Day 1:Aptitude & technical test of 1 hour each.(MCQ)
Selected candidates go for HR interview to know about your background, interests, bond, etc.
The next round for us was a month later-
Day 2:Technical interview, asked around 10 conceptual questions related to mechanical engg., took around 15 mins.
Around 2 months later-
Day 3:Selected candidates are called for one last interview with top management.Randomly question all, test of basic fundamentals usually, things every mechanical engineer ought to know!