Finite Element Modeling and CAD/CAM of Nett-Forming by Injection Forging - Manufacturing Systems Processes - page 117

FIGURE 4.17 Examples of the influence of the friction on the forming of annular flanges.

of the billet as is shown in Fig. 4.16(b-2) . When the value of friction coefficient is 0.01, the simulation
shows that the lateral sliding of the base of the billet would be severe—refer to Fig. 4.16(b-3) . This would
cause part of the base of the billet to lift off the anvil.
The influence of friction on the development of flaws was simulated by injecting the material into
a die-cavity of dimensions T

1.64 and D 3.0. The simulations for intermediate and final stages of

the die-filling for friction conditions 0.01 and 0.03 are shown in Fig. 4.17 . The billet was shown to

be unstable ( 0.01). The simulation of the deformation was continued until die-filling was achieved

to enable the identification of flaws that develop under these friction condition. Figures 4.17a and b show
the sequence of die-filling subsequent to the lateral sliding of the billet as depicted in Fig. 4.16 ; sym-
metrical die-filling was achieved by increasing interfacial friction ( Figs. 4.17c and d ) . These specimens
show that the profiles of the deformed material are sufficiently symmetrical. The simulation and
experimental results suggest that the billets are generally stable when the coefficient of friction at the
billet/anvil interface is of order of 0.03 for T 1.65.

The influence of the exit-geometry was evaluated by examining three radii:

0.00, 0.126,
and 0.24 ( Figs. 4.16(c-1) to (c-3) ). The exit-geometry cannot be considered in isolation as increases in
exit-geometry result in an effective aspect ratio of the pdz, which is higher than that derived from flange
thickness. Using a larger exit-radii would improve the flow of material at the exit and reduce punch
pressure; the incorporation of exit-radii, however, makes the billet less stable and hence more likely to
deform in a manner that will result in the initiation of flaws ( Fig. 4.16(c-3) ) .
Occasionally, batches of work-material are not metallurgically homogenous; the material property
was not uniform across the billet, this being concluded since the grain size was not uniform. Examination
of macro-etched ends of the commercially pure Aluminum billets revealed that a portion of it was of a
fibrous-form while the remainder was coarse-grained. Simulation indicates that variation in metallurgical
symmetry will result in asymmetric deformation—refer to Figs. 4.16(d-1) and (d-2) —and in extreme
cases of inhomogeneity—refer to Fig. 4.16(d-3) —will result in the sliding of the billet.

R r / d

0