Part Details Review

Ribs provide efficient means of increasing stiffness in plastic parts without adding excessive weight. Points to consider while designing ribs in injection molded parts:

Thick ribs increase section thickness at the base, creating the possibility of sink marks.
Tall ribs may result in excessive outer fiber stress at the top and are difficult to mold.
Give sufficient fillet radius on the sides of the rib to reduce stress concentration.
Gussets also perform the same function as ribs. Additionally, gussets are used to strengthen or support free-standing structures to the base wall.

Also, do not end a rib abruptly along its length. Abruptly ending a free-standing rib may cause air entrapment at the top corners (see figure). Additionally, air trapped may exit the corners behind the flow front and break through the flow front down stream of the end of the rib. This may result in the formation of unsightly tear drops and flow lines that look like weld lines. Provide a generous exit angle at the down stream end of the rib to allow air to escape ahead of the flow front.

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