452 BELL SYSTEM TECHNICAL JOURNAL 



oped may have better mechanical properties than the same material 

 in cast form*'* '^^ •*'' ■*^. The same type of fine-grain structure developed 

 in laboratory samples of iron parts compacted at high pressures 

 and sintered at relatively low temperatures also exhibit superior 

 tensile properties**. 



6. The powder method of manufacture may be more economical in 

 many instances due to factors such as rapid quantity production, 

 lower labor costs, ease of setting up for manufacture, conservation 

 of material, and elimination of machining operations*" •^-. A reported 

 instance of analysis of the normal cost of producing approximately 

 one hundred different units used in a piece of Ordnance equipment 

 revealed that powder metal parts effected a saving of about 70 per 

 cent*'. 



7. Rather close dimensional tolerances*" '^^'^^ on small or medium size 

 parts up to about two inches major dimension can be secured, aver- 

 aging ±0.001 inch. Closer tolerances of ±0.0005 inch are attain- 

 able and may be even smaller on special production jobs. On larger 

 parts, the tolerance may be in the order of ±0.002 inch. Fre- 

 quently, however, accuracy of dimensions is attained only through 

 a coining or re-pressing operation of the sintered part. 



8. There is usually very little material waste associated with powder 

 metal parts manufacture since there is little or no scrap loss-* '^^ •*'. 

 Powder losses generally run below 0.5 per cent^^. In melting and 

 casting operations on small parts, on the other hand, the sprues and 

 risers may be several times the weight of the finished casting. In 

 addition, machining operations on cast parts may remove from 10 

 to 50 per cent of the metal, and while most of it is recoverable as 

 scrap, it represents a loss in the manufacturing process^-. 



9. Highly skilled labor is not required for most operations in the powder 

 , method** •^^. Except for the construction of the necessary dies and 



die parts, semi-skilled labor may be used. This is of value in indus- 

 trial plants producing parts for Ordnance because skilled mechanics 

 who would normally be required for machining operations can be 

 made available for other work. 

 10. Tooling costs are relatively low in comparison with other high- 

 production methods, and less time is usually required to set up for 

 production**. Secondary operations such as machining of the 

 sintered products may be eliminated or greatly reduced. 



Limitations and Problems of the Powder Process 

 As has been indicated in several sections of this review, there has been 

 a recent shift in emphasis in the type of product made by powder methods, 



