Experimental observation of tool wear in rotary ultrasonic machining of advanced ceramics

As one of the cost-effective machining methods for advanced ceramics, rotary ultrasonic machining (RUM) has attracted much attention and there exist numerous publications on the process. However, few investigations on tool wear in the RUM process have been reported. This paper, for the first time in literature, presents an experimental observation on tool wear in RUM of silicon carbide (SiC). It first reviews some related wear mechanisms for grinding wheels and some techniques for studying the wheel wear mechanisms. After describing the experimental procedures, it presents and discusses the results on tool wear and cutting forces in RUM of SiC. It also discusses some practical implications of the findings from this study.     

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-speed machining of titanium alloys using the driven rotary tool

Machining of titanium at high cutting speeds such as from 4 m/s to 8 m/s is very challenging. In this paper, a new generation of driven rotary lathe tool was developed for high-speed machining of a titanium alloy, Ti–6Al–4V. The rotary tool was designed and fabricated based on the requirements of compact structure, sufficient stiffness and minimal edge runout. Cylindrical turning experiments were conducted using the driven rotary tool (DRT) and a stationary cutting tool with the same insert, for comparison in the high-speed machining of Ti–6Al–4V. The results showed that the DRT can significantly increase tool life. Increase in tool life of more than 60 times was achieved under certain conditions. The effects of the rotational speed of the insert were also investigated experimentally. Cutting forces were found to decline slightly with increase of the rotational speed. Tool wear appears to increase with the rotational speed in a certain speed range.     

Modeling of cutting forces in near dry machining under tool wear effect

A predictive model for the cutting forces in near dry machining, in which only a small amount of cutting fluid is used, is developed based on considerations of both the lubricating effect and the cooling effect. For the lubricating effect, with the material properties, lubricating parameters, and cutting conditions, the friction coefficient in near dry machining is calculated based on the boundary lubrication model for use in a modified Oxley's approach to determine the cutting forces. For the cooling effect in near dry machining, a moving heat source method is pursued to quantify the primary-zone shear deformation heating, the secondary-zone friction heating, and flank face air–oil mixture cooling. These two effects are considered collectively to estimate cutting forces under the condition of sharp tools. The predicted variables of flow stress, contact length, and shear angle obtained from the model are used to predict the cutting forces due to the tool flank wear effect based on Waldorf's model. Comparisons are made between predicted and experimental cutting forces for sharp tools and worn tools in the cutting of AISI 1045 with uncoated carbide tools. The results show that the proposed model provides average prediction errors of 14% in the tangential cutting force direction, 21% in the axial directions, and 30% in the radial directions within the experimental test condition range (cutting speeds of 45.75–137.25 m/min, feeds 0.0508–0.1016 mm/rev, and depth of cuts 0.508–1.016 mm). It is also found that the cutting forces in near dry machining are generally lower than those under dry machining condition. Under cutting speeds of 91.5 and 137.25 m/min, the deviations of the predicted forces between near dry machining and dry machining range from 5% to 39% for axial cutting forces, 3% to 36% for radial cutting forces, and 1% to 32% for tangential cutting forces. It suggests that the lubricating mechanism has a stronger effect on cutting forces than the cooling mechanism when cutting AISI 1045 with uncoated carbide tools.     

Ultra-precision machining of Fresnel microstructure on die steel using single crystal diamond tool

With the increasing demand for the replication of structured optical elements such as Fresnel lenses and prism arrays, more attention is being paid to the development of ultra-precision diamond machining technology for the fabrication of die steel molds. However, the machining process would be a catastrophic failure because of rapid and excessive tool wear if a diamond tool is used to machine die steel. In the present paper, a micromachining method for fabricating microstructures on die steel using single crystal diamond tool is presented. The presented technology is based on a thermochemical technique that uses plasma nitriding treatment to suppress the rapid and excessive tool wear in the diamond machining of steel. Experimental findings revealed that severe chemical tool wear, which is the main wear mechanism in the diamond machining of steel, was reduced significantly after plasma nitriding treatment, and a mirror-quality surface with an average surface roughness of 20 nm root-mean-square (RMS) was achieved over a cutting distance of approximately 5.4 km. Furthermore, a Fresnel microstructure with surface roughness RMS better than 40 nm was precisely fabricated on AISI 4140 die steel using single crystal diamond tool.     

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.     

New observations on tool wear mechanism in dry machining Inconel718

Tool wear is a problem in machining nickel-based alloy Inconel718, and it is thus of great importance to understand tool wear. Tool wear mechanism in dry machining Inconel718 with coated cemented carbide tools was analyzed in this paper. CCD and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS) were used to study tool wear mechanism. The results show that the main reason which causes cutting tool wear was that the tool materials fall off from the tool substrate in the form of wear debris. In addition,, element diffusion between tool and workpiece and oxidation reaction all accelerate the formation and the peeling of the wear debris. According to analysis of tool wear mechanism, tool flank wear model was established. The optimal temperature in machining Inconel718 with PVD-coated (TiAlN) tool was obtained through the established model. Excellent experimental agreement was achieved in optimal temperature calculated by the established model.     

On temperatures and tool wear in machining hypereutectic Al–Si alloys with vortex-tube cooling

This study investigates dry machining of hypereutectic silicon–aluminum alloys assisted with vortex-tube (VT) cooling. The objective is to reduce cutting temperatures and tool wear by enhanced heat dissipation through the chilled air generated by a VT. A machining experiment, cutting mechanics analysis, and temperature simulations are employed to (1) model the heat transfer of a cutting tool system with VT cooling applied, (2) explore effects of cooling setting and machining parameters on the cooling efficiency, and (3) evaluate VT cooling effects on tool wear. A390 alloy is machined by tungsten carbides with cutting forces and geometry measured for heat source characterizations as the input of temperature modeling and simulations. VT cooling is approximated as an impinging air jet to estimate the heat convection coefficient that is incorporated into the heat transfer models. The major findings include: (1) VT cooling may reduce tool wear in A390 machining depending upon machining conditions, and the outlet temperature is more critical than the flow rate, (2) cooling effects on temperature reductions, up to 20 °C, decrease with the increase of the cutting speed and feed, and (3) tool temperature decreasing by VT cooling shows no direct correlations with tool wear reductions.     

Effect of various parameters on the surface roughness of an aluminium alloy burnished with a spherical surfaced polycrystalline diamond tool

The effect of various parameters on the surface roughness of an aluminium alloy burnished with a spherical surfaced polycrystalline diamond tool are studied experimentally with a theoretical analysis. Problems in selecting the optimum burnishing parameters and some burnishing mechanisms are discussed. With suitable parameters employed, the new no-chip finishing process developed can eliminate or reduce the cutting marks left on the workpiece surface by diamond cutting tools, with its surface roughness reduced to Ra=0.026 μm from the original 0.5 μm.     

Tool wear mechanism in turning of novel wear-resisting aluminum bronze

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Study on wear mechanism of CVD diamond graver for stone machining

This paper presents a new kind of CVD diamond machining object, we studied influence of cutting speed, feed variance analysis and regression analysis. The result indicated on tool life; feed rate ranked the second; depth of cut had graver for stone machining. Taking granite as rate and depth of cut on tool life by means of that cutting speed had a more remarkable effect no significant influence on tool life. Scanning electron microscope （SEM） was used to observe wear morphologies of gravers. It was found that abrasive wear was the main wear mechanism     

基于加工尺寸检测数据的刀具磨损及寿命研究

在对机械加工尺寸跟踪检测和对检测数据进行建模分析的基础上，提出对刀具磨损状况及寿命进行估计和预测的新途径；将加工质量控制与刀具监控统一起来，为自动化机械加工设备的换刀决策提供了一种新方法。     

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.     

Tool wear mechanisms and tool life enhancement in ultra-precision machining of titanium

Titanium and its alloys are generally considered as difficult-to-machine materials due to their poor thermal conductivity and high strength, which is maintained at elevated temperatures. This paper examines the tool wear mechanisms involved in ultra-precision machining of titanium. In this study single-crystal diamond tools were used to machine commercial pure titanium (CP-Ti) and Ti-6Al-4V alloy. Industrial expectations for surface quality and tool life based on optical grade applications are presented. Results obtained from the characterization of the tool, chip and workpiece led to the identification of graphitization as the mechanism that initiates tool wear. As the cutting edge rounds-off due to graphitization the rate of adhesion of the workpiece material onto the tool increased, which caused the quality of the surface finish to deteriorate. To reduce this wear mechanism a protective barrier made of Perfluoropolyether (PFPE) polymer, was explored. Tribometer studies with PFPE coated diamond tools and titanium pins showed a reduction in the coefficient of friction (COF). Subsequent machining tests using PFPE coated diamond tools showed promising results in extending the tool life and enhancing the surface quality to a point where Ti can now be considered as a viable option for applications involving optical grade surfaces.     

Ultra-precision surface finish of the hardened stainless mold steel using vibration-assisted ball polishing process

A vibration-assisted spherical polishing system driven by a piezoelectric actuator has been newly developed on a machining center to improve the burnished surface roughness of hardened STAVAX plastic mold stainless steel and to reduce the volumetric wear of the polishing ball. The optimal plane surface ball burnishing and vibration-assisted spherical polishing parameters of the specimens have been determined after conducting the Taguchi's L₉ and L₁₈ matrix experiments, respectively. The surface roughness R_a=0.10 μm, on average, of the burnished specimens can be improved to R_a=0.036 μm (R_max=0.380 μm) using the optimal plane surface vibration-assisted spherical polishing process. The improvement of volumetric wear of the polishing ball was about 72% using the vibration-assisted polishing process compared with the non-vibrated polishing process. A simplified kinetic model of the vibration-assisted spherical polishing system for the burnished surface profile was also derived in this study. Applying the optimal plane surface ball burnishing and vibrated spherical polishing parameters sequentially to a fine-milled freeform surface carrier of an F-theta scan lens, the surface roughness of R_a=0.045 μm (R_y=0.65 μm), on average, within the measuring range of 149 μm×112 μm on the freeform surface, was obtainable.     

Micro-electrical discharge machining of polycrystalline diamond using rotary cupronickel electrode

Cupronickel was used as the electrode material to fabricate microstructures on polycrystalline diamond by electrical discharge machining (EDM). The electrodes were shaped into tiny rotary wheels driven by the flow of EDM fluid. Results showed that material removal rate was improved by a factor of five compared to conventional electrode materials. Raman spectroscopy and energy dispersive X-ray spectroscopy indicated that graphitization of diamond and diffusion-based chemical reactions between nickel and diamond dominated the EDM process. Effects of electrode rotation rate and discharge energy on the EDM characteristics were clarified. High form accuracy (∼0.5 μm/1 mm) and low surface roughness (∼0.1 μm Ra) were obtained.     

Dynamic long axis for ultra-precision machining of optical linear structures

Currently, fly cutting is the most popular manufacturing technology for the machining of planar groove structures. The disadvantage of this technology is the long machining time. A promising alternative technology for the machining of planar grooves is planing. The main disadvantage of planing in comparison to fly cutting is the limitation of conventional precision axes concerning a high dynamic movement. Regarding to this aspect the Fraunhofer IPT has developed a precise linear axis. It allows high dynamic movements by using an impulse decoupling system (AiF-FV-Nr.: 13,270 N). The paper describes the mechanical setup and the development and optimization of the mechanical main component. The detailed simulation of the drive system (including motor control loop and impulse decoupling system), results of static and dynamic measurements and test machining results are presented.     

Development of micro milling tool made of single crystalline diamond for ceramic cutting

In order to machine micro aspheric ceramic molds precisely and efficiently, micro milling tools made of single crystalline diamond (SCD) are developed. Many cutting edges are fabricated 3-dimensionally on the edge of a cylindrical SCD by a laser beam. Flat binderless tungsten carbide mold was cut with the developed tool to evaluate the tool wear rate and its life. Some micro aspheric molds of tungsten carbide were cut with the tool at a rotational speed of 50,000 min⁻¹. The molds were cut in the ductile mode. The form accuracy obtained was about 100 nm P–V and the surface roughness 12 nm R_z.     

数控加工中的对刀方法

文章介绍了数控加工中对刀的基本原理,常见的对刀方法及特点,并分别举例说明了数控车床、数控铣床对刀问题的处理.     

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.