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Introduction to injection molding
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Injection molding machine
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Injection molding cycle
• Injection of the melt into the mold
• Holding pressure and plasticating
– Additional melt is injected to compensate for
contraction due to cooling
– As the melt cools and solidifies, the pressure
should be high enough to avoid sinkmark
• Ejection
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Injection molding cycle
Mold openMold closed
Part ejectedPart coolingMold filling
Soak timeScrew recoveryHold timeScrew pushed
forward
t=0
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Characteristics
• Expensive molds – for large production runs
• Low assembly cost
• High pressure – limits the size of the product• Long products require multiple gates
• Part thickness less than 5mm – limits the cooling time
• Part thickness larger than 0.5mm – premature solidification
• Cycle time is money
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Clamping
Clamping force pushes the mold halves together, while the pressure of
the melt inside the mold pushes the mold halves apart.
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Mold
Sprue: entry channel of the mold
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Mold
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Flow into the mold
high degree of orientation of the surface layers
significant gradient in orientation and morphology
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Weldline
orientation
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Important process parameters
• Product parameters
– Product dimension, weight, appearance
• Main process parameters
– Cavity pressure, injection pressure, fill time
• Additional process parameters
– Melt temperature, mold temperature, hold pressure,
cooling time, total cycle time, barrel temperature, screw
speed, power consumption (screw, barrel heater)
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CAE S/W
MOLDFLOW- MF/VIEW : Pre/post processing
- MF/FLOW : Mold filling analysis
- MF/PACK : Packing analysis
- MF/COOL : Cooling analysis
- MF/GAS : Gas-assisted injection molding,PFP- MF/FIBER : Fiber orientation analysis
- MF/WARP : Shrinkage/Warpage analysis
- MF/STRESS : Structural/stress analysis
C-MOLD C-SET: Reactive molding
ANSYS : Structural analysis
CAD S/W : AUTO-CAD, Pro-engineer
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