Week 9 - Attachment Feature Creation - Challenge 1

Ribs creation on coin holder

Aim:

To create the Rib for the center console coin holder considering the design rules.

Introduction:

Plastic part design is a very complex process and it requires the involvement of many factors like suctional requirements, process constraints, material selection, and assembly and structural issues, Wall thickness, Draft and texture, Ribs & bosses, Hole /Depressions etc. are some of the important elements to be considered in the design of plastic parts. Adhering to this basic design guidelines for injection molded parts can improve the moldability of the designs and the life of the mold, increase the optional life of the part and reduce manufacturing cost.

Ribs:

Ribs are a feature in plastic injection molded parts. They are thin extensions that run perpendicular to a wall or plane. They are commonly used to provide additional support and strength to a part.

Thickness and location are essential to rib design, here are some helpful design guidelines:

• They should be designed with a thickness that is 0.5 the wall thickness to avoid a thick section at the wall base.
• To minimize sink marks, Design ribs that are approximately 60% of the joining wall thickness for minimum risk.
• Best practices including spacing at a distance of at least twice the wall thickness.
• Glossy materials require a thinner Rib (40% of wall thickness)

An advantage of using Rib is that they increase the strength of the part without increasing wall thickness. Walls are too thick can sink, Wrap or result in other defects. Their integration into a part result in less material usage; therefore, a more cost- effective solution.

Procedure:

Since we have the coin holder, 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 extruded along the direction of the tooling axis to a height of 12.5mm Following the design rule of H=5*t.

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

The thickened ribs are drafted by 0.5 deg. Pulling direction is taken as the tooling axis.

• The Drafted rib is then assembled into the coin holder part body.
• Another rib is created at the spacing of 2*t of design rule and assembled into coin holder.
• Lastly, Both the ribs are provided with fillets of 2.5mm radius.

Checking the ribs design:

In order to check the dimensions of the ribs, The coin holder is intersected along the XY plane to obtain the boundary lines.

Root analysis:

For the root analysis, A tri tangent circle is created from the outlines of ribs and base surface, and then the circle dimension is measured as shown in fig below.

Height:

Tip Thickness:

Draft analysis:

Now, the ribs need to be checked for the draft analysis to ensure if all the features have passed the tooling direction.

• Open the feature draft analysis form the main menu.
• Move the compass to align with the tooling axis and then select that component.
• Here, changes the minimum drafting angle to 0.5 deg since the draft provided to ribs is 0.5.

All the features of the ribs show the green line that means the current tooling axis is able to capture all the features of the ribs.

Results:

The ribs for the center console coin holder have been successfully created considering the design rules mentioned in the given data.

3D model:

Tree structure: