Radii are extremely important in diecastings and often neglected by component designers. To avoid high stress concentrations in the component and the diecasting tool, fillet radii of the appropriate size must be used in all internal and external component edges. The exception to this rule is where the feature lands on the parting line of the tool. Another important aspect concerning fillet radii is that they assist in filling the part
There is an optimum size of fillet where structural parts are concerned. Although increasing the fillet size generally will decrease the stress concentration at the bottom of a rib, eventually the mass of material added by the fillet will induce shrinkage porosity in that area. Designers should also note that fillets applied perpendicular to the parting line of the tool require draft.