The analysis of the effect of varying feed values in each pass on tool wear and surface roughness in turning of AISI 4140

Machining is a complex process between the cutting tool and the workpiece, and in this process, the cutting tool constantly wears out with various wear mechanisms. Tool-wear estimation in turning is a complicated process; thus, there is a need for a study to reveal the time-dependent behavior of tool wear. In this study, tool wear and surface roughness change during the turning process of AISI 4140 steel at low cutting speeds were examined in detail with variable feed values for the first time. For this purpose, a half-minute cutting time was applied for each pass to analyze the tool wear as gradually as possible. Tool wear (flank, notch, and nose), surface roughness (Ra, Rz, and Rt), and chip morphologies were examined after each turning operation. The flank wear reached 0.3 mm, which is one of the tool life criteria according to ISO 3685, and the experiments were terminated at the 149th minute. Initially, a significant surface improvement (approx. 300%) was observed due to the decrease in feed values. In subsequent experiments, the effect of feed was significantly reduced due to increased tool wear, and limited surface roughness improvement (approx. 30%) was observed. At the beginning of the experiment, the chip breaker function of the cutting insert was successful at almost all feeds. However, in subsequent experiments, it was found that even at higher feeds, the chip breaker geometry of the insert deteriorated due to tool wear, causing changes in chip morphology, and resulting in long and undesirable chips.