Week 8 - Challenge 5 - Core & Cavity Design

WEEK-8_CHALLENGE-5

CORE AND CAVITY DESIGN

AIM

This challenge aims to create the Core and cavity design of the switch bezel component that we designed and also to understand the parting surface and parting line for this design.

THEORY
A parting surface can be defined as the surface where the core and cavity of the component meets. It is primarily designed for the removal of plastic products and cold slugs. The selection of parting surface is an important design factor in injection molding. With a reasonable parting surface selection, the mold structure can be simpler, making it easier to mold and release the plastic product, with product quality guaranteed. If selected inappropriately, mold structure becomes complex, making it difficult to manufacture and also affecting the surface finish and aesthetics of class-A surface in some cases. Therefore, the selection of the parting surface is of great importance to the design of mold structure.

PROCEDURE

Defining the parting surface
From the results of the draft analysis, we need to define the parting surface. In this case, we also consider the aesthetics of the class-A surface. If the parting surface is present on class-A then due to the flashing defect the class-A surface aesthetics gets affected when the flash is trimmed off and also from the draft analysis we can see that there is an extra portion present in the class-B when compared to class-A. So parting surface in class-B will be a good choice in this case.

Core design
The core is the part of the tool from where the molten plastic is injected into the space. It is the movable half of the tool. For the design of the core, we need to use the tooling direction to define the surfaces which make the core, and also it is best suggested to have the parting surface in the moving half (core) because it eases the ejection process. Now with all these considerations, we arrive at the surfaces which make up the core, and by trimming them by selecting appropriate faces to give us the core’s front face and by extruding the simple rectangular profile we can obtain the sidewalls of the core. Now, by applying the fill option to the open boundary of the side walls we get a closed surface model of the core. This is further converted into a solid model using the closed surface feature in the part workbench.

Cavity design

Cavity design is similar to that of the core design. Here we take the B-surface of the final model to be the front face of the cavity and trim it with the other side of the extruded surface and finally closing the surfaces by applying fill to the open boundary of the side walls. Then the surface model is converted into a solid model using the closed surface feature in the part workbench.

Parting surface
For the parting surface first, we need a parting line. This can be obtained from the intersection of class-B and class-C surfaces. Then the working face of the core design is trimmed with this parting line to get the parting surface. Parting surface and parting line can be used to understand the design of core and cavity and also in which direction the component moves after the completion of injection molding.

FINAL MODEL