Wear of monocrystalline diamond tools during ultraprecision machining of nonferrous metals

In studying the wear behavior of diamond cutting tools, a pragmatic appraoch has been chosen in which the tool wear and the change in cutting forces have been specifically determined as a function of tool life. Several nonferrous metals, such as copper, aluminium, and electroless nickel, have been machined. The influence of microstructural characteristics, crystallographic orientation, and mechanical surface state of diamonds on tool-wear behavior is investigated in considerable detail. It has been found that wear behavior of diamond tools depends strongly on workpiece material, so that when machining aluminium, all types of diamond show considerable and almost the same degree of wear. However, machining copper and electroless nickel entails much subtler wear characteristics; in fact, great differences in wear resistance between different types of diamonds were discerned. Type all diamonds in particular, both synthetic and natural, appear to be highly resistant to wear. The best crystallographic orientation for wear-resistant diamonds depends on the way the cutting tools are used.     

Wear Characteristics of Diamond Tools in Machining Ceramics

Wear characteristics of natural diamonds used to machine ceramic materials at a depth of cut of 2 μm and a speed of 1600 m/min were investigated. The diamond tools used for the machining tests were inspected using the Laue back reflection technique and scanning electron microscopy (SEM). Wear characteristics of the diamond tools appeared to be influenced by the material properties of the ceramics being machined, the build-up on the tips of the diamond tools, and the crystallographic orientations of the diamond crystals. Three wear patterns were identified: single-flat wear, double-flat wear, and micro-chipping wear. The single-flat and double-flat wear patterns were primarily observed in machining silicon nitride and alumina; the microchipping wear pattern was observed in machining silicon carbide. The wear rate for the microchipping pattern was found to be one to two orders of magnitude higher than those for other wear patterns. Silicon nitride wore the diamond tools faster than alumina did; however, it often formed built-up lips which reduced the wear of the diamond tools.     

3D characterisation of tool wear whilst diamond turning silicon

Nanometrically smooth infrared silicon optics can be manufactured by the diamond turning process. Due to its relatively low density, silicon is an ideal optical material for weight sensitive infrared (IR) applications. However, rapid diamond tool edge degradation and the effect on the achieved surface have prevented significant exploitation. With the aim of developing a process model to optimise the diamond turning of silicon optics, a series of experimental trials were devised using two ultra-precision diamond turning machines. Single crystal silicon specimens (1 1 1) were repeatedly machined using diamond tools of the same specification until the onset of surface brittle fracture. Two cutting fluids were tested. The cutting forces were monitored and the wear morphology of the tool edge was studied by scanning electron microscopy (SEM).The most significant result showed the performance of one particular tool was consistently superior when compared with other diamond tools of the same specification. This remarkable tool performance resulted in doubling the cutting distance exhibited by the other diamond tools. Another significant result was associated with coolant type. In all cases, tool life was prolonged by as much as 300% by using a specific fluid type.Further testing led to the development of a novel method for assessing the progression of diamond tool wear. In this technique, the diamond tools gradual recession profile is measured by performing a series of plunging cuts. Tool shape changes used in conjunction with flank wear SEM measurements enable the calculation of the volumetric tool wear rate.     

Evaluation of diamond tool wear

The present study proposes a test protocol regarding the wear of sintered diamond tools. A set of parameters, which characterise the grade of wear, and its relationship with the cutting ability of the examined tools, are established. The proposed protocol establishes the procedure and the equipment for carrying out the tests, the features of the materials to use and the format of the report to present the results obtained. The developed test protocol indicates an universally applicable way for measurement of the wear of the diamond tool. It is an indispensable instrument for correctly carrying out the wear tests and for reliably interpreting the results. The protocol developed so far mainly regards laboratory tests, considering the slowness and precision of the measurements involved. Given the total absence of norms, this protocol could be absorbed by national and international norm establishing organisations. This protocol has also been applied to two types of tools and the results obtained have appeared reliable and replicable. The test protocol proposed in this study makes it possible to overcome the difficulties connected to the scarcity of technical data regarding the properties of the tool, which is typical in this field since the recipes for tool manufacturing are patented.     

Ultraprecision turning of electroless nickel: effects of crystal orientation and origin of diamond tools

This paper deals with (i) the performance of natural and artificial diamond tools and (ii) the effects of crystal orientations at rake face of diamond tool for long distance (>200 km) ultraprecision machining of electroless nickel. The criteria for cutting performance of the diamond tool include flank wear, crater wear, workpiece surface finish, and cutting forces. Experimental results show that the natural diamond tool has superior performance compared to the artificial one as it experienced lower cutting forces and lower flank and crater wears. It was also found that the cutting tool with {110} crystal orientation at rake face performs better than the tool with {100} crystal orientation in terms of amount of wear, surface finish, and cutting forces.     

Improvements in the thread cutting torque for a 6082-T6 aluminum-based alloy with tapping tools utilizing diamond coating

The use of thin film diamond as a hard tool coating offers a significant wear protection in numerous machining operations and increases considerably tool's lifetime. The extreme hardness of the diamond is especially needed in machining highly abrasive materials such as aluminum-silicon alloys. Tapping is widely used for thread fabrication and it is often a time consuming process causing a delay on an automated production line. This study investigated diamond coatings in thread cutting and the aim was to gain knowledge about the performance of diamond-coated taps. PVD diamond coatings were deposited using ultra short pulsed laser deposition (USPLD) techniques. Another type of nanodiamond coating was a chrome-nanodiamond (CND) coating deposited by a two-phase electrochemical process to produce a metal matrix with embedded detonation nanodiamond (DND) particles. The main points were the analysis of tool torques of the thread machining data, sticking of aluminum alloy and wear behavior and mechanism of tested tapping tools. The tested tools were analyzed by Scanning Electron Microscopy (SEM) regarding tool wear and sticking of aluminum on tool surface caused by mechanical interaction. Coating approaches turned out to provide 13–30% improvements in cutting and 37–51% improvements in reversing for overall mean torques compared to uncoated reference tools.     

硬脆及黑色金属材料的单点金刚石车削加工技术综述

单点金刚石车削技术是产生纳米特征表面的光学元件重要制造工艺之一。此加工技术在空间科学、生物医学工程、军事、国防和光学等领域有着广泛的应用。然而,金刚石刀具在切削硬脆和黑色金属材料时受到限制,如刀具磨损加剧、刀具寿命缩短以及工件表面加工质量降低等。为了减少刀具磨损和提高工件表面加工质量,相关学者提出了不同的解决方案,将从单点金刚石车削辅助工艺、工件改性、刀具性能改善和超硬材料及刀具方面梳理面向提高硬脆和黑色金属材料加工质量的单点金刚石车削加工技术相关研究,分析当前各种加工技术的优势与局限,提出未来将多种能场辅助的单点金刚石车削技术和基于聚焦离子束改性的金刚石刀具技术作为研究的重点。     

Tool Wear in Ultra-Precision Diamond Cutting of Non-Ferrous Metals with a Round-Nose Tool

Tool wear causes the loss of the original profile accuracy of the cutting edge and degrades the form accuracy of machined surfaces. The purpose of this research is to clarify the tool-wear mechanism and its effect on machining accuracy in ultra-precision diamond cutting with a round-nose tool. Controlled cutting tests of Al 6061 were performed on a two-axis, ultra-precision turning machine. Single-crystal diamond tools were used in the experiment. The tool-wear pattern was studied based on the observation of the wear zone using a scanning electron microscope. The topographic characteristics of the chips were examined and the effect of the micro-cutting geometry on the tool wear was investigated theoretically and experimentally. The mutual effects of crystallographic dependence of wear resistance of diamonds and the change in the cutting velocity during machining are believed to be the main reasons causing uneven wear along the cutting edge. Measures for reducing the effect of tool wear are also discussed.     

Tailoring of diamond machinable coating materials

Microturning with diamond tools is a promising technique to produce surfaces with highest precision. But only some workpiece materials are suitable for this technique, e.g., copper, aluminum, germanium, PMMA, some compounds, and organic materials. Diamond machining of most transition metal alloys like steel leads to a rapid tool wear which is believed to originate from chemical reactions in the contact zone between tool and workpiece. NiP_x>0.2 coatings are widely used as diamond machinable coating material used for optical applications. In contrast to diamond machining of pure nickel, these coatings do not wear diamond tools rapidly. The chemical reactivity of the coatings with single crystal diamond was investigated with a thermal contact test. It is shown that a sufficient amount of phosphorus suppresses reaction with diamond. Quantum mechanical cluster calculations reveal that this is mainly explained by a strong hybridization of electronic valence orbitals, i.e., covalent bonding. We also investigated magnetron sputtered TiN_x coatings. The reactivity test shows that an amount of approximately 10 at.% nitrogen can reduce the reactivity with diamond significantly. Cluster calculations reveal that this is due to covalent bonding between titanium and interstitial nitrogen atoms. Calculations and reactivity tests for NiSi_x and NiTi_x coatings were also performed. The latter case shows that also alloying of two transition metals may provide enough covalent bonding to inhibit chemical reaction with diamond. We conclude that a sufficient amount of covalent bonding in transition metal containing materials is necessary for machinability with diamond tools. On the basis of these investigations a generalized requirement profile for diamond machinable coating materials is derived.     

黑色金属的超低温金刚石超精密切削

黑色金属的超精密切削问题一直是超精加工领域中未能解决的难题。本文提出了在超低温状态下用天然金刚石单晶车刀超精密切削黑色金属的新工艺,为解决这个难题开辟了新的途径。实验结果表明,在超低温状态下,金刚石车刀切钢时的急剧磨损可以有效地被抑制,刀具寿命增加,从而使黑色金属的金刚石超精密切削成为可能。     

Wear of the blade diamond tools in truing vitreous bond grinding wheels: Part II. Truing and grinding forces and wear mechanism

Truing and grinding forces and the wear mechanism of particle and rod diamond blade tools used to generate precise and intricate forms on rotating vitreous bond silicon carbide grinding wheels are presented. A Hall effect sensor was used to measure the change of grinding spindle power during truing and grinding. A signal processing procedure was developed to identify individual truing passes and to extract the average, peak-to-valley, and standard deviation of the variation of truing force for each pass. The truing force data and SEM micrographs of worn surfaces on blade tools reveal micro- and macro-fracturing of the diamond. The attritious and erosion wear of the diamond rod and particle, erosion of the metal bond, and pulling-out of the diamond particle are also identified. Grinding force data shows that, for the same truing parameters, a wheel trued by the rod diamond blade tool has higher grinding forces than one trued by a particle diamond blade tool.     

Direct Selective Laser Sintering of Hard Metal Powders: Experimental Study and Simulation

Direct selective laser sintering (SLS) technology can be used to produce 3D hard metal functional parts from commercial available powders. Unlike conventional sintering, it does not require dedicated tools, such as dies. Hence, total production time and cost can be reduced. The large shape freedom offered by such a process makes the use of, for example, sintered carbides components viable in domains where they were not applied before. Successful results have been obtained in the production of sintered carbide or hard metal parts through SLS. The investigation focuses on tungsten carbide–cobalt (WC-Co) powder mixture. This material is characterised by its high mechanical properties and its high wear resistance and is widely used in the field of cutting tools. This paper is devoted to the experimental study and the simulation of direct selective laser sintering of WC-Co hard metal powders.     

车削加工陶瓷材料时刀具磨损表面形态的研究

分别使用硬质合金刀具、金刚石刀具、立方氮化硼刀具对氟金云母陶瓷及二硅酸锂玻璃陶瓷材料进行车削试验。利用显微镜观察刀具磨损形貌,通过能谱分析研究了刀具的磨损机理。试验结果表明,刀具磨损部位主要集中在刀尖和后刀面,刀具磨损形式主要为磨料磨损和粘结磨损。用硬质合金刀具车削氟金云母陶瓷时,切削深度越小,磨料磨损越严重。     

Friction and wear of sintered cast iron products

The wear and frictional characteristics of five types of sintered cast iron swarf powder, or the same powder decarbonized by a mechanical procedure, were investigated using a pin-and-disk-type apparatus. The contact pressure was 19.6 N cm^?2 and the sliding velocity varied from 0.1 to 4.0 m s^?1. The wear rate exhibited a maximum at a velocity of 1.0 m s^?1. A slight improvement was found in specimens which were decarbonized and forged before sintering. However, the wear rate at lower velocities of these specimens was inferior to that of a specimen containing 5% graphite. The wear mechanism was investigated by scanning electron microscopy and electron probe X-ray microanalysis, and it was found that oxidation wear had an important effect.     

On the effect of crystallographic orientation on ductile material removal in silicon

In this work the critical chip thickness for ductile regime machining of monocrystalline, electronic-grade silicon is measured as a function of crystallographic orientation on the (0 0 1) cubic face. A single-point diamond flycutting setup allows sub-micrometer, non-overlapping cuts in any direction while minimizing tool track length and sensitivity to workpiece flatness. Cutting tests are performed using chemically faceted, −45° rake angle diamond tools at cutting speeds of 1400 and 5600 mm/s. Inspection of the machined silicon workpiece using optical microscopy allows calculation of the critical chip thickness as a function of crystallographic orientation for different cutting conditions and workpiece orientations. Results show that the critical chip thickness in silicon for ductile material removal reaches a maximum of 120 nm in the [1 0 0] direction and a minimum of 40 nm in the [1 1 0] direction. These results agree with the more qualitative results of many previous efforts.     

DUCTILE-REGIME MACHINING OF PARTICLE-REINFORCED METAL MATRIX COMPOSITES

This paper presents research results on ultraprecision machining of metal matrix composite (MMC) composed of aluminum matrix and either SiC or A1₂ 0₃ particles. Ductile-regime machining of both SiC and aluminum was evaluated to improve the surface integrity of the composite. Both polycrystal-line diamond (PCD) and single crystalline diamond (SCD) tools were used to ultraprecision machine the composites at a depth of cut ranging from 0 to 1μm using a taper cut. The feedrate was normalized to the tool nose radius. A model is proposed to calculate the critical depth of cut for MMCs reinforced with either A1₂0₃ or SiC. The critical depths of cut were found to be 1 p.m and 0.2 u.m for MMCs reinforced with A1₂ 0 or SiC₃, respectively. Both depth of cut and crystallographic direction of the ceramic particles are the sufficient conditions for ductile-regime machining. Although both tools produce similar surface finish, a SCD tool removed the MMC as chips while a PCD tool simply smeared the surface. A diffusion-abrasion mechanism was suspected to cause the surprising wear of the SCD tools when machining the aluminum/SiC composite.     

Some remarks on the chemical wear of diamond and cubic BN during turning and grinding

Previous experiments using simple grinding wheels consisting of a single layer of cubic boron nitride (CBN) or diamond grits on an electroplated rod have shown that the production of wear flats on the grits leads to an increasing grinding force which eventually results in the destruction of the nib. In one of the present experiments, similar worn areas are observed on the grits in a conventional type grinding wheel. The wear of the flats appears to be similar in type to that observed on the flanks of turning tools fabricated from single crystals of diamond and CBN. Experiments with such turning tools show wide variations in the rates of wear between diamond and CBN and between different difficult metal workpieces. These and previous results imply that the flats are formed by an attritious wear process conditioned by the chemical constitution of the tool, workpiece and environment. Further consideration of these various points should lead to the enhanced performance of diamond and CBN grinding wheels.     

Dry sliding wear of diamond materials

In pin-on-disc tests, diamond composites, consisting of diamonds imbedded in a silicon matrix, were run against themselves in air at a sliding speed of 125 cm s^?1 and for loads up to 3.6 kgf. In addition, a few experiments involving sintered diamond compacts rubbing against a rotating metal ring in a ring-and-block configuration were conducted. For the diamond composite wear tests, wear was found to be proportional to load and sliding distance for P ? 3.0 kgf. For both the diamond composite and the diamond compact, the wear rates were very low and similar to those previously observed for single-crystal diamonds rubbed by diamond and metal.     

Investigation of tool wear suppression in ultraprecision diamond machining of die steel

Rapid tool wear in diamond machining of steel can cause catastrophic failures. Despite several approaches to reducing tool wear, diamond machining of steel for industrial applications remains limited. We investigated two solutions, namely plasma nitriding treatment for workpiece surface modification and elliptical vibration cutting for cutting process modification, to determine their effect on reducing tool wear in diamond machining of AISI 4140 die steel. Furthermore, a new approach by combining the two solutions was also explored. Experimental results showed that diamond tool wear could be reduced by several orders of magnitude and mirror-quality surface can be obtained by using either the plasma nitriding treatment or the elliptical vibration cutting. However, in contrast to our expectations, combining the two solutions did not yield further improvement of either the surface finish or the reduction of tool wear compared with that of elliptical vibration cutting alone due to microchipping. Care has been taken to investigate the mechanism responsible for microchipping, and it was found that microchipping is highly dependent on the crystal orientation of the diamond. A diamond tool with the (1 1 0) plane as the rake face and the (1 0 0) plane as the flank face was more resistant to damage, and the microchipping induced in the combined cutting process was almost completely suppressed.