Grinding performances of electroplated Ni–B-diamond tools prepared through composite electroplating with intermittent stirring

Fabrication and evaluation of electroplated Ni–B-diamond grinding tools made with 3-mm-diameter martensitic AISI 440C rod substrates were performed. With 25-μm-thick layer of Ni deposit serving as the undercoating, Ni–B-diamond composite deposits with a thickness of 300 μm were prepared using intermittent stirring in a Ni–B-diamond plating bath containing synthetic diamond particles ranging between 30 and 40 μm in sizes. The prepared electroplated diamond tools were then post processed by annealing and trimming by means of electrical discharge machining (EDM). Based on experimental results, it was found that the diamond density in a diamond-contained composite deposit depended on the timings of intermittent stirring cycle. The highest diamond density of 829 particles/mm² can be found in the Ni–B-diamond composite by a stirring cycle with an on-period of 5 s and an off-period of 60 s. To minimize unwanted scale formations, 150 g/L of diamond particles and 3 g/L of sodium dodecyl sulfate (SDS) were use in the plating bath. An EDM current of 6 A or more was necessary to obtain a rectangular lateral profile for machining. A suitable composite hardness for high grinding performance can be achieved with 0.43 wt% (2.29 at%) of B content in the Ni–B-diamond composite plated at a high current density and an annealing temperature between 400 and 500 °C for 30 min. Slot grinding tests were performed on Al₂O₃ plates and maximum ground lengths of more than 1000 mm were achieved. Slot width reduction due to tool wear was well within 120 μm. The main cause of tool failure was concluded to be composite deposit peeling or broken off from the substrate.