Elliptical Vibration Cutting of Tungsten Alloy Molds for Optical Glass Parts

Elliptical vibration cutting is applied to ultra-precision machining of tungsten alloy molds for optical glass parts in the present research. The tungsten alloy is expected as a new mold material instead of conventional ones such as sintered tungsten carbide and CVD-silicon carbide. However, it cannot be finished precisely by ordinary cutting because of rapid tool wear, brittle fracture and adhesion to the tool. Therefore, the ultrasonic elliptical vibration cutting is applied to the ultra-precision machining of tungsten alloy. Practical ultra-precision molds are obtained by the elliptical vibration cutting, and they are applied to glass molding successfully.     

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.     

Analysis on ductile mode processing of binderless, nano crystalline tungsten carbide through ultra precision diamond turning

Ultra precision diamond turning is usually applied for processing non ferrous metals, plastics and a few single crystal materials. The machining of hard and brittle material, such as nano crystalline, binderless tungsten carbide has only been investigated within a few publications on a theoretical basis and applying nano indenting. Therefore the goal of this paper is to qualify the ultra precision diamond turning technique for processing nano crystalline, binderless tungsten carbide applying the real process conditions identifying optimal parameters. A potential application of this process would be the mold manufacturing for precision glass molding. Within a systematical procedure the ductile to brittle transition is analyzed as well as the tool wear, varying both, tool geometry and processing parameters. Based on material analysis the critical depth of cut for the material was calculated at 165 nm. This value could be validated in the experiments at the optimal cutting speed of 50 m/min with a feed of 1 μm. Least tool wear was observed at a tool radius of 0.4 mm and a rake angle of −20°. The experiments demonstrate the strong influence of the processing conditions on the achieved results.     

Experimental study on brittle–ductile transition in elliptical ultrasonic assisted grinding (EUAG) of monocrystal sapphire using single diamond abrasive grain

This study is carried out to investigate the material removal characteristics in elliptical ultrasonic assisted grinding (EUAG) of monocrystal sapphire using single diamond abrasive grain. The scratching experiments are performed to develop a fundamental understanding of the ductile–brittle transition mechanism during EUAG of monocrystal sapphire. An elliptical ultrasonic vibrator attached with a sapphire substrate was set up on a multi-axis CNC controlled machining center equipped with a single point diamond tool. The vibrator was constructed by bonding a piezoelectric ceramic device (PZT) having two separated electrodes on a metal elastic body, and an elliptical ultrasonic vibration was generated on the end-face of the metal elastic body when two phases of alternating current (AC) voltages with a phase difference are applied to their respective electrodes on PZT. In scratching experiments, the effects of ultrasonic vibration on the critical depth of cut a_c for the ductile–brittle transition region and the material removal ratio, i.e., the ratio of the removed material volume to the machined groove volume, f_ab, are investigated by the examination of the scratching groove surfaces with SEM and AFM. The obtained results show that the critical depth of cut in EUAG is much larger than that in conventional grinding without vibration (CG), and even the bigger vibration amplitude leads to a greater improvement. Although the values of f_ab in the ductile–brittle transition region in both EUAG and CG are less than 1, that in EUAG is bigger than that in CG. Furthermore, as the vibration amplitude increases, the value of f_ab is increased to eventually be close to 1. These show that it is prone to achieve a ductile mode grinding in greater vibration amplitude. It was also found that in the process there are two kinds of material removal modes, i.e., continuous cutting and discontinuous cutting modes, which are determined by the relationship between values of vibration amplitude and depth of cut. This study validates that the elliptical ultrasonic assisted grinding method is highly effective in ductile mode machining of hard and brittle materials.     

Development of a Elliptical Vibration Milling Machine

A unique elliptical vibration milling machine is developed by utilizing a double-spindle mechanism. The developed machine generates circular vibratory motion of the cutting tool mechanically by rotating an eccentric sleeve with a built-in motor. The radius and the maximum frequency of the circular vibration are set to 0.5 mm and 167 Hz respectively. The developed machine is applied to elliptical vibration planing by clamping the tool spindle, and also to elliptical vibration end milling by rotating the inner tool spindle as well at the same time. The machining tests of hardened steel with CBN and coated carbide tools are carried out, and it was proved that the elliptical vibration cutting shows better results as compared with conventional cutting without elliptical vibration motion. A mirror surface on hardened steel with a roughness of about 0.11 μm Ra was obtained by elliptical vibration planing by employing a single crystal diamond tool.     

Micro-cutting characteristics of EDM fabricated high-precision polycrystalline diamond tools

To fabricate three-dimensional microstructures, such as micro dimples, micro grooves and micro channels, on ceramic mold materials, tool fabrication with super hard materials is an essential step. In this work, micro electro discharge machining (EDM) was used to fabricate high-precision polycrystalline diamond end mills. Form accuracy and edge sharpness in one micron level were achieved by utilizing electro discharge induced graphitization of diamond grains under extremely low discharge energy conditions. The cutting performance of the fabricated tools was examined by machining micro dimples and micro grooves on tungsten carbide mold substrates. Results showed that using the EDM-fabricated tools, ductile mode machining of tungsten carbide was realized with a surface finish of 2 nm R_a, which is comparable to that produced by polishing.     

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.     

超声椭圆振动切削技术及装置应用研究现状及进展

首先,阐述了超声椭圆振动切削技术、原理及其装置特点,着重论述了装置各构成部分的特点及其主要应用类型与材料。其次,分析了国内外学者在双激励、单激励方式下实现纵弯、纵扭、双弯曲和弯扭等复合超声振动装置结构设计及其优化方面的研究成果与进展,并且比较了超声椭圆振动切削与传统加工在加工性能、工件表面质量和加工精度等方面的加工优势与适用范围,以及不同超声振动装置在各切削加工中所能获得的加工效果。最后,对超声椭圆振动切削装置的发展趋势进行了总结和展望,指出该装置发展将朝着结合能场的方向发展。     

Analysis of orthogonal finish machining using tungsten carbide and diamond tools of different heat transfer coefficients

An orthogonal cutting model for finish machining, using diamond and tungsten carbide tools which have different coeffficients of thermal conductivity, was simulated and analyzed. It was assumed that the tool had a minute amount of tool flank wear. The distribution of strain rate and stress within the machined workpiece and the determination of the cutting force were obtained after simulation. The generation and distribution of temperature and stress within the chip through cutting of the workpiece were also acquired. In addition, the temperature of the tool, the workpiece and the chip during finish machining by the two different tools, that show the effects of the different friction coefficients of the diamond tool and the tungsten carbide tool on cutting, were compared. Finally, the cutting forces predicted by the model for orthogonal finish machining were compared with those obtained by experiment, and it appears that the present orthogonal finish machining model is reasonable.     

Machinability study of tungsten carbide using PCD tools under ultrasonic elliptical vibration cutting

Sintered tungsten carbide (WC) is an extremely hard and brittle material extensively used in tool manufacturing industries. However, the current cutting technologies for shaping this typical hard-to-machine material are still cost ineffective. In this study, polycrystalline diamond (PCD) tools are used to study the machinability of sintered WC (~15% Co) by applying the ultrasonic elliptical vibration cutting (UEVC) technique. Firstly, it presents the UEVC principle and the effects of speed ratio (i.e. the ratio of the nominal cutting speed to the maximum tool vibration speed in the cutting direction) on the tool–workpiece relative motion as the cutting speed greatly influences the UEVC performance. Then UEVC experiments are carried out to analyze the cutting force, tool-wear progression, chip formation and surface quality against the cutting time at different speed ratios. The results show that when the speed ratio decreases, the resultant cutting force and the tool flank wear decrease while the surface finish improves. Average surface roughness, R_a, in a range between 0.030 and 0.050 μm is achieved at speed ratios less than 0.107. The experimental findings suggest that the commercial PCD tools can be used to machine sintered WC to achieve ultraprecision surface by applying the UEVC technique, which will be cost effective for miniature cutting technologies in future.     

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.     

Precision Cutting of Aspherical Ceramic Molds with Micro PCD Milling Tool

In order to machine micro aspheric molds and dies made of ceramics, micro milling tools made of polycrystal diamond (PCD) are developed. Twenty cutting edges are ground and polished with diamond wheels and loose abrasives on the edge of a small cylindrical PCD tool shank. Some micro aspheric molding dies made of binder-less tungsten carbide were cut with the PCD milling tool developed. The molds and dies were cut in the ductile mode. The form accuracies of the micro aspherical mold and the micro lens array mold obtained were less than 100 nmP-V and the surface roughness 15 nmRz.     

Wear behaviour of cryogenically treated tungsten carbide inserts under dry and wet turning conditions

Cryogenic treatment has been acknowledged as a means of extending the life of tungsten carbide inserts but no study has been reported in open literature regarding the effect of coolant on the performance of cryogenically treated tungsten carbide inserts in turning. In order to understand the effect of coolant, a comparative investigation of the wear behaviour of cryogenically treated tungsten carbide inserts in dry and wet orthogonal turning has been carried out in this study. The commercially available uncoated square-shaped tungsten carbide inserts with chip breakers were procured and cryogenically treated at ?196 °C and the cutting tests were executed in accordance to the International Standard Organisation, ISO 3685-1993 for continuous and interrupted machining mode. The criterion selected for determining the tool life was based on the maximum flank wear (0.6 mm) and the selection of cutting conditions was made to ensure the significant wear at a suitable time interval. The results showed that cryogenically treated tungsten carbide inserts performed significantly better in wet turning conditions under both continuous and interrupted machining modes especially at higher cutting speeds. A considerable increase in tool life was also recorded in interrupted machining mode as compared with continuous machining mode.     

Study on Factors Determining Limits of Minimum Machinable Size in Micro EDM

This paper describes an investigation on factors determining the limits of the minimum machinable diameter of micro rods obtained by micro EDM. Possible factors which influence the limits are discharge crater size, depth of heat affected zone, residual stress, and material micro-structure. In this paper, the influences of residual stress and material micro-structure were especially examined. For the negative effects of residual stress, both residual stress already present prior to machining and residual stress generated by machining itself were investigated using tungsten and cemented tungsten carbide as micro-rod workpiece materials. To determine the effects of material micro-structure, the influence of tungsten carbide grain size on the limits of minimum machinable diameter of cemented tungsten carbide rods was investigated. Comparing the limits between poly-crystal tungsten and mono-crystal tungsten, it was found that micro-machining characteristics were affected significantly by the anisotropy of the mono-crystal tungsten.     

An experimental study on a novel diamond whisker wheel

This study proposes a novel diamond whisker wheel for grinding of advanced materials. The wheel is designed to have preferable spatial distributions and orientations of diamond whiskers which are prepared using a laser cutting technique. To obtain desirable cutting edge geometries, the whisker edges are formed on a lapping machine with diamond powders. The whisker wheel is used in a machining test on a silicon carbide particulate reinforced aluminum alloy and compared with a tungsten carbide milling cutter. The whisker wheel grinding provides better surface finish and significantly reduced machining force than for milling at the same material removal rate.     

Study on wear mechanisms and grain effects of PCD tool in machining laminated flooring

Polycrystalline diamond (PCD) tools have gained increasing application in woodworking industry for the phenomenal tool life and cutting finish compared with carbide tools. In the paper, machining experiments with PCD tools were conducted to mill laminated flooring with Al₂O₃ overlay. Four kinds of PCD products with different original diamond grain sizes were used to fabricate the cutters. Wear volume was measured by optical microscopy and wear morphology was examined by SEM and optical microscopy.The experimental results show that the wear mechanisms of PCD tools, in the machining process, involve inter-granular wear and partial cleavage fracture. The microcracks in PCD tools are a key reason for the wear of tools. By comparing the flank wear, the experiments reveal that PCD tools with middle original diamond grain size have long tool life. The influences of original diamond grain size on cutting edge and wear properties have also been discussed in detail.     

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.     

Experimental study on ultrasonic elliptical vibration cutting of hardened steel using PCD tools

Diamond tools cannot usually be applied for machining hardened steels while applying conventional cutting technique. As an alternative, ultrasonic elliptical vibration cutting (UEVC) technique was successfully applied for obtaining mirror surface on such steels using single crystal diamond (SCD) tools. In order to reduce production cost without compromising mirror surface quality, polycrystalline diamond (PCD) tools may be tested against highly expensive SCD tools. However, study on machining of hardened steel using PCD tools applying the UEVC technique has not yet been reported. The current research presents an experimental study on UEVC of hardened stainless steel (a typical Stavax, hardness 49 HRC) using the PCD tools. Face turning experiments were carried out to investigate the effects of three machining parameters: nominal depth of cut, feed rate, and nominal cutting speed on output performances such as cutting force, tool flank wear, surface roughness, and chip formation. Experimental results show that nominal cutting speed has very strong influence on the output performances, compared to the other two parameters. The surface roughness improves with a decrease in cutting speed. A mirror-like surface of approximately 804 mm² with a roughness value R_a of 11 nm was achieved at a lower cutting speed. Theoretical explanations have been given to support the results drawn from the UEVC experiments. It can be concluded that, while applying the UEVC technique, the inexpensive PCD tools instead of the SCD tools can be effectively applied to obtain optical surface for producing precise molds from the hardened steel.     

Using PCD for machining CGI with a CO2 coolant system

Polycrystalline diamond is widely used as a economic cutting material for machining non-ferrous materials such as aluminum. It is perceived that diamond cannot be used for cutting ferrous materials due to the high affinity of carbon to iron. Nevertheless, under certain conditions it is possible to use diamond materials for cutting ferrous metals. In order to avoid graphitization of the diamond matrix, it is necessary to keep the cutting temperature below the critical level of diamond graphitization. This paper presents the influence of a cryogenic CO₂ coolant strategy on the cutting process using PCD tools for cutting high strength compacted graphite iron (CGI). Investigations show, that tool wear behavior strongly correlates with the cutting speed, the cutting forces, cutting temperatures, and surface roughness of the workpiece. The test results show, that the tool life of PCD for cutting cast iron is dependent on the diamond grain size, the binder material, and the cutting parameters.     

钎焊金刚石铣磨刀具磨粒粒度尺寸与排布间距对CFRP磨削质量的影响

碳纤维增强复合材料（carbon fiber reinforced plastics,CFRP）由于其低层间结合力和各向异性导致其加工过程中易出现分层、毛刺、撕裂等加工缺陷和刀具耐用度低等问题。采用有序排布钎焊金刚石磨削刀具及"以磨代切"加工工艺能够有效减轻分层缺陷。为制备出适合CFRP磨边加工的钎焊金刚石刀具,本试验制备了不同磨粒排布间距与不同磨粒粒度尺寸的5种刀具,对比分析了刀具结构变化对CFRP磨边加工磨削力与加工表面质量的影响。试验结果表明:在一定范围内,在相同磨粒排布间距和加工参数下,随着磨粒粒度尺寸变大,磨削力变化很小,加工表面质量变差;在相同磨粒粒度尺寸与加工参数下,随着磨粒排布间距减小,磨削力先增大后减小,加工表面质量变好。