金刚石涂层刀具加工石墨的切削性能

为充分对比不同类型金刚石涂层刀具的切削性能,定制几种不同类型金刚石涂层刀具进行等静压石墨切削加工,并与WC硬质合金刀具和TiAlN涂层刀具的切削情况对比,分析不同类型金刚石涂层刀具的涂层形貌、切削寿命、加工后的表面质量以及切削力。结果表明:制备的金刚石涂层刀具的涂层形貌主要为纳米晶和微晶,其寿命是硬质合金和TiAlN涂层刀具的10倍以上,且几种不同类型的金刚石涂层刀具寿命差异较小;金刚石涂层表面的晶粒细化可以降低加工表面的粗糙度和切削力,涂层脱落是金刚石刀具的主要磨损形式。      

Use of ceramic tools for machining nickel based alloys

The paper is the first of two dealing with the use of ceramic tool materials for the machining of nickel based alloys. While the second contribution presents the results of detailed machinability tests, involving a cross-section of current nitride, superhard and whisker reinforced ceramic tooling products, this first paper comprehensively reviews existing literature on the subject.

Following an assessment of tool wear characteristics, such as depth-of-cut notching and the underlying mechanisms involved, in particular the effects of applied mechanical stress and high interface temperatures, details are given of the composition, structure, physical properties and cutting performance of various state-of-the-art ceramic tool materials. Although only recently available commercially, whisker reinforced composite tools, comprising an alumina matrix with approximately 25% by volume silicon carbide whiskers, are reported to be capable of operating at cutting speeds up to 750 m/min on some nickel based alloys.     

Wear mechanisms of PVD ZrN coated tools in machining

Medium-frequency magnetron sputtered PVD ZrN coatings (ZrN, ZrN/Zr) were deposited on YT15 (WC + 15%TiC + 6%Co) cemented carbide. Microstructural and fundamental properties of these ZrN coatings were examined. Dry machining tests on hardened steel were carried out with these coated tools. The wear surface features were examined by scanning electron microscopy. Results showed that deposition of the PVD ZrN coatings onto the YT15 cemented carbide causes great increase in surface hardness. The ZC-1 coated tool (ZrN/YT15 without interlayer) has the highest surface hardness; while the ZC-2 (ZrN/Zr/YT15 with a Zr interlayer) shows the highest adhesion load for the coatings to the substrate. The ZrN coated tools exhibit improved rake and flank wear resistance to that of the YT15 tool. The coated tools with a Zr interlayer (ZC-2) have higher wear resistance over the one without Zr interlayer (ZC-1). The rake wear of the ZrN coated tools at low cutting speed was mainly abrasive wear; while the mechanism responsible for the rake wear at high cutting speed was determined to be adhesion. Extensive abrasive wear accompanied by small adhesive wear were found to be the predominant flank wear mechanisms for the ZrN coated tools.     

Development of new ceramic cutting tools with alumina coated carbide powders

An experimental investigation is carried out to coat two types of carbide powders, TiC and (W, Ti)C, with an alumina ceramic using a sol-gel technology. The coated carbide powders are then fabricated into two kinds of new ceramic tool materials by the hot pressing method. A scanning electron microscope (SEM) observation reveals that in general the matrix (carbide) grains are uniformly coated with the alumina ceramic and the microstructure of the new tool materials is more homogeneous than that of conventionally made ceramics. The tests of mechanical properties and wear resistance in machining are finally conducted. It is shown that when machining a mild carbon steel the new tool materials can increase the tool-life by up to 100% as compared to other two ceramic tool materials that have the same matrix but fabricated in the conventional way, while the fracture toughness is improved by up to 33%. When compared with a hard coated carbide tool, the new materials exhibit a superior ability in maintaining the wear resistance during the entire tool-life.     

Cutting temperature of ceramic tools in high speed machining of difficult-to-cut materials

This paper deals with an experimental and analytical investigation into the different factors which influence the temperature distribution on Al₂O₃---TiC ceramic tool rake face during machining of difficult-to-cut materials, such as case hardened AISI 1552 steel (60–65 Rc) and nickel-based superalloys (e.g. Inconel 718). The temperature distribution was predicted first using the finite element analysis. Temperature measurements on the tool rake face using a thermocouple based technique were performed and the results were verified using the finite element analysis. Experiments were then performed to study the effect of cutting parameters, different tool geometries, tool conditions, and workpiece materials on the cutting edge temperatures. Results presented in this paper indicate that for turning case hardened steel, increasing the cutting speed, feted, and depth of cut will increase the cutting edge temperature. On the other hand, increasing the tool nose radius, and angle of approach reduces the cutting edge temperature, while increasing the width of the tool chamfer will slightly increase the cutting ege temperature. As for the negative rake angle, it was found that there is an optimum value of rake angle where the cutting edge temperature was minimum. For the Inconel 718 material, it was found that the cutting edge temperature reached a minimum at a speed of 510 m/min, and feed of 1.25 mm/rev. However, the effect of the depth of cut and tool nose radius was almost the same as that determined in the turning of case hardened steel. It was also observed in turning Inconel 718 with ceramic tools that, cutting forces and different types of tool wear were reduced with increasing the feed.     

Contour finish turning operations with coated grooved tools: Optimization of machining performance

This paper presents a new methodology for optimization of machining performance in contour finish turning operations. Two machining performance measures, chip breakability and surface roughness, are considered as optimization criteria due to their importance in finishing operations. Chip breakability covers two major factors: chip shape and size. Comprehensive case studies are presented to demonstrate the determination and application of optimal cutting conditions through experimental validation.     

Performance of nano/micro CBN particle coated tools in superfinish hard machining

A two-stage composite coating method has been developed for coating of nano/micro cubic boron nitride (CBN) particles on cutting tools. Since nano/micro CBN particle coated tools are more cost-effective than solid polycrystalline CBN (PCBN) tools, a comprehensive study on the coated tools is required. This paper studies the performance of these tools in superfinish hard machining. Specimens were machined by a solid PCBN tool and CBN particle coated tools with two different CBN particle size distributions: less than 0.5 and 2 μm. The specimen machined by a tool with small CBN particle coating (less than 0.5 μm) showed more compressive residual stresses and less thermal damage below the machined surface than other specimens. Furthermore, the specimen machined by a tool with small CBN particle showed less residual stress scatter than other specimens. The rolling contact fatigue life was predicted by using a rolling contact fatigue life model. The rolling contact fatigue life predictions indicate that the predicted life of the specimen machined by a tool with small CBN particle coating is longer than that of other specimens. The results thus indicate that a tool with small CBN particle coating provides better performance than other tools in superfinish hard machining.     

Surface integrity when machining age hardened Inconel 718 with coated carbide cutting tools

Considerable attention has been given to the use of ceramic cutting tools for improving productivity in the machining of heat resistant super alloys (HRSA). However, because of their negative influence on the surface integrity, ceramic tools are generally avoided particularly for finishing applications. As a result the main high end manufacturers are more or less dependent on carbide cutting tools for finishing operations. Still the improper use of carbide cutting tools can also result in poor surface integrity. The objective of this investigation is to develop a set of guidelines, which will assist the selection of the appropriate cutting tools and conditions for generating favorable compressive residual stresses. This paper specifically deals with residual stresses and surface finish components of surface integrity when machining (facing) age hardened Inconel 718 using two grades of coated carbide cutting tools specifically developed for machining HRSAs. The cutting conditions were obtained from investigations based on optimum tool performance. The effect of insert shape, cutting edge preparation, type and nose radius on both residual stresses and surface finish was studied at this optimum cutting condition. This investigation, suggested that coated carbide cutting tool inserts of round shape, chamfered cutting edge preparation, negative type and small nose radius (0.8 mm) and coolant will generate primarily compressive residual stresses.     

A computational approach to evaluate temperature and heat partition in machining with multilayer coated tools

In this paper, analytical models for estimating the interface temperature and heat partition to the chip in continuous dry machining of steels with flat-faced tools treated with multilayer coatings are presented. The database for modeling includes changes in the thermal properties of both workpiece and substrate/coating materials and the Peclet and Fourier numbers occurring at actual interface temperatures. Process outputs involve the average tool–chip interface temperature, the tool–chip contact length, the friction energy and the heat balance between the moving chip and stationary tool. It was found that the heat partition coefficient varies significantly from 0.65 to 0.8 when using multilayer coated tools, and changes from 0.5 to 0.6 for uncoated carbide tools. This implies that the use of multilayer coated tools causes about 30% more heat generated due to friction to be transferred into the moving chip. In general, both power and linear models can be used to estimate the interface temperature.     

Tool wear characteristics in machining of nickel-based superalloys

Nickel-based superalloy is widely employed in aircraft engines and the hot end components of various types of gas turbines with its high strength, strong corrosion resistance and excellent thermal fatigue properties and thermal stability. However, nickel-based superalloy is one of the extremely difficult-to-cut materials. During the machining process, the interaction between the tool and the workpiece causes the severe plastic deformation in the local area of workpiece, and the intense friction at the tool–workpiece interface. The resulting cutting heat coupled with the serious work hardening leads to a series of flaws, such as excessive tool wear, frequent tool change, short tool life, low productivity, and large amount of power consumption etc., in which the excessive tool wear has become one of the main bottlenecks that constraints the machinability of nickel-based superalloys and its wide range of applications.In this article, attention is mainly focused on the tool wear characteristics in the machining of nickel-based superalloys, and the state of the art in the fields of failure mechanism, monitoring and prediction, and control of tool wear are reviewed. The survey of existing works has revealed several gaps in the aspects of tool self-organizing process based on the non-equilibrium thermodynamics, tool wear considering the tool nose radius, thermal diffusion layer in coated tools, tool life prediction based on the thermal–mechanical coupling, and industrial application of tool wear online monitoring devices. The review aims at providing an insight into the tool wear characteristics in the machining of nickel-based superalloys and shows the great potential for further investigations and innovation in the field of tool wear.     

Cutting performance of solid ceramic end milling tools in machining hardened AISI H13 steel

Ceramic tools have been widely used in the cutting of hard-to-machine materials, but the applications of solid ceramic milling cutters are limited due to their design and manufacturing restrictions. This research investigates the cutting performances of four solid ceramic end milling tools including Si₃N₄, Ti(C,N), SG4 and LT55 in machining hardened AISI H13 steel (HRC 60-62). The results show that the cutting forces of ceramic end milling tools are less than that of the referenced cemented carbide tool, and such ceramic tools of Si₃N₄, Ti(C,N) and LT55 produce better surface qualities and have longer tool lives. With excellent mechanical peoperties including hardness, bending srength and fracture toughness, the ceramic tool of Ti(C,N) presents the best cutting performance taking the cutting force, machined surface quality and tool life in consideration simultaneously. The research has proven the application feasibility of ceramic materials in the manufacture of solid tools. The solid ceramic end milling tools are geometric extensions for traditional ceramic tools and they can be used in machining hardened steels.     

Physics based modelling of interface temperatures in machining with multilayer coated tools at moderate cutting speeds

A new thermal model is presented for turning with tools with multilayer coatings. In the previous paper [Int. J. Mach. Tools Manuf. 43 (2003) 1311] devoted to the thermal problems in dry turning of steels with tools treated with multilayer coatings with an intermediate Al₂O₃ layer new analytical models for estimating the heat partition to the chip and the average interface temperature were derived and the predictions were compared with experimental results. In this paper, a physics based modelling concept has been applied to both the individual layer and the composite layer approach to develop an estimate of the average and the maximum steady-state chip-tool interface temperatures in orthogonal turning. Different approaches for determining the heat partition coefficient for sliding bodies of defined thermal properties were tested. Experiments using the work and the tool as the thermocouple pair have verified that the proposed models accurately predict the temperatures for uncoated and coated tools for a range of cutting speeds. As a result a new computational algorithm, for predicting with reasonable accuracy the average and peak values of the temperatures at the chip-coating/substrate interface at cutting speeds up to 200 m/min, has been recommended.     

Key improvements in the machining of difficult-to-cut aerospace superalloys

Significant advances have been made in understanding the behaviour of engineering materials when machining at higher cutting conditions from practical and theoretical standpoints. This approach has enabled the aerospace industry to cope with constant introduction of new materials that allow the engine temperature to increase at a rate of 10 °C per annum since the 1950s. Improvements achieved from research and development activities in this area have particularly enhanced the machining of difficult-to-cut nickel base and titanium alloys that have traditionally exhibited low machinability due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation, etc. A good understanding of the cutting tool materials, cutting conditions, processing time and functionality of the machined component will lead to efficient and economic machining of nickel and titanium base superalloys. This paper presents an overview of major advances in machining techniques that have resulted to step increase in productivity, hence lower manufacturing cost, without adverse effect on the surface finish, surface integrity, circularity and hardness variation of the machined component.     

Monitoring of flank wear of coated tools in high speed machining with a neural network ART2

A monitoring system for classifying the levels of the tool flank wear of coated tools into some categories has been developed using an unsupervised and self-organizing artificial neural network, ART2. The input pattern used for the ART2 was an array of normalized mean wavelet coefficients of the feed force, which was affected by not only the flank wear but also the severe crater wear observed in high speed machining. The outputs of ART2 were classified into four or five categories of wear levels: the incipient stage, one or two intermediate stages, final stage and hazardous stage. For two apparently different series of input data obtained under the same cutting conditions, which are often experienced in the experiment, the ART2 neural network showed very similar classification of tool wear levels from the beginning to the end of cutting. Further study proved that this monitoring system detected the excessive wear in the hazardous stage for different cutting speeds 5–7 m/s and different feed rates 0.10–0.20 mm/rev.     

Documentation of tool wear progress in the machining of nodular ductile iron with silicon nitride-based ceramic tools

Nowadays, the HPM of cast irons is based on silicon nitride ceramic and CBN cutting tools. This paper characterizes and correlates several outputs of the cutting process of nodular cast iron using uncoated and Al₂O₃/TiN coated Si₃N₄ ceramic tools resulting from wear progress and destruction of tool faces. Investigations include tool wear curves, tribological behaviour of the tool–chip interface and tool wear mechanisms occurring on contact surfaces. The image-based characterization of worn surfaces employs such techniques as SEM, BSE and EDX analysis. The occurrence of various wear mechanisms, such as abrasive, adhesive and chemical wear was revealed.     

Nanocrystalline diamond coating tools for machining high-strength Al alloys

Diamond coating tools have been increasingly used for machining advanced materials. Recently, a microwave plasma-assisted chemical vapor deposition (CVD) technology was developed to produce diamond coatings which consist of nano-diamond crystals embedded into a hard amorphous diamond-like carbon matrix. In this study, the nanocrystalline diamond (NCD) coating tools were evaluated in machining high-strength aluminum (Al) alloy. The conventional CVD microcrystalline diamond coating (MCD) tools and PCD tools were also tested for performance comparisons. In addition, stress distributions in diamond coating tools, after deposition and during machining, were analyzed using a 2D finite element (FE) thermomechanical model.

The results show that catastrophic failures, reached in all except one machining conditions, limit the NCD tool life, which is primarily affected by the cutting speed. In addition, coating delamination in the worn NCD tools is clearly evident from scanning electron microscopy (SEM) and force monitoring in machining can capture the delamination incident. At a high feed, coating delamination may extend to the rake face. Furthermore, SEM observations of coating failure boundaries show intimate coating-substrate contact. Though the NCD tools are inferior to the PCD tools, they substantially outperform the MCD tools, which failed by premature delamination. The diamond coating tools can have high residual stresses from the deposition and stresses at the cutting edge are highly augmented. Further machining loading causes the stress reversal pattern which seems to correlate with the tool wear severity.     

Machining performance of pearlitic–ferritic nodular cast iron with coated carbide and silicon nitride ceramic tools

This paper concerns the fundamental cutting characteristics obtained in the turning of the pearlitic–ferritic nodular iron (EN-GJS-500-7 grade with UTS=500 MPa) when using carbide tools coated with single TiAlN and multilayer TiC/Ti(C,N)/Al₂O₃/TiN coatings, as well as silicon nitride (Si₃N₄) based ceramic tools. As a competitor, a P20 uncoated carbide grade was selected. The fundamental process readings include cutting and feed forces, the tool–chip interface temperature, Peclet number, friction coefficient and the tool–chip contact length as functions of cutting parameters. In particular, the measurements of cutting temperature were carried out using conventional tool–work thermocouple method and IR thermography. It is concluded based on many process characteristics that multilayer coated and ceramic tools can substantially improve the performance of nodular iron machining.     

Advanced monitoring of machining operations

CIRP has had a long history of research and publication on the development and implementation of sensor monitoring of machining operations including tool condition monitoring, unmanned machining, process control and, more recently, advanced topics in machining monitoring, innovative signal processing, sensor fusion and related applications. This keynote follows a recent update of the literature on tool condition monitoring and documents the work of the cutting scientific technical committee in CIRP. The paper reviews the past contributions of CIRP in these areas and provides an up-to-date comprehensive survey of sensor technologies, signal processing, and decision making strategies for process monitoring. Application examples to industrial processes including reconfigurable sensor systems are reported. Future challenges and trends in sensor based machining operation monitoring are presented.     

Development of coated ceramic components for the aluminum industry

In general, due to ceramic’s high hardness, which makes machining operations extremely difficult and very expensive, ceramic components are formed in shapes very close to the final ones. Considering this, a manufacturing process, based on a sol-gel reaction that allows rapid production of ceramic components in the final shape with a low level of shrinkage was developed. Although the ceramics obtained presented good behavior in short-term contact with molten aluminum alloys, there was no guarantee that the components produced would have adequate continuous resistance to chemical and erosive wear by liquid metals. To enhance their resistance, the ceramic parts were coated by flame spray. Different powders and conditions were used to determine the degree of coating adhesion to the substrate. The coated specimens were then submerged in a molten aluminum bath, at different temperatures and time settings, to evaluate the interaction between the ceramic components and the molten aluminum alloys.