Week 9 - Attachment Feature Creation - Challenge 2

AIM :

To create the Dog House for the Lower Door Trim Plastic component through the given Class-A surface, Consider the thickness of the component (Lower Door Trim) as 2.5 mm.

REPORT :

This report demonstrates the design of an Automotive Plastic Component – Lower Door Trim (Plastic) with Engineering feature Dog House using industry principles i.e. Draft angles, Draft Analysis, Determining and implementing of Tooling Axis, Class A, Class B, and Class C surfaces. The component is designed using Surface Design and Solid Design techniques in CATIA V5.

The above fig. shows the Door Plastic Component which will be fixed on the Door sheet metal component. For fixing plastic components to sheet metal components Engineering features are necessary i.e. Heat Stakes, Locators, Dog House, & Ribs.

"C" is where the doghouse contacts the backside of the surface

Doghouse wall thickness at the intersection of the part wall ( C ) should be 40% or less than the main wall stock ( T ).

The height of ( B ) should be between 3.0 – 6.0 mm

OBJECTIVE :

• Conduct a Draft Analysis on the Class A surface for the Door Trim Plastic for determining the appropriate Tooling Axis.
• Creation of other surfaces i.e. B & C Surface and Engineering feature Dog House for creating a solid component.
• Performing the final Draft analysis for the inspection and checking if all the features are above the Nominal Drafting for the creation of the Solid Model.

THEORY :

The terms are briefly explained below:

1) DRAFT :

The draft is an angular tapering given at the design stage to every Plastic Component that has to be manufactured. It is given in the direction of the Mold Movement. The Draft allows the parts to release easily from the mold without creating friction between the surface of the component and the core and cavity plates.

When a Plastic component cools down inside the mold, its natural tendency of it is to shrink and attach to the core or cavity half. The movement of the mold opening causes friction on the walls of the component as well as the core/cavity blocks. This reduces the life of the mold as well as the component itself. The component may also have a rough surface finish as well as a weak structure due to this. This problem can be solved by giving a draft to the component.

Most applications require minimum draft angles of around 0.5º to 1º however, 3º draft angles are widely accepted for cost-saving purposes. 7º Draft angles are given to textured surfaces like Instrument Panels. Minimum possible draft angles are given to screw bosses, ribs, and stiffeners due to their critical nature.

2) DRAFT ANALYSIS :

Draft Analysis is a tool in CATIA that identifies the zones which deviate from the specified values of angles along a defined draft direction using color codes. Draft analysis is the first step performed after receiving the Class A of the component. Draft analysis should be passed in order to make the plastic component manufacturable. Acceptable draft angles are used as a range for draft analysis.

For Analyzing the Draft of the Class A Surface:-

1. Change View Mode Customization to Material mode
2. Go to INSERT ----> ANALYSIS ----> FEATURE DRAFT ANALYSIS.
3. Select the compass from the dialog box, and move the compass to the Tooling Axis.
4. Click on the surface to apply the color region on the component.
5. Change the range to 0º to 2.9º. Apply the settings as shown in Figure.
6. As shown the target area has a 0º draft angle which was the concerned face since it's a flat surface.
7. Thus, it passes the criteria of having a suitable draft and the Class A can be further designed into a solid plastic component and manufactured.

3) TOOLING AXIS :

The tooling Axis is the direction in which the Mold opens and closes. Part Drafts are given along this axis. Identify faces that can potentially create problems while manufacturing. Surfaces at angles along a desired Tooling Axis. Extract a plain surface and create a point on its center for Axis system creation. In this case, X-axis can be a possible Tooling Axis Direction.

4) CLASS A SURFACE :

In automotive design, a class A surface is any of a set of freeform surfaces of high efficiency and quality. It is the visible aesthetic surface of any automotive component. Class A surface refers to those surfaces which are visible and abide by the physical meaning of a product. This classification is primarily used in the automotive and increasingly in the consumer goods industry. It is a requirement where aesthetics has a significant contribution. For this reason, the exterior of automobiles is deemed Class-A.

5) CLASS B SURFACE :

Class B surfaces are Engineering Surfaces that are invisible to the eyes or often on the back side of the Class A surfaces. It is mainly the thickness of the component or Class A. These surfaces need to be designed as per the Class A surface i.e., the continuity, thickness of the component, functionality, etc should be maintained. These surfaces include the main engineering features such as Screw bosses, Ribs, Snaps, Stiffeners, and fixations. B surfaces also do not contain any aesthetic styling content and textures since it is not visible to the eyes.

Below fig shows both Class A & Class B surfaces.

The blue colored surface is the Class B surface & Light pink colored surface is the Class A surface.

6) CLASS C SURFACE :

Class C surfaces are connectors between Class A and B surfaces. This surface connects both A and B surfaces along the Tooling Axis. It contains the draft as per the design. It is basically the thickened surface between both A and B surfaces.

The light pink colored surface is the Class A surface, the Blue colored surface is the Class B surface & the yellow colored surface is the Class C surface.

7) DOG HOUSE :

The dog house is an engineering feature used in the plastic trim design. Dog houses are used as supporting features. Sometimes other engineering features like snaps, locators, Screw bosses, etc. are mounded on them to increase their strength. Dog houses are subjected to draft analysis to prevent breakage of the component during ejection from mould cavity. Dog house and other engineering components are built on B-surface.

OPERATIONS :

A. Creation of Final Component without Engineering Features :

1) Creation of B surface :

• Offset the relevant surfaces from Class-A surface, the offset length is 2.5 mm since the thickness is 2.5 mm.
• Here are some patches which are not offset as required, these patches must be filled properly with their respective dimensions.
• The patches are on the edges and flat surfaces of the Door trim (shown in below figs.)
• The offset of these surfaces is shown below.

• Extract the surfaces from class A using multiple extracts and untrim them.
• Use Extrapolate to make sure that all the untrims are properly intersected to trim and offset the surfaces to 2.5 mm to create the thickness.
• Trim the extra surfaces using the trim command.
• Insert them into the new geometrical set and name them with respective part names.
• Here the Class B surface is created.

2) Creation of C surface :

• Using the Boundary feature, the surface edges of Class A Surface and create boundaries on two surface edges, i.e. the inside hollow surface and the outer edge.
• The sweep option is carried on the boundary lines to create a draft length extension (5mm) and draft angle (87°). Here instead of taking 90°, we have to take 87° because of some inclination and for trimming with the Class B surface.
• After the Sweep Operation, the Class B surface and the sweep surface are trimmed with each other in order to create the Class C surface.
• Finally, Join the Class A Surface and the trimmed Surface to create the Final component.

Draft Analysis on the Closed Surface :

Screenshots of the solid model with the proper color code of the draft angle in various orientations (Isometric, Front, Side, and Top View)

B. Creation of Engineering Features on the created Lower Door Trim :

1) Creation of Dog House :

• Create a plane on the point where the dog house is straight at 90 deg, and draw a sketch for the Dog House using the Position Sketch and created a reference plane.
• Use the sweep command for creating the walls of the dog house.
• Draw a line on the base of the dog house and extrude it. This extruded surface will help us in creating the top surface and the core. Offset this surface with 2 appropriate lengths for the top surface and core.
• Trim the offset with walls for creating the top surface. Here the inner surface of the Dog House is created.

• Now extrude the same line Vertically which is created on the Base. Offset it with the appropriate length for creating the Front and back of the Dog house.
• Trim and split as required with the inner surface of the dog house.
• Give edge fillet to the inner surface.
• Create a body and give thickness to the inner surface. Give Draft to the surface as required.
• Now extract the inner surface and offset it with the appropriate length for creation on the core.
• Extrapolate and trim it as required. Hence the core is obtained.

• Use the split command to cut the core surface from the thickened surface.
• Give edges as required. Hence Dog House is created.

Draft Analysis on the Lower Door Trim with Engineering Feature Dog House :

CONCLUSION:

The Design of the Automotive Plastic Component – Lower Door Trim with engineering feature from Class A is completed using concepts of Draft angle, Draft Analysis for Class A & Final enclosed surface, Tooling Axis creation & Implementation, Class B & Class C creation, Heat stakes with supporting ribs, Locators, Dog house, and Ribs.