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

Draft analysis on fan cover

Since thermoplastics shrink as they cool, they grip to cores or male forms in the mold. This makes ejection difficult and may lead to scuff marks on the part. To facilitate ejection, part surfaces parallel to the draw direction of the tool require taper or draft. This draft allows the part to break free by creating a clearance as soon as the mold starts to open. The amount of draft needed depends on several factors:

• Material shrinkage – Some materials shrink more than others. In general, the higher the shrinkage, the larger the draft angle needed to prevent ejection issues.
• Height and shape of wall or feature – A shallow single straight rib having not enough draft causes less problems than a high cylindrical wall.
• Surface texture – A polished surface requires a smaller draft angle than a surface that is textured.
• Aesthetic requirements – Scuff marks might not be as big of a problem on a technical part "hidden" in an assembly while, for the cover part of the assembly, they may be totally unacceptable.

Draft analysis

The above image shows the intersection of the surface taken across its mid-plane along the X-direction. The walls which are parallel or almost parallel to the direction of mold movement are to be analysed for its draft angle. Two lines are created along the walls of the fan cover which are almost parallel to the mold movement. A bisecting line for these two lines is obtained which gives the tooling direction along X-axis. The same is done for Y-axis.

The image shows tooling axis in Y-direction.

A bisecting line is obtained from tooling axis across X & Y direction. This bisecting line gives the tooling direction for the part.

The draft analysis is done w.r.t. this tooling axis. The min. draft angle required is 3 degrees.

If the draft angle is more than 3 degrees then the component is shown in green color.

If it is equal to 3 degrees then the component is shown in blue color.

If it is below 3 degrees then the cmponent turns red.