Design Guide Topic 3

Split Parting Lines

• Parting lines are the planes where moving injection molding tool components meet.
• Locations of parting lines are determined by component configuration.
• Parting line level changes should be gradual and kept to a minimum.
• A flat parting line provides for a less complex tool.

Shrinkage

• Plastic shrink toward the theoretical center of the component as they solidify and cool to room temperature.
• Shrinkage does not need to be designed into the component; it will be incorporated into the tooling.

Side Cores (Slides)

• Side cores are required to produce holes or undercut features that are with the major parting line of the injection molding tool.
• Produce features that eliminate secondary machining operations.
• Reduce the need for draft, as well as the amount of draft on external features.

Internal Threads

• For cost efficiency and speed, internal threads are commonly tapped as a secondary operation.

Application Temperature

• Zinc die cast components perform extremely well in a wide range of temperatures.
• For components under load or in high stress environments, the temperature should not exceed 1750 F (800 C).
• In an application where high stress is present, the temperature can exceed 1750 F (800 C) for only a short term.

Texture Finishes

• Surfaces are molded between 16 and 64 micro inches (0.4 - 1.6 microns).
• Through-holes formed by center gating have surface finishes of 4 - 8 micro inches (0.1 - 0.2 microns).
• Matte finishes of varying textures can be applied to improve appearance and structural integrity