The study of wear of cutting tools of cBN-based composite material and the influence of tool wear on cutting forces in turning hardened steels

The paper presents some findings of the investigation of finish turning of KhVG hardened steel using a cutting tool with an insert made of a cubic boron nitride based composite (cBN-Si₃N₄ system). The behavior of tool wear throughout the machining time as well as the influence of the tool wear on cutting force components and resulting cutting force have been clarified.     

Experimental investigations on cryogenic cooling by liquid nitrogen in the end milling of hardened steel

Milling of hardened steel generates excessive heat during the chip formation process, which increases the temperature of cutting tool and accelerates tool wear. Application of conventional cutting fluid in milling process may not effectively control the heat generation also it has inherent health and environmental problems. To minimize health hazard and environmental problems caused by using conventional cutting fluid, a cryogenic cooling set up is developed to cool tool–chip interface using liquid nitrogen (LN₂). This paper presents results on the effect of LN₂ as a coolant on machinability of hardened AISI H13 tool steel for varying cutting speed in the range of 75–125 m/min during end milling with PVD TiAlN coated carbide inserts at a constant feed rate. The results show that machining with LN₂ lowers cutting temperature, tool flank wear, surface roughness and cutting forces as compared with dry and wet machining. With LN₂ cooling, it has been found that the cutting temperature was reduced by 57–60% and 37–42%; the tool flank wear was reduced by 29–34% and 10–12%; the surface roughness was decreased by 33–40% and 25–29% compared to dry and wet machining. The cutting forces also decreased moderately compared to dry and wet machining. This can be attributed to the fact that LN₂ machining provides better cooling and lubrication through substantial reduction in the cutting zone temperature.     

Studies on Machining Parameters While Milling Particle Reinforced Hybrid (Al6061/Al2O3/Gr) MMC

In this article, response surface methodology has been used for finding the optimal machining parameters values for cutting force, surface roughness, and tool wear while milling aluminum hybrid composites. In order to perform the experiment, various machining parameters such as feed, cutting speed, depth of cut, and weight (wt) fraction of alumina (Al₂O₃) were planned based on face-centered, central composite design. Stir casting method is used to fabricate the composites with various wt fractions (5%, 10%, and 15%) of Al₂O₃. The multiple regression analysis is used to develop mathematical models, and the models are tested using analysis of variance (ANOVA). Evaluation on the effects and interactions of the machining parameters on the cutting force, surface roughness, and tool wear was carried out using ANOVA. The developed models were used for multiple-response optimization by desirability function approach to determine the optimum machining parameters. The optimum machining parameters obtained from the experimental results showed that lower cutting force, surface roughness, and tool wear can be obtained by employing the combination of higher cutting speed, low feed, lower depth of cut, and higher wt fraction of alumina when face milling hybrid composites using polycrystalline diamond insert.     

Effects of geometric angle and cutting speed on cutting forces and tool wear of ceramic cutting tools during peripheral up-milling of high-density fiberboard

In this paper, cutting forces and tool wear of ceramic cutting tools are investigated by up-milling high-density fiberboard under different geometric angles and cutting speeds. The results show that tangential force (F_t) and normal force (F_r) decrease with the increase of rake angle. The values of F_t and F_r at the higher speed cutting condition are lower than that at the lower speed condition. The flank wear (VB) declines with increased clearance angle and decreased cutting speed. The tool wear patterns observed on the ceramic cutting tools are pull-out of grain, cracking, tipping, and flanking. Abrasive wear and adhesive wear are the main mechanisms of the ceramic cutting tools. In all, on the premise of guaranteeing the ceramic cutting tools’ strength, the ceramic cutting tool with a bigger rake angle and clearance angle is advisable in high-density fiberboard machining, in terms of lowering the energy consumption and production cost required for machining.     

Development of ANFIS model and machinability study on dry turning of cryo-treated PH stainless steel with various inserts

This present investigation deals about the machinability comparison of cryogenically treated 15-5 PH stainless steel with various cutting tools such as uncoated tungsten carbide, cryogenic-treated tungsten carbide and wiper geometry inserts. Cryo-treated PH stainless steel is considered as the work material in this investigation and experimental trials were performed under dry turning condition. The machinability aspects considered for evaluation are cutting force (F_z), surface roughness (R_a) and tool wear. The outcomes of experimentation reveal that the tungsten carbide inserts which are cryogenically treated provide improved performance in machining while comparing with conventional and wiper geometry inserts at all machining conditions. The measured cutting force and the observed flank wear were less for the cryo-treated inserts. However, wiper tool produces a better surface finish during machining. An artificial intelligence decision-making tool named Adaptive Neuro Fuzzy Inference System has been evolved to determine the relation among the considered input machining variables and output measures, namely cutting force and surface roughness of the machined surface. An analysis has been performed to compare the results obtained from developed models and experimental results.     

Investigation on performance of abrasive water jet in machining hybrid composites

For machining of composites, abrasive water jet machining is widely employed. For assembly of the machine tool structure, production of slots is essential. In this paper, abrasive water jet machining of composite laminates was experimentally investigated for various cutting parameters in terms of average surface roughness (R_a) and kerf taper (K_t). By generating a response surface model, the experimental values obtained for quality characteristics (R_a and K_t) were empirically related to cutting parameters. The effects of cutting parameters on quality characteristics were analyzed by utilizing empirical models and also optimized within the tested range based on desirability approach. The optimum parameter levels were also validated by confirmation test. From this investigation, it is evident that for obtaining a minimum kerf taper, traverse speed, water pressure, and abrasive mass flow rate are significant parameters and for obtaining less surface roughness traverse speed is the significant parameter.     

Effect of cryogenic CO2 and LN2 coolants in milling of aluminum alloy

The research work was carried out on the end milling of Al 6082-T6 alloy with cryogenic CO₂, LN₂ and wet conditions. The highest axial force (F_z), normal force (F_y) and feed force (F_x) values were recorded on cryogenic LN₂ machining. Use of cryogenic LN₂ helped to reduce the cutting temperatures up to 38.29% and 32.8% when compared with wet and cryogenic CO₂ conditions, respectively. The conventional fluid coolant offered a better surface roughness value (R_a) over cryogenic coolants at a feed rate of 0.015 and 0.02 mm/tooth and cutting speed of 100 m/min. The workpiece surface quality degraded in cryogenic machining conditions during the slot end milling operation of aluminum alloy under the given machining parameters.     

Micro-mechanical modeling of machining of FRP composites – Cutting force analysis

Orthogonal machining of unidirectional carbon fiber reinforced polymer (UD-CFRP) and glass fiber reinforced polymer (UD-GFRP) composites is simulated using finite element method (FEM). A two-phase micro-mechanical model with fiber assumed elastic and the matrix elasto-plastic is used to estimate the cutting forces during machining. A cohesive zone simulated the interface debonding between the fiber and matrix. Fiber failure was based on maximum principal stresses reaching the tensile strength. The matrix elastic modulus was degraded to include damage once yield strength was reached. The model assumes plane strain and quasi-static condition. The cutting forces during orthogonal machining were studied both experimentally and numerically for a range of fiber orientations (θ), depths of cut (t) and tool rake angles (γ). The contact forces developed between the tool and the fiber provided a good estimate of the cutting (F_h) and thrust (F_v) forces during the orthogonal cutting process. The failure of fiber is found to be a combination of crushing and bending, with the bending effect becoming more significant as the fiber orientation changes from 90° to 15°.     

Prediction of cutting speed interval of diamond-coated tools with residual stress

This article deals with finite element (FE) analysis incorporating deposition stress effects to determine the optimal cutting speed interval, V_interval, and evaluate the effects of cutting speed on the interface behavior of diamond-coated tools in machining of AA356-T6 aluminum alloy. A model for predicting the V_interval limited through the lower, V_lower, and upper, V_upper, cutting speeds is also presented. The results show that the deposition process causes high residual stress around the round edge on the coating side. When machining load corresponding to the speed interval is applied, the residual stress on the coating side is decreased at the V_upper.     

Investigation on Some Machinability Aspects of Inconel 825 During Dry Turning

In the current study, attempt has been made to investigate the influence of cutting speed (Vc) (51, 84, and 124 m/min) on various machining characteristics like chip morphology, chip thickness ratio, tool wear, surface, and sub-surface integrity during dry turning of Inconel 825. Comparable study was carried out using uncoated and commercially available chemical vapor deposition multilayer coated (TiN/TiCN/Al₂O₃/ZrCN) cemented carbide (ISO P30 grade) insert. Chip morphology consists of chip forms obtained at different cutting conditions. Serrated chips were observed when machining Inconel 825 with both types of tool with more serration in case of uncoated insert. The chip thickness ratio increased as cutting speed was increased. Use of multilayer coated tool also resulted in increase in chip thickness ratio. Rake and flank surfaces were examined with scanning electron microscope and optical microscope. Abrasion, adhesion, and diffusion wears were found to be dominating tool wear mechanism during dry machining of Inconel 825. The beneficial effect of coated tool over its uncoated counterpart was most prominent during machining at high cutting speed (Vc = 124 m/min). The surface and sub-surface integrity obtained with coated tool were superior to that while machining Inconel 825 with uncoated tool.     

Machinability studies on 17-4 PH stainless steel under cryogenic cooling environment

Under higher cutting conditions, machining of 17-4 precipitation hardenable stainless steel (PH SS) is a difficult task due to the high cutting temperatures as well as accumulation of chips at the machining zone, which causes tool damage and impairment of machined surface finish. Cryogenic machining is an efficient, eco-friendly manufacturing process. In the current work, cutting temperature, tool wear (flank wear (V_b) and rake wear), chip morphology, and surface integrity (surface topography, surface finish (R_a), white layer thickness (WLT)) were considered as investigative machinability characteristics under the cryogenic (liquid nitrogen), minimum quantity lubrication (MQL), wet and dry environments at varying cutting velocities while machining 17-4 PH SS. The results show that the maximum cutting temperature drop found in cryogenic machining was 72%, 62%, and 61%, respectively, in contrast to dry, wet, and MQL machining conditions. Similarly, the maximum tool wear reduction was found to be 60%, 55%, and 50% in cryogenic machining over the dry, wet, and MQL machining conditions, respectively. Among all the machining environments, better surface integrity was obtained by cryogenic machining, which could produce the functionally superior products.     

Integrated ANN–GA for estimating the minimum value for machining performance

In this study, we proposed a new approach in estimating a minimum value of machining performance. In this approach, artificial neural network (ANN) and genetic algorithm (GA) techniques were integrated in order to search for a set of optimal cutting condition points that leads to the minimum value of machining performance. Three machining cutting conditions for end milling operation that were considered in this study are speed (v), feed (f) and radial rake angle (γ). The considered machining performance is surface roughness (R _a). The minimum R _a value at the optimal v, f and γ points was expected from this approach. Using the proposed approach, named integrated ANN–GA, this study has proven that R _a can be estimated to be 0.139?µm, at the optimal cutting conditions of f?=?167.029?m/min, v?=?0.025?mm/tooth and γ?=?14.769°. Consequently, the ANN–GA integration system has reduced the R _a value at about 26.8%, 25.7%, 26.1% and 49.8%, compared to the experimental, regression, ANN and response surface method results, respectively. Compared to the conventional GA result, it was also found that integrated ANN–GA reduced the mean R _a value and the number of iterations in searching for the optimal result at about 0.61% and 23.9%, respectively.     

Werkzeugbeschichtungen für die Trockenbearbeitung

Tool coatings for dry machining During dry machining a strain collective consisting of mechanical, thermal, and chemical loads is imposed upon the cutting edge. Compared to conventional machining using cooling lubrication fluids, the loads are increased in dry cutting. A feasible solution to protect the cutting edge from thermal wear, abrasion, and tribo‐oxidation is the application of hard coatings. Newly developed Cr_xAl_yY_zN, Cr_xAl_yB_zN and Cr_xAl_ySi_zN PVD coatings were both evaluated in tribological model tests and machining tests concerning their suitability for dry cutting applications. Herein, the used coating technology and the coating properties are described in detail. The measured tool wear and the process forces give further hints for the optimization of the coating system.     

Experimental studies on the cryogenic machining of biodegradable ZK60 Mg alloy using micro-textured tools

Reducing the contact area between the cutting tool rake surface and chip promotes the machining performance of the work material and increases the tool life. Magnesium alloys are ductile-lightweight materials that form continuous chips during machining. The present investigation discusses the orthogonal turning of ZK60 magnesium alloy with linearly textured cutting inserts under both dry and liquid nitrogen (LN₂) cooling conditions. Linear grooves that are parallel and perpendicular to chip flow direction were created using Nd-YAG laser on the tungsten carbide cutting inserts. The effect of texturing combined with the application of LN₂ cooling is studied by evaluating the machining temperature and forces, microhardness, surface roughness and tool wear. Textured tools considerably minimize the liaison area of the chip with the rake plane compared to non-textured tools, which resulted in favorable effects in machinability. In case of cryogenic machining, textured tools substantially minimize the friction by the coupled effect of micro-pool lubrication and the formation of thin-film lubrication between the tool–chip/tool–work interfaces. Parallel-textured tools aided with cryogenic cooling exhibit superior performance during machining among the different types of tools employed in the present investigation.     

Single-point scratching of 6061 Al alloy reinforced by different ceramic particles

Aluminium alloys reinforced by ceramic particles have been widely used in aerospace and automotive industries for their high stiffness and wear resistance. However, the machining of such materials is difficult and would usually cause excessive tool wear. The effect of ceramic particles on the cutting mechanisms is also unclear. The purpose of this study is to investigate the cutting mechanisms and the relationship between specific energy of scratching and depth of cut (size effect). The single-point scratch test was carried out on 6061 Al and its composites reinforced by Al₂O₃ and SiC ceramic particles using a pyramid indenter. The results indicated that the scratch process was composed of rubbing, ploughing, plastic cutting and reinforcement fracture. A simple model was proposed to interpret the apparent size effect. The effect of reinforcement on the specific energy was correlated to the ratio of volume fraction to particle radius. The paper found that for machining MMCs, a larger depth of cut should be used to maintain a lower machining energy, especially for those with a larger ratio of volume fraction to particle radius.     

On Applicability of Multilayer Coated Tool in Dry Machining of Aerospace Grade Stainless Steel

The present research work has been undertaken with a view to investigate the influence of CVD multilayer coated (TiN/TiCN/Al₂O₃/ZrCN) and cutting speed on various machining characteristics such as chip morphology, tool wear, cutting temperature, and machined surface roughness during dry turning of 17-4 PH stainless steel. In order to understand the effectiveness of CVD multilayer coated tool a comparison has been carried out with that of uncoated carbide insert. The surface roughness and cutting temperature obtained during machining with chemical vapor deposition (CVD) multilayer coated tool was higher than that of uncoated carbide insert at all cutting velocity. However, the results clearly indicated that CVD multilayer coated tool played a significant role in restricting various modes of tool failure and reducing chip deformation compared to its uncoated counterpart. Adhesion and abrasion were found to be dominating wear mechanism with flank wear, plastic deformation, and catastrophic failure being major tool wear modes.     

AWJ machinability performance of CS/UPR composites with the effect of chemical treatment

This work focuses on the effect of chemical treatment of coconut sheath/unsaturated polyester (CS/UPR) composite on the performance of abrasive waterjet machining (AWJM). Two different chemical treatments, namely alkali (NaOH) and trichlorovinylsilane, were imposed on the CS fiber. Further, the induced compressive strength arising as a result of AWJM was studied along the radial and depth directions of the composite. Experimental results revealed significantly lower induced stress at all points compared to the ultimate stress of CS/UPR composites except the free-edge loading condition. The chemically treated composites also exhibited inconsistent results in the machining characteristics such as kerf taper angle (T_a) and surface roughness (R_a) under varying cutting conditions. However, no direct correlation was seen between interfacial adhesion and T_a and R_a of the cutting zone. The maximum decrease of 12% of T_a and 22% of R_a was found for silane-treated composites compared to the untreated ones. In addition, the composite failure mechanisms such as fiber pullout, fiber breakage, interfacial debonding, matrix failure, and voids were identified in the cutting surfaces through scanning electron microscopy analysis.     

Mechanical micro-drilling of nimonic 80A superalloy using uncoated and TiAlN-coated micro-drills

Micro-drilling is a complex mechanical machining process. Micro-drilling experiences an early tool damage which is a major drawback for nickel-based superalloy. This paper examines the wear condition on the micro-tool cutting edge, surface roughness of machined holes, and hole diameter analysis in micro-drilling of Nimonic 80A, using two types of micro-drills (uncoated and TiAlN coated) with 0.79?mm diameter. Micro-drilling tests, using cutting speed (V_c), feed rate (f_z), and the micro-drill diameter as experimental parameters were carried out to bring out the best optimized machining conditions in micro-drilling of Nimonic 80A. Wear on the tool cutting edge and burr height occurring at the entrance of drilled holes were measured at constant period to give the lastingness of micro-drill. Quality of holes were analyzed in terms of surface roughness inside the hole and the hole diameter after every five drilled holes. The result obtained from the above analysis showed that TiAlN-coated micro-drill performs way better than the uncoated micro-drill in terms of wear, surface roughness, hole quality, and burr. Thus, the above performed study gives the knowledge to select micro-tool for machining of Nimonic 80A which could be useful in the aerospace industry.     

The influence of lubrication on tribological properties of Si3iNi4/1045 steel sliding pairs

Compared with cermet cutting tools, ceramic cutting tools have much better thermal stability and higher hardness. Si₃N4-based composite ceramics have been used progressively more for machining cast iron at very high speed. However, they have been found to be unsuitable for machining steel. One of the factors influencing this difference in behaviour is thought to be serious chemical wear of the ceramic at the high temperatures reached at the cutting tools. Lubrication could reduce the friction and the high temperature of the cutting tool/workpiece contact zone. A simulation test was carried out on a pin-on-disc tribometer in order to investigate the effect of lubrication on the friction and wear of Si₃N₄/1045 steel sliding pairs; the effects of load and speed on friction and wear were also investigated. The results show that suitable lubrication could greatly reduce the friction coefficient and wear rate of Si₃N₄ ceramic. Scanning electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy were used for examinations of the worn surfaces. A wear mechanism of the Si₃N₄ ceramic in sliding contact with 1045 steel is proposed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Proposal of a concept of future oriented machine tools for advanced manufacturing systems

In order to satisfy the recent various consumers’?needs, an advanced manufacturing system will be required. So, the innovative concept of Future Oriented Machine Tools (FOMT), which consists of four function blocks to realize the advanced manufacturing system, is proposed. The four function blocks are Management, Prediction, Observation and Strategy, and intelligent manufacturing processes are realized by utilizing these function blocks. FOMT can make a significant contribution in four stages: design stage, production scheduling stage, machining stage and post-machining stage. In the design stage, the product information such as accuracy can be evaluated in CAD, considering the manufacturing ability concurrently. In the production scheduling stage, the product schedules can be generated automatically and flexibly for the various products. In the machining stage, cutting conditions adjusted autonomously according to the machining status and machining problems. In the post-machining stage, the machining know-how data are accumulated and stored for future production and human engineers. The feasibility of it, especially the machining stage, is discussed using the developed cutting process simulator called VMSim (virtual machining simulator) from the view points of cutting force, machining error and environmental burden (CO₂ emission).