Week 8 - Challenge 2 - Base Bracket Design

Plastic design base Bracket

Aim:- Create the base bracket plastic component through the given class-A surface. And perform the draft analysis on the model.

Objective:- Generating Plastic component for base bracket from given Class-A surface. Brief about Class-B and C surface and use it to prepare solid plastic components.

Procedure: -

Tooling Axis:

Tooling Axis is an imaginary axis in which direction the tooling operation is performed. In Injection molding, the direction in which the mold is opened/ closed is called the tooling direction.

The draft angle, which also plays a major role in plastic component design, is decided with reference to the main tooling axis of the component.

Method:

1. The given Class-A surface of the component needs to verify for boundary discontinuities.
2. Then we make a dummy tooling axis. Observing components from different directions, we can assume the dummy tooling axis location. Assuming the tooling axis is in the X direction, It is clear that the hole in the component will not be cleared by the X-direction tooling axis. Similarly, If we assume, the tooling axis is in the Y direction, the hole, as well as the sidewall drafts, are not easy to clear by the Y-direction tooling axis. Now the Z direction tooling axis clears the hole on the top as well as the draft on the sidewalls of the component. Z-direction should be the tooling axis of the given component.
3. Now that the tooling direction is defined, we can make a temporary tooling axis. Taking it as a reference, we can proceed to define the actual tooling axis using the bisecting method.
4. The bisecting method will use reference lines created from different intersections of components with reference planes. Firstly, take the intersection of the component with the XZ plane to get the profile as a reference. Create 2 lines parallel to the profile. After creating 2 parallel lines, create a bisecting line from those two lines.
5. The last bisecting line would be the main tooling axis for the given component.

Class-A surface

In automotive design, a class A surface is any of a set of freeform surfaces of high efficiency and quality. Although strictly, it is nothing more than saying the surfaces have curvature and tangency alignment – to ideal aesthetical reflection quality, many people interpret class A surfaces to have G2 (or even G3) curvature continuity to one another (see free form surface modeling). Class A surfacing is done using computer-aided industrial design applications. Class A surface modelers are also called "digital sculptors" in the industry. Industrial designers develop their design styling through the A-Surface, the physical surface the end-user can feel, touch, see, etc.

Class-B surface

These are the surfaces we see sometimes, are secondary surfaces, but are less important. These surfaces also must be smooth and free from any errors but are held below Class-A quality as these surfaces will not affect the aesthetic appearance of the part. It usually has ribs, boss, snap, etc.

Class-C surface

These are the backside of the surface of the component which comes in contact with other assembling parts/components. These surfaces can have tooling marks, abnormalities, or flashes. These surfaces are equally important for fit and assembly purposes. These are not majorly important from an aesthetic perspective.

1. Generating Class B surface from given Class A

We are given a Class A surface as an input. Firstly, we have to generate Class B surface from given surface to generate solid Component. Class B is generated by offering class B is generated by offsetting Class A surface. The critical parameter to consider is the component thickness. Class B is surface offset equal to part thickness. Given Class A is divided into three main surfaces which will be helpful in generating Class B surface.

1. Offsetting the first rib: The first rib can be divided into 3 surfaces. Each surface is extracted from Class A, Untrimmed, and extrapolated to get the desired output. It will form the base for the final Class B surface. Extract the surface highlighted in green, using the” Exact” command. After extracting the surface, Untrimmed it using the “Untrim” command. The green surface is untrimmed to some extent.

To further extend the surface, we can use the “Extrapolate” command. It will extend the surface tangentially in all directions. It will be useful in the final trim of the component.

This is how the first surface is extracted from Class A to form the base of Class B surface. Further, continue the same process to exact, Untrimmed, Extrapolate the surface to form the base for rib 1 Class B surface. Surfaces in pink are extracted from Class A input. These surfaces, after Untrimmed, Extrapolated. These, the Extrapolated surface needs to be trimmed to achieve the desired output as a Class A surface. Using the “Trim” command, we can achieve the output.

After trimming, the final output is shown as below, green surfaces. This creates the base for rib 1 Class B surfaces.

This surface needs to be offset from Class A surface, by the value equal to part thickness. Here the part thickness is 2.5 mm. So offset value is set to 2.5 mm. The surface in the blue color is the final output of the rib1 Class B surface. Similarly, we can generate, extract, untrimmed, and extrapolated and offset surfaces for rib2. The surface with a hole is also extracted, Untrimmed, extrapolated, and offset which is shown in pink color.

As in the above image, Surface 1, Surface2, surface 3 need to be trimmed to get desired final Class B. Trimming surface 2 and surface 3. Our next task is to extract the base surface from class A and offset it to get the base for class B. Extract the base surface highlighted in green. Untrimmed and extrapolated the surface. Now, we can trim the base surface with the previously created output surface. It will result in a Class B surface.

Generating fillets on class B is an easy task. But the critical parameter is the value of radius to be given. Class B surface is offset from class A, by a value equal to part thickness. So there can be 2 possible types of radius in class B. One is internal radius and the other is External radius with reference to class A surface. Both concepts are equally important to design parts with uniform wall thickness through the component. A detailed explanation can be derived from the following slide. Final class B after giving fillets as per the above method is shown in the pink-colored surface below. We can clearly identify the difference between Class A and Class B.

2. Generating Class C surface from given Class A

Class A surface is used as a reference to generate Class C surface. WE need to extract the outer boundary from the Class A surface. Extract boundary using the “Boundary” command. Extract boundary is used to generate Class C surface using the “sweep’ command. This surface is sweep along the tooling axis to generate a draft angle along the tooling direction. We need to be careful while generating draft angles with respect to the tooling axis.

The sweep command has an option called, ”with draft direction”. The blue arrows show the drafting direction. Generating an improper draft angle can result in the wrong draft analysis. Orang arrow will indicate the selected drafting direction. Here, we are generating an outward draft with respect to the tooling axis so that the whole component can be cleared in the tooling direction. The required draft angle is 3 degrees. The surface in brown represents the final Class surface. Similarly, we can sweep two circular profiles for holes in the tooling axis direction, together we can join with another surface.

3. Joining Class A and Class C surfaces

In the above methods, we have generated Class B and Class C surfaces using the given Class-A surface of the component. Now to create a closed surface part, we need to trim these three surfaces accordingly. First, we will be joining, Class A and Class C surfaces. We can use the “trim” command.

4. Generating Closed surface component from Class B trim

Following output, we get after joining Class A and Class C. Now we aim to trim the output surface with Class B to get the final output as the surface part.

5. Generating Final plastic component from surface component

The above method has given a closed surface component as output. But, for manufacturing purposes, we need to have a solid body part. For that, we need to migrate to Catia V5 part workbench. Here, In the part workbench, we need to insert a new body, insert the menu “body” command. This creates a new body inside a part module. In the body, we use the “close surface” command to convert our closed surface component to the solid body part. As the name suggests, all surfaces should be closed to get a proper solid body. Choose the command and select our surface component. It will be converted to a solid body component. One of the main points is that it won’t convert the surface part to a solid body if any of the boundaries are open from the surface component. And the final output solid part will be as shown in the image.

Conclusion:-

• Created the tooling axis using the bisecting method.
• Created Class B and Class C surface from given Class-A surface.
• Generate solid body components using the closed surface features.
• Used the main tooling axis for creating draft analysis on the component.

The conclusion here is, if we get any surface draft angle below the defined value, it will be shown in red color. As of now, all surfaces have an appropriate draft angle. It shows our part will clear the tooling axis direction without any difficulty.