7.9 STANDARDIZING THE MACHINABILITY OF PM STEELS

To obtain data for a broad range of PM steels in machining under controlled identical conditions which would enable standardizing their machinability, nearly 100 sintered steels materials were subjected to the drilling test.

In this test series, average machinability values were taken for specimens with 6.7 and 7.0 g/cm ³ density levels. Iron-carbon steels, copper as well as nickel alloyed ones, in prealloyed and diffusion alloyed variants, without and with MnS anddition as well as resin impregnated ones were involved in the test programme. The materials are listed here in the ascending order by the number of holes drilled, Tab. 7.45. Once 192 holes have been reached (which was set as the test limit), the list continues by decreasing drilling force values. Thus, in this table the very poorly machinable materials are at the top of the list (least number of the holes and highest drilling force). In the MPIF Standard 35 [296] only corresponding 'Rating' values are listed. In Tab. 7.45 these are complemented by the corresponding number of holes drilled, cutting edge wear, and axial drilling force values (as machining indices) from Refs. 145 and 277.