Design Course
Designing of Plastic Products for Injection Moulding
Manufacturing Methods and Technologies
by
Corner Radius
The walls of the part usually meet the base at angle greater than 90o because of draft given to the part. If the walls are joined making a sharp corner then the wall thickness will not be uniform at corners, the maximum thickness at the sharp corner is about 1.4 times the nominal wall thickness. This will result in longer cooling time accompanied by sink marks and warping. Sharp corners have increased stress concentration. At the time of flow there is a turbulence created at the corner which causes the air entrapment and weakens the molding. The problem can be overcome by providing radius at the corners.
Design Considerations
- Internal radii should be at least 0.5 and preferred is 0.6 to 0.75 times the wall thickness.
- External radii should be equal to internal radii plus wall thickness.