Week 9 - Attachment Feature Creation - Challenge 2

Screw Bose Design:

Bosses are used main for attachment & assembly. Most common variety is cylindrical boss with hole to receive self threading screw. Outer diameter should be 2.0 to 2.4 times the inner diameter.

Rules for Designing screw Bose:

Draft Angle:

Draft angle should be 0.5 degree for internal & external cylinder.

Thickness of cylinder:

Thickness should be 0.6 times the wall thickness in each side & inner diameter.

Height to diameter ratio:

Height to diameter ratio should be 3:1.

Hole should be projected inside the main wall 0.3 times of main wall thickness.

Optimal Radii:

Fillet radius for screw bose should 0.25mm.

Support Rib:

Support ribs are used to the give strenght to screw bose with 40% of wall thickness.

Doghouse Design:

Dog House is mainly used to avoid sink marks on Class A surface.

To solve the length problem with increasing the doghouse & place the engineering feature at the top.

Creating the boss or other engineering feature perpendicular to the tooling axis.

Wall thickness of the joint at main wall & dog house should be 40% of main wall thickness to avoid sink mark.

Height of reduced wall thickness in dog house should be 3.0~0.6 mm.

Dog House width at inner area should be minimum 12mm.

Draft angle of dog house should be 1.5 degree at outer area & 0.5 degree in the inner wall.

Height ratio of dog house 3:1 or 2:1.