Grinding with electroplated cubic boron nitride (CBN) wheels
Electroplated cubic boron nitride (CBN) wheels are manufactured with a single layer of CBN superabrasive grains held on the wheel hub by an electroplated nickel bond. Unlike other conventional and superabrasive wheels, these wheels are not periodically trued or dressed. Consequently, their performance during grinding varies significantly as the wheel wears down and its topography changes.
An investigation was undertaken of the grinding process with electroplated CBN wheels. The topography of unused wheels of various different grain sizes was characterized in terms of areal grain density and protrusion height distribution of the grain tips. Internal cylindrical and straight surface grinding tests were then conducted to investigate the wheel wear and its effect on the wheel topography and grinding performance. Grinding tests were performed mostly on hardened AISI 52100 steel over a wide range of operating conditions. Measurements were made of the forces, grinding power, surface roughness, radial wheel wear, and wheel topography.
The overall radial wheel wear in each case was found to consist of an initial transient followed by a steady state regime. With continued grinding, a progressive increase in power and a decrease in surface roughness were observed. Wheel failure tended to occur by stripping of the abrasive layer when the radial wear reached about 70–80% of the grain dimension.
Wheel wear was found to occur by attrition, grain fracture, and grain pullout. Attritious wear increases the active grain density and causes wheel dulling which lead to a smoother workpiece and higher forces. The effects of attritious wear are offset to a greater or lesser degree by grain fracture and grain pullout. Grain fracture which dominates in the steady state is shown to be related to the uncut chip thickness taken by an individual cutting point. The initial transient wear at the start of grinding is mainly due to pullout of loosely held grains, although grain fracture also contributes to the transient.
The results of this work provide the technological basis for predicting grinding behavior, design of grinding cycles, and optimal utilization of the process with electroplated CBN wheels.