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Preparing Design Models for the Mold Process

You may not be able to create a mold from a perfectly valid design model.
• Design model requirements for molding typically include:
– Draft on “vertical” surfaces.
– Uniform thickness.
– Ribs.
– Ejector pin “pads.”
• Preparation guidelines:
– Draft applied to “vertical” faces.
– Ribs should be about half the model thickness and drafted where needed.
– Create ejector pin “pads” where needed.
– Reorder or insert draft features before rounds if possible.

Preparing Design Models for the Mold Process 1
Figure 1 – Original Design Model
Preparing Design Models for the Mold Process

Preparing Design Models for the Mold Process 2
Figure 2 – Design Model Prepared for Molding
Even though the design model you receive may be a valid design model, you may not be able to use the model to create a robust mold. The following items are typically required of the design model to create a robust mold and part:
• Draft — Facilitates the removal of the part from the mold.
• Uniform thickness — Areas of a part that are thicker than others can result in sink zones or warping when cooling occurs.
• Ribs — Add strength and rigidity to the molded part.
• Ejector pin “pads” — Sufficient material is needed for the full diameter of an ejector pin at the location where it pushes against the resulting part to eject it from the mold.
These items may not be present in the design model when you receive it because the design engineer does not know where the parting surface or ejector pins will be located in the mold. Therefore, you must prepare the design model for the mold process by adding the necessary features needed to make a mold from the model.
Guidelines for Proper Design Model Preparation
The following guidelines indicate how to properly prepare a design model for molding.
• Try to create models that are of uniform thickness to prevent sink zones or warping in the resulting molded part.
• Create ribs that are approximately half the model’s wall thickness to prevent sink. Apply draft to the rib walls if they are “vertical” faces. Vertical faces are those that are vertical with respect to how the mold opens. In Figure 2, two ribs have been created and draft has been applied.
• Be aware of the need to accommodate ejector pins in your design model for proper ejection from the mold. Create ejector pin “pads” at these locations in the model where the ejector pins push against the model to eject it. In Figure 2, four ejector pin pads have been created.
• Apply draft in the proper direction at least 0.5 degrees on all “vertical” faces. Draft has been applied to all faces that are vertical with respect to how the mold opens.
• When creating Draft features in Creo Parametric, either reorder them to be created before any related rounds or insert them before the rounds. This practice results in a more robust Creo Parametric model. In Figure 2, the draft has been inserted before the adjacent rounds.

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