# Cutting Force When Machining Hardened Steel and the Surface Roughness Achieved
###### Abstract
Surface finish is a very important aspect for designing mechanical elements and is also presented as a quality indicator of the manufacturing processes, which is necessary for proper part geometries [17]. The 3D measurement of technical surfaces plays a crucial role in checking and controlling the properties and the function of materials or engineering parts [17]. Therefore, the effect of different cutting parameters on the surface roughness of machined hardened steel parts is a widely studied phenomenon. [PERSON] et al. [18] investigated the effect of different cutting parameters on surface roughness Ra and cutting force during hard turning of dry hardened tool steel 1.2367 (55 HRC). In this experimental study, constant depth of cut, three different cutting speeds and three different feeds were selected as the cutting parameters. The effect of the cutting parameters on surface roughness and cutting forces was evaluated by performing an analysis of variance. According to the results, the value of surface roughness increased as the feed rate increased, but the effect of cutting speed on surface roughness was negligible. In contrast to [PERSON] et al. [18], [PERSON] et al. [19] considered the depth of cut as a variable when studying the effect of cutting speed, feed rate, workpiece hardness and depth of cut on the surface roughness and cutting force components in hard turning. AISI H11 steel was hardened to (40, 45 and 50) HRC and machined using cubic boron nitride (CBN 7020 from Sandvik), which was essentially composed of 57% CBN and 35% TiCN. Four-factor (cutting speed, feed rate, hardness and depth of cut) and three-level sub-experimental designs were performed, supplemented by a statistical analysis of variance. The results showed that the components of cutting force were significantly affected by depth of cut and workpiece hardness. The main topic of this article is the discussion of the potential of using experimentally obtained data of individual cutting force components for determining the methodology of mathematical calculation of a particular cutting force component. The theoretical empirical calculation of the structural equation will approximate the actual cutting force value the closer that the actual cutting conditions of the machining are to agreeing with the cutting conditions of the experiment. It must, therefore, be stated here that the derived theoretical calculation of the structural equation of a particular cutting force component will be valid over a certain range of cutting conditions. Thus, it will be possible to predict a relatively simple calculation of the cutting force component without having to make measurements. This is very important in practice, where companies do not have the necessary measuring instruments, but at least need to determine the predicted magnitude of the relevant cutting force components. This knowledge then enables the required power for machining to be determined and the input energy to be used economically. So far, the applied research has focused mainly on machining functional surfaces of the body and shaft ring [2; 5]. This paper's contribution is mainly concerned with the machining of rolling hardened bodies, the real-time measurement of the cutting force  
Unlike previous experiments with bearing rings, the SP280 SY machine was not used because of the near-impossible placement of the Kistler measuring system on this machine, namely the placement of the measuring probes on the vertical slide of the machine. In previous experiments [2] cutting tools from SECO were used, but in this experiment alternative tools from Dormer Pramet were applied.