Different die punch parameters such as punch radius, punch angle and die-lip radius are varied.
The process parameter considered is punch radius. The FEM simulation results clearly and theoretically clarified the spring-go phenomenon on the material flow analysis and stress distribution.
Numerical simulation and experiments have been carried out to verify the effect of punch radius
, die opening, and punch stroke on springback.
where F is the acting force, R is the punch radius
, h is the actual thickness of the specimen and tan[alpha] is the local slope at the perimeter of contact area.
where V is the impression velocity in the steady state creep, a is the punch radius
, F is the normal force applied to the punch, and c is a constant depending on primarily the ratio of elastic modulus to yield strength ([E/[[sigma].sub.y]]), the stress exponent, the indenter geometry, and the friction at the indenter-sample interface (10), (26), (27).
Influence factors Factors Levels of variations 1st 2nd 3rd level level level Punch radius
Rp[mm] 54 55 56 Die radius Rf[mm] 5 6 7 Blankholder force BHF[kN] 30 50 70 Clearance between 1 1.2 1.4 punch and die c[mm] Tab.
Three parameters were taken into account in this design of experiment: blankholder force (A), punch radius (B) and die radius (C).
Parameters Minimum Maximum value value A: Blankholder force [kN] 40 200 B: Punch radius [mm] 10 12 C: Die radius [mm] 5 6
Figure 6 shows the punch radius
dependence of the penetration velocity.
At this stage when the force on the punch creates stresses in the billet flange equal to the resistance magnitude of the material to plastic deformation and contact stresses due to friction, drawing of the billet to the matrix opening and coverage of the punch radius
The springback parameter is predicted as a function of the bending parameters: thickness g, angle as, punch radius
[r.sub.p], and die radius [r.sub.pl].
The influence of punch radius
and punch stroke upon punch load is also presented.