Injection Molding Process

The plastic injection molding process is a manufacturing method for producing custom plastic parts.  The service takes place at injection molding companies often referred to as a custom molder.  Before the process begins, an experienced mold maker must construct a mold or tool in order to produce a part.  The construction of the mold will include 2 halves and contain all the geometry and features that make up the part specifications.

Once the mold is constructed, it is then loaded into an injection molding machine where the process begins.  A hopper is use to hold and feed plastic virgin material into the barrel of the machine, where it becomes molten.  From here, a reciprocating screw will continue to feed and mix the proper amount of material.  After this, the screw will ram inject the material into the mold cavity.  Once the material enters the mold, it begins to cool and harden to conform to the geometry of the mold.  After the material cools, it is safe to remove the part from the mold, and this completes the cycle.  Plastic Injection Molding Machine

The injection molding cycle is as follows;

  1. Material Enters Barrel
  2. Material melts and mixes
  3. Volume of material (Shot sizes in barrel is created)
  4. Mold closes
  5. Injection of the plastic into the mold cavity
  6. Molten material cooled (during this process steps 1-3 are preparing for next cycle)
  7. Mold Opens
  8. Part Ejects
  9. Jump to step 4

Calculating an injection molding cycle is as follows;

Cycle = Mo+Mc+I+C

Mc = Time to close the mold (this is the time it takes to actually close the tool)

I = Time to inject material into the mold

C = Cooling Time (Time to solidify molten material)

To = Time to open a mold and eject the part (these can overlap and together make up total open time)

 

Design Characteristics of Plastic Injection Molded Parts

Custom components for the molding process, should be designed and engineered by an experienced industrial designer or engineer.  Producing a dimensional and stable part requires many factors to be considered.  Failure to follow the design guidelines for injection molding can end up with undesirable results.  Many factors to consider are as follows;

  • Material Selection
  • Shrink Rate
  • Draft
  • Ribs
  • Bosses
  • Undercuts
  • Integrated Fasteners
From Website
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

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