eFunda: Introduction to Injection Blow Molding
engineering fundamentals Introduction to Injection Blow Molding
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Injection Blow Molding
Injection blow molding is a process combining injection molding and blow molding. Its procedures are illustrated and described in the following table:
1. The blow stem is placed in an injection mold.
2. The melted thermoplastic material is injected into the injection mold and formed around the blow stem.
3. The blow stem is now wrapped with the "preform".
4. The preform along with the blow stem are then placed in the blow molding chamber.
5. Compressed air is injected through the blow stem into the preform. The preform is expanded like an inflated balloon.
6. Compressed air continues to blow in until the preform reaches the wall of the mold.
7. The molded plastic stays in the mold until it cools and hardens.
Pros and Cons of Injection Blow Molding
  • Pros
    • Faster production speed than extrusion blow molding
    • Higher precision than extrusion blow molding, but still not exactly a precision process
    • Net cost may be lower in high volume production
  • Cons
    • Higher setup costs due to two different molds.
    • May take longer to setup to produce the first product.
    • Less flexible in adjusting for different product gram weights.
    • Limited to hollow parts.
    • Limited to smaller containers.
    • Limited to simple shapes with no handles.

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