Machinery's Handbook, 31st Edition
1552 Powder Metallurgy Materials materials of appropriately different characteristics. Copper infiltration during sintering can be used to bond steel parts. Bearings: Bearings are natural products for PM because of its controlled porosity and the resulting self-contained lubricant. Plane bearings, flanged bearings, spherical bearings, and thrust washers are commonly produced with PM technology. The operation environment should be carefully considered: external lubrication, cooling, and hardened or chromium- plated shafts tend to increase permissible loads. Repeated start-stop operation, oscillatory or reciprocating motion, high speed, and temperature extremes tend to decrease permissible loads. Economics of Powder Metallurgy Powder metallurgy is a continually and rapidly evolving technology that embraces most metallic and alloy materials and a wide variety of shapes. PM is a highly developed method of manufacturing reliable ferrous and nonferrous products. The growth of the PM industry during the past few decades is largely attributable to the cost savings associ- ated with net- or near-net-shape processing compared to other metalworking methods such as casting or forging. The following will explain why powder metallurgy is competitive against alternative produc- tion processes. There are two principal reasons for using a powder metallurgy product: 1) cost savings 2) unique properties attainable only by the PM method In the automotive sector, which accounts for about 80 percent of structural PM produc- tion, the reason for choosing PM is, in the majority of cases, an economic one. Why then is PM more cost-effective? • A sintered PM part of comparable quality may be cheaper than a cast of wrought component. • It provides better material utilization with close dimensional tolerances. • It is suited to high-volume parts production requirements. • It provides long-term performance reliability in critical applications. Conventional metal forming or shaping processes, against which PM competes, gener ally involve significant machining operations from bar stock or from forged or cast blanks. These machining operations can be costly and are wasteful of material and energy. This fact is illustrated in Table 7, which shows that material utilization in excess of 95 percent can be achieved with close dimensional tolerances. Table 7. Raw Material Utilization and Energy Requirements of Various Manufacturing Processes
Energy Requirement per kg Finished Part MJ (BTU)
Raw Material Utilization %
Manufacturing Process
Casting Sintering
90 95 85
30–38 (23,434–36,017)
29 (27,486) 41 (38,860)
Cold or warm extrusion Hot-drop forging Machining process
75–80 40–50
46–49 (43,599–45,495)
66–82 (66,555–77,721) The example in Table 7 compiles data for a comparison for a production of notch seg ments for track transmission. The PM process (sintering) has the highest raw material uti lization (95 percent) and the lowest energy requirement per kg of finished part compared with other manufacturing processes. The energy savings alone contribute significantly to the economic advantage offered by PM. Compared with forging, machining, and a num- ber of other processes, PM consumes only around 45 to 50 percent of the energy and the number of process steps is greatly reduced. Equipment costs for conventional PM processing are somewhat similar to those for bulk forging, but the cost increases significantly for HIP methods. Labor costs are not as high in
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