Max[bk[[;; , 3]]], lamina, medidas, dibujo, i, rec = {}},
For[i = 1, i <= placas, i++,
lamina = Most[#] & /@ Cases[bk, {{_, _}, {_, _}, i}];
dibujo = Graphics[Prepend[{EdgeForm[{Blue, Thick, Dashed}], Green, Rectangle @@@ lamina},
{Red, Rectangle[{0, 0}, {120, 100}]}],
PlotLabel -> "Lámina número " <> ToString[i]
];
AppendTo[rec, dibujo]
];
rec
]
as