Len Graham Consulting

The success of any molding program is determined at the mold design stages. It can be difficult…. if not impossible…. to add critical performance features to a finished mold… if they are not designed and built in….At the very least, provisions should be made to proactively design a mold to be able to add them later

Years of experience has shown us that the majority of mold issues could have been resolved at the design stage. Although each mold is unique unto itself we find that, when a mold has issues, one or more of the examples below were not applied appropriately, if at all. Not all examples could be listed here, but these are a few important ones experience has told us to look for.

Wear/maintenance issues or mold foundation is not built to perform for the cycles prescribed in its SPI mold classification:

  • Improper allowance in mold components for heat expansion (primarily hot manifold applications)
  • Individual cavity alignment not used or improperly applied – plastic part P/L can exhibit premature flash issues – resulting from one-sided wear on cavity alignment features or non existent alignment features
  • Steel (material) selection incompatible for high wear situations
  • Tapered shut-offs not applied where needed
  • Improper running clearances/surface finishes applied in wear areas
  • Venting location/application choice causes undue wear on other inserts or flashing
  • Improper use of platings – plating will chip
  • Latch mechanism choice too weak-will unduly stress plates and mold components
  • Shut-off areas not appropriately protected through piloting - not incorporating primary/secondary alignment
  • Slides and/or lifters are high wear design
  • Unscrewing mechanism is not a good design and components will wear prematurely
  • Not enough steel outside cavity areas for long term support
  • Mold plates not appropriate thickness – can experience P/L flash – mold component fracturing issues
  • Improper pre-load on inserts
  • Mold designed for a molding press that is too small

Part quality issues and/or cycle will be affected:

  • Steel safe strategy not used when needed – critical part dimensions too close to high/low or both simultaneously
  • Inadequate cavity/core cooling
  • Inadequate plate cooling
  • Features not in design to assure part will positively stay on desired half of mold upon mold open at desired molding parameters/cycle
  • Inadequate venting in all necessary areas – secondary vents not escaping to atmosphere –burning/no fills or short fills/discoloration can result
  • Inserting not properly applied and/or allowing for atmospheric bleeding of gas/air in cavity
  • Self-cleaning venting principles not appropriately applied, both in static and dynamic situations
  • Hot manifold choice or hot nozzle selection not appropriate for plastic/part requirements
  • Part cooling issues (hot manifolds)
    • No isolated cooling in gate areas
    • Improper plate cooling
    • Air insulation distance not properly observed
    • Contact area too great
  • No insulator plates

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