CUTTING TOOL HARDNESS VS. PARENT METAL HARDNESS 1

[ibf]

Hello:

Could anybody help me out by advising whether there is a correlation (or a rule of thumb) between cutting tool HB vs. parent metal HB or not ?

We are currently buying a gear in China and the vendor reported that the Hobbing cutting tool is wearing - out prematurely. We then asked for the HB of the tool and it was reported 300 HB. That surprised us , because :

a) It seems to be too low of a hardness for high speed steel.

b) That`s the hardness of the gear thus, a 300 HB - cutting tool will never be able to rough cut the teeth of that gear.

Any comment would be very welcome.


Thank you.

 

[TVP]

Cutting tool hardness must be significantly higher than 300 HB, which is equivalent to about 32 HRC/320 HV. Cutting tools made out of steel are quenched & tempered to hardnesses of ~ 60-70 HRC/700-940+ HV, with 650 HV = 618 HB. Keep in mind that the indenter for HB is tungsten carbide, not diamond like HRC and HV, which means that it is not suitable for measuring very hard materials with hardness > ~ 58 HRC. The following reference should clarify the general range of tool hardness (80 HRA is 57.8 HRC/618 HB and 85.6 HRA is 68 HRC). Obviously cemented carbides and ceramics are harder than tool steels.

http://www.manufacturingcenter.com/online_book/chap_1.pdf

 

[ibf]

Thank you very much TVP. Your reply was very informative and useful.