Week 9 - Attachment Feature Creation - Challenge 1

Aim:

With the given coin holder create an rib in the part with the given rules for the rib.

Procedure:

With the thickness of the component the rib thickness should be 0.4-.05 times the thickness(i.e, 0.4*t). The height should not cross 5 times the thickness(≤5t). The top side should be greater than 0.75mm. Because the mould melt has to reach to the top of the rib.

Rib draft should be 0.5degree more than that top of the wall changes.

Design Rules for ribs

• Draft - 0.5 degree per side minimum
• Thickness - typically 40% wall thickness
• Height ≤ 5x wall thickness
• Spacing - 3:1 - steel height/ width ratio maximum
• Minimum thickness at tip - 0.75mm
• Radii - 0.25mm maximum
• Ribs on opposite side of wall should be offset
• Ribs should be connected to other structural feature where possible.

Designing with Ribs

The position and orientation of a rib relative to load and reaction forces is critical to its effectiveness. By being conscious of part geometry, designers can ensure that ribs added to the design will improve bending stiffness. Here are some rules of thumb to keep in mind during the design process:

Ribs thickness

Ribs should be designed to be 50-60 percent of the nominal wall thickness. Thinner does not provide much structure and may be hard to fill. Thicker ribs are tempting, but they can begin to introduce sinks on the cosmetic surface.

Rib height

For maximum effectiveness, rib height should be no more than three times the nominal wall thickness. Since the rib will be thinner than the wall, it may be hard to fill it if it is taller.

Rib spacing

Increase the number of ribs rather than their height in order to increase stiffness. Ribs should be spaced a minimum of two times the nominal wall thickness apart from one another.

Rib draft

A minimum 1 degree draft will ensure that they release from the tool during molding.

Rib coring

Core thick ribs from the back or below to create a blank area and thinner rib walls. This will help mitigate cosmetic sinks.

Rib radii

Radii at feature intersections should be a minimum of 0.5 - 1.0x nominal wall thickness to increase rib strength.

Result:

With the given measurement for the creation of rib, rib is created on the coin holder. Double the rib stronger the component.