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Rubber is used extensively in the automotive industry, in items such
as tires, windshield wiper blades, and profiles used for sealing windows,
roofs, and doors. The fabrication of these items is usually done by the
extrusion of a rubber compound through a die. Because of variations in
the flow conditions inside the die, deformations in the extruded product
are common. Adjustments in the die shape need to be made to compensate
for the anticipated deformations, but directing these adjustments has,
until recently, been more of an art than a science, a costly and time-consuming
process largely dominated by the know-how of expert tool manufacturers.
New features in POLYFLOW now allow this painstaking process to be performed
quickly and easily through CFD simulation.
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Roof profile
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Door profile
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For several years, POLYFLOW has provided a practical and cost-effective
way to improve the die design process. CFD simulations give an in-depth
knowledge about the motion of fluid inside a die, where observations are
not possible. This valuable information, which includes thermal history
and shear stresses, can be used to avoid resin deterioration due to overly
high shear stresses or unexpected curing, for example. Many die designers
have replaced hand-made trial-and-error dies, formed by hammering or cutting
steel, with virtual die balancing, formed by modifications in GAMBIT and
simulations in POLYFLOW.
One of the biggest challenges facing die engineers is the residual deformation
of the extrudate due to the frictional forces on fluid elements moving
along the wall. The resultant non-uniform speed inside the die induces
velocity redistribution in the extruded free jet, hence deformation. One
particularly helpful feature in POLYFLOW is the "inverse extrusion"
option, an automatic die lip design functionality. Based on the deforming
mesh technique, a prediction of the shape of the extrudate, together with
the die shape required to generate it, is made. The prediction is governed
by the deformation generated by the non-uniform velocity profiles inside
the die. When the number of different complex rubber profiles involved
in each new car is considered, along with a reduction in the die design
cost, it is clear that the use of this feature in POLYFLOW can directly
affect the production cost per vehicle. It is now being used around the
world for numerous automotive products, and is helping to reduce the time-to-market
and the generation of unwanted scrap material.
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