Week 9 - Attachment Feature Creation - Challenge 2

OBJECTIVE:

To create the dog house and screw boss in the centre console model based on the above design criteria using catia.

PROCEDURE:

SCREW BOSS CREATION:

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.

GIVEN DESIGN CRITERIA:

• 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.
• Draft angle - inside & out > 0.5°
• 3:1 ratio h

SCREW BOSS CREATION IN CATIA:

i) First i created two circles in the sketch

The inner-circle diameter was assumed to be 5.2mm, the outer circle was arrived by using the design parameter, thickness of the screw boss should not be higher than 40% of the base.we know that the base of the coin holder is 2.5 mm, therefore 2.5*0.40 = 1mm, thereby the diameter of the outer circle = (1+2) + 5.2 = 8.2 mm.

ii) Height of the screw boss is given by the height to diameter ratio = 3:1, thereby the value of height = 3*5.2 = 15.6 mm.

iii) As per the given design parameters the draft angle and the fillet is provided, the optional edge fillet here is given as 0.25 mm thereby meeting the design parameter.

NOTE: As shown in the above model the screw boss created was strengthed using the ribs (which were designed based on the previous challenge design parameters).

FEATURE TREE FOR SCREW BOSS:

DOG HOUSE CREATION:

The dog house is an engineering feature used in plastic trim design. Doghouses are used as supporting features. 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.

i) First i created a base sketch in a rectangular pattern (with one side made as construction, this was intentionally done inorder avoid plastic defects like flow lines).

ii) The sketch was then extruded to a height of 12mm as shown below,

iii) Next i used the command "sweep" to get the dog house to draft along the inner direction of 1.5 deg then to adjust the heigh and bring it a perfect dog house shape i used the command surface untrim, offsett and trim.

As we can observe in the above image, the 3d solid was made out of the surface design using the "thickening command". but still the edges are not proper so i used the command extract, surface untrim of the dog house and made it a complete one using split command.

iv) The draft angle of the inner side of the dog house for 0.5 deg.

v) The edge fillet for the inner side of the dog house is given a nominal diameter of 1 mm.

vi) The height of the dog house is given as 4 mm whereas in the given design parameters it was indicated between (3-6mm).

vii) To achieve the c value in the dog house as mentioned in the question, i have made an extract on the inner face of the dog house and made an offset for imm (0.4*2.5mm = 1 mm)

viii) Fillets - edge fillets were done on the inner side of dog house (intersection of part wall c) for a nominal 0.5mm. this was done to achieve a proper draft analysis result.

ix) The earlier created screw boss was translated to a position above the dog house, thereby the dog house serving its purpose of strengthing the coin holder and also acts a bridge by joining the screw boss with adjoining part.

FEATURE TREE FOR DOG HOUSE: