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Injection Molding Technology
Material From Dr. Piyawit Khumphong (MTEC)
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Injection Molding System
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Tpe of Mold for Injection Molding
Two-piece mold
Three-piece mold
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Flow Channels for Molten Plastic
Sprue Runner Gate Cavity
Sprue
Runner
Gate
Cavity
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Cooling System for Injection Mold
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Injection Molding Cycle
1. Filling 2. Repeat Filling
(Packing) and Cooling
3. Mooo ooooing 4. Product
ejecting 5. Mold closing
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Temperature and Pressure Setting
Unmolten
Tem
p (T
)
Pressure (P)
Degrade
Flash
Short shot Tg + 100Tm + 50
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Temperature Setting for Injection Molding Machine
• Depending on Screw (Diameter, D)
1D 1.5D 3D
D
Shot size
Viscous heat ====> shear heating
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Mold Filling
Fountain flow
Surface
Center
Skin - core morphology
Birefringence microscopy of HDPE
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• Short Shot• Discoloration • Air traps• Burn marks, Black specks-black streaks• Brittleness, Fish Eyes• Flow marks, Ripples• Flash, Jetting, Silver Streaks, Sink Marks• Shrinkage and Warpage• Weld Lines and Meld Lines• Overpacking• Flow into thin section
Defect Problems in Injection Molded
Products
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• Air traps >>> Burn marks
Problems that arrived from poor mold design
Front View
Top View
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Burn marks Black specks-streaks
Brittleness Fish Eyes
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Flash Jetting
Silver Streaks Sink Marks
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Flow marks
Ripples
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Shrinkage and Warpage
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Weld Lines and Meld Lines
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Sandwich-Molding Overmolding
Simultaneous
Sequential
1. Coinjection2. Gas assisted
1. Monosandwich2. Airpress III
1. Core-Back-Technique2. Sandwich-Overmoulding3. Insert-Moulding*4. Outsert-Moulding*5. Textile-Overmoulding*6. In-Mould-Labeling*
1. Turntable2. Transfer3. Overmoulding-Stackmould
Single Cavity
Multi-Cavity
Multi-component molding
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Sandwich molding
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Viscosity ratio
Viscosity ratio = viscosity 2nd melt / viscosity 1st melt
Desired structure
Sandwich molding
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Barrel A
Barrel B
Connec ting
pipe
Needle
Simultaneous Technique
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Sequential Technique
core material (B)
skin material (A)
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Monosandwich molding
core material (B)
skin material (A)
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skin material (A)
core material (B)
Monosandwich molding
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Door Handle
Monosandwich molding
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Compatibility
ABS PA6 PP PE PS PET PC
ABS + ? - - * + +
PA6 ? + - - - ? *
PP - - + + - - -
PE - - + + - - -
PS * - - - + - -
PET + ? - - - + +
PC + * - - - + +(- ) : No adhesion, (*) : Poor adhesion, (+) : Good adhesion, (?) : N/A or Depend on Condition
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Depend on
• Chemical bonding• Inter-diffusion
>>>>Time & Temp
PP-PP under 110 °C >>> Poor adhesionABS-ABS under 130 °C >>> Poor adhesion
Compatibility
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Corrects:Warpage
Shrinkage
Section change
Surface aesthetics
Developments:
Cold Gas Injection
Water Injection
Gas Assisted Injection Molding
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Airpress III
1 2
3 4
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Bottle Crades
Airpress III
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OVERMOLDING
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Overmolding can be ...
multi colour technique
(e.g. buttons for key boards)
multi material technique
(hard and soft, e.g. for integrated seals)
in-mold assembling
(e.g. hinges, air vents ...)
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Core – Back Technique
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Transfer - Technique
ABS Tray with anti-slip TPE material
Tooth Brush with soft-feel TPE material
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TurnTable Technique
Tube shoulder for thoothpastewith barrier layer from PET and over-molded skin from PP
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Stack-Turning-Technique
process phase 1process phase 2
preform
Injection unit 2
Main injection
unit
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Stroke 3
2nd injection unit
Stroke 2
Assembling
Stroke 4
Demolding
Stroke 1
1st injection unit
Stack-Turning-Technique
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Vertical turn with the Cube-Technique
Production cost reduction about 25%
4 sides of the cube usable
Siemens M35
Stack-Turning-Technique