A comparative study on performance of multilayer coated and uncoated carbide inserts when turning AISI D2 steel under dry environment

The present work deals with a comparative study on flank wear, surface roughness, tool life, volume of chip removal and economical feasibility in turning high carbon high chromium AISI D2 steel with multilayer MTCVD coated [TiN/TiCN/Al₂O₃/TiN] and uncoated carbide inserts under dry cutting environment. Higher micro hardness of TiN coated carbide samples (1880 HV) compared to uncoated carbide (1430 HV) is observed and depicts better resistance against abrasion. The low erosion rate was observed in TiN coated insert compared to uncoated carbide. The tool life of TiN coated insert is found to be approximately 30 times higher than the uncoated carbide insert under similar cutting conditions and produced lower surface roughness compared to uncoated carbide insert. The dominant wear mechanism was found to be abrasion and progression of wear was steady using multilayer TiN coated carbide insert. The developed regression model shows high determination coefficient i.e. R² = 0.977 for flank wear and 0.94 for surface roughness and accurately explains the relationship between the responses and the independent variable. The machining cost per part for uncoated carbide insert is found to be 10.5 times higher than the multilayer TiN coated carbide inserts. This indicates 90.5% cost savings using multilayer TiN coated inserts by the adoption of a cutting speed of 200 m/min coupled with a tool feed rate of 0.21 mm/rev and depth of cut of 0.4 mm. Thus, TiN coated carbide tools are capable of reducing machining costs and performs better than uncoated carbide inserts in machining D2 steel.     

Modeling and prediction for 3D surface topography in finish turning with conventional and wiper inserts

Wiper insert have the characteristics of achieving an excellent surface finish and improving the productivity in turning processes. Wiper insert can provide twice feed rate while maintaining the comparable surface roughness compared to that provided by the conventional insert. In the present study, surface topographies in finish turning with conventional and wiper inserts are investigated. The key element of this work is that the cutting edge path equation in the cutting tool coordinate system is transformed into the machine tool and workpiece coordinate system by the use of spatial coordinate transformation. Following that a surface topography simulation algorithm based on the cutting edge path equation and cutting parameters is put forward. The output of this work is that both the simulated surface topography and surface roughness profile are good agreement with the experimental results. Both the simulated and the actual machined surface results show that better surface topography is obtained in finish turning with the wiper insert than that with conventional insert. Burnishing effect of the wiper insert leads to half decrease of the Ra and Rz. The actual surface profiles are no longer regular wave shapes due to ploughing effect and side flow existing in the cutting zone. In addition, a surface roughness map has also been developed to optimize the selection of wiper radius and feed rate to satisfy the requirement of surface finishing with higher productivity. From the viewpoint of cutting tool design, the wiper radius with five times larger than tool nose radius can fully come into its role. This provides a novel insight into the design of wiper insert over conventional techniques. Above all, the proposed model gives a better prediction of surface roughness in finish turning process compared to the previous empirical and regression roughness models. The prediction of surface roughness in finish turning with wiper insert is also realized.     

Experimental investigations on machinability aspects in finish hard turning of AISI 4340 steel using uncoated and multilayer coated carbide inserts

The present work deals with some machinability studies on flank wear, surface roughness, chip morphology and cutting forces in finish hard turning of AISI 4340 steel using uncoated and multilayer TiN and ZrCN coated carbide inserts at higher cutting speed range. The process has also been justified economically for its effective application in hard turning. Experimental results revealed that multilayer TiN/TiCN/Al₂O₃/TiN coated insert performed better than uncoated and TiN/TiCN/Al₂O₃/ZrCN coated carbide insert being steady growth of flank wear and surface roughness. The tool life for TiN and ZrCN coated carbide inserts was found to be approximately 19 min and 8 min at the extreme cutting conditions tested. Uncoated carbide insert used to cut hardened steel fractured prematurely. Abrasion, chipping and catastrophic failure are the principal wear mechanisms observed during machining. The turning forces (cutting force, thrust force and feed force) are observed to be lower using multilayer coated carbide insert in hard turning compared to uncoated carbide insert. From 1st and 2nd order regression model, 2nd order model explains about 98.3% and 86.3% of the variability of responses (flank wear and surface roughness) in predicting new observations compared to 1st order model and indicates the better fitting of the model with the data for multilayer TiN coated carbide insert. For ZrCN coated carbide insert, 2nd order flank wear model fits well compared to surface roughness model as observed from ANOVA study. The savings in machining costs using multilayer TiN coated insert is 93.4% compared to uncoated carbide and 40% to ZrCN coated carbide inserts respectively in hard machining taking flank wear criteria of 0.3 mm. This shows the economical feasibility of utilizing multilayer TiN coated carbide insert in finish hard turning.     

Surface roughness measurement in turning carbon steel AISI 1045 using wiper inserts

Surface roughness of the workpiece is an important parameter in machining technology. Wiper inserts have emerged as a significantly class of cutting tools, which are increasingly being utilized in last years. This study considers the influence of the wiper inserts when compared with conventional inserts on the surface roughness obtained in turning. Experimental studies were carried out for the carbon steel AISI 1045 because of its great application in manufacturing industry. Surface roughness is represented by different amplitude parameters (R_a, R_zD, R_3z, R_q, R_t, R_a/R_q, R_q/R_t, R_a/R_t). With wiper inserts and high feed rate it is possible to obtain machined surfaces with R_a < 0.8 μm (micron). Consequently it is possible to get surface quality in workpiece of mechanics precision without cylindrical grinding operations.     

Performance studies of multilayer hard surface coatings (TiN/TiCN/Al2O3/TiN) of indexable carbide inserts in hard machining: Part-I (An experimental approach)

In recent years, hard machining using CBN and ceramic inserts became an emerging technology than traditional grinding and widely used manufacturing processes. However the relatively high cost factors associated with such tools has left a space to look for relatively low cost cutting tool materials to perform in an acceptable range. Multilayer coated carbide insert is the proposed alternative in the present study due to its low cost. Thus, an attempt has been made to have an extensive study on the machinability aspects such as flank wear, chip morphology, surface roughness in finish hard turning of AISI 4340 steel (HRC 47 ± 1) using multilayer coated carbide (TiN/TiCN/Al₂O₃/TiN) insert under dry environment. Parametric influences on turning forces are also analyzed. From the machinability study, abrasion and chipping are found to be the dominant wear mechanism in hard turning. Multilayer TiN coated carbide inserts produced better surface quality and within recommendable range of 1.6 μm i.e. comparable with cylindrical grinding. At extreme parametric conditions, the growth of tool wear was observed to be rapid thus surface quality affected adversely. The chip morphology study reveals a more favorable machining environment in dry machining using TiN coated carbide inserts. The cutting speed and feed are found to have the significant effect on the tool wear and surface roughness from ANOVA study. It is evident that, thrust force (Fy) is the largest component followed by tangential force (Fz) and the feed force (Fx) in finish hard turning. The observations yield the machining ability of multilayer TiN coated carbide inserts in hard turning of AISI 4340 steel even at higher cutting speeds.     

Performance studies of multilayer hard surface coatings (TiN/TiCN/Al2O3/TiN) of indexable carbide inserts in hard machining: Part-II (RSM,grey relational and techno economical approach)

This paper presents the mathematical modelling and parametric optimization on flank wear and surface roughness based on response surface methodology and grey-based Taguchi method in finish hard turning of AISI 4340 steel (HRC 47 ± 1) using multilayer coated carbide (TiN/TiCN/Al₂O₃/TiN) insert under dry environment. The economical feasibility of utilizing multilayer TiN coated carbide insert has been described. Model adequacy has been checked using correlation coefficients. From main effect, it is evident that, cutting speed is the most significant factor for flank wear followed by depth of cut and feed. Again, feed is the most significant factor for surface roughness followed by cutting speed and depth of cut. The coefficient of determination (R²) is more than 75% for RSM models developed, which shows the high correlation exist between the experimental and predicted values. The experimental vs. predicted values of flank wear and surface roughness (Ra and Rz) are also found to be very close to each other implying significance of models developed. The improvement of grey relational grade from initial parameter combination (d2–f3–v4) to the optimal parameter combination (d1–f1–v3) is found to be 0.3093 using grey relational analysis coupled with Taguchi method for simultaneous optimization of responses. Flank wear (VBc) and surface roughness parameters (Ra and Rz) are decreased 1.9, 2.32 and 1.5 times respectively considering optimal parametric combinations for multi-responses. The calculated total machining cost per part is only Rs. 3.17 due to higher tool life (47 min at their optimal level) of multilayer TiN coated carbide insert. It brings to the reduction of downtime and increases the savings.     

Surface morphology in engineering applications: Influence of roughness on sliding and wear in dry fretting

Influence of initial surface roughness on friction and wear processes under fretting conditions was investigated experimentally. Rough surfaces (Ra=0.15-2.52 μm) were prepared on two materials: carbon alloy (AISI 1034) and titanium alloy (Ti-6Al-4V). Strong influence of initial surface roughness on friction and wear processes is reported for both tested materials. Lower coefficient of friction and increase in wear rate was observed for rough surfaces. Wear activation energy is increasing for smoother surfaces. Lower initial roughness of surface subjected to gross slip fretting can delay activation of wear process and reduce wear rate; however, it can slightly increase the coefficient of friction.     

Performance of coated and uncoated mixed ceramic tools in hard turning process

The present contribution deals with the study of the effects of cutting speed, feed rate and depth of cut on the performance of machining which traditionally named “machinability”. The focus is made on the effect of the pre-cited cutting parameters on the evolution of surface roughness and cutting force components during hard turning of AISI D3 cold work tool steel with CC6050 and CC650 ceramic inserts. Also, for both ceramics a comparison of their wear evolution with time and its impact on the surface equality was proposed. The planning of experiments was based on Taguchi’s L₁₆ orthogonal array. The analysis of variance (ANOVA), the signal-to-noise ratio and response surface methodology (RSM) were adopted. Consequently, the validity of proposed linear regression model was checked and the most important parameter affecting the surface roughness and cutting force components were determined. Furthermore, in order to determine the levels of the cutting regime that lead to minimum surface roughness and minimum machining force the relationship between cutting factors was analyzed. The results revealed that the surface quality obtained with the coated CC6050 ceramic insert is 1.6 times better than the one obtained with uncoated CC650 ceramic insert. However, the uncoated ceramic insert was useful in reducing the machining force.     

Process investigation on meso-scale hard milling of ZrO2 by diamond coated tools

This paper investigates the feasible machining of zirconium oxide (ZrO₂) ceramics, in the hard state, via milling by diamond coated miniature tools (from here on briefly indicated as meso-scale hard milling). The workpiece material is a fully sintered yttria stabilized tetragonal zirconia polycrystalline ceramic (Y-TZP). Diamond coated WC mills, 2 mm in diameter, four flutes and large corner radius (0.5 mm) are chosen as cutting tools, and experiments are conducted on a state-of-the-art micro milling machine centre. The influence of cutting parameters, including axial depth of cut (a_p) and feed per tooth (f_z), on the achievable surface quality is studied by means of a one-factor variation experimental design. Further tests are also conducted to monitor the process performance, including surface roughness, tool wear and machining accuracy, over the machining time. Mirror quality surfaces, with average surface roughness Ra below 80 nm, are obtained on the machined samples; the SEM observations of the surface topography reveal a prevailing ductile cutting appearance. Tool wear initiates with delamination of the diamond coating and progresses with the wear of the WC substrate, with significant effect on the cutting process and its performance. Main applications of this research include three dimensional surface micro structuring and superior surface finishing.     

An experimental analysis and measurement of process performances in machining of nimonic C-263 super alloy

Nimonic C-263 alloy is extensively used in the fields of aerospace, gas turbine blades, power generators and heat exchangers because of its unique properties. However, the machining of this alloy is difficult due to low thermal conductivity and work hardening characteristics. This paper presents the experimental investigation and analysis of the machining parameters while turning the nimonic C-263 alloy, using whisker reinforced ceramic inserts. The experiments were designed using Taguchi’s experimental design. The parameters considered for the experiments are cutting speed, feed rate and depth of cut. Process performance indicators, viz., the cutting force, tool wear and surface finish were measured. An empirical model has been created for predicting the cutting force, flank wear and surface roughness through response surface methodology (RSM). The desirability function approach has been used for multi response optimization. The influence of the different parameters and their interactions on the cutting force, flank wear and surface roughness are also studied in detail and presented in this study. Based on the cutting force, flank wear and surface roughness, optimized machining conditions were observed in the region of 210 m/min cutting speed and 0.05 mm/rev feed rate and 0.50 mm depth of cut. The results were confirmed by conducting further confirmation tests.     

灰口铸铁面铣加工中修光刃磨损特性的研究

采用具有不同前角和表面处理形式的刀片,对HT250灰口铸铁进行了平面铣削试验。通过观察刀片修光刃处前后刀面的磨损状况,发现修光刃磨损可分为均匀磨损和刀尖破损导致的非均匀磨损两个阶段。结合对切削过程中刃口形貌变化规律的研究,分析了铸铁面铣过程中刀片几何形状、表面处理形式等因素对修光刃磨损特性的影响。     

Performance comparison of conventional and wiper ceramic inserts in hard turning through artificial neural network modeling

Hard turning with ceramic tools provides an alternative to grinding operation in machining high precision and hardened components. But, the main concerns are the cost of expensive tool materials and the effect of the process on machinability. The poor selection of cutting conditions may lead to excessive tool wear and increased surface roughness of workpiece. Hence, there is a need to investigate the effects of process parameters on machinability characteristics in hard turning. In this work, the influence of cutting speed, feed rate, and machining time on machinability aspects such as specific cutting force, surface roughness, and tool wear in AISI D2 cold work tool steel hard turning with three different ceramic inserts, namely, CC650, CC650WG, and GC6050WH has been studied. A multilayer feed-forward artificial neural network (ANN), trained using error back-propagation training algorithm has been employed for predicting the machinability. The input?Coutput patterns required for ANN training and testing are obtained from the turning experiments planned through full factorial design. The simulation results demonstrate the effectiveness of ANN models to analyze the effects of cutting conditions as well as to study the performance of conventional and wiper ceramic inserts on machinability.     

Application of Taguchi method for determining optimum surface roughness in turning of high-alloy white cast iron

This paper focused on optimizing the cutting conditions for the average surface roughness (R_a) obtained in machining of high-alloy white cast iron (Ni-Hard) at two different hardness levels (50 HRC and 62 HRC). Machining experiments were performed at the CNC lathe using ceramic and cubic boron nitride (CBN) cutting tools on Ni-Hard materials. Cutting speed, feed rate and depth of cut were chosen as the cutting parameters. Taguchi L₁₈ orthogonal array was used to design of experiment. Optimal cutting conditions was determined using the signal-to-noise (S/N) ratio which was calculated for R_a according to the “the-smaller-the-better” approach. The effects of the cutting parameters and tool materials on surface roughness were evaluated by the analysis of variance. The statistical analysis indicated that the parameters that have the biggest effect on R_a for Ni-Hard materials with 50 HRC and 62 HRC are the cutting speed and feed rate, respectively. Additionally, the optimum cutting conditions for the materials with 50 HRC and 62 HRC was found at different levels.     

Robust weighting applied to optimization of AISI H13 hardened-steel turning process with ceramic wiper tool: A diversity-based approach

A mixed ceramic is a type of cutting-tool material widely employed for machining hardened steels. The usage of a mixed ceramic along with a wiper geometry can help double the feed rate, thereby increasing productivity while keeping the surface roughness (Ra) as low as possible. Analyses of manufacturing processes, such as a machining process, show that the various possible controlled parameters can be modeled by multiobjective mathematical models to ensure their optimization. Hence, the aim of this study was optimize a hard turning process using a robust weighting based on diversity to choose the final Pareto optimal solution of the multiobjective problem. The responses of the material removal rate (MRR), Ra parameter, and cutting force (Fc) were modeled by using the response surface methodology; in this methodology, decision variables, such as the cutting speed (Vc), feed rate (f), and depth of cut (d), are employed. The diversity index, as a decision-making criterion, proved to be useful in mapping the regions of minimum variance within the Pareto optimal responses obtained in the optimization process. Hence, the study demonstrates that the weights used in the multiobjective optimization process influence the prediction variance of the obtained response.     

Pneumatic non-contact topography characterization of finish-ground surfaces using multivariate projection methods

This paper reports on the application of multivariate analysis methods for the non-contact topography assessment of finish-ground surfaces of roughness in the range of 0.1-0.8 μm Ra. The roughness information is extracted from the frequency spectrum of the back pressure signal acquired using a pneumatic gauge as the surface traverses past the nozzle. Principal components analysis is demonstrated to be effective in the unsupervised classification of lapped and ground surfaces of an identical nominal roughness of 0.1 μm Ra, even under conditions that the corresponding frequency spectra are contaminated with noise and affected by vibration. Projection to latent structures analyses are further shown to be capable of discriminating cylindrical ground surfaces based on along-the-lay measurements from a rotating component, and formulating multivariate regression models appropriate for process monitoring.     

Modeling and optimization of Al/SiCp MMC machining using Taguchi approach

This paper presents the influence of process parameters like cutting speed, feed and depth of cut on flank wear (VBc) and surface roughness (Ra) in turning Al/SiCp metal matrix composites using uncoated tungsten carbide insert under dry environment. The experiments have been conducted based on Taguchi’s L₉ orthogonal array. Abrasion and adhesion are observed to be the principal wear mechanism from images of tool tip. No premature tool failure by chipping and fracturing was observed and machining was steady using carbide insert. Built-up-edge formation is noticed at low and higher cutting speed and at high feed combination and consequently surface quality affected adversely. The optimal parametric combination for flank wear and surface roughness are found to be v1–f1–d3 and v3–f1–d3 respectively and is greatly improved through Taguchi approach. Mathematical models for flank wear and surface roughness are found to be statistically significant.     

Influence of tool wear on surface roughness in hard turning using differently shaped ceramic tools

Hard turning has been applied in many cases in producing bearings, gears, cams, shafts, axels, and other mechanical components since the early 1980s. Mixed ceramics (aluminum oxide plus TiC or TiCN) is one of the two cutting tool materials (apart from PCBN) widely used for finish machining of hardened steel (HRC 50–65) parts, especially under dry machining conditions and moderate cutting speed ranging from 90 to 120 m/min. This paper reports an extensive characterization of the surface roughness generated during hard turning (HT) operations performed with conventional and wiper ceramic tools at variable feed rate and its changes originated from tool wear. Moreover, it compares some predominant tool wear patterns produced on the two types of ceramic inserts and their influence on the alteration of surface profiles. After the hard turning tests, the relevant changes of surface profiles and surface roughness parameters were successively registered and measured by a stylus profilometer. In this investigation, a set of 2D surface roughness parameters, as well as profile and surface characteristics, such as the amplitude distribution functions, bearing area curves and symmetrical curves of geometrical contact obtained for the machined surface, were determined and analyzed. A novel aspect of this research is that the notch wear progress at the secondary cutting (trailing) edges was found to produce the substantial modifications of the individual irregularities, and constitute the altered surface profiles. Moreover, this research contributes to practical aspects of HT technology due to exploring the relations between the tool state at different times within the tool life and the relevant surface roughness characterization.     

On the prediction of surface roughness in the hard turning based on cutting parameters and tool vibrations

This research work concerns the elaboration of a surface roughness model in the case of hard turning by exploiting the response surface methodology (RSM). The main input parameters of this model are the cutting parameters such as cutting speed, feed rate, depth of cut and tool vibration in radial and in main cutting force directions. The machined material tested is the 42CrMo4 hardened steel by Al₂O₃/TiC mixed ceramic cutting tool under different conditions. The model is able to predict surface roughness of Ra and Rt using an experimental data when machining steels. The combined effects of cutting parameters and tool vibration on surface roughness were investigated while employing the analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of cutting parameters and tool vibration with respect to announced objectives which are the prediction of surface roughness. The adequacy of the model was verified when plotting the residuals values. The results indicate that the feed rate is the dominant factor affecting the surface roughness, whereas vibrations on both pre-cited directions have a low effect on it. Moreover, a good agreement was observed between the predicted and the experimental surface roughness. Optimal cutting condition and tool vibrations leading to the minimum surface roughness were highlighted.     

WEAR PERFORMANCE OF MULTILAYER-COATED CARBIDE TOOLS

Three multilayer-coated carbides [two trigon-shaped inserts: Ti(C,N)/TiC/Al₂O₃ (T1), Ti(C,N)/ Al₂O₃/TiN (T2) and one 80°-rhomboid shaped insert: TiC/Al₂O₃/TiN (T3)] were used to machine a martensitic stainless steel at various combinations of cutting speed and feed rate without coolant to assess their wear performance. Significant nose wear and chipping/fracture of the cutting edge were the predominant failure modes affecting tool performance at higher speed conditions. Plucking of tool materials was the main rake face wear phenomenon observed on T1 grade insert with alumina as the top-layer coating when machining at the lower speed conditions. Attrition and plastic flow were the main wear mechanisms observed on the ceramic coating layers, with dissolution-diffusion being the probable wear mechanism of the tool grades where tungsten carbide substrate had direct contact with the flowing chip. The fitted statistical wear models revealed T3 grade insert with 80°-rhomboid shape as having the highest speed-feed capability, resulting in the highest material removal rate relative to T1 and T2 grade inserts with trigon shapes.     

Turning titanium metal matrix composites (Ti-MMCs) with carbide and CBN inserts

Despite excellent mechanical and physical features of titanium metal matrix composite (Ti-MMC), hard and abrasive ceramic particles within the matrix structure, as well as high price, may lead to severe difficulties on machining and machinability of Ti-MMCs. Review of literature denotes that only limited studies are available on machining Ti-MMCs with commercial cutting tools under various cutting conditions and cutting tools/inserts. Furthermore, limited studies are available on machinability attributes of Ti-MMC under various cutting conditions used. Therefore, to remedy the lack of knowledge observed, this work intends to report turning Ti-MMCs with carbide, and cubic boron nitride (CBN) inserts under various cutting conditions. The mean values of surface roughness (R_a) and directional cutting forces, as well as flank wear (V_B) were studied as the machinability attributes. The microstructural evaluations were conducted to discover the wear modes. Furthermore, the statistical tools were used to present the factors governing machining attributes studied. Adhesion, abrasion, and oxidation were observed as the principle wear modes on the flank sides of the tested inserts. According to experimental results and statistical analysis, the R_a and V_B could be controlled by cutting parameters only when CBN inserts were used. Despite the inset used, factors governing both responses were not identical. Although average cutting forces were directly affected by cutting parameters used, however, the relatively low correlation of determination (R²) of directional cutting forces can be attributed to effects of cutting speed, elevated temperature in the cutting zone as well as rapid tool wear which are all correlated to others.