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 DR-50/450 Applications


     For finish-machining of hardened steels and certain softer ferrous materials:
  • Surface and through hardened steels
  • High speed steels
  • Bearing steels
  • Hot - work die steels
  • Cold - work tool steels
  • Grey and chilled cast iron
  • Sintered Irons 


   Applying DR-50 & DR-450

     PCBN cutting tools machine hardened steels with apparent ease because, using relatively high surface speeds
    heat is generated at the point of cutting so the PCBN tool cuts locally softened material. The heat is carried
    away by the  swarf, which becomes brittle and harmless, and the PCBN tool, which has a high co-efficient of
    thermal  conductivity. If a light cut is required, however, a tool with a high CBN content conducts too much
    heat away from the shear zone and the conditions for efficient machining cannot be  achieved.
    DR-50 & DR-450 have a low CBN content and the individual CBN particles are isolated within a ceramic matrix. This gives
    the materials a lower thermal conductivity and greater wear resistance in finish cutting operations. Low CBN tools can     therefore keep sufficient heat at the cutting point to enable the optimum cutting conditions to be achieved when a
    light cut is taken. In most cases, even when very light cuts are required, low CBN tools employ negative rake geometry
    to provide a strong edge. Due to the nature of cutting, however, cutting forces are still very small.
    Low CBN can be used to provide a productive and cost effective alternative to grinding. Tolerances achieved are
    comparable but machining time can be dramatically reduced. The quality of a component finished with the tool is
    dependant on the machine used. Vibration will affect the surface finish and free play will limit the tolerances that can
    be achieved. When turning or boring hollow sections, chucking pressure should be reduced to encourage roundness
    and concentricity. Although the component may be hard, cutting forces will be very small.
    DR-50 contains TiC and is the grade with the best ultimate tool life under ideal conditions.
    DR-450 contains TiN and has a smaller CBN particle size. This results in a tougher material that produces marginally
    better surface finishes. DR-450 is only used when the application is not successfully achieved using DR-50.
    Coolant has little effect on the cutting mechanism since the heat generated in the shear zone is sufficient to vaporise
    any coolant provided. Coolant does however serve three major purposes:-
    Although most of the heat essential for efficient cutting exits with the chip, any increase in the temperature
    of the component will make accurate measuring difficult. Coolant can be used to reduce this effect.
    Coolant can be used to drive away any swarf which might interfere with the cutting edge, particularly in
    boring operations. Coolant can help to reduce vibration, especially where rigidity is limited.
    Where interrupted cutting occurs, coolant should not be used as this will thermally shock the CBN tool as
    it comes out of cut, resulting in premature failure. Although interrupted cutting with coolant will  never
    improve tool life, it is possible to use coolant machining hardened steel with DR-450 and coolant can be
    used machining cast iron, that is not hardened, under all conditions.






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David Richards Engineering  2013