Machinery's Handbook, 31st Edition
1542 Powder Manufacturing Processes Secondary operations are performed as appropriate. Major advantages of MIM over con ventional compaction are that complex shapes can be produced having wall thicknesses as small as 0.1 in. (2.5 mm) and features as small as 0.02 in. (0.5 mm); they can be molded and then easily removed from the dies, and their mechanical properties are nearly equal to those of wrought parts; there is good dimensional tolerance, and high production rates can be achieved using multi-cavity dies. Binder Mixing Powder
Pelletizing
Feedstock
Injection Molding
Green Part
Debinding
Finished Part
Sintering
Fig. 18. Outline of the Powder Injection Molding Process The major limitations of MIM are the limited availability of fine metal powders and the relatively high cost of production. Powder Rolling, Extrusion, and Forging.— Rolling, extruding, and forging are plastic deformation metal-forming processes. In this section, these processes are described in the context of powder metallurgy. Powder Rolling: This term is applied to the process, now established on an industrial scale, wherein a metal powder is fed continuously into a rolling mill (Fig. 19), which may be heated, and compacted between the rolls into strip at speeds of up to 1.6 ft/s (0.5 m/s). This strip is passed through a sintering furnace and rerolled to the finished size. In gen - eral, the product does not have any advantage over strip produced by conventional metal- rolling from bulk, although in some cases superior homogeneity can be demonstrated, as well as freedom from laminations that can arise from bulk defects. Powder Hopper
Green Sheet
Coiler
Hot Rolls
Shaping Rolls
Sintering Furnace
Cooling
Fig. 19. Powder Rolling Illustration
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