Abstract: Aim at the surface patch message in finite element, an improved automatic reverse normal arithmetic is presented: seed element inside surface patch arithmetic. The arithmetic can reverse part normal on every surface patch independently according as surface patch message and adapts fault such as break, overlap between surface patches preferable. It makes finite element normal consistent rapidly and accurately, and provides necessary precondition for the follow contact arithmetic in numerical simulation technology of sheet forming process.

Key words: Automatic reverse normal, Finite element, Seed element, Surface patch