Designing cast shapes.
Intersecting surfaces forming junctions of metal thickness are
properly joined with fillets in order to avoid high stress
concentrations in the diecastings, and to control and facilitate
maintenance of otherwise squared edges in the casting die. Fillets
projected in a direction normal to the parting plane require a draft
angle, but the amount is always governed by the draft of the
intersecting surfaces. Draft in corners or fillets projecting in a
direction normal to the parting plane have approximately 1.5 the amount
of draft of the intersecting walls.
In the sketches given below, consideration has been given to the
stresses of use and the stresses induced in the diecastings by the
process, as well as to die manufacturing and maintenance costs. The
suggestions apply to fillets in corners which are projected normal to
the parting plane in diecastings of moderate depth. Shallow castings may
have much smaller fillets, while deep pockets and other inside corners
may have larger fillets. Sharply squared corners with considerable
length projecting in a direction normal to the parting plane may cause
spalled edges in withdrawing the diecastings from the die.
It should be noted that the recommendations on this page represent
normal production practice at the most economical level. Sharp inside
surface junctions, acute angle corner conditions and delicate, deep and
closely spaced ribs should only be specified where and when necessary
since additional costs may be involved.