Experimental investigation on flank wear and tool life, cost analysis and mathematical model in turning hardened steel using coated carbide inserts

Turning hardened component with PCBN and ceramic inserts have been extensively used recently and replaces traditional grinding operation. The use of inexpensive multilayer coated carbide insert in hard turning is lacking and hence there is a need to investigate the potential and applicability of such tools in turning hardened steels. An attempt has been made in this paper to have a study on turning hardened AISI 4340 steel (47 ± 1 HRC) using coated carbide inserts (TiN/TiCN/Al2O3/ZrCN) under dry environment. The aim is to assess the tool life of inserts and evolution of flank wear with successive machining time. From experimental investigations, the gradual growth of flank wear for multilayer coated insert indicates steady machining without any premature tool failure by chipping or fracturing. Abrasion is found to be the dominant wear mechanisms in hard turning. Tool life of multilayer coated carbide inserts has been found to be 31 minute and machining cost per part is Rs.3.64 only under parametric conditions chosen i.e. v = 90 m/min, f = 0.05 mm/rev and d = 0.5 mm. The mathematical model shows high determination coefficient, R2 (99%) and fits the actual data well. The predicted flank wear has been found to lie very close to the experimental value at 95% confidence level. This shows the potential and effectiveness of multilayer coated carbide insert used in hard turning applications

Performance evaluation of PCBN, coated carbide and mixed ceramic inserts in finish-turning of AISI D2 steel

The present study compares the performance of three different cutting tools, viz., PCBN, mixed ceramic and coated carbide tool in finish turning of hardened D2 tool steel in terms of tool wear, surface roughness, and economic feasibility under dry cutting conditions. Results showed that tool life of PCBN inserts was better than mixed ceramic and coated carbide inserts. The flank wear of PCBN tools was observed to be lower than mixed ceramic and coated carbide inserts. The surface roughness achieved under all cutting conditions for mixed ceramic and coated-carbide inserts was comparable with that achieved with PCBN inserts and was below 1.6μm. Experimental results showed that the wear mechanism of ceramic tool is pre-dominantly abrasive wear at lower speeds and abrasive wear followed by adhesive wear at medium and higher speeds and for PCBN tools the dominant wear mechanism is abrasive wear and cratering at lower speeds followed by adhesive wear at higher speeds. For carbide tool the dominant wear mechanism was abrasive wear and cratering at lower speeds followed by adhesion and chipping at higher speeds. Obtained results revealed that PCBN tools can outperform both ceramic and carbide tools in terms of tool life under different machinability criteria used

Modelling and verification of TiO2/ZnO/EGW nano coolant on the tin milling tool performance

Surface roughness, tool life and wear mechanism plays major role for optimizing tool performance in machining process. Introducing nanoparticles into coolant has been proved to improve the optimization of the tool performance. This research has conducted to study the effect of nano particle based coolant (TiO2/EGW) and hybrid nano particle based coolant (TiO2/ZnO/EGW) on the Titanium Nitrate (TiN) tool enhancement. The linear model equation of surface roughness and tool life are developed using response surface methodology (RSM). From the RSM the most significant parameter is feed rate then axial depth of cut and lastly cutting speed. The end-milling operation by using hybrid nano particle based coolant (TiO2/ZnO/EGW) obtains lower surface roughness and high tool life. End-milling operation by using nano particle based coolant (TiO2/EGW) and water soluble coolant (EGW). Hybrid nano particle based coolant (TiO2/ZnO/EGW) lower the surface roughness 38% than EGW and 17% than TiO2/EGW. According to ISO 8688-2-1989 (E) the wear criteria for milling with water soluble coolant reached at average of cutting distance of 885 mm. Cutting distance for milling with nano particle based coolant (TiO2/EGW) performed better at distance of 55.55% to reach the wear criteria at average cutting distance of 1450 mm. Meanwhile for the cutting distance for milling with hybrid nano particle based coolant (TiO2/ZnO/EGW) perform better at 80% to reach the wear criteria at average cutting distance of 1585 mm. Hybrid nanofluid and single nanofluid’s thermal conductivity higher than EGW 13% and 11%.Hybrid nanofluid and single nanofluid specific heat capacity higher than EGW about 30% and 22%. The models between cutting parameters and response for surface roughness and tool life have been established. For surface roughness the error for the predicted value vs the actual value is 7%. Meanwhile for tool life the error for the predicted value vs the actual value is 11%. High cutting speed, low feed rate and low axial depth will provide fine surface roughness. Low cutting speed and Low feed rate will increase the tool life. The multi objective optimization for the parameters has been established. Where the optimum cutting speed= 2166 rpm, Feedrate = 0.02 mm/tooth and axial depth of cut = 0.1 mm which produces tool life = 37.07 min and surface roughness = 0.1452 μm. The desirability is nearly 1 (0.713), and it satisfy the goal of the optimization

Performance of coolant strategies when turning hardened martensitic stainless steel using tialn coated carbide tool

Coolant strategies in turning hardened stainless steel are important, due to the fact that heat cannot be removed efficiently from the cutting area. This heat issue shortens the tool life and reduces machined surface integrity, resulting in higher machining cost and lower productivity. Conventional cutting fluids cause health problems, workshop pollution and higher recycling cost. Dry, minimum quantity lubricant (MQL) and cryogenic machining are alternatives of green coolant to eliminate conventional cutting fluids. Thus, the objective of this research is to study the feasibility and performance of using new green coolant strategies that contribute to the sustainable process. Experiments were carried out in two different stages when turning 48 ±1 HRC martensitic stainless steel (AlSI420) uses a wiper PVD-TiAIN coated carbide cutting tool. Cutting speeds (l00, 135, and 170 m/min) and feed rates (0.16, 0.2, and 0.24 mm/rev) were investigated. The depth of cut was kept constant at 0.2 mm. Nitrogen gas pressure was 0.5 MPa and the oil mist (castor oil) flow rate was 40 ml/h. In the first stage, comparison between three cutting conditions were evaluated, namely cold nitrogen gas (cold N2), nitrogen gas with oil mist (N2+MQL) and cold nitrogen gas with oil mist conditions (cold N2+MQL). Dry cutting was used as the benchmark. In the second stage, the best cutting condition from first stage was used for further experiments to investigate the effect of cutting speed and feed on machining responses such as tool life (TL), volume of material removed (VMR), surface roughness (Ra) and cutting forces (Fx, Fy and Fz), chip morphology and microstructures of machined surface. Full factorial design was used to model the relationship between cutting responses (tool life, surface roughness, and cutting forces) and different cutting speeds and feed rates. These models were verified by performing confirmation experiments. The results obtained showed that cold N2+ MQL improved performance in terms of tool life, surface roughness and cutting forces in comparison to dry, cold N2, and N2+MQL conditions. At cutting speed of 100 m/min and feed rate of 0.16 mm/rev, cold N2+MQL condition prolongs the tool life by 135%, decreases the cutting forces by 18%, and improves surface roughness by 19% as compared to dry cutting. Flank and crater were observed at the tool nose. Abrasion and adhesion were the dominant wear mechanisms when turning hardened martensitic stainless steel. The machined surface had less alteration of grain microstructure and higher hardness in cold N2+MQL condition compared to the dry cutting condition. The longest tool life was obtained at low cutting speed and low feed rate, whereas lower cutting forces and better surface roughness were observed at high speed and low feed rate. Analysis based on the mathematical models of machining responses (tool life, surface roughness and cutting forces) would be helpful in selecting cutting variables for optimization of turning hardened stainless steel, which is in line with sustainable and green machining by using cold N2+MQL condition

Hard turning of martensitic AISI 440B stainless steel

Hard turning has been in use for some time to achieve close dimensional tolerances to eliminate time consuming and costly grinding operations. The most widely used cutting tools for finish machining of hardened steels under dry cutting conditions are the ceramics and PcBN cutting tools. The purpose of this study was to investigate the machinability of hardened martensitic AISI 440 B stainless steel (HRC 42-44) using commercially available cutting tools: alumina based ceramic and PcBN, by hard turning under different machining conditions, by providing an in-depth understanding of wear mechanisms of these cutting tools. The study also developed a serrated chip formation mechanism of the workpiece and provided a deep understanding of the chemical interaction between workpiece and cBN cutting tools, through microstructural analysis of the adhered layer on the worn cutting tool. Experimental studies on the effects of cutting parameters on the tool wear mechanism, cutting forces; surface roughness, dimensional accuracy, and chip formation mechanism were investigated. The characterization of the workpiece, cutting tools, chips and wear scars on the cutting tools was performed using an X-ray diffractometer, and optical, scanning and transmission electron microscopes, as well as an energy dispersive spectroscope (EDS). The cutting speeds selected for testing the cutting tools were in the range of 100 m/min and 600 m/min, depending on the type of parameter investigated. Two depths of cut, 0.1and 0.2 mm, and three feed rates, 0.05, 0.1 and 0.15 rev/min, were selected for the experiments. Experimental results showed that the flank wear in the PcBN cutting tool is lower than that of the mixed alumina, with PcBN showing better wear resistance at all cutting conditions (about five times longer in some instances). Apart from the cutting speed, the feed rate was found as a parameter that directly influences the flank wear rate of the cutting tool. The wear mechanism for the ceramic cutting tool is predominantly abrasive wear, and for PcBN tools it was adhesive wear and abrasive wear. The abrasive wear was caused by hard carbide particles in the workpiece material resulting in grooves formed on the flank face. There was formation of a transferred layer followed by plastic deformation of the workpiece material on the rake face of the PcBN tool when cutting at low cutting speed and feed rate. At much higher cutting speeds, some form of chemical wear preceded by adhesion and abrasion was the main tool wear resulting from the chemical affinity between the PcBN tool and the workpiece. Better surface finish (Ra) was recorded for mixed ceramics but with deteriorating surface topography. The increase in the cutting speed results for improvement in the surface finish produced by both cutting tools was investigated. The final part, using the PcBN cutting tool, produced better dimensional accuracy resulting from its better wear resistance at the flank face. The results also show that good dimensional accuracy can be achieved with cBN tools using a CNC machine with high static and dimensional stiffness coupled with high precision hard turning. The influence of cutting conditions on the chip formation showed production of continuous chip at a cutting speed of 100 m/min and segmented chip at higher cutting speeds above 200 m/min by both cutting tools. The increasing cutting speed affects the formation of shear localised chips with rapid increase in shear strain rate and degree of segmentation at cutting speeds higher than 200 m/min. The microstructure of the chip produced shows the distinct carbide grain in the martensite of the work material with intense shear localisation in the primary deformation zone of the cutting tool and formation of white layer in the secondary deformation zone. The microstructure of the crater of the worn PcBN cutting tool at cutting speeds of 100 m/min and 600 m/min were studied in detail. A situ lift-out technique, in a Focused Ion Beam/SEM instrument, was used to produce thin foil specimens, which were taken out of the crater face of the PcBN tool and observed using SEM and TEM. The SEM and TEM study showed evidence of chemical interaction between the work material and the PcBN tool. Fe from the work material was found in the vicinity of TiC and AlB grains of the PcBN tool, with TiC having greater affinity for Fe. Oxidation of the elements was common in all Fe-rich areas. The microstructure of the worn PcBN cutting tool at the cutting speed of 600 m/min showed deeper penetration of Cr and Fe into the cBN tool, which was not easily detected by SEM at the cutting speed of 100 m/min. The hard turning operations using the PcBN cutting tool for substituting traditional machining operations was successfully performed in the industrial environment. The overall surface finish and dimensional accuracy generated during the application of CBN-100 for machining within the industrial environment on specified mass produced shape showed a component acceptable tolerance range with good surface finish similar to that of the grinding operation

ENHANCEMENT OF TOOL-LIFE OF HARD TURNING PROCESS VIA CRYOGENIC COOLANT AND MICROPATTERNED INSERT

Department of Mechanical EngineeringHigh hardness and high strength of materials are essential for advanced engineering applications to guarantee the safety and durability of the manufactured products. The hard turning process enables the machining of hardened materials which makes it one of the most widely used operation in automobile and heavy machinery industries. However, the problem with the hard turning is extreme machining conditions such as high cutting force and temperature generation leading to accelerated tool wear. Cubic boron nitride (CBN) is the essential insert of the hard turning operations. However, due to the higher production cost of CBN cutting tool, its performance should be maximized to achieve the higher machining and economic efficiency. The cryogenic liquids were mainly applied to machining of difficult-to-cut materials. The cryogenic liquids such as liquid nitrogen and carbon dioxide have been used as the cutting fluids to remove the heat generated in the cutting zone. Furthermore, some researchers have found that the textured (or patterned) functional surfaces can improve the frictional and tribological conditions between the two contacting surfaces. Hence, a proper development of the textured surfaces on the cutting tool can enhance the machining performances in the hard turning process. This dissertation presents a framework for the development of a numerical model and experimental investigations for enhancing the performance of the hard turning process using a cryogenic coolant and micropatterned tool. The first of this research presents the developed cutting model based on the modified Oxley???s theory. The cooling effects of cryogenic coolant were included in the model by implementing the proper heat transfer coefficient. Thermal effects generated in the primary and secondary zones were also modeled using the moving heat source technique. The model provides the predictions of cutting force, temperatures and tool wear, which were validated by experimental works. It was found that the use of LN2 coolant can reduce the effect of thermal softening in secondary deformation zone, which in turn increases the cutting forces. However, the cryogenic cooling mainly contributed the decrease in the diffusive and abrasive wear mechanisms to the improvement of tool life. The tool wear of CBN cutting tool was reduced by 20~34% in cryogenic cooling condition as compared to dry condition. Furthermore, finite element method (FEM) simulations were used to analyze the various pattern geometries and dimensions of micropatterned inserts. The simulation results showed that the micopatterned tool can decrease the stress distribution, force, and friction in the tool-chip interfaces. When the perpendicular and parallel type micropatterned tool having 100 ????m edge distance, 100 ????m pitch size and 50 ????m in height was used, the force and the friction was reduced by 6% and 25%, respectively. The experiments were conducted using micropatterned tool for the hard turning process and the variations in the chip morphology, cutting force, friction, and tool wear were analyzed. The results showed that the micropatterned tool was able to reduce the forces by 18.7%, friction by 34.3% and tool wear by 11.4% within the given ranges of experimental conditions. The model and the experimental findings of this research can be beneficial for the enhancing efficiency of the hard turning processes used in different industries. The techniques developed in this work can be further extended to see its applicability in other cutting operations such as drilling and milling.ope

Comparative evaluation of surface quality, tool wear, and specific cutting energy for wiper and conventional carbide inserts in hard turning of aisi 4340 alloy steel

This paper presents an experimental study into the comparative response of wiper and round-nose conventional carbide inserts coated with TiCN + AL$_{2}$O$_{3}$ + TiN when turning an AISI 4340 steel alloy. The optimal process parameters, as identified by pre-experiments, were used for both types of inserts to determine the machined surface quality, tool wear, and specific cutting energy for different cutting lengths. The wiper inserts provided a substantial improvement in the attainable surface quality compared with the results obtained using conventional inserts under optimal cutting conditions for the entire range of the machined lengths. In addition, the conventional inserts showed a dramatic increase in roughness with an increased length of the cut, while the wiper inserts showed only a minor increase for the same length of cut. A scanning electron microscope was used to examine the wear for both types of inserts. Conventional inserts showed higher trends for both the average and maximum flank wear with cutting length compared to the wiper inserts, except for lengths of 200–400 mm, where conventional inserts showed less average flank wear. A higher accumulation of deposited chips was observed on the flank face of the wiper inserts than the conventional inserts. The experimental results demonstrated that edge chipping was the chief tool wear mechanism on the rake face for both types of insert, with more edge chipping observed in the case of the conventional inserts than the wiper inserts, with negligible evidence of crater wear in either case. The wiper inserts were shown to have a higher specific cutting energy than those detected with conventional inserts. This was attributed to (i) the irregular nose feature of the wiper inserts differing from the simpler round nose geometry of the conventional inserts and (ii) a higher tendency of chip accumulation on the wiper inserts

Analysis of tool vibration and surface roughness with tool wear progression in hard turning: An experimental and statistical approach

The machined surface quality and dimensional accuracy obtained during hard turning is prominently gets affected due to tool wear and cutting tool vibrations. With this view, the results of tool wear progression on surface quality and acceleration amplitude is presented while machining AISI 52100 hard steel. Central Composite Rotatable Design (CCRD) is employed to develop experimental plan. The results reported that vibration signals sensed in a tangential direction (Vz) are most sensitive and found higher than the vibrations in the feed direction (Vx) and depth of cut direction (Vy). The acceleration signals in all three directions are observed to increase with the advancement of tool wear and good surface finish is observed as tool wear progresses up-to 0.136mm. The vibration amplitude is discovered high in the range 3 kHz – 10 kHz within selected cutting parameter range (cutting speed 60-180mm/min, feed 0.1-0.5mm/rev, depth of cut 0.1-0.5mm). The investigation is extended for the development of multiple regression models with regression coefficients value 0.9. These models found statically significant and give dependable estimates between a tool vibrations and cutting parameters