Week 9 - Attachment Feature Creation - Challenge 1

AIM: To Create the rib for the Centre console coin holder considering the design rules.

RIBS: Ribs are thin wall-like structures that add support and rigidity to injection molded parts. They are thinner than primary walls and are used to support these walls, as well as bosses, by running perpendicular to these structures. Ribs are often used to replace thick wall sections to avoid sink marks, warp, and voids.

DESIGN RULES for RIBS:

Rib thickness - Ribs should be designed to be 40 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 - The Rib height should be greater than or equal to 5 times the wall thickness.

Rib spacing - Increase the number of ribs rather than their height to increase stiffness. Ribs should be spaced a minimum of two times the nominal wall thickness apart from one another. or it can be done in the ratio as well. The ratio will be of a height to width ratio.

Minimum thickness at the tip - We have to ensure that the minimum thickness at the rib tip must be 0.75 mm

Draft - A minimum 0.5-degree draft will ensure that they release from the tool during molding.

Radii - The fillets provided in the ribs should be in the range of 0.25mm to 0.5mm.

Generally, it is recommended to give 0.25mm fillets.

Given data: t = 'Wall Thickness' = 2.5mm.

To calculate the following data using rib design rules

θ = ' Rib Draft' = 0.5°

r = 'Rib Fillet radius' = 0.25mm

tt = 'Rib Tip Thickness' = 0.75mm

w = ' Rib Thickness ' = 0.4 * t = 0.4 * 2.5 = 1mm.

d = ' Rib Depth ' ≤ 5*t = 5*2.5 = 12.5mm.

Procedure:

Using the coin holder model, ribs creation is started with extracting the plane over which the construction for the ribs can be performed.

On this plane, the line is drawn that will be then this line is extruded along the direction of the tooling axis to a height of 12.5mm following the design rule of H=5*t.

Afterward, moving to part workbench this line is thickened by 1mm since the rib thickness has to be 0.4*t.

The thickened ribs later on drafted by 0.5 degrees pulling direction is taken as the upper face of the ribs.

The drafted rib is then assembled into the coin holder part body. (We can use the add the Boolean operation here).

Another rib is created at the spacing of 2*t of design rule and assembled to coin holder.

Lastly, both ribs are provided with fillets of 0.25mm radius.