Week 9 - Attachment Feature Creation - Challenge 2

Screw bosses & Doghouse Design - Attachment Feature Creation

Create the boss and Dog House for the Centre console coin holder considering the design rules.

Creating screw bosses and doghouse for the Centre console coin holder using CATIA v5

I. Screw Bosses

Boss features are commonly found in injection molding designs. They are used to aid in the assembly of molded parts by providing a channel for a screw. Designing plastic screw bosses is fairly straightforward but there are a few considerations to ensure a strong connection between parts and mitigate cosmetic defects.

Guidelines-

• Draft - 0.5 degrees on walls of boss.
• Thickness - Typically 40 %* of the nominal wall at the base.
• Height to Diameter Ratio - 3:1.
• Radii - 0.25 mm maximum radii.

Measure the thickness of the base surface for rib-

• This thickness value 2.5 mm will be required in upcoming stages.

Create sketch for the Screw boss on the part wall.

• Thickness = 1.5 mm.

Extrude the boss-

• Height = 12mm

Provide draft on both sides-

• Draft = 0.5 degree
• Using boolean operations assmbel the boss with coin holder main body.

Create sketch for the ribs of boss-

Extrude the Ribs and provide draft and chamfer-

• Thickness = 1 mm
• Draft = 0.5 degree

Trim-unwanted region and give fillets-

• Fillet = 0.25 mm

Similarly create more bosses as per product requirement

Draft analysis-

• Analyse at 0.5 degree

II. Doghouse

Dog house is an engineering feature used in plastic trim design. Dog houses are used as supporting feature. Sometimes other engineering features like snaps, screw bosses, locators etc. are mounded on them to increase their strength. Dog houses are subjected to draft analysis to prevent breakage of the component during ejection from mould cavity. Dog house and other engineering components are built on B-surface.

Guidelines-

• Doghouse wall thickness at the intersection of the part wall (C) should be 40% or less than the main wall stock (T).
• Height of (B) should be between 3.0 – 6.0 mm

Create sketch on main body for the doghouse-

Create side wall surfaces using sweep-

Close the top of dog house by trimming the offset surface

Create solid body of doghouse using thicken and give fillet and draft-

Create C section of doghouse-

Extract inner surface and trim off with offset surface of1mm-

Split the doghouse body using this trim surface to get C section-

Give draft to new created surface and provide fillet -

Create tooling axis for doghouse body-

• As it is evident that the doghouse will not be cleared with main tooling axis so there will be a side core for this.

Draft Analysis-

Thus, for more height the boss can be place on the top of the doghouse and any plastic deffect marks can be avoided on Class A surface.