Week 9 - Attachment Feature Creation - Challenge 2

OBJECTIVE - This project intends to create the screw boss and Dog House for the Centre console coin holder considering the design rules.

SCREW BOSS

Screw boss is an engineering feature that helps to screw two components. Screw bosses are used to joining and assembling many components. Commonly consist of cylindrical projection with a center hole, where it can be threaded by a hardware tool. While joining two components using screws and when we don't want those to be visible on the A surface, in that area these bosses are used.

In this project, a screw boss is created for a plastic component coin holder following the screw boss design rules.

Design rules for the screw bosses:

Draft - A maximum draft angle of 0.5 degrees is used inside and outside of the screw boss

Thickness - If 't' is the thickness of the component. One wall of the screw boss should have a thickness of 0.6*t. This is the ideal case but can be increased w.r.t requirement.

Height - The height of the boss has a height to diameter ratio which is 3:1

Fillet radius - A maximum of 0.25mm is given.

SCREW BOSS DESIGN

Here a screw boss is designed for an M6 hole.

The diameter of the M6 hole is 5.2mm. So using the design rule the outer diameter is 0.6*t = 0.6*2.5 = 1.5mm

The total diameter of the outer circle is 5.2+3 = 8.2mm

The height of the boss is taken using the design rule H/D = 3:1

Using tooling direction a draft angle of 0.5 degrees is applied on the outer surface

A fillet of 0.25mm is given

Ribs are created to strengthen the screw boss. To create the ribs, ribs rules are followed here. Where the thickness of the rib is 0.4*thickness of the component.

DOG HOUSE

The dog house is also an engineering feature used in the plastic trim design. Dog houses are used as supporting features. Dog house and other engineering components are built on B-surface. There are 3 main purposes of having a dog house.

They are: To avoid sink marks, to solve length issues, and when we want a perpendicular screw boss

DOG HOUSE DESIGN

A dog house is designed to mount the screw boss on the coin holder.

A draft of 0.5 degrees is applied inside the dog house along the side core axis

• Dog houses are built on B surface. At the very junction of B surface and dog house, the dog house should have a wall thickness of 40% thickness of the component. And it should have a height of 3 to 6 mm.
• In the below figure T is the thickness of the component, B is the initial height, C is the initial thickness of the dog house

• Since the component has a thickness of 2.5mm, the dog house designed in this project has an initial thickness of 1mm. An initial height of 5mm is taken.
• here the part with a draft angle of 0.5mm is already given. So the output values have a small variance

After creating a dog house, a screw boss is mounted on it

Draft analysis along tooling axis

Draft analysis using side core axis

Conclusion

Following the design rules for the component coin holder, a screw boss and dog house are created and draft analysis along the tooling axis and side core axis is made.