Part Details Review
| Height |
Very tall ribs may contribute to excessive outer fiber stress in bending if the part is subjected to such loading. See Figure 1. Also, it becomes difficult to chase all the air out of the deep rib cavity during filling. This may cause burning at the top of the rib due to compression of the trapped air and form unpleasant tear drops or flow lines in the part.
Machining and polishing of the blind rib cavity becomes more difficult as the ribs become taller and thinner at the top. If the cavity is not polished properly in the direction of draw, ejection problems may be encountered.
As a general rule, rib height should be limited to a maximum of six times the rib thickness at the base. Equivalent structural rigidity can be achieved by replacing tall ribs with an increased number of smaller ribs. Ribs introduce another level of complexity in the part geometry and can contribute to warpage issues. Also, as the ribs get taller, the differential shrinkage increases and the warpage problems worsen.
