Each injection mold design must have a gate, or an opening that allows the molten plastic to be injected into the cavity of the mold.  Gate design and location can have a drastic affect on your part that could result in incorrect parts and/or significant cost increase to fix your tools.The Affects of Gate LocationGate design and location are crucial to creating a successful part.  The type of gate and the location can have affects on the part including:

  • Part packing
  • Gate removal or vestige
  • Cosmetic appearance of the part
  • Part dimensions and warping

As you can see, using the incorrect gate can spell disaster, or at the least a mold rework, which can quickly and sharply increase manufacturing costs.Recommended Gate LocationsTo avoid problems from your gate location, here are 7 tips on choosing the proper gate location(s):

  1. Place gates at the heaviest cross section to allow for part packing and minimize voids & sink.
  2. Minimize obstructions in the flow path by placing gates away from cores & pins.
  3. Be sure that stress from the gate is in an area that will not affect part function or aesthetics.
    1. If you are using a plastic with a high shrink grade, the part may shrink near the gate causing “gate pucker” if there is high molded-in stress at the gate.
  4. Be sure to allow for easy manual or automatic degating.
  5. Gate should minimize flow path length to avoid cosmetic flow marks.
  6. In some cases, it may be necessary to add a second gate to properly fill the parts.
  7. If filling problems occur with thin walled parts, add flow channels or make wall thickness adjustments to correct the flow.

Gates vary in size and shape depending upon the type of plastic being molded and the size of the part.  Large parts will require larger gates to provide a bigger flow of resin to shorten the mold time.  Small gates have a better appearance but take longer time to mold or may need to have a higher pressure to fill correctly.