Week 8 - Challenge 1 - Base Bracket Design

CHALLENGE 1 - BASE BRACKET DESIGN

AIM

To create the Base Bracket Plastic component through the given Class-A surface. To begin with, the tooling axis for the given Class-A Surface should be created meeting the requirements of the draft angle and at the end perform the Draft analysis on the model.

1. INTRODUCTION

CLASS-A Surface

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.

CLASS-B Surface

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.

CLASS-C Surface

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

DRAFT

When developing parts for plastic injection molding, applying draft (or a taper) to the faces of the part is critical to improving the moldability of your part. Without it, parts run the risk of poor cosmetic finishes, and may bend, break, or warp due to molding stresses caused by the plastic cooling. Equally important, an absence of draft may prevent parts from ejecting from the mold, damaging not only the parts, but possibly the mold itself—a costly and time-consuming detour.

Here the image shows the molded part without draft angle

Most parts require a minimum draft angle of 0.5 to 1 degree; however, 3 degree is widely accepted as the norm.

General guidelines for giving draft angle to a part are

• 5 degrees on all vertical faces is strongly advised.
• 1 to 2 degrees works very well in most situations.
• 3 degrees is minimum for a shutoff (metal sliding on metal).
• 3 degrees is required for light texture (PM-T1).
• 5 or more degrees is required for heavy texture (PM-T2).

Some advantages of giving draft angle to the parts are

• Minimizes the warping to your geometry
• Increases the tool life of the mold
• Improves the surface finish on your plastic parts
• Cuts down costs by reducing the cooling time

2. THE DRAFT ANALYSIS AND THE TOOLING AXIS CREATION.

The Draft Analysis allows the user to easily analyse a part for proper draft angle. A Draft Angle describes the amount of taper for molded or cast parts perpendicular to the parting line.

Every part should clear the draft analysis test to ensure the easy manufacturability of the component.

Procedures to follow when performing the Draft analysis of the given Class-A surface are as follows

2.1 FOR CREATING THE TOOLING AXIS

• STEP 1: Check the connectivity of the Class A Surface

• We have been given the Class-A surface and he first thing to do is to make sure that the given surface has no gap in between them. We can check it visually and also with help of Join or boundary commands.
• The given surface has only three boundaries which are one outer boundary and two inner circle boundaries. So, there is no other gaps found.

• STEP 2: Find the tooling axis of the component.

The tooling axis represents the opening and closing of mold.

A plastic product designer should consider the best tooling direction to cutdown the cost of the component very less.

We can find out the best tooling direction by cross checking all the three axis

• Here along X axis, it is possible since it would not clear the holes and which make the manufacturing expensive.

• Along Y direction it is not possible.

• Here Z axis is the best possible direction for tooling. It clears both holes. Hence no need to implement side cores and which leads to less cost for the molding.

Creating the tooling axis along z direction

• We have a hole on the surface, so create boundary of the hole and create midpoint.
• Create a dummy tooling axis by creating a line on the midpoint of the circle

Hence the tooling axis is along the z axis we need to ensure that all the faces are clearing the tooling. For that

Make two sketches as intersection along x and y axis.

• Intersection along x direction

• Intersection along y direction

By creating the intersection line, we confirmed that along y direction all the faces are clearing the tooling.

Now, create on the two faces and create bisecting line with those two lines and with the point we created earlier. We will get the tooling axis.

2.2 PERFORM THE DRAFT ANALYSIS

• Make sure the view mode of the part is in material shading

• Then do to insert menu and insert the featured draft analysis tool
• Pick the compass and align it with the tooling axis by dragging it.

• Then lock the draft direction and perform draft analysis by clicking on the component.

• The green colour shows the positive daft tooling direction and the given surface passes the draft analysis.
• Click on the analyses under the running point to check the draft analysis on the individual faces. It shows how much draft on specific points when we move the cursor point.

Representation of Color variations in the draft analsis

GREEN COLOR - Positive Draft (3 degree)

RED COLOR - 0 degree draft

BLUE COLOR - Negative Draft

3. Creating the Class-B surface

Procedure followed for creating the Class-B surfaces are

1.Extract the ribs from the class-A surface one by one.

• Untrim the extracted surfaces
• Extrapolate the untrimmed surfaces with a required length
• Trim the extrapolated surfaces to achieve the desired rib shape
• Then offset the trimmed surface to 2.5mm downwards

2.Create slant surface

• Extract the slant surface from the class-a surface
• Untrim the extracted surface
• Extrapolate the untrimmed surface

3.Create the base surface

Same procedure followed for the slant surface creation is implemented.

After creating all the required faces and surfaces preform the final trim and and gives the required fillets on the edges results in final class-B surface.

4. Creating the class-C surface

First step is to create the boundary of the CLASS-A surface using the boundary command.

Then using the sweep command create the CLASS-C surface

Then join the CLASS-A surface with the CLASS-C surface using the join command

5. Creating the Final surface

Then create the final surface by trimming the B-surface with joined surface.

6. Go to the part design work bench and using the close surface command create the base bracket solid part body

6.1 3D Part model in various orientations (Isometric, Front, Side, and Top View)

6.2 The expanded Tree Structure for the Geometrical set and the Part Body

6.3 DRAFT ANALYSIS of the Final PartBody

Conclusion

I have successfully created the class-B and Class-C surfaces of base bracket using the given Class-A surface along with the tooling axis in the CATIA surface workbench. And also created the final part body using the close surface command in the part design workbench and performed draft analysis for the same.