# Cutting Force When Machining Hardened Steel and the Surface Roughness Achieved
###### Abstract  
This article deals primarily with the problem of determining the cutting force when machining hardened steels. For this study, the steel used was 100 Cr6, number 1.3505. The secondary aspects of the study focused on the evaluation of the surface quality of machined samples and the recommendation of cutting conditions. A wide variety of components are used in engineering, the final heat treatment of which is hardening. These components are usually critical in a particular product. The quality of these components determines the correct functioning of the entire body of technical equipment, and ultimately, its service life. In our study, these are the core parts of thrust bearings, specifically the rolling elements. The subject of this experiment involves machining these components in the hardened state with cubic boron nitride tools and the continuous measurement of the cutting force using a dynamometer. The machining is carried out on a conventional lathe. A total of 12 combinations of cutting conditions were set. Specifically, for three cutting speeds of 130, 155 and 180 m-min\({}^{-1}\), the feed rates of 0.05 and 0.1 mm-rev\({}^{-1}\) and the cutting widths of 0.2 and 0.35 mm, were evaluated The evaluation assessed the surface quality by both touch and non-touch methods. A structural equation with the appropriate constants and exponents was then constructed from the data obtained using the dynamometer. The experiment confirmed the potential of achieving a value of the average arithmetic profile deviation Ra in the range of 0.3-0.4 when turning hardened steels with cubic boron nitride. hardened steel; cubic boron nitride; rolling body; structural equations; surface roughness; cutting force; turning +
Footnote †: journal: Applied Sciences  
Hard steel (45-65 HRC) turning has been a subject of many research studies over the last years. [PERSON] et al. [6] presented a comparison of the performance of four cutting-tool materials when turning bearing steel 100 Cr6 hardened to 62-64 HRC with regard to tool life and surface roughness. An interesting experimental investigation was conducted by [PERSON] et al. [7] to determine the effect of tool edge geometry and workpiece hardness on surface roughness and cutting forces during the hard turning finishing of AISI 52100 steel. Cubic boron nitride inserts with different representative cutting edge modifications were used as cutting tools. This study showed that the effect of cutting edge geometry on surface roughness and cutting forces was statistically significant. It was also found that the two-factor interaction of cutting edge geometry and workpiece hardness had a significant effect on surface roughness. A similar study was conducted by [PERSON] et al. [8] who presented the surface roughness model with respect to the main cutting parameters such as cutting speed, feed and depth of cut using a response surface methodology. Machining tests were carried out for turning hardened AISI 1050 steels with cubic boron nitride (CBN) cutting tools under different conditions. Based on the experimental data during steel machining, model equations predicting the surface roughness, Ra, Rz and Rmax, were developed. In investigating the effect of different cutting conditions when machining hardened steel parts, significant attention is often paid to studying the behavior and wear of used cutting tools of various materials. Changes in cutting edge and cutting speed are the frequently monitored parameters that strongly influence the tool wear [9]. Another important parameter is the material of the cutting tool itself. [PERSON] [10] examined the wear of low CBN-content cutting tools for the hard turning of 100 Cr6 bearing steel (HRC = 62 \(\pm\) 2). The performance of the CBN cutting tool, more specifically the (Ti, Al) N-coated CBN tool that is formed on a CBN substrate by the physical vapor deposition method, was tested also by [PERSON] et al. [11].