Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

46.2.2 Molds

 

· Injection molds are mainly made of steels and alloys steels. A simple mold is shown below.

 

 

  1. Locating ring - guides the injection nozzle into the mold.
  2. Sprue Bushing - where the injected material enters the mold cavities.
  3. Clamp front plate - Secures the front cavity, locating ring, and other components to the stationary platen.
  4. Front cavity - holds half of the negative of the shape to be molded. Guide pin holes are put in this plate.
  5. Rear cavity - the mating half for the front cavity that completes the negative of the final part. Guide pins are mounted on this to ensure correctly aligned cavities.
  6. Spacer Blocks/Rails - used to separate the rear cavity from the rear clamp plate.
  7. Ejector housing - contains the ejector pins to knock the parts out of the mold and forces the cavity back when the mold is closed.
  8. Rear Clamp Plate - Supports the rear half of the mold on the moving platen, and provides rigidity under molding pressures.

 

· Components to consider in mold design,

  1. - part design
  2. - material
  3. - machine used

 

· Factors that are often altered in the design are,

  1. - gating
  2. - runners
  3. - mold cooling
  4. - ejection

 

· Gating can be done a number of ways

 

 

· Runners carry the plastic to the injection gates and are often considered disposable or reusable. Typical runner systems are,

  1. - cold runner
  2. - hot runner
  3. - insulated runner

 

· Cooling systems allow rapid uniform cooling to increase cycle times, and reduce scrap. Typical techniques are,

  1. - water lines
  2. - baffles
  3. - fountains
  4. - thermal pins

 

· Ejection systems will push the part out of the mold when it is opened.

  1. - knockout pins
  2. - blades
  3. - stripper rings
  4. - air
  5. - hard stripping