Week 9 - Attachment Feature Creation - Challenge 2

SCREW BOSS AND DOG HOUSE

Objective :

To create the screw boss and Dog House for the Centre console coin holder, considering the design rules.

SCREW BOSS -

The screw boss is commonly used for the injection moulded parts. They are used to aid in the assembly of moulded parts by providing a channel for a screw. Design of screw bosses is simple, but we have to follow the design rules to ensure strong connection between the mating parts. The part with screw bosses is assembled with the another part by fastening screws to the screw bosses, which make the assembly to held together.

The most common variety consist of cylindrical projections with holes designed to receive screws, threaded inserts, or any other types of fastening hardware. The screw boss is required to have enough strength to withstand forced incurred between the assembly. A draft angle is also provided to ensure the proper removal of the part from the mould.

Design rules for screw boss :

• There should be minimum draft of 0.5 degrees should be applied to the all faces of the screw boss.
• The thickness of each wall should be 40% of the thickness of the part.
• The ratio of height of the screw boss to the diameter of the screw boss should be 3:1
• Optional fillet radius is 0.25 mm
• The screw holed is impinged into the main part up to a maximum thickness of 30% of part thickness.
• The number of gussets will be depended on the height of the screw boss.

DOG HOUSE -

The dog house is the feature used in the plastic trim design. Mainly, the dog houses are used as supporting features. In this design, we have used the dog house to support the screw boss.

If the assembly of other part with the current part should have required to happen at a certain distance from the base surface of the current part. For incurring this, we have to increase the height of the screw boss. Increasing the screw boss alone after a certain limit should cause the failure of the part. So we use the dog hose as the support for the screw boss.

Design rules for dog house :

• The C should be less than or equal to 40% of the T (thickness) of the part.
• The B should between 3 - 6 mm

Procedure :

SCREW BOSS -

Create the two circles on the bottom side of the coin holder as shown. The position sketch is drawn on the extraction of bottom surface

Apply a draft of 0.5 degrees to the face

Create sketch for the gusset creation

Thicken the sketch

Apply draft to the gusset

Union trim gusset and screw boss

Assemble boss with the main body

Apply minimal fillet of 0.25 mm radius to all faces

Draft analysis -

All faces of the screw boss are drafted perfectly

DOG HOUSE -

Create the positioned sketch as shown in the below picture

Swept the profile with the draft direction with an angle of 0.5 degrees and up to a length of 20 mm

Offset the bottom surface to top

trim the both surfaces

Offset the rear extract of the dog house

Split the extra surface at the front of the dog house and add the material to the thickness of 2 mm

The inner pocket of the dog house is not cleared by the main tooling axis. So, it is required to define the side core axis for the dog house.

Create the side core axis from the point used for the main tooling axis.

We have to create the bottom packet for the dog house. Use offset surface, position them according to the design standards. Trim the unwanted

Split the unwanted pocket

Apply 0.5 degrees draft to the faces with respect to both the main tooling axis and side core axis. Finally apply fillets

Draft analysis -

With main tooling axis

With side core axis

Assemble the dog house with the coin holder

T

Translate the copy of the screw to the top of the dog house

Assemble the screw boss with dog house

Final views of finished part

Draft analysis -

Using main tooling axis

Using side core axis

From the draft analysis it is observed that all the faces will satisfy the minimum and they are designed by considering the design rules.

Tree structure :

Conclusion :

The attachment features for the centre console coin holder are created such screw boss and dog house by considering the design rules and the designed component have minimum draft on all faces.

Thank You