Face milling of the EN AB-43300 aluminum alloy by PVD- and CVD-coated cemented carbide inserts

Two commercially available WC-6Co cemented carbide substrates (Extramet EMT100 and Pramet H10), were industrially coated with PVD TiB₂ or CVD diamond. Subsequently, the coated inserts were submitted to dry sliding tests (slider on cylinder contact geometry) against the aluminum alloy EN AB-43300, for preliminary performance ranking and identification of basic wear mechanisms. The best substrate/coating combination (CVD-Diamond coated Extramet EMT100) was then tested in face milling EN AB-43300 with milling tool characterized by two different geometries (A and B), using PCD inserts as a reference for comparison. In milling tests, the influence of both insert geometry and cutting fluid feed rate were taken into account. The geometry of the tool was identified as the main parameter in influencing the tool performance. In particular, in the case of the A geometry, the relative flank wear of CVD coated tools increased abruptly during the test due coating detachment, whilst with the B geometry no catastrophic failure of the CVD coated insert was observed. The influence of Cutting Fluid Feed Rate (CFFR) also changed with tool geometry: in particular, with the B geometry, which allowed to obtain the best results with the CVD coated inserts, a decrease of CFFR from 100 to 25% did not affect significantly the wear resistance of CVD-coated inserts and allowed to maintain the roughness of the workpiece (R_a) below 0.6 μm, notwithstanding a slightly increased tendency towards the formation of Al-based transfer layers.     

Cutting performance of multilayer diamond coated silicon nitride inserts in machining aluminum–silicon alloy

Aluminum–silicon (Al–Si) alloy is very difficult to machine and diamond tools are considered by far the best choice for the machining of these materials. Experimental results in the machining of the Al–Si alloy with diamond coated inserts are presented. Considering the fact that high adhesive strength and fine surface morphology play an importance role in the applications of chemical vapor deposition (CVD) diamond films, multilayer technique combining the hot filament CVD (HFCVD) method is proposed, by which multilayer diamond-coating on silicon nitride inserts is obtained, microcrystalline diamond (MCD)/ nanocrystalline diamond (NCD) film. Also, the conventional monolayer NCD and MCD coated inserts are produced for comparison. The as-deposited diamond films are characterized by field emission scanning electron microscopy (FE-SEM) and Raman spectrum. All the CVD diamond coated inserts and uncoated insert endure the aluminum-silicon alloy turning to estimate their cutting performances. Among all the tested inserts, the MCD/NCD coated insert exhibits the perfect behavior as tool wear due to its very low flank wear and no diamond peeling.     

抛光涂层硬质合金刀片加工钛合金的耐用度分析

目的提高涂层硬质合金刀具加工钛合金的切削性能及加工效率。方法采用化学机械抛光(Chemical Mechanical Polishing,CMP)对经过磨削加工的YG8硬质合金车削刀片前刀面进行抛光预处理,并使用CVD与PVD涂层工艺制备涂层。运用单因素试验法,对抛光涂层硬质合金刀片进行切削TC4钛合金的刀片耐用度试验,分析钛合金加工过程中刀具种类及切削参数变化对刀片耐用度的影响规律。采用扫描电子显微镜(SEM)和能谱仪(EDS)分析刀片的磨损机理。结果经过化学机械抛光处理后,硬质合金刀片的平均粗糙度由87 nm降低为19 nm,降低幅度达78.2%。相同切削参数时,抛光CVD硬质合金刀片的耐用度最大程度上比磨削CVD硬质合金刀片提高了75%,抛光PVD硬质合金刀片的耐用度最大程度上比磨削PVD硬质合金刀片提高了8.3%。可见采用化学机械抛光对硬质合金刀片进行加工是提高刀片表面平整度及耐用度的重要途径。结论抛光CVD硬质合金刀片的耐用度优于磨削CVD硬质合金刀片,抛光PVD硬质合金刀片的耐用度优于磨削PVD硬质合金刀片。     

Investigations on the effects of multi-layered coated inserts in machining Ti-6Al-4V alloy with experiments and finite element simulations

This paper presents investigations on turning Ti-6Al-4V alloy with multi-layer coated inserts. Turning of Ti-6Al-4V using uncoated, TiAlN coated, and TiAlN + cBN coated single and multi-layer coated tungsten carbide inserts is conducted, forces and tool wear are measured. 3D finite element modelling is utilized to predict chip formation, forces, temperatures and tool wear on these inserts. Modified material models with strain softening effect are developed to simulate chip formation with finite element analysis and investigate temperature fields for coated inserts. Predicted forces and tool wear contours are compared with experiments. The temperature distributions and tool wear contours demonstrate some advantages of coated insert designs.     

Analysis of tool wear and residual stress of CVD diamond coated cemented carbide tools in the machining of aluminium silicon alloys

Aluminium alloys have found increasing applications in the automotive and aeronautical industries in recent years. Due to their extraordinary properties however, the machining of these alloys still poses difficulties, and requires the optimized combination of cutting tool material and geometry. The potential of CVD diamond coated carbide tools has been demonstrated in recent years, however tool wear and short tool life remain as issues to be resolved. Key to increasing the tool life of CVD diamond coated tools is the further development of the coating process to optimize the coating adhesion. An understanding of the substrate and coating residual stress profiles must be gained in order to achieve this. Compressive residual stresses in cutting tools can lead to a higher crack resistance, but also to early coating delamination and tool failure. To analyze the influence of residual stresses on the coating quality and tool life, the residual stress profiles of tungsten carbide substrates and CVD diamond coatings were measured using X-ray and synchrotron radiation. The influence of the tungsten carbide substrate type and the CVD diamond coating process on the residual stress profiles was thus determined. In order to analyze the performance of the coated tools and the influence of the residual stresses on the tool lifetime, machining tests were performed with two aluminium silicon alloys. The tool wear, tool lifetime and workpiece quality were examined. Finally, many of the commonly used wear tests used to analyze the wear resistance of tool coatings cannot be implemented for CVD diamond coatings due to their high hardness. An impact test was therefore constructed to allow the determination of the wear resistance of CVD diamond tools.     

Influence of melt treatments and turning inserts on cutting force and surface integrity in turning of Al-12Si and Al-12Si-3Cu cast alloys

The microstructures, machinability and surface characteristics of Al-12Si and Al-12Si-3Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al-12Si-3Cu alloys have microstructures consisting of uniformly distributed α-Al dendrites, eutectic Al-silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts (un-coated, PVD and Polished CVD diamond coated) were evaluated in machining Al-12Si and Al-12Si-3Cu cast alloys under dry environment using a lathe. The Polished CVD diamond coated insert outperformed the un-coated or PVD-coated cutting inserts which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The Polished CVD diamond coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of grain refinement, modification and combined action of both on the microstrutural changes in the Al-12Si and Al-12Si-3Cu cast alloys and their machinability and surface finish when different turning inserts used.     

Experimental investigation on tool wear characteristics of PVD and CVD coatings during face milling of Ti6242S and Ti-555 titanium alloys

Ti6242S and Ti-555, as two typical titanium alloys, are often used to manufacture high-temperature aeroengine parts and landing gear components, respectively. They have different chemical composition and microstructure, which make them have different mechanical properties, and also affect their machinability. In this paper, face milling experiments were carried out to evaluate the wear performance by using CVD-Ti(C, N) + Al₂O₃ + TiN, PVD-(Ti, Al)N + TiN coated and uncoated tools. The results show that Ti-555 has the worse machinability than that of Ti6242S. When milling Ti6242S, all tools suffered adhesive wear and diffusion wear; the wear of Ti(C, N) + Al₂O₃ + TiN coated tool was more serious than that of other tools due to the blunt cutting edge; (Ti, Al)N + TiN coated tool suffered micro chipping and coating peeling with the minimal wear loss. When milling Ti-555, uncoated tool suffered serious chipping, abrasive wear and adhesive wear; Ti(C, N) + Al₂O₃ + TiN coated tool suffered serious chipping and coating peeling with short tool life; (Ti, Al)N + TiN coated tool suffered coating peeling, adhesive wear and diffusion wear. Overall, (Ti, Al)N + TiN coated tools have the longest tool life and are preferred for face milling of Ti6242S and Ti-555 titanium alloys.     

Temperature of internally-cooled diamond-coated tools for dry-cutting titanium

The role of cutting fluids is well known for the importance of removing heat from the cutting edge, lubricating the sliding chip contact and transporting the metal chips away from the cutting zone. Dry machining leads to increased cutting temperatures and higher wear rates resulting in shorter tool life; this is particularly evident in the cutting of high strength materials. Diamond coated cutting inserts are not usually considered for machining titanium due to rapid oxidation of the coating at the temperatures typical of titanium machining. This paper examines the formation of hot-spots on the rake face during dry and near-dry turning of titanium using conventional cemented carbide inserts. Machining performance is assessed by measurement of tool wear and tool life. Trials with an internally cooled tool with a specially designed, diamond coated insert have shown that the heat from the cutting operation can be rapidly diffused over the entire surface of the insert and thus successfully drawn away from the tool via closed loop recirculation of coolant through the tool holder. This enables wear to be inhibited by management of rake face temperature to keep it below the critical temperatures at which these prominent wear mechanisms operate. Measurements of change in coolant temperature before and after circulation are used to quantify the heat removed from the cutting process. The low friction coefficient and high thermal conductivity of diamond, assisted by the indirect cooling, results in longer tool life whilst maintaining high standards of surface finish.     

Brittleness and fatigue effect of mono- and multi-layer PVD films on the cutting performance of coated cemented carbide inserts

The effect of brittleness and fatigue of mono- and multi-layer PVD films on coated tools cutting performance is introduced. Cemented carbide inserts were coated to the same overall film thickness with various numbers of layers. Nanoindentations were conducted to evaluate the hardness of the diverse coating structures. The film brittleness and fatigue were characterized by nano- and macro-impact tests respectively. The coated inserts’ wear behaviour was investigated in milling hardened steel. The attained results revealed the coatings’ brittleness and fatigue endurance enhancement by increasing the number of film's layers. This increase leads simultaneously to the coated tool life improvement.     

Bias voltage optimum adjustment considering coatings’ strength and adhesion requirements when cutting various steels

PVD coatings were deposited at various bias voltages on cemented carbide inserts. The coating’s mechanical properties, fatigue and adhesion were determined via FEM-supported evaluation of nanoindentation, perpendicular and inclined impact test results. The coated inserts were applied in milling hardened and normalized steel. For explaining the wear evolution based on the cutting loads and stress fields developed in the coating and its substrate, FEM calculations were performed considering among others the films’ strength and adhesion. According to the workpiece properties, certain coating’s parameters become prevailing for the tool life. These depend on the bias voltage and facilitate its optimum adjustment.     

Tool wear and machining performance of cBN–TiN coated carbide inserts and PCBN compact inserts in turning AISI 4340 hardened steel

PCBN is the dominant tool material for hard turning applications due to its high hardness, high wear resistance, and high thermal stability. However, the inflexibility of fabricating PCBN inserts with complex tool geometries and the prohibitive cost of PCBN inserts are some of the concerns in furthering the implementation of CBN based materials for hard turning. In this paper, we present the results of a thorough investigation of cBN plus TiN (cBN–TiN) composite-coated, commercial grade, carbide inserts (CNMA 432, WC–Co (6% Co)) for hard turning applications in an effort to address these concerns. The effect of cutting speed and feed rate on tool wear (tool life), surface roughness, and cutting forces of the cBN–TiN coated carbide inserts was experimented and analyzed using analysis of variance (ANOVA) technique, and the cutting conditions for their maximum tool life were evaluated. The tool wear, surface roughness, and cutting forces of the cBN–TiN coated and commercially available PCBN tipped inserts were compared under similar cutting conditions. Both flank wear and crater wear were observed. The flank wear is mainly due to abrasive actions of the martensite present in the hardened AISI 4340 alloy. The crater wear of the cBN–TiN coated inserts is less than that of the PCBN inserts because of the lubricity of TiN capping layer on the cBN–TiN coating. The coated CNMA 432 inserts produce a good surface finish (<1.6 μm) and yield a tool life of about 18 min per cutting edge. In addition, cost analysis based on total machining cost per part was performed for the comparison of the economic viability between the cBN–TiN coated and PCBN inserts.     

Inclined impact–sliding wear tests of TiN/Al2O3/TiCN coatings on cemented carbide substrates

A chemical vapor deposition (CVD) TiN/Al₂O₃/TiCN coating has been commercially used as a protective coating on cemented carbide cutting tools to improve tool life and superficial quality of the workpiece. However, the CVD coating is relatively brittle and could fail due to fatigue cracking induced wear under localized contact stresses during the milling operation. Traditional coating evaluation techniques such as tribo tests, scratch tests and impact tests only involve single movement, i.e., either sliding or impacting. In the present work, the fatigue and wear behavior of the triple-layered coatings on cemented carbide substrates was investigated using a novel impact–sliding wear tester, which simulates a repetitive movement of combined impact and sliding motions between cutting tools and workpieces during interrupted milling operations. The coatings on the surface and cross-section were studied using Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) analysis. The results from the impact component showed that fatigue cracking increased for the coating on a harder substrate likely due to the lower toughness of the substrate. The results from the sliding component showed that the wear resistance of the coating decreased as the substrate was softer. The test results provided constructive knowledge in selection and development of coatings for impact and sliding involved applications.     

Roughing,semi-finishing and finishing of laser surface modified nickel bonded NbC and WC inserts for grey cast iron (GCI) face-milling

An attempt to improve the machining performance of NbC-Ni cutting inserts by rapid pulse electric current sintering (PECS), TiC and Mo₂C additions and laser surface modification (LSM) was done. Use of a nickel binder and additions TiC and Mo₂C to liquid phase sintered (LPS) NbC based samples led to comparable hardness (>13 GPa) and K_IC (~10 MPa.m^1/2) to LPS WC-Co/Ni samples. The laser surface modification (LSM) technique produced a ~2.5 μm thick self-carbide coating, increasing the surface hardness of all the samples. Laser surface modification was done to improve abrasion and attrition wear resistance. Face-milling of grade 17 grey cast iron (BS 1452/GG35) was conducted at 100–500 m/min cutting speeds (v_c) and 0.25–1.5 mm depths of cut (a_p). The insert wear was measured after every pass, and analyzed by annular dark field scanning transmission electron microscopy (ADF-STEM). During roughing, WC-Co based inserts had the lowest flank wear rate (FWR) values, with the WC-10Co (LPS) insert having a FWR of 10.15 μm/min after 20 min cutting time. However, during semi-finishing and finishing, NbC-4TiC-12Ni (PECS) and NbC-4Mo₂C-4TiC-12Ni (PECS) inserts had the lowest FWR values, showing up to six times longer tool life than the WC-Co (LPS) inserts based inserts and 12 times longer life than the WC-Ni based inserts. Generally, LSM improved the NbC inserts' tool life, reducing the FWR values in all NbC based inserts in all cutting tests.     

Model of quality management of hard coatings on ceramic cutting tools

For the development and introduction of new coated cutting tools (i.e. new combinations of cutting materials and hard coatings), it is necessary to carry out a number of studies with the purpose of optimizing the coatings composition and processing procedures, and also to test new tools under working conditions. The aim of this paper is to establish a common model for environmentally oriented quality management in the use and development of coated ceramic cutting tools with new coating systems. The paper also presents an investigation of the results of tribological and cutting properties of the coatings deposited with the PVD and CVD techniques on cutting inserts made from (Al₂O₃ + TiC) tool ceramics. Tests were carried out on ceramic inserts, uncoated and PVD or CVD-coated, with gradient, mono-, multi- (nano) layers and multicomponent hard wear resistant coatings composed of TiN, Ti(C, N), (Ti, Al)N, (Ti, AlSi)N and Al₂O₃ layers.     

Increasing tool life by adjusting the milling cutting conditions according to PVD films’ properties

The coated tools cutting performance in up and down milling depends significantly on the PVD film material properties. The related wear mechanisms at various cutting speeds can be sufficiently explained considering the developed tool loads and the non-linear coating impact resistance versus temperature. Various PVD coated cemented carbide inserts were tested at different cutting conditions. The corresponding cutting loads and temperatures were determined by FEM simulations and the films’ impact resistance by impact tests. A correlation between the impact resistance and the cutting performance at corresponding temperatures contributed to the optimum adjustment of the cutting parameters to the film properties.     

MILLING PERFORMANCE OF COATED INSERTS WITH VARIABLE COATING THICKNESS ON THEIR RAKE AND FLANK

During the Physical Vapour Deposition of coatings, the orientation of cemented carbides insert surfaces to the plasma flux direction affects the occurring film thickness distribution on the rake and flank, which in turn might influence the wear propagation in cutting processes. In the present paper the cutting performance in milling of PVD coated cemented carbides inserts with variable film thickness on the rake and flank is introduced and with the aid of FEM-supported calculations explained. The investigation results revealed that a thicker film on the tool rake in comparison to the existing one on the flank and moreover a thick and uniformly deposited film in the cutting wedge region significantly enhances the cutting performance in milling.     

Influence of tool edge preparation on performance of ceramic tool inserts when hard turning

Coating, as a form of tool edge preparation, changes the properties, geometry and roughness of the active parts of tool inserts. The performance of both uncoated and coated ceramics was tested in machining tests and the results were related to the tool edge and the machined surface as well as cost indices. The presented results show that tool edge preparation by coating does affect forces, tool wear and the machined surface, while friction force from scratch tests and the coating thickness and its hardness have been identified as being relevant to the results of machining tests. The relationship between the thickness of the surface layer and residual stress at the surface due to coating has been evaluated. Though the tool life of coated ceramics is shorter than that of cubic boron nitride, tool edge preparation by coating contributes to the reduction in machining costs due to the application of higher cutting speeds.     

High bandwidth temperature measurement in interrupted cutting of difficult to machine materials

High-speed milling is used across industries from aerospace to electronics. Tool wear can be affected by cutting interruptions in milling that lower tool-chip interface temperatures but also cause thermal and stress cycling. Micro-thermal imaging was used to determine the temperature during interrupted cutting of titanium alloy Ti6Al4V and AISI 4140 steel for percentage of time-in-cut from 100% to 10%. TiAlN/TiN coated carbide milling inserts were used with cutting speeds up to 180 and 640 m min⁻¹. This technique is the first to allow spatial mapping of thermal fluctuations on the tool which may be critical to determining causes for tool failure.     

Investigating the correlation between nano-impact fracture resistance and hardness/modulus ratio from nanoindentation at 25-500 °C and the fracture resistance and lifetime of cutting tools with Ti1−xAlxN (x = 0.5 and 0.67) PVD coatings in milling operations

A novel laboratory technique, nano-impact testing, has been used to test Ti_1−xAl_xN (x = 0.5 and 0.67) PVD coated WC-Co inserts at 25-500 °C. Cutting tool life was studied under conditions of face milling of the structural AISI 1040 steel; the end milling of hardened 4340 steel (HRC 40) and TiAl6V4 alloy. A correlation was found between the results of the rapid nano-impact test and milling tests. When x = 0.67 improved resistance to fracture was found during milling operations and also in the nano-impact test of this coating compared to when x = 0.50. The coating protects the cutting tool surface against the chipping that is typical for cutting operations with intensive adhesive interaction with workpiece materials such as machining of Ti-based alloys. The results give encouragement that the elevated temperature nano-impact test can be used to predict the wear and fracture resistance of hard coatings during milling operations. At 500 °C nanoindentation shows there is a lower H/E_r ratio for the PVD coatings compared to room temperature, consistent with reduced fracture observed at this temperature in the nano-impact test.     

电弧离子镀和高功率脉冲磁控溅射AlTiN涂层及其切削性能研究

目的 比较两种沉积方法制备的AlTiN涂层的切削性能.方法 利用高功率脉冲磁控溅射技术(HiPIMS)和电弧离子镀技术(AIP),在硬质合金车刀片上沉积AlTiN涂层,比较和研究两种AlTiN涂层的组织形貌特性及综合性能.利用扫描电子显微镜和X射线能量色散谱仪,观察和检测涂层的生长形貌和元素含量.采用激光共聚焦扫描显微...