Rib Located At Edge Of Forging With Parting Line At Center

Figure 2.47 Four basic types of rib designs. (From Forging Industry Handbook, Forging Industry Association, Cleveland, OH, 1970.)

metal flow similar to that in reverse extrusion. Ribs thinner than the other three types are possible with this design.

Type 3. Ribs at the edges of forgings with the parting line at the base are also formed by an extrusion type of flow. Section thickness limits are similar to type 1.

Type 4. Ribs and bosses at the edge of a forging with a central web are the most difficult to forge. Such rib designs almost always require preliminary tooling to gather the volume of metal necessary for filling the final die. Minimum thicknesses for type 4 ribs are generally larger than are those for the other three types.

There are no hard-and-fast rules that apply to the dimensions of ribs. In general, the rib height should not exceed eight times the rib width. Most forging companies prefer to work with rib height-to-width ratios between 4:1 and 6:1. Figure 2.48 summarizes, for several alloys, suggested minimum section size limits for ribs and webs with conventional fillet and corner radii and draft angles. Fillet and corner radii are shown in Figure 2.49. In Figure 2.49a, the influence of impression depth on corner radii of ribs, bosses, and other edges for steel and aluminum forgings of average proportions is seen; in Figure 2.49b, the influence of rib height on minimum filet radius for steel and aluminum is shown; in Figure 2.49c, are representative fillet and comer radii for forgings of several materials with 1-in.-high ribs; and in Figure 2.49d. representative minimum fillet and corner radii of steel forgings on a weight basis are given. Figure 2.50a shows various die fillets for comer radii for steel and aluminum forgings. showing order of preference for 1-in.-high bosses and ribs. The schematic diagram (Figure 2.50b) shows the influence of fillet radius on metal flow during progressive stages of die closure.

Many forgings are used with little or no machining, where the normal forging variations and the surface condition typical for the material are acceptable. Finish allowance for machining varies with cost considerations, size of part, the way the


Minimum Rib Thickness, in., for Forgings of Given Plan Area, sq. in.

Minimum Web Thickness, in., for Forgings of Given Plan Area. sq. in.

Up to 10

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