Week 9 - Attachment Feature Creation - Challenge 2

AIM: To create a SCrew Boss and dog House for the center console coin holder as per the OEM standard and design considerations.

SCREW BOSS

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. Screw bosses can be reinforced with ribs or gussets for added strength and durability. A boss should not be next to exterior walls, but you can use coring ribs to keep it connected to the part’s exterior wall without risking a sink.

DESIGN CONSIDERATIONS FOR SCREW BOSS

• Draft - 0.5 Deg per side.
• The wall thickness at the base should be 40% of the thickness of the component(T).
• The screw can penetrate into the base 0.3*T Max.
• The outer diameter of the boss should range between (2 - 2.4)*(D)

Inner diameter.

• Height to diameter ratio should be 3:1.

STEPS INVOLVED IN MAKING OF THE SCREW BOSS

• Extract the surface on which the screw boss has to be created.
• Create a sketch on the extracted surface with all the required dimensions.
• Extrude the sketch created with the required height.
• Provide a minimum of 0.5 Deg Draft.
• Give the nominal filets.
• Create the ribs connected with the boss for providing stiffness to it.

Creation of ribs

DOG HOUSE

Dog house is an engineering feature used in plastic components. Dog houses are used as supporting features. Sometimes other engineering features like snaps, screw boss, locators etc. are mounted on them to increase their strength.

Reasons which facilitates the use of Dog House:

• To avoid sink marks on the high quality surface.
• To solve the length factor in case of screw boss.
• To make a screw boss in the direction perpendicular to the tooling axis.

DESIGN CONSIDERATIONS FOR DOG HOUSE

• "C" is where the doghouse contacts the backside of the surface.
• 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.
• Minimum height should be 6mm, less than 6mm causes weak steal condition.
• Draft should be minimum 1.5 Deg.

STEPS INVOLVED IN MAKING OF THE DOG HOUSE

• Extract the surface on which the dog house has to be created.
• Create a sketch on the extracted surface with all the required dimensions.
• Sweep the sketch created with the required height along the tooling axis.
• Convert into a solid part with appropriate thickness.
• Provide a minimum of 1.5 Deg Draft.
• Give the nominal filets.
• Assembled with the main component
• Create a side core tooling axis for draft analysis of the dog house.

Draft Analysis For Screw Boss

Draft Analysis For Dog House