Fillets & Radii

Adequate fillets (or outside corner) and radii (or inside corner) are essential for maximum strength and serviceability. The fillet radius should be at least equal to the wall thickness of the sheet and never less than 0.031 inches (0.80 mm). An ideal fillet radius would be more than 10 times the wall thickness.

The radii should be at least 80% of the wall thickness of the sheet and they will form the sheet as well as prevent excessive corner thinning. (Figure 1)

Lack of adequate fillets will result in an excessive concentration of mechanical stress. The service life and structural strength of a part may only be 30% of the design when the stress concentration factor is high. (Figure 2)

Figure 1                                                                    

Figure 2 - Corner Radii Verses Stress

• Introduction
• Mechanical Properties
• Thermal Properties
• Environmental Considerations
• Design
  • Thermoforming
  • Fillets & Radii
  • Draft Angles
  • Depth of Draw
  • Undercuts and Inserts
  • Shrinkage
• Assembly
• Machining
• Finishing