Challenge

Week 9 - Attachment Feature Creation - Challenge 1

RIB DESIGN

AIM:

To Create the rib for the Centre console coin holder.

INTRODUCTION:

Ribs provide a means to economical stiffness and strength in molded parts without increasing overall wall thickness.

They also facilitate

This section deals with general guidelines for ribs and part design.

Proper rib design involves five issues:

Consider these carefully when designing ribs.

RIB THICKNESS:

Thick ribs often cause sink mark and in turn cosmetic problems on the opposite Surface of the wall to which they are attached. The material, rib thickness, surface texture, color, proximity to a gate, and a variety of Processing conditions determine the severity of sink.
Highly glossy, critical surface may require thinner ribs. Placing ribs opposite character marks or steps can hide rib read through.
Thin walled parts (<1.5mm) can often tolerate ribs that are thicker than the percentages in these guidelines.
On Parts with wall thicknesses that are 1.0 mm or less, the rib thickness should be equal to the wall thickness.
Rib thickness also directly affects mould ability. Very thin ribs can be difficult to fill. Because of flow hesitation, thin ribs near the gate can sometimes be more difficult to fill than those further away.

RIB HEIGHT:

Rib height should not exceed 3 times the thickness of the primaryy wall. This height cap is recommended because if your ribs are too tall, they can break during use or ejection from the mold. If damage occurs during ejection of tall ribs, it is likely due to draft angles tapering them to slivers at their tips. Ideally, you want to keep your ribs as shot as possible while still being functional.
Rib height: 3*W (wall thickness)
An additional problem that this combination of tall ribs and draft
Causes is that the plastic may not be able to reach the tip of the rib.
This can cause voids if the plastic can not flow into the very tip of the rib.
Deep ribs can also be expensive to tool. To avoid these problems,you can use several short ribs in place of one tall rib.

RIB WIDTH:

Thick ribs can result in huge problems in your part. If a rib is too thick, the point where it attaches to the primary wall or boss will be thickened as well. This can easily cause sink marks, warp and voids where there is this excess material. In particular, sinks are visible indicators of bad design, which will affect the appearance of your finished part. If serve enough, sinks and voids can reduce a parts strength as they become concentrated centres of stress. To prevent
0.5 and 0.75 times the primary walls thickness.
Rib width: 0.5 – 0.75*W (wall thickness)
Top rib thickness should be minimum of 0.75mm

RIB SPACING:

Increase the number of ribs rather than height in order to increase stiffness. Ribs should be spaced a minimum of two times the nominal wall thickness apart from one another.
Rib spacing: minimum 2 *W (wall thickness)

RIB DRAFT:

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

RIB RADII OR FILLET:

Radii at feature intersections should be a minimum of 0.25 of nominal wall thickness to increase rib strength
Rib radii or filletor fillet: 0.25W (wall thickness)

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.

Design rules for ribs in class A surface

COMPONENT:

RIB ON THE COIN HOLDER:

TREE STRUCTURE:

RIB ON THE COIN HOLDER

SIDE VIEW

RARE VIEW

FRONT VIEW

ISO VIEW

DRAFT ANALYSIS OF RIB DESIGN:

CONCLUSION:

Ship work like this
in your own course.