SOME ASPECTS OF POWDER METALLURGY 453 



and in addition to those materials that are (hl'llcult or impossible to make 

 by other methods, parts are now being manufactured in direct competition 

 with those made by conventional, established procedures. 



Under these circumstances, economy of production, in addition to tech- 

 nical feasibility, becomes a major factor in the utilization of the process. 

 Of the numerous limitations of the process, some are inherent and definitely 

 limit its application while others are incidental and susceptible to certain 

 measures of control. The more important of these limitations and problems 

 are outlined below: 



1. The cost of metal powders is high in comparison with metal for 

 other methods of producing similar parts, and availability of suitable 

 powders is another problem''''*^. Both cost reduction and avail- 

 ability have received considerable attention in recent years, and 

 with increased use of metal powders and the large-scale powder 

 production entailed, substantial price reductions have been efTected 

 and a wider variety of types of powder have been made avilable. 

 The development of domestic sources of supply of a satisfactory 

 low-cost iron powder to replace Swedish sponge iron is an example 

 of a successful attempt to overcome a limitation of the process^^. 



In a final analysis, metal powder costs must be balanced against 

 overall costs before a raw material cost standard can be set up. 



2. Die expense^"* •^'* '^^ '^^ is high, especially for large and complicated 

 parts and for high pressures. New dies are required for each part 

 of different shape and size, and each die must be installed and carefully 

 adjusted for operation. With the entry of the powder metallurgist 

 to the low cost part field, there will be need for more complicated 

 dies to meet the competition of intricately shaped parts produced 

 by casting methods. The tool cost, however, for the powder process 

 is generally lower for a given part than with other processes. Die 

 cost may range from about $150 for small simple parts up to SI 800 

 or more for large parts or complicated shapes^^. 



3. Sintering furnaces pose many problems in the production of powder 

 metal parts^**. Close temperature control and uniformity are essential 

 for control of dimensional changes in compacts. The fabrication 

 of iron or alloy steel parts requiring higher temperatures than have 

 been previously utilized in the industry add to the diflEiculties of 

 furnace design. 



4. The size and form of powder metal products is limited^^ •^- •*^. Large 

 samples require huge presses to obtain the desired compacting 

 pressures and both tool and press costs increase. Increase in size 

 of compacts leads to a non-uniform distribution of pressure and may 

 adversely affect the shape and dimensions of the article in the sintering 



