Design
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Ribs
Did you know?
The thickness of the rib at the intersection with the nominal wall should be typically 60% of the nominal wall thickness (see figure 1). When suitable draft is applied to the sides of the rib, the rib thickness will decrease in going away from the wall
(see figure 1).
The intersection of the rib to the nominal wall may contain a mass of material too great for adequate cooling and proper filling. Result on molded part may be a sink mark on side of wall opposite the rib location and voids in the wall section (see figure 2).
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t = wall thickness
t r = rib thickness at wall, 60% t , typical for appearance parts
L = rib height, 3 t maximum
r = radius, 25% t minimum |
Figure 1. Rib Design for Reinforcing Thermoplastic Parts
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Figure 2. Poor Rib Design for Thickness with Respect to Wall Thickness |
Did you know?
The height of the rib should be kept to a maximum of 3X the nominal wall thickness
(see figure 1).
Deep ribs when combined with draft become difficult to fill at the thinnest section and may stick in the mold. Ejecting the part from the mold may become a problem. Consider more than the minimum draft on each side of the rib.
Did you know?
The intersection of the rib and the base should have a radius. Maintain uniform wall thickness at these intersections. The minimum radii should be 25% of wall thickness
(see figure 1).
The smooth transition from rib to wall will improve filling of the mold, cooling of the part and strengthening the rib attachment.
Did you know?
Spacing between two parallel ribs should be a minimum of 2 X wall thickness
(see figure 3).
Adequately spaced ribs eliminate thin sections of steel in the mold and assist mold cooling.
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t = wall thickness |
Figure 3. Spacing of Multiple Ribs |
Did you know?
For deep ribs and protrusions, deeper than 3 x wall thickness, , you should allow for knockouts on the top of ribs or at intersections (see figure 4).
Adding knockout areas on top of a rib for part ejection will provide for less complex mold design.
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Figure 4. Adding Knockout Pads for Ejecting Part |
Rib geometry based on the design guidelines is reviewed by the Project Team at the onset of the project. Where changes are required, the customer is consulted for modifications to the part design.
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