Week 9 - Attachment Feature Creation - Challenge 2

AIM:

To create a screw boss and a dog house on the given Centre console coin holder and to perform draft analysis on it.

SCREW BOSS:

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, threaded insert or other type of fastening hardware.

DESIGN RULES FOR SCREW BOSS:

• As a rule of thumb, the outside diameter of bosses should remain within 2.0 to 2.4 times the outside diameter of the screw or insert.

• Avoid bosses that merge into side walls because they can form thick sections that lead to sink. Instead position the bosses away from the sidewall, and if needed, use connecting ribs for support.

• Wall thickness at the base, W = 0.6T, where T is the thickness of the component.
• Optional rib fillet radius – 0.25mm maximum
• Draft angle (Inside and outside walls) – 0.5degrees
• If H is the height of the boss and B is the hole diameter at the top, then H/B < 3.

DOG HOUSE:

Dog house is an engineering feature on which screw boss, snaps, locators, etc. are mounted. The main use of the dog house is to avoid sink marks. It is also used to increase the length of the other features mounting on it and also to change the direction of such features if required.

DESIGN RULES FOR DOG HOUSE:

• The wall thickness at the base (C) should be 40% or less than the main wall thickness (T), for a height (B) of 3.0 to 6.0mm.

• Minimum Height (H) of dog house is 6mm. Less than 6mm causes weak steel condition.
• Minimum dog house width (X) is 12mm.
• 3:1 ratio of steel width to height. 2:1 is preferred.
• Minimum Draft (D) for doghouses is 1.5 degrees to die draw.

SCREW BOSS DESIGN:

Step 1: Extract the surface on which the boss should be created and create an axis system on this surface.

Step 2: Draw two circles on this surface as per the standards and pad it. This represents the screw boss.

Step 3: Create draft on both outside and inside walls.

Step 4: Draw another sketch for ribs and pad the sketch and draft on all sides of the ribs.

Step 5: Assemble the boss and ribs to the main part and finally provide fillets to the edges.

Step 6: We can copy and paste this boss and translate it wherever required for multiple times.

DRAFT ANALYSIS ON SCREW BOSS:

Step 1: Change the view to customized view and enable the material in shading option.

Step 2: Insert the feature draft analysis.

Step 3: Click the compass icon and place the compass along the tooling direction.

Step 4: Lock the draft direction and select the component to draft.

Step 5: Enable the color scale and change the draft value as required. Here 0.5 degree is given as draft angle.

Step 6: The green color indicates that the surface is more than 0.5 degree from the tooling direction. The blue color indicates that the surface is 0 to 0.5 degree from tooling direction. Red color indicates that the surface is less than 0 degree from tooling direction which indicates the negative draft.

DOG HOUSE DESIGN:

Step 1: Create a sketch on the surface where the dog house should be created and sweep it at an angle of 1.5 degrees along the tooling direction.

Step 2: Close the top side by offsetting and trimming the surfaces and thicken the resulting surface.

Step 3: Split the uneven part at the front by extracting and offsetting surfaces.

Step 4: Then provide draft of 0.5 degree to the inner surfaces and give fillets to the corners.

Step 5: Then reduce the thickness at the bottom portion as per the design rules.

Step 6: Provide draft of 0.5 degree to the surface shown in the figure.

Step 7: Assemble the dog house to the main part and provide fillets as required.

Step 8: Create a side core axis for the dog house along the Z direction.

DRAFT ANALYSIS ON DOG HOUSE:

ALONG MAIN TOOLING AXIS:

By following the steps mentioned above, draft analysis is performed at 1.5 degrees along the main tooling axis.

ALONG SIDE CORE AXIS:

By following the steps mentioned above, draft analysis is performed at 0.5 degree along the side core axis.

ISOMETRIC VIEW:

FRONT VIEW:

SIDE VIEW:

TOP VIEW:

RESULT:

Thus screw boss and dog house are created on the given coin holder and draft analysis is performed on it.