PSI - Issue 10

N.M. Vaxevanidis et al. / Procedia Structural Integrity 10 (2018) 333–341 N.M. Vaxevanidis et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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1. Introduction

Brass alloys are characterized by excellent workability, high thermal and electric conductivity, corrosion resistance as well as exceptional antibacterial properties and are therefore widely used in various industries, such as electric and electronics, automotive and sanitary industry. To enhance their machinability, lead is commonly added to brass alloys, leading to excellent chip breakage, low tool wear, and high applicable cutting parameters. Main applications are in electric and electronics, automotive, and sanitary industry. Since the amount of cutting operations when manufac turing brass components is high, different alloying elements enhancing the machinability are usually added to brass. The most essential element in this context is lead (Pb), improving the machinability referring to chip breakage, tool wear, cutting forces, and applicable range of cutting parameters (Kuyucak and Sahoo (1996)). The machinability of these low-leaded brasses is significantly worse compared to leaded free-cutting brass. Depending on their chemical composition and microstructure, different machinability problems arise. For the silicon alloyed materials, such as CuZn21Si3P (CW724R), tool wear is supposed to be higher due to a silicon-rich and hard j-phase in the microstructure (Klocke et al. (2016)). For other low-leaded brass alloys, such as CuZn42 (CW510L) and CuZn38As (CW511L), the main problems are due to the formation of long chips and higher thermal as well as mechanical tool load (Nobel et al. (2014)). Moreover, high adhesion tendency may result in chipping of the cutting edge and reduced work piece quality. Kato et al. (2014) enhanced the chip evacuation in micro-drilling of CuZn21Si3P by optimizing tool geometry. Klocke et al. (2016) and Nobel et al. (2014) published approaches to enable high-performance cutting of low-leaded brass alloys. Nobel et al. (2015) investigated also the chip formation, the flow and its breakage in free orthogonal cutting. Metal cutting operations are widespread in manufacturing industry and the prediction and/or the control of relevant machinability parameters always attracts interest. One basic machinability parameter is the surface texture, as it is closely associated with the quality, reliability and functional performance of components (Petropoulos et al. (2010); Vaxevanidis et al. (2014)). Turning is the primary operation in metalworking industry for producing axisymmetric components. These components, typically, possesses critical features that require specific surface finish and the best possible functional behaviour. Due to inadequate knowledge of the complexity of the process and factors affecting the surface integrity in turning operation, an improper decision may cause high production costs and low machining quality (Grzesik et al. (2010)). The proper selection of cutting tools and process parameters for achieving high cutting performance in a turning operation is a critical task (Grzesik et al. (2010); Vaxevanidis et al. (2010)). An arc chain surface pattern is typical for turning but significant deviations appear due to irregular chip formation phenomena, namely built-up edge, discontinuous chip, very low feed rates, chatter and intense tool flank wear. These phenomena occur many times, especially when limitations in productivity or in material selection exist (Petropoulos et al. (2010)). The various manufacturing processes applied in industry produce the desired shapes of the components within pre scribed dimensional tolerances and surface quality requirements. Therefore, any proposed description of a techno logical surface should take into account the features of the profile imparted by the machining process performed. This is a crucial point because the process can be controlled through surface texture recognition, and also be used to generate suitable profiles for tribological functioning (Petropoulos et al. (2006)). In the common industrial practice surface roughness is evaluated mainly by Ra (mean) and Rt (maximum) rough ness parameters. However, it should be noted that the aforementioned parameters alone, do not provide information on the shape of the profile. Characteristics like inclination and curvature of the surface roughness asperities, “ empti ness” or “fullness” of the profile, distribution of the profile material at various heights are registered in the profile shape. The essential tribological aspects (e.g. friction, wear, state of lubrication) are highly dependent on profile shape (Petropoulos et al. (2007); Petropoulos et al. (2009); Vaxevanidis et al. (2014); Toulfatzis et al. (2014)). Cutting forces are the result of extreme conditions experienced during the tool-work piece contact (Gaitonde et al. (2012); Vaxevanidis et al. (2014); Hanief et al. (2017)). The interaction can be directly related to the tool wear and, in worst cases, to the failure of the tool. Consequently, the tool wear and cutting forces are related to each other. Therefore, it is necessary to study the turning process so as to characterize machinability of materials in terms of cutting force components as well. Surface roughness as well as cutting force monitoring is essential in order to determine the per formance of machining processes and expand the tool life. This study focuses on some of the major machinability characteristics ( Fc, Ra and Rt ) during the longitudinal turning of CuZn39Pb3 alloy. Experimental results have shown that depth of cut holds dominant effect of cutting force whilst its contribution equals to 73.61%. Rotational speed and feed rate have just as important effect on arithmetic