Injection Molding Process

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Injection Molding Process
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Process Control
Phold Holding pressure thold Holding
time tpostfill Postfill time Tmold Mold
temperature Tdemold Demolding
temperature tfill Filling time tcool Cooling
time Tmelt Melt temperature Tsolidify
Solidifying temperature
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Molding Defects
Burnt Streak Visible streak on the surface as
brownish or silvery discoloration. Delamination
A separation or layering of the surface of a
molded part. It can also appear as
fish-scaling. Diesel Effect A small, dark brown
or black discoloration on the surface of a molded
part, usually found at the end of the material
flow path or in blind pockets. Discoloration A
change in the original color of a polymer
material.
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Molding Defects

• Flash An excess plastic material forced out of
  the mold, usually at parting lines but also at
  any point where two surfaces meet.
• Flow Mark Very fine grooves show up on the
  surface of the molded part, which is very similar
  to those of records. It is also known as Record
  Grooves Effect.
• Jetting A snake-like pattern on the surface of
  a molded part.
• Low Gloss A dulling of part surface finish.

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Molding Defects

• Short Shot An incomplete molded part.
• Shrinkage An extreme decrease in the dimensions
  of a molded part after it has cooled.
• Sink Mark A depression, resembling a dimple or
  groove.
• Void A voided area trapped within a molded part.

9. Short Shot 10. Shrinkage
11. Sink Mark 12. Void

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Molding Defects

• Warpage An excessive dimensional change in a
  molded part after it is ejected from the mold.
• Weld Line An inability of two flow fronts to
  weld together during the filling stage. This
  normally occurs around holes or obstructions and
  causes very weak areas in the molded part.

13. Warpage 14. Weld Line
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Typical Molding M/C Setting
Table 6.8 Machine setting for film-gated plate
and PP
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Molding Simulation
Filling phase
Arrhenius temperature dependence of viscosity
where n is the power law index, ?o the zero shear
viscosity, t is the parameter that describes the
transition region between zero shear rate and the
power law region of the viscosity curve.
where u is the velocity vector, T the
temperature, t the time, p the pressure, s the
total stress tensor, ? the density, ? the
viscosity, k the thermal conductivity, Cp the
specific heat and the shear rate.
INTEGRATED NUMERICAL SIMULATION OF INJECTION
MOLDING USING TRUE 3D APPROACH, Moldex3D
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Molding Simulation
Filling phase
Arrhenius temperature dependence of polymer melt
viscosity
where n is the power law index, ?o the zero shear
viscosity, t is the parameter that describes the
transition region between zero shear rate and the
power law region of the viscosity curve.
where u is the velocity vector, T the
temperature, t the time, p the pressure, s the
total stress tensor, ? the density, ? the
viscosity, k the thermal conductivity, Cp the
specific heat and the shear rate.
INTEGRATED NUMERICAL SIMULATION OF INJECTION
MOLDING USING TRUE 3D APPROACH, Moldex3D
10
Molding Simulation
Filling phase

• A volume fraction function f tracks the
  evolution of the melt front within a cell
• f0 the air phase,
• f1 the polymer melt phase,
• The melt front is located within the cell, then
  0ltflt1.
• The melt front f over time is governed by the
  transport equation

The flow rate or injection pressure is prescribed
at mold inlet. No slip is assumed at mold wall.
INTEGRATED NUMERICAL SIMULATION OF INJECTION
MOLDING USING TRUE 3D APPROACH, Moldex3D
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Molding Simulation
Packing phase Modified Tait equation
INTEGRATED NUMERICAL SIMULATION OF INJECTION
MOLDING USING TRUE 3D APPROACH, Moldex3D
12
Molding Simulation
Cooling phase Transient heat transfer problem
with convective boundary condition represented by
a 3D Poisson equation
where T is the temperature, t is the time, x, y,
and z are the Cartesian coordinates, ? is the
density, PC is the specific heat, k is the
thermal conductivity.
Warpage analysis
Where s is the stress tensor, C is a 4th tensor
related to the material mechanical properties, e
is the strain tensor, a is CLET tensor and u is
the displacement tensor.
INTEGRATED NUMERICAL SIMULATION OF INJECTION
MOLDING USING TRUE 3D APPROACH, Moldex3D
13
Molding Simulation
INTEGRATED NUMERICAL SIMULATION OF INJECTION
MOLDING USING TRUE 3D APPROACH, Moldex3D
14
Examples
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Example
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Example Mold insert
THREE-DIMENSIONAL INSERT MOLDING SIMULATION IN
INJECTION MOLDING, Moldex3D