Below 60% in class 12th means no placement and summer internship through MBA even though it'sfrom ximb ??

No,that is not the case. Although you might face some problem for getting shortlisted for a couple of companies bt their are many companies which dnt consider earlier academic background.

The institute would not have taken you in if it knew that it would affect your chances at a job if you did your MBA after scoring less than 60%. There are students who after scoring 60% get summer internship and placements.