Now-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. The 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). The 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. From 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.

中文翻译：

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带有涂层硬质合金刀片的AISI 4340硬化钢加工过程中的表面粗糙度，后刀面磨损，切屑形态和成本估算的实验研究

如今，由于其在各个工程领域的广泛应用，更新的硬化钢材料正迅速进入市场。因此，在实际加工之前，对这些钢材的可加工性进行调查是实践工程师最关心的问题之一。本研究解决了使用CVD（TiN / TiCN / Al2O3 / TiN）多层涂层硬质合金刀具对AISI 4340钢（49 HRC）进行干硬车削时的表面粗糙度，后刀面磨损和切屑形态。使用Taguchi的L9正交阵列（OA）和方差统计分析（ANOVA）进行了三个因素（切削速度，进给和切削深度）和三级阶乘实验设计，以研究这些切削参数对刀具和刀具的后续影响。工件的侧面磨损和表面粗糙度。为了更好地了解切割过程，通过扫描电子显微镜（SEM）观察了加工工件的表面形貌，磨损的硬质合金刀具的磨损机理以及产生的切屑的形态。因此，采用多元回归分析为每种反应建立数学模型，并进行各种诊断测试以检验所提出模型的有效性和有效性。最后，为证明涂层硬质合金刀具在硬车削应用中的经济可行性，基于吉尔伯特的方法，通过评估优化切削条件下的刀具寿命（由响应优化技术建议），进行了成本分析。结果表明，表面粗糙度和后刀面磨损在统计上受进给和切削速度的影响。事实上，切削速度的提高导致更好的表面光洁度以及侧面磨损的增加。刀具磨损描述了切削刀具的逐渐失效，这是由于齿面刃口与机加工表面中的坚硬颗粒的摩擦作用以及较高的切削温度导致的磨损而造成的沟槽。切屑的形态证实了锯齿形切屑的形成，由于塑性变形引起的周期性裂纹扩展，切屑的锯齿严重。发现使用涂层硬质合金刀具加工硬化的AISI 4340钢，每个零件的总加工成本为0.13美元（即印度卢比8.21卢比）。从研究中 多层TiN / TiCN / Al2O3 / TiN涂层硬质合金刀具在干切削条件下进行硬车削加工的有效性和潜力，具有高产量和具有成本效益的优点，可替代传统的圆柱磨削操作。此外，它还为昂贵的CBN和陶瓷工具提供了合理的选择。