Part Details Review
| Spacing |
Stiffness of a structure can be increased with the help of ribs. Making the rib base thickness equal to half the adjoining wall thickness is preferred as discussed in the section "Base Thickness". Equivalent stiffness can be achieved by using a larger number of thin ribs instead of fewer thick ribs as suggested in that section.
Also, as discussed in the section "Rib Height", increasing the number of shorter ribs may achieve equivalent stiffness of a structure with tall ribs. Hence, using the preferred "thinner and shorter" ribs may drastically increase the number of ribs required to attain the desired level of stiffness.
Increasing the number of ribs excessively in a structure, however, can present a different problem. Adequately and uniformly cooling the part in the mold becomes a challenging task and may create difficult warpage issues. This imposes a practical limit on the number of ribs a particular structure can have without these side effects.
Keep a minimum clear spacing of twice the nominal wall, as shown below, to get better control on cooling. If higher stiffness is required than can be achieved with a reasonable number of ribs then ,the nominal wall thickness of the part can be increased. This may not be cost effective from the material usage and cycle-time points of view. It will, however, alleviate warpage problems resulting from inefficient and uneven cooling.
