Issue 30

C.J.Su et alii, Frattura ed Integrità Strutturale, 30 (2014) 502-514; DOI: 10.3221/IGF-ESIS.30.61 504 y  － the normal stress caused by y F vx vy ,   － the normal stress caused by component of v F in the X, Y direction n  － the normal stress caused by N , z  － the normal stress caused by mould to restrict materials,  － shear stress caused by friction force. Take a coordinate system for OXYZ in deformation zone and its stress tensor is T T T        (1) where T   － spherical stress tensor T   － stress deviator. x n xy m yx y vy m z m vy y z n vx yx vx n z y vy vx vy n n vx 0 - 0 0 ( ) 0 = 0 - 0 0 0 0 0 - 1 2 ( ) ( ) 0 3 3 1 2 ( ) ( ) 0 3 3 1 2 0 0 ( ) ( ) 3 3 yx T                                                                                      (2) m m m 0 0 0 0 0 0 T                   (3) m y z vx vy z 1 ( ) 3            (4) The plasticity of material (point o) is affected by the hydrostatic pressure in the department of spherical stress tensor. The spherical stress tensor is the static pressure in deformation zone of fine blanking, and the factors that influence the hydrostatic pressure in deformation zone are known from formula 3, so following ways can increase the hydrostatic pressure and then improve the quality of blanking pieces: 1. magnify v  by increasing the kicking force; 2. magnify n  through reduce the intensive clearance to some extent; 3. magnify vx vy    by enlarging BHF; 4. pressure angle of blank holder sets for optimum value, as shown in Fig. 1(a), vx vy v (cos sin ) F F F      (5) Take the extreme value: x y d ( ) 0 v v F F d    v d (cos sin ) (cos sin ) v F F        (6)