Key Engineering Materials Vol. 933

Abstract: Parallel turning is one among the advanced unconventional turning process. It employs two turning tools operating concurrently to cut the material from the workpiece. For turned rotary components, surface integrity is a major quality indicator that determines the fatigue life of the finished workpiece. Tool parting distance, rake angle and edge radius affects surface integrity. Part I dealt with numerical analyses to determine the effect of parting distance on surface integrity using finite element based commercial software Abaqus 6.14. Here in Part II, the impact of rake angle over surface integrity for various cutting speeds and feeds are numerically analyzed. It was observed that with the rise in negative rake angle the negative residual stresses decreased for the machined surface of leading and lagging cutting tool. When the rake angle is increased from-10 ̊ to-2 ̊, percentage reduction of negative residual stresses is same for the turned surfaces of both tools. The cutting velocity was 250 m/min and feed 0.2 mm/rev. With the rise in rake angle, the friction angle reduced but shear angle raised. When the cutting velocity increased, the shear angle of the leading and lagging cutting tool reduced. Lower shear angle causes higher stagnation region which further causes higher compressive surface residual stress.

Abstract: Machining is a complex process which uses cutting tool for finshing the workpiece material. A sequence of machining tests costs a lot of expense and effort to complete. It's critical to avoid time-consuming runs and put technology first. Surface roughness (Ra) has been used to signal quality of product in the turning process as part of an automated monitoring system deployed in-process. This research uses machine learning models to estimate surface roughness while machining AISI 304 stainless steel rods. The key elements impacting surface quality are the input variables of turning, namely feed rate, depth of cut, and spindle speed. Four machine learning (ML)-based algorithms were used to predict surface roughness in this study: Gradient Boosting Regression (GBR), Decision Tree Regression (DTR), Extreme Gradient Boosting Regression (XGB), and Random Forest (RF) of Surface Roughness (Ra). The baseline models' predictive ability was measured using error measures such as Root Mean Square Error (RMSE), mean squared error (MSE), and coefficient of determination (R²). Overall, the XGB and GBR models appear to have the most accuracy in predicting surface roughness (Ra).

Abstract: Machining induced tensile residual stress of components made from Duplex Stainless Steel (DSS) is a major factor affecting their functional performance. This work used a multi-regression modeling approach for establishing the relationship amongst process parameters of turning operation and residual stress for standard DSS components. Four turning parameters namely, cutting speed, cutting depth, rate of feed & radius of tool nose were varied. Each of the selected parameters had three levels of values. The influence of these variations on residual stress was noted. Experiments were performed using Definitive Screening Design (DSD). Surface residual stress was measured using X-ray diffraction method. Step Wise regression approach with forward selection of terms and alpha value of 0.25 resulted in a quadratic model with R square value of 94.8 %. Validation experiment with new specimens yielded prediction accuracy of 88%.

Abstract: Nowadays, 316L stainless steel implant materials exhibit a promising position in the field of biomaterials application, especially in medical due to their higher strength compared to other ceramic base materials. Therefore, in this work, the production of 316L implant materials and examination of the mechanical characteristics were carried out. Powder Metallurgy process has been chosen to produce the implant materials due to its high advantages in demonstrating the high mechanical properties of the green sample. 316L stainless steel with zinc streate powder of three different compositions, i.e., the first of 99% 316L stainless steel and 1% zinc stearate, the second of 97% 316L stainless steel and 3% zinc streate, and the third of 95% 316L stainless steel and 5% zinc streate, were cold pressed individually at 600 MPa pressure using UTM and sintered the green samples at 1120 °C for 1 hour and 30 minutes. Sintering temperature and time were the same for all the specimens. We investigated the mechanical behaviour of 316L stainless steel implant materials of different compositions at the same temperature for the same duration of time. After that, the mechanical properties and densification of this material were investigated.

Abstract: Metal cutting is the way of processing the workpiece with tool having sharp cutting edges of different materials generating chips of different shapes and sizes. In present era of industry 4.0, metal machining should not be unrated during processing of hard grades metals and superalloys where large amount of cutting forces are generated. Also, the measurement of cutting forces provides the basic of economical machining and hence accurate evaluation in experimental and analytical manner has great importance. The traditional models of metal cutting have disagreement with experimental results due to missing of important mechanics terms. With the development of digital technology, the errors in calculation of cutting force have also been shortened due to consideration of terms absent in conventional models. In present investigation, the cutting forces have been evaluated experimentally using dynamometer and analytically with Astakhov’s methodology during turning of EN-31 steel. The results revealed that 12.9% observations have deviation more than 20%, whereas 16.67 % has zero deviation. Further, the feed rate has more influence on cutting forces as compared to speed and nose radius. In addition, the minimum quantity lubrication (MQL) of vegetable oil has lowered the cutting forces appreciably compared to dry machining.

Abstract: Copper is a widely used material in various industries due to its properties like good corrosion resistance, thermal and electrical conductivity, stability at high temperatures, etc. To increase the mechanical and tribological properties, additional reinforcement should be added to the copper matrix. Adding tin into copper will result in the formation of bronze which is stronger and harder than either of the pure metals. This study deals with the comparative study of mechanical and tribological properties of microwave sintered and conventionally sintered Cu-6Sn. The mechanical properties of Cu-6Sn processed through powder metallurgy are compared with that of Cu-6Sn processed through casting. Hardness and wear resistance was observed to be higher for conventionally sintered specimens. Microwave sintered Cu-6Sn exhibit enhanced mechanical properties compared to Cu-6Sn processed through casting.

Abstract: In this current article, an effort was made to briefly study the impact of magnesium content on the mechanical and metallurgical performance of as-cast Zn-Al-Si-Mg alloy. Zinc, aluminium, and silicon of appropriate weight quantities were melted in an electric furnace, and magnesium of varying quantities (1-5wt%) was added to the melt to obtain rectangular cast specimens. Microstructural, hardness and mechanical property analysis was conducted for the developed alloy in the as-cast condition. It was noted that an addition of Mg to the Zn matrix refines the grains but more than 3wt-% of Mg to the matrix forms clusters which deteriorate the property of the alloy in the as-cast condition. The value of hardness and tensile strength were noted to enhance, and ductility was observed to decrease from the baseline alloy to the alloy with 3wt% of Mg. Further addition of Mg decreased the properties of the alloy.

Abstract: Friction Stir Back Extrusion (FSBE) is a new grade of severe plastic deformation process capable of producing metallic tubular geometries that exhibit ultrafine grain structure and superior mechanical properties. FSBE of tubular sections provide opportunities for producing lightweight rigid structures for the automotive, aerospace and construction industries. This research investigates the effect of submerging conditions (in water at 25 °C and 2 °C) for Magnesium AZ31-B tubes on the grain size, mechanical properties, temperature history and power consumption. Submerged FSBE is compared to FSBE in air at fixed process parameters of 90 mm/min and 2000 rpm. It is shown that the impact of submerging is statistically insignificant in terms of the mechanical properties, ultimate tensile strength and percent elongation, of the produced tubes according to the conducted t-tests. On the other hand, the optical microscopy results indicated finer grains at the inner wall of the seamless tubes for FSBE in air and underwater FSBE at 25 °C when compared to underwater FSBE at 2 °C.

Abstract: Dry EDM is a variation of the standard EDM method in which the liquid dielectric is replaced with a gaseous medium during the machining process. This paper presents comparative analysis of stationary and rotary electrode on Dry EDM in machining of Hastelloy C276 using copper EC grade rod as electrode and air as dielectric medium. Solid cylindrical (stationary and rotary) tool electrodes are used, and high-velocity gas is fed between the electrode and the workpiece through it into the discharge gap. The high-velocity gas flow into the gap assists debris clearance and reduces tool and workpiece overheating at the discharge areas. The dry EDM technique is currently known to have reduced tool wear, a smaller discharge gap, fewer residual stresses, a smaller white layer, and a smaller heat-affected zone, in addition to being ecologically friendly. To improve response factors such as material removal rate (MRR), surface roughness (Ra), and tool wear rate (TWR), Taguchi's L9 orthogonal array approach is utilised to design the trials and study the effects of different process parameters. Discharge current (I), pulse on time (Ton), Voltage (V), pressure (P), and tool rotational speed (N) were the varied input parameters. It is observed that the rotary electrode gives better MRR compared to stationary. The analysis of results show that current (I), pulse on time (Ton) and pulse off time (Toff) are the dominant factors that influence MRR and EWR.