Week 8 - Challenge 1 - Draft Analysis on a Fan Cover

DRAFT ANALYSIS ON A FAN COVER

JEEVA R

Some terms to be defined before proceeding to the analysis are as follows:

Draft:

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 component and the core and cavity plates.

When a Plastic component cools down inside the mold, the natural tendency of it is to shrink and attach to the core or cavity half. The movement of 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 rough surface finish as well as weak structure due to this. This problem can be solved by giving draft to the component.

Most applications require minimum draft angles of around 0.5˚ to 1˚, however 3˚ draft angles are widely accepted for cost saving purpose. 7˚ 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.

Tooling Axis:

Tooling Axis is the direction in which the Mold opens and closes. Part Drafts are given along this axis.

Draft Analysis:

Draft Analysis is a tool in CATIA which identifies the zones which deviates from the specified values of angles along a defined draft direction using color codes. It highlights the regions of draft using colors. Draft analysis is the first step performed after receiving the Class A of the component.

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.

Procedure to be followed:

Figure 1: Procedure for Draft Analysis

Draft Analysis on Fan Cover:

Step 1: Design Check on Class-A:

After receiving the Class-A for the fan cover check for the connectivity of the surfaces on it. Use Join operation, boundary operation and disassemble. The check is over if any discontinuities do not arise. Delete the operations after the check.

Step 2: Determine the Tooling Axis:

• Create a Dummy Tooling axis along the best possible direction as per the Class A as shown in Figure 2. In this case we have chosen Z axis as dummy as it doesn't interfere with any slots or holes.

Figure 2: Dummy tooling axis on Class A of Fan Cover

• Create an Axis System on this line and a suitable point as shown in figure3.

Figure 3: Axis System on Class A of Fan Cover

• Create an Intersect between the two planes and the Class A surface i.e., the XZ and YZ plane intersection with the fan cover as shown in Figure 4 and Figure 5.

Figure 4: Intersection of XZ plane with Class A of Fan Cover

Figure 5: Intersection of YZ plane with Class A of Fan Cover

• Create extended Lines for the faces which may create problems in terms of Draft angles. In this case the lines are created for each intersect as shown in Figure 6 and Figure 7.

Figure 6: Extended Lines for faces on XZ plane

Figure 7: Extended Lines for faces on YZ plane

• Create a Bisecting Line for the extended lines along the center point on both the planes and name it as Tool Clearing X and Tool Clearing Y as shown in Figure 8 and Figure 9.

Figure 8: Tool Clearing for X

Figure 9: Tool Clearing for Y

• Create a Bisecting Lines between Tool Clearing for X and Tool Clearing for Y along the center point. This is the main Tooling Axis required. Name it as Tooling Axis and publish it using Insert --- Publication.

Figure 10: Tooling Axis and its Publication.

Step 3: Performing Draft Analysis:

• Change View Mode Customization to Material mode as shown in Figure 11.

Figure 11: Material Mode.

• Go to INSERT --- ANALYSIS --- FEATURE DRAFT ANALYSIS and move the compass to the Tooling Axis. Change the range to 3˚. Apply the settings as Shown in Figure 12.

Figure 12: Draft Analysis on Fan Cover.

Figure 13: Screenshot of Draft Analysis of Fan Cover.

Figure 14: Screenshot of Draft Analysis of Fan Cover with expanded Tree Structures.

Conclusion:

Green Color indicated the draft angles are all having permissible values and the draft analysis status for the Fan cover is Passed.