Week 9 - Attachment Feature Creation - Challenge 2

SCREW BOSS AND DOG HOUSE - ATTACHMENT AND FEATURE CREATION

OBJECTIVE:

To create a screw boss and dog house feature at the coin holder with design rules.

SCREW BOSS:

Screw boss is used in plastics parts to assist in assembly, as a receptacle for a screw or threaded insert or as the locator for a mating pin on another part. This adds strength to the component and helps avoid plastic defects such as sink.

Followings are the guidelines for Screw Bosses:

1. Draft - 0.5 degrees on walls of boss
2. Thickness - Typically 60% of the nominal wall at the base.
3. Height to Diameter Ratio - 3:1
4. Radii - 0.25mm maximum radius.

Screw boss is designed as per above guidelines. I have designed for M6 standard bolt,So diameter taken as 5.2 mm and boss diameter taken as 8.2 mm.

This sketch is thickened and to support this boss ribs are created and drafted with 0.5 degree as shown in the figure:

The cross section of screw boss with ribs shown below.

DOG HOUSE:

Dog houses are created at the bottom side of the bosses to avoid plastic defects. Doghouse wall thickness at the intersection should be 40% or less than the main wall thickness here 1 mm is the thickness. Height of the doghouse should be between 3 to 6 mm and here I have taken 4 mm height. Rectangle is created at the base of coin holder.

This sketch is sweeped with 1.5 degree and height of 21 mm as shown in the figure.

Base is extracted from class A surface and offsetted to 20 mm then this surface is trimmed as shown in the figure.

This surface is thickened as a part body.

Uneven edges are removed by creating surface offsetted from back side as split tool.

Inside edges are drafted with 0.5 degree with side core axis and edges are filleted

Bottom side material is removed by using surface as a split tool.

Bottom side is drafted with 5 degree and same is filleted with 0.5 mm

Finally screw boss is assembled above this dog house.

Cross section of this assembly is checked with the measurement and the design rules are satisfied.

DRAFT ANALYSIS:

Top side of the part is cleared with main tooling axis as shown in the figure.

Inside of dog house is cannot able clear with the main tool axis. So it is cleared with side core tooling axis.

Different views of the part are as follows:

Front view:

Right side view:

Left side view:

Top view:

Isometric view:

TREE STRUCTURE:

RESULT:

Screw boss with dog house feature is created as per the design rules and draft analysis was done to ensure every side is cleared proper tooling direction.