Part Details Review
| Transitions |
When you can't avoid thick and thin wall sections in a part, do the next best thing by incorporating smooth transitions from one thickness to the next. Abrupt wall thickness transitions create undesirable flow problems, higher molded-in stress ,and locations for stress concentrations.
Smooth transition with a generous taper between the thick and thin wall section and use of radii at the inside and the outside corners, reduce excessive melt shear during flow and help drive the air out of the cavity (see figure 1b). Smooth transition along the length of a rib is discussed under the heading "Ribs" also.
Abrupt change in wall thickness is detrimental to the strength of the part. The thick section keeps cooling and shrinking long after the thin section has frozen resulting in shrinkage stresses developing in the thick section. These stresses remain in the part as residual stresses and will be concentrated at the site of the abrupt wall thickness transition (see Figure 1a).
