Experimental Investigation on the Performance of Different Cutting Fluids on Cutting Force During Turning of Duplex Stainless Steel-2205 under MQL Technique

Machining is a vital process in manufacturing components to remove the material with the help of a cutting tool to get the final size and shape of the component. Several machining operations are turning, milling, grinding, and drilling. The various factors considered during turning operation include cutting speed, feed, depth of cut, cutting tool, workpiece material, type of the cutting fluid, and application of the cutting fluid. Kuram et al. [1] studied the applications of cutting fluid on the traditional method are not economical, and hence the Minimal Quantity Lubrication (MQL) has been gaining as an alternative solution for flood cooling. MQL is a technique in which the cutting fluid introduces into a chamber having high compressed air broken into small particles called aerosol. Aerosol is a mixture of fluid and air is applied in the cutting zone under high pressure in the form of a jet. Yusof et al. [2] worked on the MQL technique to prove that MQL has more benefits than dry machining. Nowadays, several cutting fluids are available for turning operations in industries such as natural oils, synthetic, mineral, and semi-synthetic oils. Mohd Saleem et al. [3] studied Mustard oil (vegetable oil) with MQL as an alternative cutting fluid while performing Turning operations on a Centre lathe machine using a single-point cutting tool of HSS compared with dry machining and other coolants. The results obtained indicate that vegetable oil performed a great cooling effect and lubrication similar to other coolants. Sathisha et al. [4] studied the effect of machining parameters like spindle speed, feed rate, and depth of cut under the dry and wet machining conditions during the turning of AISI 1018 steel. The experiment was conducted with dry and two types of cutting fluids, soluble oil and palm oil, to find tool tip temperature. Soluble oil gives better results compared with Palm oil. Kuram et al. [5-12] studied the three different vegetable-based cutting fluids refined sunflower oil and two commercial types (vegetable and mineral-based cutting oils) is used to determine for thrust force and surface roughness during drilling of AISI 304 austenitic stainless steel. The uses of vegetable cutting oils were investigated to reduce thrust force and improve surface finish at different spindle speeds and feed rates. Belluco and De Chiffre [13] Evaluated the performance of six cutting fluids (commercial mineral oil and five vegetable-based cutting fluids) in drilling AISI 316L stainless steel. Tool life, tool wear, chip formation, and cutting forces were studied as performance criteria, and results were better with vegetable cutting oil than that of the mineral cutting fluid. Vishal Gandhe and Jadhav [14] studied the optimize the pressure (P) and flow rate (Q) of cutting fluid in an MQL system with a different type of cutting fluid to obtain improved machining performances in turning EN-8 steel. The results obtained indicate that neat oils with extreme pressure additives provide excellent lubrication and anti-weld properties over a wide range of temperatures. In day-to-day life, several verities of materials can be found for different applications, among one of these are Duplex Stainless Steels (DSS) have a mixed microstructure of austenite and ferrite. DSS has roughly twice the yield strength of austenitic stainless steels for their mixed microstructure provides improved resistance to chloride stress corrosion cracking compared to austenitic stainless steels. High work hardening rate, low thermal conductivity, high fracture toughness, strong tendency to form the built-up edge (BUE), and relatively high austenite and nitrogen content modern duplex stainless steels are regarded as poorly machinable materials [15, 16]. Selvaraj et al. [17] have optimized dry turning parameters of two different grades of nitrogen alloyed duplex stainless steel by using the Taguchi method. Their results revealed that the feed rate is the most significant parameter influencing the surface roughness and cutting force. Thiyagu et al. [18] studied dry machining of DSS material using RSM; the second-order response surface models for surface roughness and cutting force were developed to study the effect of machining parameters and tool geometry in turning. The results obtained indicate that feed rate and nose radius are significant factors in minimizing cutting force followed by cutting speed. Chauhan et al. [19-22] studied machining parameter cutting speed optimization, feed rate, depth of cut, and approach angle with surface roughness and tangential cutting force as response variables using Response surface methodology (RSM). The results obtained indicate that the surface roughness increases with the cutting speed and the feed rate, whereas tangential force increases with an increase in approach angle and depth of cut. The RSM is practical, economical, and relatively easy to use, and many researchers use it for modeling, analysis, and optimization of machining processes. RSM is a collection of mathematical and statistical techniques useful for the modeling and analyzing problems in which a dependent variable y called response is influenced by several independent variables x₁, x₂, …, x_n called factors, and the objective is to optimize the response [23-28]. Many researchers are very little work has been carried on the determination of optimum machining parameters on stainless steel materials and other materials under dry machining, and some researchers have used vegetable, soluble and mineral oils as cutting fluids; very little work has been done on turning of DSS in dry machining. In this study, turning tests were carried on DSS-2205 under MQL with three different cutting fluids and find out significant factors that affect the cutting force and suitable cutting fluid to reduce cutting force.

It is evident from the literature following literature gaps were identified.

• Very limited investigations were reported on the studies on cutting force under dry turning but not undercutting fluids.
• In the current work, investigate the performance of DI water, neat cut oil, and emulsified fluid during turning of duplex stainless steel-2205 on cutting force under MQL to identify significant process parameters affecting the response through ANOVA.

Turning experiment was carried out using Response surface Methodology (RSM). Table 5 shows the order of the experiments with varying Speed, Feed and Depth of Cut with three levels and Cutting Force values for different cutting fluids.

Table 5 shows the Cutting force obtained for all base fluids turning, and Figure 2 shows the experimental run versus cutting force. From the results, the minimum value of cutting force obtained during all cutting parameters is low (-1), but increasing the cutting parameters to a higher level (0 and+1) increases the cutting force. In the initial stage, the tool cutting edge is very sharp, and with low speed, low feed and low DOC, very less force is required to shear the material. This is observed all base fluids turning. When increasing the speed, feed, and DOC, the tool contact will be more with material leads to the formation of high friction between tool and work, tool and chip and increased wear of tool, the sharpness of the tool reduces and also strain hardening of the material leads to increasing the cutting force. The emulsified fluid (1:20 concentration with DI water) gives better results, followed by neat cut oil and DI water. The emulsified fluid is thicker than DI water; the oil content mixed with water has good flowability in the MQL nozzle compared to high viscous neat cut oil and produced the lubrication and cooling effect, reduced the friction between the tool and work, reduced wear rate of tool and also maintains the sharpness of the tool for a longer time due to that cutting force are reduces. The other base fluid, neat cut oil, has a high viscosity and less flowability through the MQL nozzle. It provides lubrication, but the low cooling effect increases the cutting force compared to the emulsified fluid. DI water has more flowability in the MQL nozzle. It gives a more cooling effect, but less lubrication for reducing friction during turning leads to the formation of a high wear rate of tool and high cutting forces compared to other fluids. The minimum cutting force value obtained was 89 N for emulsified fluid when all parameters were at a low level (-1), and the maximum force obtained was 780 N for DI water.

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Figure 2. Actual cutting force values for different cutting fluids

3.1 Analysis of variance (ANOVA) of cutting force for different cutting fluids

Table 6 depicts the Anova for when DI water is used as a cutting fluid. The Prob> F is the probability of seeing the observed F value if the null hypothesis is true (there is no factor effect). Small probability values call for rejection of the null hypothesis. In the present model, the F-value of 989.00 implies that the model is significant. There is only a 0.01% chance that an F-value this large could occur due to noise. P-values less than 0.0500 indicate that the model is significant. This model shows A, B, C, AB, AC, BC, A², C² are significant model terms. Table 7 shows the significance level of factors Depth of Cut is the most Significant Factor, followed by Feed and Cutting Speed when DI Water is used as a cutting fluid.

Table 8 depicts the Anova for when Neat Cut Oil is used as a cutting fluid. In the present model, the F-value of 71.81 implies the model is significant. There is only a 0.01% chance that an F-value this large could occur due to noise. P- values less than 0.0500 indicate model terms are significant. In this case, B, C, AC, BC, A² are significant model terms. Table 9 shows that level of significance of factors Feed Rate is the most Significant Factor Followed by Depth of cut and Cutting Speed when Neat Cut Oil Used as a cutting fluid. Table 9 shows the ranking of input variables and found that feed rate (ranked I) and depth of cut (ranked II) influence significantly than speed.

Table 6. ANOVA for DI water cutting fluid

Table 7. Level of significance of factors for DI water cutting fluid

Table 8. ANOVA for Neat Cut oil cutting fluid

Table 9. Level of significance of factors for Neat Cut oil cutting fluid

Table 10. ANOVA for emulsified cutting fluid

Table 11. Level of significance of factors for emulsified cutting fluid

Table 10 depicts the Anova for when Emulsified Fluid used as a cutting fluid. In the present model, the F-value of 188.20 implies that the model is significant. There is only a 0.01% chance that an F-value this large could occur due to noise. P-values less than 0.0500 indicate model terms are significant. In this case, B, C, BC, A² are significant model terms. Table 11 shows that level of significance of factors Feed Rate is the most Significant Factor Followed by Depth of cut and Cutting Speed when Emulsified Used as a cutting fluid. Table 11 shows the ranking of input variables and found that feed rate (ranked I) and depth of cut (ranked II) influence significantly than speed.

3.2 Fit statistics for different cutting fluids

Table 12. R² values for different cutting fluids

The model Adequacies checked by analysis of variance technique. The R squared (R²) correlation coefficient measures the variation proportion in the data points ranging from -1 to +1. The value of R is close to 1 indicates that the model equation is significant. Table 12 shows the R² values for all cutting fluids; the Predicted R² is in reasonable agreement with the Adjusted R². The difference is that 0.2 Adeq Precision measures the signal-to-noise ratio. A ratio greater than 4 is desirable. The ratio Adeq Precision indicates an adequate signal for all three models.

3.3 Predicted and actual values

Evaluate the predicted values using multiple linear regression coded equations and compare them with actual values in Table 13.

Table 13. Predicted and actual values for cutting force of different cutting fluids

Figures 3, 4 & 5 shows that Predicted versus Actual cutting force for different cutting fluids with DI water as cutting fluid the cutting force are maximum for all experimental runs followed by neat cut oil and emulsified fluid. It is clearly observed that emulsified fluid is better cutting fluid than Neat cut oil and DI water. It is also observed that the predicted value of neat cut oil is very much similar to actual, and error is very minimal compared to DI water and Emulsified Fluid. In the case of DI Water, the cutting force is more than neat cut oil and Emulsified Fluid. Form this; it clears that using Emulsified Fluid, the cutting force value can be reduced to a maximum extent compared to DI water and neat cut oil.

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Figure 3. Predicted versus actual cutting force for deionized water

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Figure 4. Predicted versus actual cutting force for neat cut oil

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Figure 5. Predicted versus actual cutting force for emulsified fluid

We acknowledge the support rendered by the National Institute of Technology, Warangal-Telangana, India, for providing us an opportunity to conduct experimental work on the lathe and tool materials, measurement instruments, and all the necessary logistics as and when required.