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].
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.
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.
According to the analytical and numerical calculation within slow viscous flow (16), the ratio of sample thickness to the punch radius has effect on the impression velocity as the ratio approaches unity.
Hence, based on the test and the correction by considering the effect of the ratio of the sample thickness to the punch radius, the nominal viscosity of PC together with that from the punch radius effect is calculated and plotted in Fig.
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
The influence of punch radius and punch stroke upon punch load is also presented.
Tests were performed using calculated punch stroke for each punch radius, using the conventional metallic die, in order to have the specimen completely fixed between the die and the punch, when bending is finished.