Determination of the Third Digit for Injection Molded and Die Cast Parts
(Used under permission of Dixon and Poli,
Engineering Design and Design for Manufacturing)
To determine the cavity detail, and thus the value of the third digit, enter the appropriate values into the following form. Remember to include only those features which are parallel to the direction of mold closure.
For details concerning the types of features mentioned, read the text following the form.
- A boss is an isolated projection with a length of projection which is less than about three times its overall width, the latter measured parallel to the surface from which it projects.
- A rib is a narrow elongated projection with a length generally greater
then about three times its width (thickness), both measured parallel to the surface from
which the feature projects, and a height less than six times its width. A cluster of
two closely spaced logitudinal ribs or lateral ribs (spacing less than three times the rib
width) are counted as one rib.Bosses and ribs are sometimes supported by a cluster of ribs
of variable height called gusset plates. This cluster of ribs is counted as
one rib or one cluster of ribs. Examples of these three features can be found in the figure
- Holes in a part that are not considered undercuts are classified as
side shutoffs. Isolated grooves or cutouts on the external surface of a part
are also considered side shutoffs. It is considered isolated if the dimension of the cutout
normal to the direction of mold closure is less than 0.33 times the envelope dimension in
the same direction. NB: For parts with a first digit of 2, 4 or 6 side
shutoffs are not to be taken into consideration. The following figure shows examples of side