How to design mold cavity and core in 2D Autocad

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The old fashioned way but still being used by some mold manufacturers. Designing a mold cavity and core in 2D. Some mold designers may use different procedure. You can use Autocad, Solidworks, ProE, or just plain tracing paper and pencil in this mold design tutorial.

7 Steps:

1. Calculate for the mold dimension using the shrinkage factor.
   • The shrinkage factor can be determined by resin material properties or by experimenting. For example the PBT has a shrinkage of 18/1000.
   • Compensate for the tolerance and other possible deformation.
   • Include the draft angle whenever possible. The draft angle should be within the dimensional tolerance.
2. Draw product drawing using the calculated mold dimension. Include the embossed texts if it is a part of the product drawing. It is a good idea to draw the embossed texts using lines and curves. If your CAD is capable of “reflecting a text” then you are in advantage.
3. Mirror or flip your product drawing. The mirrored drawing will be your mold drawing. Notice that the embossed texts were also mirrored and they became engraved text.
4. Decide and draw the gate location. Locate it away from small core pins to avoid damaging those pins during resin injection process. For our example, I would like to use “side-gate”.
5. Decide the parting line. Input the parting line changes if there are any. Parting line changes should be visible on the top view, draw that too.
6. Decide the ejector location. Divide the mold drawing as you wish or as your process capability would dictate. Consider dividing on gas vents.
7. You can then derive or trace your cavity and core drawings using your mold drawing as reference.