Challenge

Week 9 - Attachment Feature Creation - Challenge 2

HHarish Ram29 Nov 2021

Attachment Feature Creation - Challenge 2

OBJECTIVE:

To create screw bosses and dog house for a plastic component by adhering to plastic design rules.

SCREW BOSS:

Screw Boss is a Engineering feature which is 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.

Design Considerations for Bosses:

When Bosses are supposed to be created along side walls,it is better to design it with ribs supporting it rather than to design along the side walls as it may increase the cross section of that particular area which may lead to sink mark

Draft - 0.5 deg on walls of the bosses.
Thickness - 40% of the plastic product's thickness
Radii - 0.25 radius
Height to Diameter ratio must be 3:1

DOG HOUSE:

Dog house is also a B side/engineering feature used in plastic design. Dog houses are used as supporting feature. Sometimes other engineering features like snaps and locators are mounted on them to increase their strength. It sometimes solves the length issue for the screw boss as bosses can be designed over them and also perpendicular to the tooling direction if required .It also helps in evading sink marks

Design Considerations for Dog House:

C must be 40% or less than the wall thickness at the base (T)
B should be 3-6 mm

TOOLING AXIS:

Tooling axis is created normally along the flat surface

BOSS DESIGN:

Sketch Solving status:

Here the hole size is considered to be 5.2 mm so the outside diameter tends to be 40% of the wall thickness for one side of the wall . Therefore it is 7.2 mm for the outside diameter.

As screw bosses need some support ribs are created around it following the plastic product rules:

Draft:

Thickness of the rib is 1mm.

Fillet:

Now the feature is added into the main body.

DRAFT ANALYSIS ON SCREW BOSS:

VARIOUS ORIENTATION OF THE TEST:

CREATION OF DOG HOUSE:

As aforementioned dog house are also designed to resolve the length issue.Let's consider we have a assembly sequence at 20 from the base surface. We tend to design a dog house and then place/create the screw boss over it as we cannot create a lengthy screw boss due to its weak factor.

Sketch solving status:

Instead of padding and giving draft to it here the sketch is swept along tooling direction with 1.5 degree.

Using class A as reference the top surface is closed by offsetting it to a nominal level and trimmed.

SIDE CORE:

The inside surface of the dog house should be cleared using a different tooling axis. As a result the side core axis is created along the Z axis.

Thickening and Drafting:

Draft is 0.5 deg

Using extract,offset,extrapolate and trim C portion of the dog house is created following the plastic design rules.

Length of the C portion falls between 3-6 mm

Thickness of C is 40% or less than the main wall thickness
Fillets are given accordingly.

DRAFT ANALYSIS ON THE DOG HOUSE:

MAIN TOOLING:

SIDE CORE:

Now using copying the already created screw boss and using simple translation command,the boss is placed over the dog house in order to compensate the length factor.The screw boss can also be placed perpendicular to the tooling direction using the dog house when it is required.