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

Create the rib for the Drill Handle considering the design rules mentioned in the video.

AIM

Create the rib for the Drill Handle considering the design rules.

INTRODUCTION

Ribs and screw bosses are engineering features which are created on the B side of the plastic components.

RIBS

Ribs are used to strengthen the walls of your mould without increasing wall thickness which means that you minimise the problems that come into play when the wall thicknesses have to be increased.

In essence, if the wall is too thick, warping and sinking can result so that the entire design may need to be rejected.

SCREW BOSS

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. Designing plastic screw bosses is fairly straightforward but there are a few considerations to ensure a strong connection between parts and mitigate cosmetic defects.

Design methodology

Class-A surface means visible surface. It gives the aesthetic of the component which is created by the styling team and gives to the part design engineer to create the part with all engineering aspects.

Tooling axis creation

• Arrange the view manually to check the best tooling direction which covers most of the surfaces.
• Tooling direction along Y axis can clear most of the surfaces. So we can create tooling axis along y direction.
• I have created tooling axis using normal to the surface method. For that extract a plane surface and create a midpoint on it.
• Create a line on the point and direction along y axis.

CALSS A SURFACE

CLASS-B surface creation

• Class-B surface means thickness of a part it is not visible and is inside part. In other words, Class-B surface is a surface below a certain thickness from the class-A surface. This is the surface that contains engineering aspects of a model.
• Offset the class-A surface about 2.5mm inward direction.

CLASS-C surface creation

• Surface that joins class-A and class-B surfaces is class-C surface. Class C is often specified for interior surfaces not readily visible, surfaces that will be covered by another part when assembled.
• Multi extract the boundary edges and sweep it with reference to surface at 90 degrees, this method is useful when the created sweep surface is facing perpendicular to the tooling axis.

FINAL PART BODY

• Join the CLASS-A surface with CLASS-C surface.
• Extrapolate the CLASS-B surface and trim it with Joined surface.

Rib Creation

• Draft - 0.5 degrees on the walls of boss
• Thickness - Typically 40%* of the nominal wall at the base.
• Height to Diameter Ratio - 3:1
• Radii - 0.25mm maximum radii

RIB DESIGN

• Create a reference plane on the b surface.
• Create positioned sketch for the ribs and extrude the sketch with reference to the tooling axis or other method is create thicken pad with reference to the tooling axis.
• Perform union of ribs with the drill handle part body.

Screw Boss creation

• Draft - 0.5 degrees on the walls of boss
• Thickness - Typically 40%* of the nominal wall at the base.
• Height to Diameter Ratio - 3:1
• Radii - 0.25mm maximum radii.

SCREW BOSS DESIGN

• Create sketch of screw boss and extrude it with reference to the tooling axis.
• Add boss gussets to support and add strength to the screw boss
• Using the Boolean operation union trim the boss gusset with the screw boss and then add it of the main body.

Final part after creating ribs and screw bosses on the b side of the component

Rib root thickness Analysis

Draft analysis

• To clear the faces which are not cleared with a 3deg draft angle, I gave a 0.9deg draft angle to clear every face.

ISOMETRIC VIEWS

TREE STRUCTURE

Conclusion

I have created the tooling axis using the given CLASS-A surface and created B side Features on the drill handle solid body. Also performed draft analysis on both Class-A surface and Final part body.