AGMA 12FTM10 PDF

The unique requirements of an electroplatable superabrasive CBN grit used in profile grinding of hardened steel gears as well as the attributes and grinding behavior of a new CBN developed specifically for this application are discussed. Profile gear grinding parameters were simulated in through-hardened AISI 4140 steel (56 HRC) and the grinding performance of the newCBNwas compared against a competitiveCBNgrade widely used in the application. Consistent with field criteria, grinding performance was characterized based on occurrence of ‘burn' or ‘form' failure. The ‘burn' or metallurgical phase transformation failure was detected by Barkhausen Noise Analysis (BNA) and corroborated by microstructural and microhardness evaluations. The ‘form' failure was simulated by tracking average radial wheel wear to a threshold value where form loss was expected to occur. Grinding tests indicate that the new CBN grit can grind 35% more parts compared to the competitive CBN grade before burn failure. In addition, the new CBN displayed a lower wear rate. The new CBN grade also exhibited a unique ability to grind with lower grinding power, resulting in a near constant BNA response on the ground surface throughout the test. This impliedminimal microstructural change on the ground part from start to end of the test compared to the progressive softening of ground surface noticed with the competitive CBN.