Week 9 - Attachment Feature Creation (Ribs & Screw Boss) - Challenge 1

AIM: Create Drill Handle with Ribs & Screw Boss

OBJECTIVES:

• Create the rib for the Drill Handle considering the design rules
• Create the Screw boss for the Drill Handle considering the design rules

INTRODUCTION:

In this project, we are designing a drill handle with ribs & screw boss from a Class-A surface using the Catia software, from that we create a Class-B surface with a thickness of 2.5 mm throughout the component. And Class C is also created using both Class A & B. Draft analysis is also conducted with a minimum of 3 degrees as standard. Make sure that the surface model is completely closed before converting into solid.

Draft

In engineering, draft is the amount of taper for molded or cast parts perpendicular to the parting line. It can be measured in degrees or mm/mm (in/in)

• Drafts (or taper) in a mold, facilitate part removal from the mold. The amount of draft angle depends on the depth of the part in the mold, and its required end-use function.
• The draft is in the offset angle in a direction parallel to the mold opening and closing.
• It is best to allow for as much draft as possible for easy release from the mold. The minimum taper angle is 0.5 to 1 degree but 3 degrees is a widely accepted norm.
• The mold parting line can be relocated to split the draft in order to minimize it. If no draft is acceptable due to design considerations, then a side action may be required at a greater expense in tooling.

Draft Analysis

Displays a color gradient on the faces of selected bodies to help evaluate the manufacturability of your design. Select the bodies to evaluate and the axis to define the direction. Use the options to refine the gradient display. In Catia, we use the feature draft analysis tool for this.

Tooling Axis

It is the direction in which the mold or core and cavity open is the tooling axis

Bisector Method: It is a common method used to create a tooling axis for Class-A surface, firstly select the direction in which tooling is difficult there may be one or two directions on a single surface. Then, create an intersecting curve with respect to the surface by taking a plane as a reference and draw lines that coincide with the intersection curve where the draft occurs, then bisect these lines to get the tooling axis. Use this method in another direction if needed. Finally, bisect those axes to get the tooling axis for the surface.

Class-A

Class-A surface given to us

Ribs

Ribs are indispensable functional structures on many plastic parts. It can effectively improve the rigidity and strength of plastic parts like the H beam. By using ribs, it is not necessary to greatly increase the wall thickness of the plastic parts, and ribs are not undercut structures like the H beam whose structure will be difficult to make for plastic injection molding.

Screw Boss

Screw Boss features are commonly found in injection molding designs. They are used to aid in the assembly of molded parts by providing a channel for a screw. Their primary use is to strengthen holes or slots in the surface present in the part model.

PROCEDURES

Step 1 - Creation of Tooling Axis

On this surface, we are going with the trial and error method by selecting a random point on the surface. For that, I take the center of the flat surface as a reference point as shown below. Then extend it in the Y direction, ie taken as the tooling axis for this surface.

In this design, the bisector method is more difficult compared to this method.

 

Step 2 - Draft Analysis for Class A

In this Class A surface, there is some inbuilt defect in the draft angle from the styling team. And this axis is taken as a tooling axis for further steps.

Color Scale Used: 

Draft more than 3 degrees shown as green. Less than 3 degrees to 0 degrees are shown in red color.

Step 3 - Creation of Class-B Surface

In this, the Class-A surface is offset to 2.5 mm but we may face some gaps occur. Close the gaps using the multi-section command. Finally, join all the filled surfaces with offset surface into a single surface using the join command.

Step 4 - Creation of Class-C Surface

Class C Surface is the connection surface of Class-A and B. For this, take the boundary of class-A and then extend it using the sweep command.

Step 5 - Final Trim

Class-A + Class-C

In this, we connect both Class-A and C using the join command and make sure there is no gap between A & C.

Class-A + Class-B + Class-C

This made the final output from the surface workbench by trimming all the unnecessary portions and check the surface is completely closed.

Step 6 - Draft Analysis of Solid Body

Color Scale Used: 

Draft more than 3 degrees shown as green. The draft below 0 degrees is shown as blue. Draft between 0 and 3 degrees shown as red.

Step 7 - Rib Root Thickness Analysis

The value of rib root thickness must be within 30% greater than the wall thickness

In this case, the wall thickness is 2.5 mm and so the maximum limit is 3.25 mm. So our rib root thickness is within the limit.

Step 8 - Draft Analysis of Ribs and Screw Boss

Color Scale Used:

The draft for both rib and screw boss is 0.5 but there might be some change in draft angle at some of the points so we take 0.49 degrees for analysis.

Draft more than 0.49 degrees shown as green. The draft below 0 degrees is shown as blue. Draft between 0 and 3 degrees shown as red.

FINAL COMPONENT

1. Isometric View

2. Front View

3. Side View

4. Top View

CONCLUSIONS

Ribs and screw boss for the Drill Handle are created by considering the design rules.