Die lip build-up is the unwanted material accumulation on extrusion die lip
s. Here, flared dies are shown experimentally to suppress die lip build-up.
A semiempirical method for flared die design is also provided. Nonlinear v
iscoelastic constitutive equations are used to calculate the wall shear str
ess and first normal stress difference in flared dies. Dy incorporating mel
t memory, a promising design method for die flaring is presented. The stres
s history upstream of the die exit governs the die design. The upstream gap
Is selected to maximize undershoot of the first normal stress difference N
-1 at the die wall caused by flaring. The flare length, on the other hand,
is selected to ensure a steady N-1 at the die lips.