Optimization of grinding depth to avoid grind-induced burns in 35NCD16 alloy

Abstract

Grind-induced burns are defined as any thermal damage done to the workpiece during the grinding process. It is most recognizable by the white layer (untempered martensite) formation in ferrous materials. The aerospace industry use parts that are made of 35NCD16 steel, one such part being bolt, used in the landing gear of an airplane. These bolts are mass-produced and inspected for defects. Grinding burns on any product are considered to be a defect that leads to its rejection, causing a loss to the manufacturer. Hence studies are done on this issue, to optimize grinding parameters, to avoid these defects. In this experimental study, specimens of tempered 35NCD16 are subjected to a surface grinding process with the depth of cut as a variable in two cases: with coolant and without coolant. The other grinding parameters, such as the cutting speed and coolant feed rate are kept constant. In each case at intervals of the depth of cut, Vickers hardness values are taken. Microstructures are photographed to observe martensite formation in the experimental and control set-up specimens. The obtained hardness results are compared with the tempered hardness value to find an optimized depth of cut in coolant applied condition and, in the absence of coolant grinding condition. The effect of depth of cut is investigated along with the thickness of the white layer for a given depth of cut, which is found from the microstructure images.