Week 8 - Challenge 6 - Core & Cavity Design

Core and Cavity Design for Switch Bezel - Plastic Component Mold

This report demonstrates the design of Core and Cavity Bloacks for an Automotive Plastic Component – Door Switch Bezel using industry principles such as Parting Surface and Parting Line definition, Draft angles, Draft Analysis, Determining and implementing of Tooling Axis, Class A, Class B, Class C surfaces and maintaining the Thickness of the part at 2.5mm. The Molds are designed using Surface Design and Solid Design techniques in CAD package CATIA V5.

Fig: CORE & CAVITY for Switch Bezel

The terms are briefly explained below:

Parting Surface:

• Generally Injection Molding has 2 major components: the Movable Half and the Fixed Half.
• During Injection Molding process, these 2 halves are pressed together tightly to form a sealed hollow to avoid the melt flow leakage and maintain certain holding pressure.
• The pressed surface is called the Parting Surface.
• Usually the parting surface are the biggest projection outline of the part.
• Parting Surface directly affects the Product Quality, Ease of Construction and Operation of the Injection of the Mold, the Mold Design is one of the key factors to the success.
• Design of Parting Surface should follow the following Design Principles:
  
  • Designing the Mold Structures as simple as possible.
  • Avoid or reduce side parting as much as possible to reduce complexity of mold making.
  • Ease of De-Molding. The plastic component must stay at the fixed half in most cases and ejected by the Ejection System and avoid side De-molding action.
  • Ensure Dimensional Acccuracy of the molded parts and try to make parts with similar dimensional accuracy requirements in the same module to reduce manufacturing and assembly errors.
  • Ensure Appearance Requirement of the molded parts.
  • Flash or mismatch usually occurs on the Parting Surface, so it shoul not be designed on a High quiality requirement Surface.
  • Ensure adequate Venting or De-Gassing. If possible Parting Surface should be placed at the end of the Mold Flow. This can be a good advantage for Filling and Venting.

Parting Line:

• Intersection of the Plastic Component with the Parting Surface is called the Parting Line.
• It is the Bordered Outline of the Component along the Parting Surface.

Draft:

• Draft is an angular tapering given at the design stage to every Plastic Component that has to be manufactured.
• It is given in the direction of the Mold Movement.
• The Draft allows the parts to release easily from the mold without creating friction between the surface of component and the core and cavity plates.
• When a Plastic component cools down inside the mold, the natural tendency of it is to shrink and attach to the core or cavity half.
• The movement of mold opening causes friction on the walls of the component as well as the core/cavity blocks.
• This reduces the life of the mold as well as the component itself.
• The component may also have rough surface finish as well as weak structure due to this.
• This problem can be solved by giving draft to the component.
• Most applications require minimum draft angles of around 0.5º to 1º , however 3º draft angles are widely accepted for cost saving purpose.
• 7º Draft angles are given to textured surfaces like Instrument Panels.
• Minimum possible draft angles are given to screw bosses, ribs and stiffeners due to their critical nature.

Tooling Axis:

• Tooling Axis is the direction in which the Mold opens and closes. Part Drafts are given along this axis.

Figure3: Tooling Axis

Draft Analysis:

• Draft Analysis is a tool in CATIA which identifies the zones which deviates from the specified values of angles along a defined draft direction using colour codes.
• It highlights the regions of draft using colours.
• Draft analysis is the first step performed after receiving the Class A of the component.
• Draft analysis should be passed in order to make the plastic component manufacturable.
• Acceptable draft angles are used as range for draft analysis.

Class- A Surface:

• In automotive design, a class A surface is any of a set of freeform surfaces of high efficiency and quality.
• It is the visible aesthetic surface of any automotive component.
• Class A surface refers to those surfaces which are visible and abide to the physical meaning, in a product.
• This classification is primarily used in the automotive and increasingly in consumer goods industry.
• It is a requirement where aesthetics has a significant contribution.
• For this reason, the exterior of automobiles is deemed Class-A.

Class- B Surface:

• Class B surfaces are Engineering Surfaces which are invisible to the eyes or often on the back side of the Class A surfaces.
• It is mainly the thickness of the component or Class A.
• These surfaces need to be designed as per the Class A surface i.e., the continuity, thickness of the component, functionality etc should be maintained.
• These surfaces include the main engineering features such as Screw bosses, Ribs, Snaps, Stiffeners and fixations.
• B surfaces also do not contain any aesthetic styling content and textures since it is not visible to eyes.

Class- C Surface:

• Class C surfaces are connectors between Class A and B surfaces.
• This surface connects both A and B surfaces along the Tooling Axis.
• It contains the draft as per the design.
• It is basically the thickened surface between both A and B surface.

SWITCH BEZEL DESIGN:

Procedure to be followed:

CORE BLOCK

CAVITY BLOCK

CORE AND CAVITY BLOCK

CORE AND CAVITY WHEN TRANSLATE

CLOSED SURFACES:

GEOMETRICAL SET TREE

Conclusion:

The Design of Core and Cavity for the Mold of Automotive Plastic Component – Door Switch Bezel is completed using concepts of Parting Surface, Parting Line, Draft angle, Draft Analysis for Class A and Final enclosed surface, Tooling Axis creation and implementation, Class B and Class C creation and conversion to a solid part maintaining the part thickness at 2.5mm.