Core & Cavity Design

Aim: Creating core & cavity blocks for Switch Bezel Plastic component.

Workbench and its Toolbar used:

Generative Shape Design Workbench

• Surface Toolbar
• Wireframe Toolbar
• Operation Toolbar

Part Workbench

• Surface Based Feature Toolbar

Theory:

Tooling Axis - Tooling Axis is the direction in which the component will be ejecting after the molding process is completed. The rules of selecting an optimum direction of tooling axis for any particular component is as follows :-

• The direction of the tooling axis should be clearing the maximum number of portions of the component once the molding process is completed.
• The direction of the tooling axis should be selected such that the number of side cores required should be minimum, as inserting side cores causes a rise in production cost.

Drafting - Draft is the inclination given to any particular plastic component’s cavity walls in order to achieve easy ejection, once the process is completed.

• Consider that the draft angle between the plastic component and the core is zero.
• When the molten plastic inside the cavity cools, it sticks to the walls of the core.
• During such zero draft condition, the ejection of the plastic component causes friction between them which might bring damage to both the core and the component.
• This damage further leads to inefficiency in the production & also affects the product’s surface finish.
• Hence, a minimum of ½ to 1 deg draft is provided to help in releasing the component.
• However 3 deg draft is widely accepted as a norm in the industry.

Prerequisites before creating the tooling axis and performing draft analysis-

1. Ensure that the Class A surface imported should be a single surface.
2. This can be checked using the Boundary tool in the Operation Toolbar.
3. If the surfaces are disassembled, join them using Join command which is also found in the Operation toolbar.

Creating any component from Class A Surface ( Overview ) -

1. Decide a suitable tooling axis direction and create the Tooling Axis.
2. Perform Draft analysis for analyzing whether the drafts on the component follow the industry standards.
3. Create another surface ( B Surface ) offset to the Class-A Surface. The offset distance should be equal to the thickness of the component.
4. Create a C- Surface ‘Sweeping’ the boundary of Class-A -Surface along the Tooling Axis.
5. Trim Class- A surface with B-Surface and C Surface to create a closed surface.
6. Finally create the solid part from this surface to obtain the desired component.

Procedure:

I] Troubleshooting the problems in the imported Class-A Surface:

1. The Class A Surface was disassembled when imported which violates the rule for proceeding further.
2. Use Join Command from the Operations Toolbar to join these surfaces together.

II] Creation of Tooling Axis:

1. The Tooling axis was decided along Z- Direction considering its selection rules mentioned above.
2. Next we created an axis system along a suitable point according to the boundary and design of the component ensuring the rules of selection of tooling axis direction are not violated.
3. Here we have an unclosed pocket which has to be cleared along the tooling direction.
4. Hence we create a sketch line bisecting two opposite faces of the pocket and another sketch line at a certain angle to the one remaining face ( say 3 deg ) which can be changed according to the draft analysis report.
5. Bisect the two lines in order to create the Tooling Axis.

III] Draft Analysis Of Class-A Surface:

• Draft Analysis is performed on the component in order to check whether the component can be manufactured or not.
• This Draft Analysis tool in Catia allows us to analyze the drafts provided on the surface.
• We can check whether they follow industry standards and if not we can modify it accordingly.

The procedure of Draft Analysis is as follows-

1. Before starting the draft analysis ensure that the ‘Materials’ option is selected under Customize View Parameters in order to view the results of the analysis.
2. Click on Insert >> Analysis >> Feature Draft Analysis.
3. Draft analysis window will be opened having three sections - Mode , Display and Direction.
4. In the Display section select the compass and drag it onto your component. Place it along the tooling axis.
5. Lock the direction of the draft.
6. Another window will be displaying ranges of draft on the component. The ranges are - Green for more than zero , Red for zero and Blue for negative draft value.
7. Assign the lower limit as 3 deg to the Green range from the value edition dialogue box.
8. Once you do it, click on the component to see the results.
9. You can also check the draft value at any point using the ‘Analysis under running point' option in the Display Section.

IV] Creation of B Surface:

1. To simplify the process, we extracted the simpler surfaces using the Extract Tool in Operations Toolbar.
2. The extracted surface offset is created with offset distance equal to the thickness of the component.
3. Further we untrim the offset surfaces using Untrim Tool and extend them to a certain suitable value using Extrapolate Tool so that they intersect each other.
4. Using the Trim Tool we trim them to a single continuous surface.
5. Finally we provide necessary fillets and the B-Surface is created.

V] Creation of C Surface:

1. We create the boundary of the Class-A Surface using the Boundary Tool.
2. Using the Sweep Command we sweep the boundary along the tooling axis as the draft direction.
3. Then we extrapolate the faces and trim them using the Trim tool.
4. Lastly we join the Class-A Surface and the sweeped surfaces along with the holes using Join Command to form the C + A Surface.

VI] Creating a closed surface and forming a solid part from it:

1. Use the Trim Tool to form a closed surface from B-Surface and C+A Surface.
2. Create a solid part from this closed feature using the Surface based feature in part workbench.

VII] Draft Analysis of Solid Part:

Following the similar steps performed for draft analysis of Class-A surface we obtained the following result.

VIII] Creating the Core:

1. Trim the C+A Surface with the B surface such that projections of the Switch Bezel Components are visible on the surface.
2. Further extrude a rectangular profile along the tooling direction.
3. Ensure that the parting surface and the rectangular profile intersect.
4. Trim them together and form a closed body using Fill command to closed the open section.
5. Create a solid part from this closed feature using the Surface based feature in part workbench.

XI] Creating the Cavity:

1. Trim the B surface with the exxtruded rectangular profile such that inward projections of the Switch Bezel Components are visible on the surface.
2. Ensure that the surface and the rectangular profile intersect. Trim them together and form a closed body using Fill command to closed the open section.
3. Create a solid part from this closed feature using the Surface based feature in part workbench.

Core Cavity Formed:

Core:

Front View:

Top View:

Side View:

Isometric View:

Cavity:

Front View:

Top View:

Side View:

Isometric View:

Visualization Of All the three together:

Conclusion:

Hence we have successfully created Core & Cavity for the given Switch Bezel plastic component.