Week 8 - Challenge 3 - Switch Bezel Design

Since thermoplastics shrink as they cool, they grip to cores or male forms in the mold. This makes ejection difficult and may lead to scuff marks on the part. To facilitate ejection, part surfaces parallel to the draw direction of the tool require taper or draft. This draft allows the part to break free by creating a clearance as soon as the mold starts to open. The amount of draft needed depends on several factors:

• Material shrinkage – Some materials shrink more than others. In general, the higher the shrinkage, the larger the draft angle needed to prevent ejection issues.
• Height and shape of wall or feature – A shallow single straight rib having not enough draft causes less problems than a high cylindrical wall.
• Surface texture – A polished surface requires a smaller draft angle than a surface that is textured.
• Aesthetic requirements – Scuff marks might not be as big of a problem on a technical part "hidden" in an assembly while, for the cover part of the assembly, they may be totally unacceptable.

Draft analysis

Given Class A - surface

An intersection of the surface is created along its mid-plane

Two lines are drawn on the surfaces which are parallel or almost parallel to the direction of die movement.

Using these two lines a bisecting line or mean line is created which is the tooling axis of the part.

Using this bisecting line as tooling axis draft analysis is carried out. The min. draft angle is 3 degrees.

Using the class A surface a class B surface is created.

A class C surface is created using class A surface which is used to join both class A&B surfaces.

Both class A&C surfaces are joined together and trimmed using class B surface to obtain a thickened component.

Finally the part is converted into an solid component in the part workbench.