Week 9 - Attachment Feature Creation - Challenge 2

DESIGNING SCREW BOSS AND DOG HOUSE FOR THE COIN HOLDER

Objective

To design the screw boss and dog house for the coin holder considering the design rules.

Screw boss

Boss features are commonly found in injection moulding 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.

General Guidelines for Bosses:

• 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 - 0.25mm maximum radii.

Dog house

Dog house is an engineering feature used in plastic trim design. Dog houses are used as supporting feature. Sometimes other engineering features like snaps; 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.

Design Rules 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

Steps for Screw boss

1. Sketch the screw boss circles and paded to 12.5mm then drafted angle should be 0.5 degree.

2. Sketch the rib for screw boss and paded to 10mm then draft to 0.5 degree.

3. Unitrim the rib body to screw boss select the removed part.

4. Edge fillet to the screw boss and ribs of 0.25mm

Steps for Dog house

5. Sketch the dog house and Sweep the sketch upto 20mm with draft direction 0.5 degree to tooling direction.

6. Extract the class-A surface and offset to 22.5mm then trim the offset surface with sweep surface.

7. Give edge fillet of 1mm to the suface and thicken the surface in part modeling.

8. Extract the back side of dog house surface and extapolate then offset to 22mm and split with the dog house thicken model.

9. Extract the dog house inside surface and offset to 1mm then offset the Class-A suface to 4mm and trim with the inside surface.

10. Use line command to create side core direction and draft the trim surface to 0.5 degree then split with the trim surface.

11. Edge fillet of 0.5mm split area and edge fillet of 3mm to outer surface of the dog house.

12. Assemble the dog house part body to the main body then screw boss is transulate and move to top of the dog house and assemble with the main part body then give fillet of 0.25mm to the screw boss and ribs.

13. Draft analysis of screw boss, rib and dog house outer surface with tooling direction and inside of the dog house is draft analyse with the side core direction.