Ribs, Bosses And Gusset Design

Ribs are longitudinal protrusions on a plastic workpiece that way be used for a number of purposes. The first purpose is to add strength to a workpiece or to add aesthetic features to a  workpiece. The second is to minimize warpage in a workpiece. The third is to add flowing of plastic material during filling. The use of ribs also results in workpieces that are lighter in weight because the thickness of workpiece can be reduced, that leads to use less material, shorten molding cycles, and avoids sink marks on the surface. A thickness of 0.5 times the nominal wall thickness and a maximum height of 3.0 times the nominal wall thickness add a minor amount to the total workpiece eight but can provide the same rigidity as designing a thick nominal wall section for ribs design. Fig.2.8 illustrates what a ribs, boss, hole, and gusset on a molded plastic workpiece. Fig.2.9 illustrates proper rib design.

Bosses is defined as assisting in the assembling of one plastic workpiece with another piece,such as plastic, metallic, or other type of material. Bosses are protruding, hollowed-out posts on a workpiece, because there are frequently used to fasten members, by using methods such as inserts, self-tapping scres. drive pins, cut threads, and plug and force fits. Usually bosses are exposed to different forces, and stress. To reduce or eliminate sink, the outside diameter should remain between 2.0 and 2. 4 times the outside diameters of the insert, screw, or drive pin. The wall thickness of boss is the same as those used for ribs, 0.5 times the nominal wall thickness. Fig 2.10 is recommended boss deisgn.

Gussets are reinforcing plates just as both ribs and bosses to add strength, further structural

boss design support and improve structural integrity. The design is consist of the size and location of gusset. As general guideline, the gusset rib thickness should be designed between 0.050 and no greater than 0.75 times the nominal wall thickness, and the length of the gusset rib should not exceed 2.0 times the nominal wall to avoid sinks in exterior of the workpiece. Fig 2.11 and Fig. 2. 12 illustrate gusset design. Gussets are supporting arrangements for an edge. This design is used in most thermoplastic materials for injection-mold workpieces