Abstract
BackgroundNow-a-days, newer hardened steel materials are coming rapidly into the market due to its wide applications in various fields of engineering. So the machinability investigation of these steel materials is one of the prime concern for practicing engineers, prior to actual machining.MethodsThe present study addresses surface roughness, flank wear and chip morphology during dry hard turning of AISI 4340 steel (49 HRC) using CVD (TiN/TiCN/Al2O3/TiN) multilayer coated carbide tool. Three factors (cutting speed, feed and depth of cut) and three-level factorial experiment designs with Taguchi’s L9 Orthogonal array (OA) and statistical analysis of variance (ANOVA) were performed to investigate the consequent effect of these cutting parameters on the tool and workpiece in terms of flank wear and surface roughness. For better understanding of the cutting process, surface topography of machined workpieces, wear mechanisms of worn coated carbide tool and chip morphology of generated chips were observed by scanning electron microscope (SEM). Consequently, multiple regression analysis was adopted to develop mathematical model for each response, along with various diagnostic tests were performed to check the validity and efficacy of the proposed model. Finally, to justify the economical feasibility of coated carbide tool in hard turning application, a cost analysis was performed based on Gilbert’s approach by evaluating the tool life under optimized cutting condition (suggested by response optimization technique).ResultsThe results shows that surface roughness and flank wear are statistically significant influenced by feed and cutting speed. In fact, increase in cutting speed resulted in better surface finish as well as increase in flank wear. Tool wear describes the gradual failure of cutting tool, caused grooves by abrasion due to rubbing effect of flank land with hard particles in the machined surface and high cutting temperature. Chip morphology confirms the formation of saw-tooth type of chip with severity of chip serration due to cyclic crack propagation caused by plastic deformation. The total machining cost per part is found to be $0.13 (i.e. in Indian rupees Rs. 8.21) for machining of hardened AISI 4340 steel with coated carbide tool.ConclusionsFrom the study, the effectiveness and potential of multilayer TiN/TiCN/Al2O3/TiN coated carbide tool for hard turning process during dry cutting condition possesses high yielding and cost-effective benefit to substitute the traditional cylindrical grinding operation. Apart, it also contributes reasonable option to costlier CBN and ceramic tools.
Highlights
Now-a-days, newer hardened steel materials are coming rapidly into the market due to its wide applications in various fields of engineering
Several experimental studies have been performed to investigate the influence of cutting parameters, machining time, tool geometry, workpiece hardness, tool materials, different coatings on machinability characteristics like surface roughness, cutting forces and tool flank wear with various workpiece materials (MDN 250, American Iron and Steel Institute (AISI) 4340, 4140, 52100, 6150, D2, D3, H10, H11 and H13 die steel) in hard turning for process optimization and machining performance prediction through experimental methods (Tamizharasan et al 2006; Lalwani et al 2008; Hosseini et al 2016; Das et al 2016), mathematical models (Singh & Rao 2007; Al-Ahmari 2007; Ozel et al 2007; Sieben et al 2010; Asiltürk & Çunkaş 2011) and statistical analysis (Davim & Figueira 2007; Caydas 2010; Bouacha et al 2010; Nabil et al 2012)
– analysis of variance (ANOVA) analysis indicates that feed becomes the most influential parameter for surface roughness (70.22%) followed by cutting speed (21.93%) and depth of cut (6.21%)
Summary
Now-a-days, newer hardened steel materials are coming rapidly into the market due to its wide applications in various fields of engineering. Aslan et al (2007) conducted an optimization study by machining a hardened AISI 4140 grade (63 HRC) steel with Al2O3 + TiCN mixed ceramic inserts in order to analyze the effect of cutting parameters (cutting speed, feed rate and depth of cut) on surface roughness and flank wear by employing Taguchi technique, ANOVA and regression analysis. Later, using similar tool material, Das et al (2015) studied flank wear and surface roughness during machining of hardened AISI 4140 steel (52 HRC) and showed that feed followed by cutting speed and cutting speed-depth of cut significantly affected surface roughness; whereas cutting speed had the largest influence on flank wear Their results highlight the cost estimation based on Gilbert’s approach of economics in machining to vindicate the economical viability of coated ceramic tool in hard turning process
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