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.     

Modeling of tool wear during hard turning with self-propelled rotary tools

In this paper, an attempt is made to evaluate the self-propelled rotary carbide tool performance during machining hardened steel. Although several models were developed and used to evaluate the tool wear in conventional tools, there were no attempts in open literature for modeling the progress of tool wear when using the self-propelled rotary tools. Flank wear model for self-propelled rotary cutting tools is developed based on the work-tool geometric interaction and the empirical function. A set of cutting tests were carried out on the AISI 4340 steel with hardness of 54–56 HRC under different cutting speeds and feeds. The progress of tool wear was recorded under different interval of time. A genetic algorithm was developed to identify the constants in the proposed model. The comparison of measured and predicted flank wear showed that the developed model is capable of predicting the rate of rotary tool flank wear progression.     

Wear maps for some uncoated cutting tools

The method of using maps and diagrams to present wear rates and wear mechanisms, as well as showing the relationships between them, has been applied to cutting tools. In this summary paper, wear maps obtained earlier for uncoated high-speed steel (HSS) cutting tools are presented together with maps for uncoated carbide cutting tools. Within the two-dimensional area of a wear map defined by two easily controlled machining parameters, namely feed rate and cutting speed, the rates of tool wear, and the wear mechanisms observed during actual dry turning operations, are displayed. The presence of safety zones and least-wear regimes in these maps suggests that it may be possible to optimise actual machining operations so that compromises between rates of material removal, for an acceptable level of productivity, and tool costs can be reached. The concept of using machining-regions maps for practical tool-wear minimisation during machining is also discussed.     

TURNING STUDIES OF DEEP CRYOGENIC TREATED P-40 TUNGSTEN CARBIDE CUTTING TOOL INSERTS – TECHNICAL COMMUNICATION

In the present work, coated tungsten carbide tool inserts of ISO P-40 grade were subjected to deep cryogenic treatment at ?176°C. Turning studies were conducted on AISI 1040 workpieces using both untreated and deep cryogenic treated tungsten carbide cutting tool inserts. The turning performance was evaluated in terms of flank wear of the cutting tool inserts, main cutting force and surface finish of the machined workpieces. The flank wear of deep cryogenic treated carbide tools was observed to be lower than that of untreated carbide tools in machining of AISI 1040 steel. The cutting force during machining of AISI 1040 steel was lower with the deep cryogenic treated carbide tools when compared with the untreated carbide tools. The surface finish produced on machined AISI 1040 steel workpieces was superior with the deep cryogenic treated carbide tools as compared to the untreated carbide tools.     

Experimental estimation and optimization of process parameters under minimum quantity lubrication and dry turning of AISI-4340 with different carbide inserts

An experimental study has been performed on AISI 4340 steel in this paper. The influence of approach angle, feed rate, cutting speed and depth of cut has been on cutting forces and tool tip temperature has been experimentally investigated. Before conducting experiments on the AISI 4340 steel work-piece, the chemical composition test, microstructure test were performed and hardness of the work-piece was improved by heat treatment. A total of 64 experiments each by two different coated carbide inserts (PVD and CVD-coated) were conducted on AISI-4340 steel under different environmental conditions (dry and MQL machining). During the experiments, approach angle, cutting speed, feed rate are varied to four levels and the depth of cut is kept constant to investigate the effect of the same on the three cutting forces component and the temperature variations on the tool-tip. It is observed that the main cutting force was largest among the three cutting force components in case of AISI 4340 steel turning and MQL machining show beneficial effects compared to dry machining.     

Some studies on hard turning of AISI 4340 steel using multilayer coated carbide tool

Hard turning with multilayer coated carbide tool has several benefits over grinding process such as, reduction of processing costs, increased productivities and improved material properties. The objective was to establish a correlation between cutting parameters such as cutting speed, feed rate and depth of cut with machining force, power, specific cutting force, tool wear and surface roughness on work piece. In the present study, performance of multilayer hard coatings (TiC/TiCN/Al₂O₃) on cemented carbide substrate using chemical vapor deposition (CVD) for machining of hardened AISI 4340 steel was evaluated. An attempt has been made to analyze the effects of process parameters on machinability aspects using Taguchi technique. Response surface plots are generated for the study of interaction effects of cutting conditions on machinability factors. The correlations were established by multiple linear regression models. The linear regression models were validated using confirmation tests. The analysis of the result revealed that, the optimal combination of low feed rate and low depth of cut with high cutting speed is beneficial for reducing machining force. Higher values of feed rates are necessary to minimize the specific cutting force. The machining power and cutting tool wear increases almost linearly with increase in cutting speed and feed rate. The combination of low feed rate and high cutting speed is necessary for minimizing the surface roughness. Abrasion was the principle wear mechanism observed at all the cutting conditions.     

Optimization of cutting tool properties through the development of alumina cermet

As a means of optimizing the wear resistance and the toughness of cutting tools, alumina cermet tools have been developed, characterized and tested at high cutting speeds. These tools combine the chemical stability afforded by metal oxides and the toughness imparted by metal binders. Alumina is bound to nickel through zirconia by reacting alumina with a Ni-Zr alloy. The wear properties of these tools were characterized by cutting heattreated AISI 4340 steel at speeds ranging from 3 to 15.2 m s^?1, feed rates of 0.13 – 0.28 mm rev^?1 and depths of cut of 1.27 – 2.54 mm. Tests indicate that its wear resistance is comparable with that of pure alumina tools but that its toughness is greater.     

An investigation on wear mechanism of high-speed turning of free-cutting steel AISI 1215 using uncoated and multi-layer coated tools

AISI 1215 is a new kind of green and non-toxic free-cutting steel with minimum environmental pollution and excellent machinability, which receives wide promotion, investigation, and application in manufacturing industries. In machining of AISI 1215 steel, tool wear has a close relation with the presence of manganese sulfide lubricant zone formed on the tool surface. In this work, with the aid of cutting temperature and tool Von Mises stress simulations, tool wear analysis on the uncoated and multi-layer (Al₂O₃/TiCN) coated carbide tools was performed in high-speed turning operation. Wear pattern and wear mechanisms were studied through the experimental results. The main findings showed that the uncoated tool suffered high cutting temperature and severe tool wear and was not conducive to form a manganese sulfide lubricant zone in the turning operation. In contrast, the multi-layer coated tool could form a manganese sulfide lubricant zone on the chip–tool contact area. The beneficial roles of the manganese sulfide lubricant zone formed on the coated tool surface can be summarized as lubrication and diffusion blocking. The main wear mechanisms of the uncoated tool were crater wear, oxidation wear, adhesive wear, and abrasive wear, whereas for the multi-layer coated tool, they were crater wear, adhesive wear, and abrasive wear.     

Effect of very high cutting speeds on shearing, cutting forces and roughness in dry turning of austenitic stainless steels

Behavior of austenitic stainless steels has been studied at very high cutting speeds. Turning tests were carried out using the AISI 303 austenitic stainless steel. In particular, the influence of cutting speed on tool wear, surface quality, cutting forces and chip geometry has been investigated. These parameters have been compared when performing machining at traditional cutting speeds (lower than 350?m/min) versus high cutting speeds. The analysis of results shows that the material undergoes a significant change in its behavior when machining at cutting speeds above 450?m/min, that favors the machining operation. The main component of cutting forces reaches a minimum value at this cutting speed. The SEM micrographs of the machined surfaces show how at the traditional cutting speeds the machined surfaces contain cavities, metal debris and feed marks with smeared material particles. Surfaces machined at high cutting speeds show evidence of material side flow, which is more evident at cutting speeds above 600?m/min. Tool wear is located at the tool nose radius for lower cutting speeds, whereas it slides toward the secondary edge when cutting speed increases. An analysis of chips indicates also an important decrement in chip thickness for cutting speeds above 450?m/min. This study concludes that there is an unexplored range of cutting speeds very interesting for high-performance machining. In this range, the behavior of stainless steels is very favorable although tool wear rate is also significant. Nevertheless, nowadays the cost of tool inserts can be considered as secondary when comparing to other operation costs, for instance the machine hourly cost for high-end multitasking machines.     

The performance of TiN-coated high speed steel tool inserts in turning

While it is well known that thin, hard coatings can reduce tool wear and improve tool life and productivity, there is still little consensus over the degree of advantage coated tools have over their uncoated counterparts. This paper compares the behaviour of titanium nitride- (TiN-) coated and uncoated high speed steel (HSS) tool inserts during turning. Wear maps describing the crater wear characteristics of these tools are used to show that the extent of tool wear reduction due to the coatings depends strongly on the cutting speed and feed rate. The maps also demonstrate that the benefits of TiN coatings on HSS tools may be easily realized over a wide range of machining conditions.     

Performance evaluation of CBN,coated carbide,cryogenically treated uncoated/coated carbide inserts in finish-turning of hardened steel

In the present work, the performance of cubic boron nitride (CBN) inserts was compared with coated carbide and cryogenically treated coated/uncoated carbide inserts in terms of flank wear, surface roughness, white layer formation, and microhardness variation under dry cutting conditions for finish turning of hardened AISI H11 steel (48–49 HRC). The flank wear of CBN tools was observed to be lower than that of other inserts, but the accumulated machining time for all the four edges of carbide inserts were nearer to or better than the PCBN inserts. Results showed that tool life of carbide inserts decreased at higher cutting speeds. The surface roughness achieved under all cutting conditions for coated-carbide-treated/untreated inserts was comparable with that achieved with CBN inserts and was below 1.6 μm. The white layer formation and microhardness variation is less while turning with cryogenically treated carbide inserts than the CBN and untreated carbide. At low to medium cutting speed and feed, the performance of carbide inserts was comparable with CBN both in terms of tool life and surface integrity.     

Wear Mechanism of Cemented Carbide Tool in High Speed Milling of Stainless Steel

Adhesion of cutting tool and chip often occurs when machining stainless steels with cemented carbide tools. Wear mechanism of cemented carbide tool in high speed milling of stainless steel 0Cr13Ni4 Mo was studied in this work. Machining tests on high speed milling of 0Cr13Ni4 Mo with a cemented carbide tool are conducted. The cutting force and cutting temperature are measured. The wear pattern is recorded and analyzed by high?speed camera, scanning electron microscope(SEM) and energy dispersive X?ray spectroscopy(EDS). It is found that adhesive wear was the dominant wear pattern causing tool failure. The process and microcosmic mechanism of the tool's adhesive wear are analyzed and discussed based on the experimental results. It is shown that adhesive wear of the tool occurs due to the wear of coating, the a nity of elements Fe and Co, and the grinding of workpiece materials to the tool material. The process of adhesive wear includes both microcosmic elements di usion and macroscopic cyclic process of adhe?sion, tearing and fracture.     

A comparative study of the tool–chip contact length in turning of two engineering alloys for a wide range of cutting speeds

Tool chip contact length is an important parameter in machining, as it provides an indication of the size of area of interaction between the hot chip and the tool surface and hence the interface heat transfer zone. Heat transfer and thermally activated wear modes usually dominate tool wear in the high speed machining of steels and machining of titanium alloys at most cutting speeds. In this study, existing models for the prediction of tool–chip contact length are reviewed and examined for their suitability in high speed machining of two widely used engineering alloys. Orthogonal turning tests for AISI 1045 steel and Ti6Al4V titanium alloy are conducted for a range of cutting speeds from conventional to high speeds. New contact length models are presented for both materials covering a wide range of cutting speeds. More significantly, these contact length models are appropriate for high speed machining where thermal loads significantly influence process performance. Additionally, the work discusses how the machinability of engineering materials influences the ability to predict contact length.     

Elliptical vibration cutting of hardened die steel with coated carbide tools

Elliptical vibration cutting of hardened die steel with coated carbide tools is examined in this research in order to achieve low-cost high-precision machining. Diamond coated tools are applied because of superior hardness of their polycrystalline diamond coating and its low manufacturing cost. TiN coated tools are also tested, since they are widely used for conventional machining of steels. Machinability of hardened die steel by the elliptical vibration cutting with coated carbide tools is discussed in three aspects in this study, i.e. transferability of cutting edge profile to cut surface, cutting force, and tool life. The transferability is evaluated quantitatively by calculating correlation coefficients of measured roughness profiles. It is clarified that the diamond coated tools have high transferability which leads to diffraction of light on the surface machined at micro-scale pick feed. Total cutting forces including ploughing components are measured at various feed rates, and then shearing components and ploughing components are separated utilizing linear regression. The measured results indicate, for example, that the all forces become considerably smaller only when elliptical vibration is applied to the TiN coated tool without cutting fluid. It is also found that this considerable reduction of forces interestingly corresponds to higher friction coefficient, which is identified from the ploughing components. Tool life tests are carried out by various machining methods, i.e. elliptical vibration/ordinary wet/dry cutting with diamond/TiN coated tools. The result shows, for example, that the flank wear is smallest in the wet elliptical vibration cutting with the diamond coated tool.     

Assessment of the machinability of Ti-6Al-4V alloy using the wear map approach

The high strength to density ratio of titanium alloys coupled with excellent corrosion resistance even at elevated temperatures make them ideal for aerospace applications. Moreover, the biocompatibility of titanium also enables its widespread use in the biomedical and food processing industries. However, the difficulty in machining titanium and its alloys along with the high cost of its extraction from ore form presents a major economic constraint. In the context of machining economics, the wear map approach is very useful in identifying the most suitable machining parameters over a feedrate–cutting velocity plane. To date, wear maps have only been prepared for the machining of ferrous alloys. In this article, a review of the machinability of Ti-6Al-4V alloy is presented with emphasis on comparing the wear performance of various tool materials. In addition, a new wear map for Ti-6Al-4V alloy is presented based on unified turning tests using H13A grade carbide inserts. This wear map can be used as a guide in the selection of cutting variables that ensure the least tool wear rates. This article contrasts the occurrence of a safety zone in the case of machining steels to that of an avoidance zone for Ti-6Al-4V alloy.     

Wear behaviour of alumina based ceramic cutting tools on machining steels

The advanced ceramic cutting tools have very good wear resistance, high refractoriness, good mechanical strength and hot hardness. Alumina based ceramic cutting tools have very high abrasion resistance and hot hardness. Chemically they are more stable than high-speed steels and carbides, thus having less tendency to adhere to metals during machining and less tendency to form built-up edge. This results in good surface finish and dimensional accuracy in machining steels. In this paper wear behaviour of alumina based ceramic cutting tools is investigated. The machining tests were conducted using SiC whisker reinforced alumina ceramic cutting tool and Ti[C,N] mixed alumina ceramic cutting tool on martensitic stainless steel-grade 410 and EN 24 steel work pieces. Flank wear in Ti[C,N] mixed alumina ceramic cutting tool is lower than that of the SiC whisker reinforced alumina cutting tool. SiC whisker reinforced alumina cutting tool exhibits poor crater wear resistance while machining. Notch wear in SiC whisker reinforced alumina cutting tool is lower than that of the Ti[C,N] mixed alumina ceramic cutting tool. The flank wear, crater wear and notch wear are higher on machining martensitic stainless steel than on machining hardened steel. In summary Ti[C,N] mixed alumina cutting tool performs better than SiC whisker reinforced alumina cutting tool on machining martensitic stainless steel.     

Tool vibration in internal turning of hardened steel using cBN tool

The machining of hardened materials with hardness over 45 HRC has been an alternative to grinding since the 1970s, with the commercial availability of cubic boron nitride (cBN) and ceramic tools. However, the low toughness of these types of tool materials makes them very sensitive to damages caused by vibrations, which are critical for operations like internal turning, where the tool resembles a cantilever beam and therefore is susceptible to large deflections. This work aims to contribute to the study of tool performance in internal turning of long holes in hardened AISI 4340 steel in finishing conditions. Different machining conditions, two different tool holders (steel and carbide), and several tool overhangs were tested. The surface finish, acceleration (vibration) signals, and tool wear of cBN inserts were evaluated. The results show that vibration and the material of the tool holder may play a secondary role in the surface finish for stable turning, but the use of carbide tool holders makes the process stable for longer tool overhangs. Moreover, when the cutting becomes unstable, surface roughness is increased severely.     

Wear behavior and cutting performance of nanostructured hard coatings on cemented carbide cutting tools in hard milling

The influence of nanolayer AlTiN/TiN and multilayer nanocomposite TiAlSiN/TiSiN/TiAlN hard coatings on the wear behavior and cutting performance of carbide cutting tools was investigated in face milling of hardened AISI O2 cold work tool steel (∼58 HRC) at dry conditions. Characterization of the coatings was performed using nanoindentation, scratch test, reciprocating multi-pass wear test. The chips forming during cutting process were also analyzed. Results showed that abrasive and oxidation wear are dominant tool failures. The nanolayer AlTiN/TiN coating gives the best adhesion to the substrate, the best wear resistance in machining and thus provides the longest lifetime with carbide inserts.     

Wear of AISI 4340 steel under boundary lubrication

Wear tests were conducted using AISI 4340 steel sliding on AISI 01 tool steel under boundary lubrication conditions. The AISI 4340 steel was heat treated to obtain different microstructures and hardness levels. The results indicated that the wear behavior depends on the heat treatment procedure. It was found that hardness alone cannot be used as a measure of wear and that the microstructure and other mechanical properties should also be used. Chemical reaction products containing phosphorus, sulfur and zinc were found on the wear surfaces lubricated with a fully formulated light oil containing zinc dithiophosphates. The chemically reacted film was nonuniform and consisted of patches 1–1500 μm in size. The larger patches were formed on the surface of steel with a pearlite-ferrite microstructure and resulted in a high wear rate. In contrast, the small patches and the thin blue and brown films were formed on the wear surface of tempered martensite steel and produced low wear rates.     

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.