Combined ultrasonic vibration and chemical mechanical polishing of copper substrates

This paper introduces an ultrasonic, vibration-assisted, chemical mechanical polishing (UV-CMP) method and an ultrasonic, vibration-assisted, traditional diamond disk (UV-TDD) dressing method. A copper substrate is polished by traditional CMP and UV-CMP. UV-CMP combines the functions of traditional CMP and ultrasonic machining (USM) with small-amplitude, high-frequency tool vibration to improve the fabrication process and machining efficiency. The removal rate of the copper substrate, torque force, and polished surface morphology of CMP and UV-CMP are compared. The polishing pad is also dressed by traditional diamond disk (TDD) and UV-TDD. The pad cut rate, torque force, and pad surface profiles of TDD and UV-TDD are also investigated in experiments. Experimental results reveal that UV-TDD can produce twice the pad cut rate and reduce torque force compared to TDD. Consequently, a dressing time reduction by half is expected, and hence, the diamond life is extended. It is found that the removal rate of the copper substrate polished by UV-CMP is increased by approximately 50-90% relative to that of traditional CMP because in UV-CMP, a passive layer on the copper surface, formed by the chemical action of the slurry, will be removed not only by the mechanical action of CMP but also by ultrasonic action. In addition, the surface roughness improves and the torque force reduces dramatically. This result suggests that the combination processes of CMP/USM and TDD/USM are feasible methods for improving polishing and dressing efficiency.     

Thermal stresses in diamond coatings and their influence on coating wear and failure

Thermal stresses in diamond coatings deposited onto cemented carbide substrates are calculated using the finite element method. The thermo-elastic stress fields for some coating-substrate geometries are presented. The results are compared with experimental data on the tribological behaviour of diamond coatings. Residual stresses can explain many of the observed patterns of coating wear and failure. A model for the abrasive wear of brittle coatings under large compressive biaxial stresses is described. These stresses prevent cracks initiated at the surface to propagate towards the interface and may promote crack paths parallel to the interface, thus causing the formation of a smooth coating surface. Once the smooth appearance is reached it will become extremely hard to initiate and propagate cracks into the coating and consequently the wear rate becomes very low. Thus, large compressive residual stresses increase the already high wear resistance of diamond coatings. When diamond coatings are deposited onto substrate edges, intense concentrations of normal and shear stresses may lead to coating failure by interfacial spalling. These stresses are lowered by increasing the ratio r/h, where r is the edge radius and h is the coating thickness.     

Effect of machining parameters in ultrasonic vibration cutting

The ultrasonic vibration cutting (UVC) method is an efficient cutting technique for difficult-to-machine materials. It is found that the UVC mechanism is influenced by three important parameters: tool vibration frequency, tool vibration amplitude and workpiece cutting speed that determine the cutting force. However, the relation between the cutting force and these three parameters in the UVC is not clearly established. This paper presents firstly the mechanism how these parameters effect the UVC. With theoretical studies, it is established that the tool–workpiece contact ratio (TWCR) plays a key role in the UVC process where the increase in both the tool vibration parameters and the decrease in the cutting speed reduce the TWCR, which in turn reduces both cutting force and tool wear, improves surface quality and prolongs tool life. This paper also experimentally investigates the effect of cutting parameters on cutting performances in the cutting of Inconel 718 by applying both the UVC and the conventional turning (CT) methods. It is observed that the UVC method promises better surface finish and improves tool life in hard cutting at low cutting speed as compared to the CT method. The experiments also show that the TWCR, when investigating the effect of cutting speed, has a significant effect on both the cutting force and the tool wear in the UVC method, which substantiates the theoretical findings.     

Suppression mechanism of tool wear by phosphorous addition in diamond turning of electroless nickel deposits

An appropriate phosphorous addition to electroless nickel deposits remarkably reduces tool wear in diamond turning. To understand the wear suppression mechanism of phosphorous addition, erosion tests simulating tool wear process and ab initio molecular dynamics calculations of interactions between diamond and Ni-P and Ni are carried out. The erosion tests show that carbon diffusion into the workpiece is reduced, and the ab initio calculations suggest that dissociation of carbon atoms on diamond surface due to the interaction with the workpiece is reduced. The results suggest that another possible additive to suppress tool wear can be found by the method proposed.     

Predictive simulation of damping effects in machine tools

A predictive simulation of the different damping effects in machine tools is required to optimize the dynamic behavior and thus increase their performance and working accuracy. Previously, holistic optimization based on damping was not possible due to non-predictive damping models and the lack of adequate modeling approaches. This paper presents a modeling approach, which allows the efficient simulation of the dynamic behavior. By applying this procedure and suitable damping and friction models, the dynamic behavior of a four-axes machining center was simulated with high accuracy – FRAC values above 95% were achieved.     

Development of monitoring system on the diamond tool wear

Recently, ultra-precision machining using a single crystal diamond tool has been developing very rapidly, especially in the fields of production processes for optical or magnetic parts such as magnetic discs, laser mirrors, polygon mirrors and copier drums. As a result, it has been successfully extended to machine various soft materials, generating mirror-like surfaces to sub-micron geometric accuracy with the ultra-precision CNC machine and the single crystal diamond tool. With the real cutting operation, the geometric accuracy and the surface finish attainable in machined surfaces are mainly determined by both of the sharpness of a cutting tool and stability of the machine vibration. In this study, for monitoring the progress of machining state for assuring the machining accuracy and the surface quality, a new monitoring method of machining states in face-cutting with diamond tool is proposed, using the frequency response of multi-sensors signal, which includes wear state of tool in terms of the energy within the specific frequency band. A magnetic disc is machined on the ultra-precision lathe.     

High surface quality micro machining of monocrystalline diamond by picosecond pulsed laser

In micro machining of monocrystalline diamond by pulsed laser, unique processing characteristics appeared only under a few ten picosecond pulse duration and a certain overlap rate of laser shot. Cracks mostly propagate in parallel direction to top surface of workpiece, although the laser beam axis is perpendicular to the surface. This processed area can keep diamond structure, and its surface roughness is smaller than R_a = 0.2 μm. New laser micro machining method to keep diamond structure and small surface roughness is proposed. This method can contribute to reduce the polishing process in micro machining of diamond.     

超声波对电镀金刚石工具性能的影响

分别在有超声波和无超声波条件下,制备了镍镀层和电镀金刚石工具。采用显微硬度计测试了镍镀层硬度,采用热震法和锉削法测试镀层与基体的结合强度,用显微镜观察镀层金相组织,计算了工具磨削比。研究结果表明:在电镀金刚石工具制备过程中,应用超声波可以细化镀层晶粒,提高镀层硬度,增强镀层与基体的结合强度。上砂前应用超声波可提高电镀金刚石工具磨粒密度和工具的磨削比。     

Monitoring of distance between diamond tool edge and workpiece surface in ultraprecision cutting using evanescent light

The interaction between a tool and a workpiece during machining determines the quality of a machined workpiece. This study presents a novel direct monitoring method using evanescent light, which detects the distance between a diamond tool edge and the workpiece surface. In the proposed method, evanescent light is generated around the diamond tool edge, and the intensity of the reflected laser beam corresponds to the distance between the tool edge and the workpiece surface. Experimental results confirmed that the proposed method is capable of monitoring the distance change of a sub-micrometer scale.     

A new approach to determine the wear coefficient for wear prediction of sheet metal forming tools

Accounting for the increase of wear in metal forming tools, it is eminent to have detailed information about the tool lifetime already during the tool design. With the wear simulation tool REDSY—developed at the Institute of Metal Forming and Casting—tool wear can be simulated qualitatively and quantitatively for sheet metal forming processes. The calculations are based on Archard’s wear model, a model using contact mechanics to describe the wear behavior. In this project, a new approach to determine the wear coefficient has been developed using a simple cylindrical cup deep drawing experiment for the wear measurements. Several tool and sheet material combinations were analyzed using a five-stage progressive die tool in a precision automatic punching press in order to achieve a high wear volume in a short period of time. The wear coefficient for the respective material combination could be determined combining the experimental results with simulation. This method is verified by comparing the wear simulation results with actual measurements. This project was funded by Germany’s Bundesministerium für Wirtschaft und Arbeit (BMWA) over Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. (AiF). Project code: AiF14291N.     

High performance grinding of zirconium oxide (ZrO2) using hybrid bond diamond tools

Hybrid bond (metal–ceramic) diamond tools are proposed for grinding zirconium oxide used in medical implants. Compared to conventional grinding tools, material removal rates and tool life time are drastically increased without deterioration in mechanical properties of the workpiece. This is achieved within a selected process window in combination with an elaborate oil cooling system, where material removal is mainly occurring within the ductile cutting mode. Self-sharpening effect of the tool can be observed and the dressability of the tool further improves the grinding performance.     

Study of machining accuracy in ultrasonic elliptical vibration cutting

The cutting speeds of the tool, the rake angle and clearance angle through the cycles of elliptical vibration cutting for separating type ultrasonic elliptical vibration cutting are defined initially in the present paper. Subsequently, a theoretical model of the thrust cutting force in ultrasonic elliptical vibration cutting is proposed, and the reason of the machining accuracy improvement by applying ultrasonic elliptical vibration is clarified theoretically. Finally, the effect of ultrasonic elliptical vibration cutting on machining accuracy is verified experimentally by utilizing an ultrasonic elliptical vibration cutting system.     

A study on the effect of tool nose radius in ultrasonic elliptical vibration cutting of tungsten carbide

Nowadays, ultrasonic elliptical vibration cutting (UEVC) technique is being successfully applied for ultraprecision machining of difficult-to-cut materials. Previous study reported that the tool geometry especially tool nose radius notably influences the performance of 1D ultrasonic vibration cutting (UVC). However, the effect of tool nose radius in the UEVC technique is yet to be studied. This study aims to investigate the effects of tool nose radius on the UEVC performance in terms of cutting force, tool wear and surface finish when machining a hard-to-cut material, sintered tungsten carbide (WC), using PCD tools. The experimental results show that the UEVC technique performs remarkably better in all aspects at a 0.6 mm nose radius compared to a lower (e.g. 0.2 or 0.4 mm) and a higher nose radius (e.g. 0.8 mm). When machining about 412 mm² surface area, an average surface roughness, R_a of 0.010 μm is achieved with a 0.6 mm nose radius. Analyses are conducted to justify the findings in this study.     

Neural image processing of the wear of cutting tools coated with thin films

Small milling cutters are susceptible to very small changes in geometry on the surface of the cutting edge that are substantial when machining at the microscale. The purpose of this paper is to show how to design a neural image processing program to accurately determine the amount of wear accumulated on small milling cutters after successive machining operations. After determining the amount of wear on a small milling cutter, the program creates the appropriate amount of compensation to be used for a computer numerical control (CNC) machining program that will account for in-process tool wear. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

Analysis for the wear resistance anisotropy of diamond cutting tools in theory and experiment

In this work, the dynamic micro-mechanical strengths of diamond crystal are deduced in theory, including the tensile, shearing and compressive strengths. The calculated results reveal that the dynamic micro-mechanical strengths have great anisotropy, but the tensile strengths are less than the shearing and compressive ones in any orientation of any plane. Subsequently, a novel evaluation factor is proposed, which integrates from the theoretical tensile strength in the orientation of flank face paralleling to the cutting direction and the theoretical tensile strength in the orientation of rake face paralleling to the chip flowing direction. And then as expected, the anisotropy of the resistance to wear of diamond cutting tools can be predicted exactly through comparing the evaluation factor. Theoretical analyses indicate the larger the evaluation factor, the greater the wear resistance of diamond cutting tool is. Finally, the cutting experiments are carried out on the (1 1 1) silicon wafers, and the sampled data are well consistent with the theoretical predictions, which validates that the proposed evaluation factor is suited for predicting the anisotropy of the resistance to wear of diamond cutting tools.     

Investigation of wear behavior and chip formation for cutting tools with nano-multilayered TiAlCrN/NbN PVD coating

A comprehensive investigation of the wear progress and chip formation was performed on an ultra-fine-grained cemented carbide ball nose end mill coated with a novel nano-multilayered TiAlCrN/NbN coating, by dry machining-hardened steel AISI H13 (HRC 55–57) at a cutting speed of 300 m/min. Flank wear and cutting forces were measured as the wear progressed; chip temperatures were estimated. The surface morphology of the tools were studied by using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis techniques. Results showed that protective oxide films (Al–O, Cr–O and Nb–O) were formed during cutting. With the combination of the protective oxide films and the fine-grain tough substrate, the tool wear rate was greatly reduced compared to the other coatings tested. Continuous and saw-tooth chips were identified, corresponding to a new sharp tool and a worn tool, respectively. The mechanisms of saw-tooth chip formation were found to be a combination of “crack theory” and “adiabatic shear theory”. The characteristics of the chips were studied in detail with the results showing that during formation the chips underwent a combined effect of strain hardening and thermal softening, followed by a quenching phenomenon.     

Toward a new tribological approach to predict cutting tool wear

This work aims at improving the numerical modelling of cutting tool wear in turning. The key improvement consists in identifying a fundamental wear model by means of a dedicated tribometer, able to simulate relevant tribological conditions encountered along the tool–workmaterial interface. Thanks to a design of experiments, the evolution of wear versus time can be assessed for various couples of contact pressure and sliding velocities (σ_n, V_s) leading to the identification of a new wear model. The latter is implemented in a numerical cutting model to locally simulate tool wear along the contact with regard to each local tribological loading.     

An ultrasonic elliptical vibration cutting device for micro V-groove machining: Kinematical analysis and micro V-groove machining characteristics

Micro V-groove machining characteristics of an ultrasonic elliptical vibration cutting (UEVC) device have been experimentally investigated and compared with the conventional micro V-grooving. From the initial experiments performed on ductile material such as aluminum and brass with a single crystal diamond cutting tool, it was found that the cutting force was significantly decreased and the formation of burrs at the machining boundaries was greatly suppressed in the UEVC. The elliptical vibration of the cutting tool was achieved using two parallel stacked piezoelectric actuators with assembling metal structures. Kinematical analysis of the UEVC system has shown that the manipulation of the cutting tool path is possible by changing dimension of the mechanism, phase difference, and relative magnitude of the voltages applied to the piezoelectric actuators.     

The ultimate sharpness of single-crystal diamond cutting tools—Part I: Theoretical analyses and predictions

In this paper, the brittle–ductile transition lapping mechanism is presented for mechanical lapping of single-crystal diamond cutting tools. The calculated critical depths of cut for controlling brittle–ductile transition in different orientations and on different planes are used to direct tool lapping and deduce the dynamic micro-mechanical strengths (such as tensile, shearing and compressive strengths) of diamond cutting tools, while in the tool fabrication. The investigation illustrates that the dynamic micro-mechanical strengths have great anisotropy, and the strengths in the ‘soft’ direction are all less than those in the ‘hard’ direction on any crystal plane. The lapping of designed cutting tools, oriented (1 1 0)–(1 0 0) and (1 0 0)–(1 0 0) as tool rake and flank faces respectively, is carried out in ductile mode based on the optimal lapping parameters as selected. Both atomic force microscope (AFM) and scanning electron microscope (SEM) measurements results show that the lapping quality of diamond cutting tools is much improved with the proposed lapping approach. The surface roughness on the tool rake face is 0.8 nm (Ra) and lapped cutting edge radius is 35–50 nm as achieved when (1 1 0)–(1 0 0) orientations are selected as rake and flank faces; and the rake face surface roughness is 0.7 nm (Ra) and lapped cutting edge radius is 30–40 nm as the rake and flank faces oriented with (1 0 0)–(1 0 0) combination. Theoretical analyses of the dynamic impact effects on the cutting edge radius are undertaken to predict their ultimate cutting edge radii. Theoretical calculations indicate that the extreme cutting edge radius can be sharpened down to 1–6 nm of the (1 1 0)–(1 0 0) oriented tools, and 2–5 nm for the (1 0 0)–(1 0 0) oriented cutting tools.