Injection Overmolding

3-d Manufacturing Description

Students will learn how 3-d objects are made, molded and cast by hand and manufactured. Students will Utilize software to make 3-d objects on the computer. Use a 3-D printer to manufacture those objects. Everything from artistic sculptures to mechanical parts will be made.

Outcomes:
  • Students will develop problem-solving skills
  • Students will develop their own 3-d objects and make clay prototypes
  • Students will make single and multi-piece molds of their clay objects
  • Students will cast their objects in resin or other materials
  • Students will use an injection mold machine
  • Students will make their own molds for the injection mold machine
  • Students will be introduced to industry-standard 3-d software and vocabulary
  • Students will understand elements of planning and design
  • Students will develop mechanical and artistic 3-d pieces on the computer
  • Students will utilize a 3-d printer to turn their computer files into real-life objects.
  • Students will make multi-piece prints that fit together for final assembly

    • Overmold Injection is where plastic or rubber is injected around a previously made part. Using CAD software, Students are to make an object, then reverse that object so that it fits into two blocks that can be put into our blank injection mold for quick reproduction.

    Students must first create a shape that can be molded with a simple two part mold. Only undercuts that can be separated into two parts are allowed to be used. Things like a tool handle, sculpted face, custom keychain tab, and toys (army men, game pieces, airplanes, etc.) are good ideas.

    Next, students should make the two halves of the injection mold, imbed their shape into each part halfway and make it a negative shape or "hole", cutting into each side of the mold.

    Students must consider how the hot plastic will flow into and around the molded part to fill the entire mold cavity and must consider the thickness of specific parts so as not to create "unfillable" areas.

    The students' injection mold must fit inside our injection mold blank and align with the fill hole. Below are the specific measurements: (click the image to bring up a larger view) Note corner radius is 1/4 inch.


    Vital considerations:
  • Sprue, runners, and gates
  • Thinness of parts
  • Undercuts
  • Placement of fill line(s) (Runners and Gates)
    • The teacher illustrates how to use negative shapes or "holes" to produce pieces that fit together perfectly.

    Students' work will be printed to proof the fit of each part.

    Evaluation:
    2 point -- No unmoldable undercuts
    4 points -- Mold and sprue line fits our blank
    4 points -- Complexity (don't make it too simple)
    10 points -- Successfully set up in preform, printed and 3 injections made.
    ALWAYS spray Mold Release into mold before injecting!
    20 points total

    Original part (Keychain)


    Part with sprue, runners and gates added imbedded into mold block.


    Part cavity in mold block