Uncoated WC Research Articles

Influence of microstructure on wear behaviour of uncoated WC tools in turning of Alloy 718 and Waspaloy

The effect of grain size in wrought Alloy 718 and Waspaloy on the wear of cemented carbide tools was examined by measuring the progression of wear in a specific transverse turning operation. Work material with different microstructure was achieved through heat treatments of the material from a single batch, for each alloy. The worn cutting tools were analysed by means of scanning electron microscopy and X-ray microanalysis to study the wear mechanism. The grain size of the work material in relation to undeformed chip thickness is found to control the depth of cut (DOC) notch wear, which is the tool life limiting factor when machining the work material with large grain size. The adhesive wear is shown to dominate on the rake face, but this wear is not tool life limiting since the cladding of work material to the tool surface basically protects the tool from further wear. Concerning the flank wear, machining of Waspaloy is associated with less such wear than machining of Alloy 718 irrespective of grain size. The analysis shows that higher cutting forces and expected cutting resistance due to higher work to fracture cannot explain the difference in flank wear. Instead, from the analysis of the oxidized surface below the flank wear it is supposed that the difference in tribological conditions is an important factor for flank wear development.

Metallurgical and mechanical characteristics of cryogenically treated tungsten carbide (WC–Co)

This paper aims to present the metallurgical and mechanical characterization of cryogenically treated tungsten carbide (WC–Co) in terms of α-, β-, γ-, and η-phase particles and wear behavior, respectively. The specimens of commercially available uncoated WC–Co in the form of round turning inserts were procured and subjected to cryogenic treatment at two levels −110°C (shallow treatment) and −196°C (deep treatment) of temperature. The microstructures obtained after cryogenic treatments have been characterized with a prominence to comprehend the influence of cryogenic treatment on the nature, size, and distribution of α-, β-, γ-, and η-phase particles as compared to untreated specimen. The mechanical properties such as hardness and wear rate of the specimens have also been compared by performing Rockwell A hardness test and pin-on-disk wear test, respectively. Microstructures, hardness, wear rate, and analysis of worn surface divulge the underlying metallurgical mechanism responsible in improving mechanical properties of the WC–Co.

Wear evaluation of WC inserts coated with TiN/TiAlN multinanolayers

TiN/TiAlN multilayers were deposited by radio frequency, r.f., reactive magnetron sputtering by using titanium and aluminum targets with 10 cm diameter and 99.99% purity in an argon/nitrogen atmosphere, applying a substrate temperature of 300 oC. WC inserts were used as substrates to improve the mechanical and tribological properties of TiN/TiAlN multilayered coatings compared to other types of coatings like TiAlN monolayers and to manage greater efficiency of these coatings in different industrial applications, such as machining, and extrusion. Their physical, mechanical, and tribological characteristics were investigated, including cutting tests with AISI 4340 hardened steel (50 HRC) to assess wear as a function of the period and number of bilayers. A comparison of the properties of TiCN-Al2O3-TiN monolayers coatings and the [TiN/TiAlN]300 multilayers with individual layer thicknesses of 10 nm revealed a decrease of flank wear (around 33%) for [TiN/TiAlN]300 multilayers and a reduction of flank wear (around 13%) for coatings with 300 layers when is compared with [TiN/TiAlN]200 coatings. They also showed better machining properties onto hardened AISI 4340 steel pieces, when compared to uncoated WC inserts. These results open the possibility of using [TiN/TiAlN] multilayers as new coatings for tool machining with excellent industrial performance.

Finite element analysis of residual stresses in machining

Residual stresses play an important role in the service quality of a component. Therefore, it is essential to predict and control residual stresses on the machined surface and subsurface. The paper is focused on the numerical prediction of residual stresses in the orthogonal cutting process of a mild steel. An advanced approach to model heat transfer phenomena at the tool-chip interface was included in the numerical simulation. The FEM results were compared with some experimental data obtained turning AISI 1045 steel using uncoated WC tool.

Study on tribological behavior and cutting performance of CVD diamond and DLC films on Co-cemented tungsten carbide substrates

The tribological behaviors of diamond and diamond-like carbon (DLC) films play a major role on their machining and mechanical applications. In this study, diamond and diamond-like carbon (DLC) films are deposited on the cobalt cemented tungsten carbide (WC–Co) substrate respectively adopting the hot filament chemical vapor deposition (HFCVD) technique and the vacuum arc discharge with a graphite cathode, and their friction properties are evaluated on a reciprocating ball-on-plate tribometer with counterfaces of silicon nitride (Si 3N 4) ceramic, cemented tungsten carbide (WC) and ball-bearing steel materials, under the ambient air without lubricating condition. Moreover, to evaluate their cutting performance, comparative turning tests are conducted using the uncoated WC–Co and as-fabricated CVD diamond and DLC coated inserts, with glass fiber reinforced plastics (GFRP) composite materials as the workpiece. The as-deposited HFCVD diamond and DLC films are characterized with energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Raman spectroscopy and 3D surface topography based on white-light interferometry. Furthermore, Rocwell C indentation tests are conducted to evaluate the adhesion of HFCVD diamond and DLC films grown onto WC–Co substrates. SEM and 3D surface topography based on white-light interferometry are also used to investigate the worn region on the surfaces of diamond and DLC films. The friction tests suggest that the obtained friction coefficient curves that of various contacts exhibit similar evolution tendency. For a given counterface, DLC films present lower stable friction coefficients than HFCVD diamond films under the same sliding conditions. The cutting tests results indicate that flank wear of the HFCVD diamond coated insert is lower than that of DLC coated insert before diamond films peeling off.

Comparison of the machinabilities of Ti6Al4V and TIMETAL ® 54M using uncoated WC–Co tools

Single-point turning tests of cylindrical bars were undertaken to analyse and compare the machinability of Ti6Al4V, the most common titanium alloy, and TIMETAL ® 54M, a newly developed alloy with similar mechanical properties as Ti6Al4V but with better machinability. Conventional cooling and uncoated WC–Co tool inserts were used in the study, because they are the most recommended for machining these materials. The feed and the depth of cut were maintained constant, and only the cutting speed was varied because it is the most affecting parameter. Adhesion of workpiece material in the form of a built-up edge appeared in all the cutting inserts after machining both alloys, which was removed for flank- and crater-wear measurements. Lower wear rates were observed for the Ti54M alloy, especially at high cutting speeds. In the same manner, cutting-force measurements showed lower specific cutting- and feed-force values for the Ti54M alloy. Adiabatic shear bands, a typical feature in the machining of titanium alloys, were observed in chips from both alloys under all cutting conditions. Finally, scanning electron microscopy observations were carried out to analyse the adhered material on the cutting edges of the worn tools where signs of diffusion and attrition were detected.

Analyzing the performance of diamond-coated micro end mills

A method is presented to improve the tool life and cutting performance of 300 μm diameter tungsten carbide (WC) micro end mills by applying thin (<300 nm) fine-grained diamond (FGD) and nanocrystalline diamond (NCD) coatings using the hot-filament chemical vapor deposition (HF-CVD) process. The performance of the diamond-coated tools has been evaluated by comparing their performance in dry slot milling of 6061-T6 aluminum against uncoated WC micro end mills. Tool wear, coating integrity, and chip morphology were characterized using SEM and white light interferometry. The initial test results show a dramatic improvement in the tool integrity (i.e., corners not breaking off), a lower wear rate, no observable adhesion of aluminum to the diamond-coated tool, and a significant reduction in the cutting forces (>50%). Reduction of the cutting forces is attributed to the low friction and adhesion of the diamond coating. However, approximately 80% of the tools coated with the larger FGD coatings failed during testing due to delamination. Additional machining benefits were attained for the NCD films, which was obtained by using a higher nucleation density seeding process for diamond growth. This process allowed for thinner, smaller grained diamond coatings to be deposited on the micro end mills, and enabled continued operation of the tool even after the integrity of the diamond coating had been compromised. As opposed to the FGD-coated end mills, only 40% of the NCD-tools experienced delamination issues.

Study on fabrication and cutting performance of high quality diamond coated PCB milling tools with complicated geometries

The diamond film was deposited on a complex shaped WC–Co printed circuit board (PCB) milling tool in a revised hot filament chemical vapour deposition apparatus, in which the vertical spiral hot filament arrangement was adopted. The SEM investigation on the surface of the fabricated diamond coated PCB milling tool exhibited a continuous layer of fine grained diamond films, with grain size of about 2–3 μm, was uniformly deposited. To evaluate the cutting performance of the fabricated diamond coated tool, comparative milling tests were conducted for both diamond coated and uncoated WC–Co PCB milling tools, with glass fibre reinforced composite materials as the workpiece. The milling test results showed that the flank wear on circle and end cutting edge of the fabricated diamond coated PCB milling tool were only 0·08 and 0·18 mm respectively after 40 min milling, about one-fifth and a quarter of that for uncoated WC–Co PCB milling tool, which could attribute to both the good wear resistance of the deposited diamond coating and the strong adhesion between them and the tool surface. Additionally, the thrust forces acted on the milling tools during the milling process were measured using a Kistler dynamometer measuring system. The results presented that all measured axial, radial and tangential thrust forces were smaller for diamond coated PCB milling tool, which was due to the low friction coefficient of the diamond film that could facilitate the chip evacuation.

3D finite element analysis of tool wear in machining

The paper is focused on the 3D numerical prediction of tool wear in metal cutting operations. In particular, an analytical model, able to take into account the diffusive wear mechanism, was implemented through a specific subroutine. Furthermore, an advanced approach to model heat transfer phenomena at the tool–chip interface was included in the numerical simulation. The adopted simulation strategy gave the possibility to properly evaluate the tool wear. The 3D FEM results were compared with some experimental data obtained turning AISI 1045 steel using uncoated WC tool; a good agreement was found out.

Effectiveness of uncoated WC–Co and PCD inserts in end milling of titanium alloy—Ti–6Al–4V

Abstract Titanium and its alloys have found wide application in the aerospace, biomedical and automotive industries owing to their good strength-to-weight ratio and high corrosion resistance. However, these alloys have very poor machinability, which is attributed to their inherent high strength maintained at elevated temperature and low thermal conductivity leading to high cutting temperatures. Chips formed are serrated in nature as a result of a cycle of compression and adiabatic plastic shear phases in the chip formation process, causing high fluctuations of cutting force acting over a small chip tool contact area (about one-third that in the case of steel). High chemical reactivity of titanium at high-elevated temperatures, especially with titanium-based tools or coatings limits their application during machining. So the strategy of titanium machining is to use tools which show less reactivity, has higher thermal conductivity to increase the chip–tool contact length and effectively take away the generated heat and to use tougher and harder tools grades which could withstand the dynamic action of the cutting force. The recommended tools for many years had been the uncoated tungsten carbide grade K. But these tools cannot be used at high cutting speed since they too fail due to dynamic normal component of cutting force that acts on the very small contact area of the tool and high cutting temperature, leading to intensive diffusion and superficial plastic deformation, causing catastrophic failure of the tool. In this work, the effectiveness of polycrystalline diamond inserts (PCD) has been compared to that of uncoated tungsten carbide–cobalt inserts in machining titanium alloy Ti–6Al–4V. The comparison has been made with respect to the applicable cutting speed ranges, metal removal per tool life and tool wear rates, tool wear morphology, surface finish, chip segmentation and chatter phenomena.

Investigating the machinability of tool steels in turning operations

In this work a series of test were conducted in order to determine the machinability of tool steels. In these test the effects of tool material, type of coating on the insert (for coated tools) and the cutting parameters that affect the machinability were taken into considerations. The cutting force data used in the analyses were gathered by a tool breakage detection system that detects the variations of the cutting forces measured by a three-dimensional force dynamometer. The workpiece materials used in the experiments are cold work tool steel, AISI O2 (90 MnCrV8); hot work tool steel, AISI H10 (X32CrMo33) and mould steel, AISI improved 420 (X42Cr13). The cutting tools used are HSS tools, uncoated WC and coated TiAlN and TiC + TiCN + TiN inserts (ISO P25). The type of inserts is DNMG 150608. No cutting fluid was used during the turning operations. During the experiments cutting forces, flank wear and surface roughness values were measured throughout the tool life and the machining performance of tool steels were compared.

Optimisation of surface roughness with GA approach in turning 15% SiC&lt;SUB align=right&gt;p reinforced AlSi7Mg2 MMC material

In this study, 15% SiCP reinforced Metal Matrix Composite (MMC) AlSi7Mg2 material was turned by an uncoated WC cutting tool (K10) at cutting speeds of 50, 100 and 150 m/min, feed rates of 0.1, 0.2 and 0.3 mm/rev and depths of cut of 0.5, 1 and 1.5 and surface roughness values have been examined after each workpiece machined. A mathematical expression was derived by means of regression analysis method using the results obtained from the experiments performed under these conditions. Then, with the help of this expression, optimum turning parameters for minimum surface roughness were found via Genetic Algorithm (GA).

Determination of the optimum TiN coating thickness on WC inserts for machining carbon steels

Developing coated cemented carbide inserts exhibiting enhanced wear performance has been of major interest for the cutting tool industry in recent years. This study evaluates the influence of titanium nitride (TiN) coating thickness deposited by the physical vapor deposition (PVD) technique on the machining performance of cemented carbide inserts. TiN coatings with thickness ranging from 1.75 to 7.5μm were deposited onto CNMG 432 cemented carbide inserts (6% Co). Coating adhesion was assessed using the Rockwell indentation method, while coating thickness was determined using scanning electron microscopy (SEM) and optical profilometry. The glancing angle X-ray diffraction (XRD) technique using Cu Kα radiation was used to determine the influence of coating thickness on peak intensity. The intensity of the (111) peak was found to increase with increase in TiN coating thickness. The influence of TiN coating thickness on the machining performance of the WC inserts was evaluated by dry external cylindrical turning of AISI 1040 carbon steel.Based on these tests, the TiN coating with thickness of 3.5μm was found to exhibit the best turning performance on the WC inserts. For these coatings a minimum of a 40-fold increase in tool life in comparison to the uncoated WC tool was recorded during dry machining using the specified turning parameters. The inferior performance of the thicker coatings is due to their higher levels of compressive stress resulting in coating failure due to chipping of the coating at the cutting edge exposing the WC substrate.

Performance and characterisation of CVD diamond coated, sintered diamond and WC–Co cutting tools for dental and micromachining applications

Diamond coatings are attractive for cutting processes due to their high hardness, low friction coefficient, excellent wear resistance and chemical inertness. The application of diamond coatings on cemented tungsten carbide (WC–Co) tools was the subject of much attention in recent years in order to improve cutting performance and tool life. WC–Co tools containing 6% Co and 94% WC substrate with an average grain size 1–3 μm were used in this study. In order to improve the adhesion between diamond and WC substrates, it is necessary to etch away the surface Co and prepare the surface for subsequent diamond growth. Hot filament chemical vapour deposition with a modified vertical filament arrangement has been employed for the deposition of diamond films. Diamond film quality and purity have been characterised using scanning electron microscopy and micro-Raman spectroscopy. The performance of diamond coated WC–Co bur, uncoated WC–Co bur, and diamond embedded (sintered) bur have been compared by drilling a series of holes into various materials such as human teeth, borosilicate glass and porcelain teeth. Flank wear has been used to assess the wear rates of the tools. The materials subjected to cutting processes have been examined to assess the quality of the finish. Diamond coated WC–Co microdrills and uncoated microdrills were also tested on aluminium alloys. Results show that there was a 300% improvement when the drills were coated with diamond compared to the uncoated tools.

Performance and characterisation of CVD diamond coated, sintered diamond and WC–Co cutting tools for dental and micromachining applications

Diamond coatings are attractive for cutting processes due to their high hardness, low friction coefficient, excellent wear resistance and chemical inertness. The application of diamond coatings on cemented tungsten carbide (WC–Co) tools was the subject of much attention in recent years in order to improve cutting performance and tool life. WC–Co tools containing 6% Co and 94% WC substrate with an average grain size 1–3 μm were used in this study. In order to improve the adhesion between diamond and WC substrates, it is necessary to etch away the surface Co and prepare the surface for subsequent diamond growth. Hot filament chemical vapour deposition with a modified vertical filament arrangement has been employed for the deposition of diamond films. Diamond film quality and purity have been characterised using scanning electron microscopy and micro-Raman spectroscopy. The performance of diamond coated WC–Co bur, uncoated WC–Co bur, and diamond embedded (sintered) bur have been compared by drilling a series of holes into various materials such as human teeth, borosilicate glass and porcelain teeth. Flank wear has been used to assess the wear rates of the tools. The materials subjected to cutting processes have been examined to assess the quality of the finish. Diamond coated WC–Co microdrills and uncoated microdrills were also tested on aluminium alloys. Results show that there was a 300% improvement when the drills were coated with diamond compared to the uncoated tools.

On the performance and application of CrN coating

Two sets of experiments, cylinder-on-plate reciprocating wear tests and milling tests, were carried out to evaluate the performance of CrN coating layers on ferrous metals. Micro-hardness, adhesion and phases within the coating layers were also studied. The results were compared with uncoated and TiN-coated WC specimens. The experimental results show that the CrN-coated WC specimens exhibited good wear performance on wear testing, but performed poorly on milling, even poorer than the uncoated material. The main difference between these two sets of experimental results was due to the chemical affinity of Cr for Fe and the difference in the forces acting in the tests. There is detailed discussion in the report, and a fracture mechanism for the CrN-coated tungsten carbide (WC) insert in the milling of ferrous metal is proposed.