RADII AND FILLETS:

                                                                   

Definition:

1.       Radii: Rounded external angle between two surfaces.

2.       Fillet: Rounded filling of the internal angle between two surfaces.

Significance:                                                                                                                                             

·         Stresses tend to concentrate at the junction of two sections like corners, ribs, or external corners.

·         Rounding of the corners will reduce the stress concentration hence proper radius should be used for a given wall thickness.

·          When external corners are sharp, the section at the corner should be increased by about 30%

·         Rounding of the corner with an external radius will tend to maintain a uniform thickness and therefore relieves stress concentration.

·         Radii and fillets promote the distribution of internal load and stresses and thus release the stress concentration associated with changes in wall thickness and changes in direction of internal loads.

·         Radii and fillets also promote even flow of material during molding, hence lower pressure can be used or the cycle time can be reduced.

·         When stress concentrations are minimized, the strength of the part is increased.

·         When generous radii are used at the junction of two walls, there is less possibility of cracks to occur.·        

A minimum radius of 1/64” should be provided, if possible.