The only chance you have is to work as a volunteer, or if you are already registerwd as a jobseeker, find an unpaid internship. Please take care, that you can nly volunteer in so-called Verein or NPOs, non-profit organisations, but there are a lot in the mechanical field in Berlin, you could volunteer at any church/mosque if you ask, they can even gve you a good report about your doings and provide you with meals sometimes...