EXPERIMENTAL ANALYSIS OF THE EFFECT OF MECHANICAL PROPERTIES AND MICROSTRUCTURE ON TOOL VIBRATION AND SURFACE QUALITY IN DRY TURNING OF HARDENED AISI 4340 STEELS

Abstract

AISI 4340 (34CrNiMo6) steel is a difficult to machine steel material because of its high hardness and tendency to get strain hardened. These steels are mostly used in manufacturing of the axle parts, drive coupling, and rotating shafts due to their high mechanical properties. In this experimental study, the effects of mechanical properties and microstructure on tool vibration and surface quality in dry turning of hardened AISI 4340 steels were investigated. Test samples were classified as Raw Material (RM), Conventional Heat Treatment (CHT) and Tempering process (T). The experiments were carried out under dry cutting conditions by different cutting parameters on the CNC turning lathe. Three axes vibration amplitude values (along the [Formula: see text]-, [Formula: see text]- and [Formula: see text]-directions) were measured using accelerometers as online and surface roughness (Ra) values were measured with the surface roughness device. Tool vibrations and Ra values were found to be lower in T sample compared to the RM and CHT samples. When the samples were analyzed in terms of microstructure and mechanical properties, it was seen that the tensile strength increased as the hardness values increased. After the tempering process at 200∘C, pearlite and bainitic structures emerged along with the martensite structure. The surface quality that can be obtained on a cylindrical grinding lathe, has been reached with the dry turning process. Significant gains have been achieved in terms of cost and time.