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.     

A study on ultrasonic elliptical vibration cutting of tungsten carbide

Sintered tungsten carbide (WC) is a versatile metal matrix composite (MMC) material widely used in the tool manufacturing industries. Machining of this material with conventional cutting (CC) method is a real challenge compared to other difficult-to-cut materials. Ultrasonic elliptical vibration cutting (UEVC) method is a novel and non-conventional cutting technique which has been successfully applied to machine such intractable materials for the last decade. However, few studies have been conducted on cutting of WC using single point diamond tool (SPDT) applying the UEVC technique. This paper presents an experimental study on UEVC of sintered WC (～15% Co) using polycrystalline diamond (PCD) tools. Firstly, experiments have been carried out to investigate the effect of cutting parameters in the UEVC method in terms of cutting force, flank wear, surface finish while cutting sintered WC. The tests have revealed that the PCD tools in cutting of WC by the UEVC method results in better cutting performance at 4 μm depth of cut (DOC) as compared to both a lower DOC (e.g. 2 μm) and a higher DOC (e.g. 6 or 8 μm). Moreover, the cutting performance improves with the decrease in both the feed rate and cutting speed in the UEVC method like conventional turning (CT) method. A minimum surface roughness, R_a of 0.036 μm has been achieved on an area of about 1257 mm² with the UEVC performance. The CT method has also been employed to compare its cutting performance against the UEVC method. It has been observed that the UEVC method results in better cutting performances in all aspects compared to the CT method. Theoretical analysis on the UEVC method and analysis of the experimental results have been carried out to explain the reasons of better surface finish at 4 μm DOC and better cutting performance of the UEVC method.     

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.     

Wear and tool life of tungsten carbide, PCBN and PCD cutting tools

The wear mechanisms of cutting tools made of tungsten-carbide (WC), PCBN and PCD were investigated using the tool life and temperature results available in the literature. For tool/work combinations WC/steel and PCBN/hardened-steel, under practical conditions, tool wear was found to be greatly influenced by the temperature. It was concluded that the most likely dominant tool wear mechanism for WC is diffusion and that for PCBN is chemical wear. For PCD, more experimental results and hence further research is required to determine the dominant wear mechanism.     

Machinability of ultrafine-grained copper using tungsten carbide and polycrystalline diamond tools

Equal channel angular extrusion (ECAE) is an effective process to produce bulk ultrafine-grained (UFG) materials from regular coarse-grained materials. Such ECAE-processed materials typically excel in strength, wear resistance, ductility, and high strain-rate superplasticity, with promising applications in lightweight transportation and medical industries. Precision machining work is generally indispensable for further applications after bulk materials are produced by ECAE. To effectively and efficiently machine such ECAE-processed materials for further broad applications, machining issues such as machinability and tool material selection should be considered. This study was undertaken to investigate the machinability of ECAE-processed pure copper using both tungsten carbide (WC) and polycrystalline diamond (PCD) cutting tools in order to facilitate broad applications of ECAE-processed UFG coppers. It is found that despite its higher cost, PCD is favored to machine UFG copper based on this study since it has better wear resistance, gives lower cutting forces, yields a better workpiece surface finish, and results in no smearing on the workpiece. In machining UFG copper, depth of cut notching was observed as the wear pattern and abrasion as the wear mechanism for the WC tool, while flank wear was observed as the wear pattern and diffusion as the wear mechanism for the PCD tool.     

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.     

Machinability of bronze–alumina composite with tungsten carbide cutting tool insert

Bronze–alumina metal matrix composites have been attracting the interest of researchers in recent years, as they have many advantageous characteristics. The mechanical properties of the bronze–alumina composite are improved by the addition of alumina in the matrix. In this present work, bronze was reinforced with 10 wt% alumina particles. The bronze–alumina composite was prepared by stir-casting method. Preheated alumina particles were introduced into the vortex of the molten alloy created by a rotating impeller. Machining studies were conducted on bronze and bronze–alumina composite using tungsten carbide cutting tool insert. The flank wear of the carbide tools on machining bronze–alumina composite is higher than on machining bronze because of the abrasive characteristics of alumina. The cutting force during machining of bronze is lower when compared to that on machining bronze–alumina composite. The bronze exhibited slightly better surface finish than bronze–alumina composite.     

Fundamental investigation of ultra-precision ductile machining of tungsten carbide by applying elliptical vibration cutting with single crystal diamond

This paper presents essential investigations on the feasibility of ductile mode machining of sintered tungsten carbide assisted by ultrasonic elliptical vibration cutting technology. It lays out the foundations toward efficient application of elliptical vibration cutting technology on tungsten carbide. Tungsten carbide is a crucial material for glass molding in the optics manufacturing industry. Its grain size and binder material have significant influence not only on the mechanical and chemical properties but also on the machining performance of tungsten carbide. In order to investigate the influence of material composition on tungsten carbide machining, a series of grooving and planing experiments were conducted utilizing single crystal diamond tools. The experimental results indicated that as compared to ordinary cutting where finished surface deteriorates seriously, ductile mode machining can be attained successfully by applying the elliptical vibration cutting technique. It was also clarified that the binder material, the grain size, cutting/vibration conditions as well as crystal orientation of the diamond tool have significant influence on the tool life and the machined surface quality. Based on these fundamental results, feasibility of micro/nano-scale fabrication on tungsten carbide is investigated. By applying amplitude control sculpturing method, where depth of cut is arbitrary changed by controlling the vibration amplitude while machining, ultra-precision textured grooves and a dimple pattern were successfully sculptured on tungsten carbide in ductile mode.     

Suppression of burrs in turning with ultrasonic elliptical vibration cutting

The approximate cutting force models in three-dimensional separating type ultrasonic elliptical vibration cutting are proposed in present paper. The theoretical models of the stresses of deformation zone on the workpiece edge in burr formation in ultrasonic elliptical vibration cutting are derived based on three-dimensional cutting model, and the reason for the burr being suppressed by applying ultrasonic elliptical vibration is clarified theoretically. Finally, the effect of ultrasonic elliptical vibration cutting on the burr is verified experimentally.     

Machinability of hardened steel using alumina based ceramic cutting tools

Alumina based ceramic cutting tool is an attractive alternative for carbide tools in the machining of steel in its hardened condition. These ceramic cutting tools can machine with high cutting speed and produce good surface finish. The wear mechanism of these ceramic cutting tools should be properly understood for greater utilization. Two types of ceramic cutting tools namely Ti[C,N] mixed alumina ceramic cutting tool and zirconia toughened alumina ceramic cutting tool are used for our investigation. The machinability of hardened steel was evaluated by measurements of tool wear, cutting forces and surface finish of the work piece. These alumina based ceramic cutting tool materials produce good surface finish in the machining of hardened steel. In this paper an attempt is made to analyse the important wear mechanisms like abrasive wear, adhesive wear and diffusion wear of these ceramic cutting tool materials and the performance of these ceramic cutting tools related to the surface finish is also discussed here.     

基体热处理使PCD刀具适于断续切削

聚晶金刚石（PCD）刀具的韧性较差,极少用于带有冲击性的断续切削加工,限制了其应用范围。为改良刀具性能,通过热处理工艺优化刀具基体,加固PCD和基体的结合,制成新型的PCD刀具。通过断续切削铝合金实验,分析新型刀具的使用寿命以及表面磨损状况。结果表明:刀具基体优化后,金刚石层与硬质合金基体之间的结合力提高,刀具抗冲击能力提高。新型刀具在切削128 min后没有出现崩刃现象,其磨损量仍在可控范围,适用于断续切削生产。      

超声波椭圆振动加工技术的研究进展

超声波椭圆振动加工是功率超声加工技术的重要分支之一,在硬脆性材料加工方面具有非常广阔的应用前景。综述了超声波椭圆振动加工系统的研究进展和超声波椭圆振动加工技术在车削、镗削、钻削、铣削、磨削、化学机械抛光、砂轮修整、表面滚压与焊接等方面的最新应用,最后对超声波椭圆振动加工技术的发展方向提出了一些建议。     

Oxygen-shielded ultrasonic vibration cutting to suppress the chemical wear of diamond tools

Ultrasonic vibration has been applied to reduce intense chemical tool wear in ultra-precision diamond cutting of steel and other alloys since a few decades ago. But still, its tool wear suppression mechanisms have not been fully understood. In this paper, the effect of oxygen in suppression of diamond tool wear for ultrasonic vibration cutting is investigated. Experimental results show that the wearing rate is reduced by applying oxygen shielding to the cutting zone in comparison with air and argon. Scientific explanations are also provided for the observed phenomenon through low-pressure metal oxidation experiments and X-ray photoelectron spectroscopy surface analyses.     

PCD刀具切削天然大理石的磨损特性研究

通过PCD刀具切削天然大理石的试验研究,分析了在不同加工参数条件下对PCD刀具切削性能的影响以及刀具的磨损机理。试验结果表明:PCD刀具在加工过程中的磨损机理主要表现为磨粒的磨损、剥落,聚晶层的破损与结合剂破坏等;刀具主轴转速为12 000 r/min、进给速度为1 000 mm/min、切削深度为0.5 mm时,刀具的磨损量最小;且磨损量随刀具主轴转速的增加而降低,随刀具的进给速度和切削深度的增加而增加。     

PCD刀具加工氮化硅陶瓷孔的试验研究

使用PCD刀具对氮化硅陶瓷内孔进行切削试验,首先研究氮化硅陶瓷材料的去除机理,主要包括脆性去除和塑性去除,且以脆性去除为主。其次,研究刀具前角、切削速度、背吃刀量和进给量对切削力的影响。结果表明:刀具前角对切削力的影响不明显;随切削速度、背吃刀量和进给量的增加,切削力均增大,且背向力大于进给力和主切削力。最后,重点研究各参数对内孔侧壁表面粗糙度的影响。结果表明:进给量对表面粗糙度的影响最显著,其次是背吃刀量和切削速度,刀具前角几乎没有影响,且当刀具前角为-5°,切削速度为32.97m/min,背吃刀量为0.10mm,进给量为0.08mm/r时,可以得到较好的表面粗糙度和刀具寿命的综合效益。      

Significance of residual stress in PVD-coated carbide cutting tools

The performance of PVD-coated carbide cutting tools is influenced by their residual stress state, where coating and substrate subsurface have to be considered. The substrate stress is the result of different impacts caused by pre-coating processes and the PVD-coating itself. This presentation demonstrates the significance of residual stress in coating and substrate as well as the influence of each step of a conventional commercial process chain on the respective residual stress state for the manufacture of PVD-coated carbide cutting tools. Alterations of the process chain for tool micro geometry preparation by laser beam removal are considered.     

A new combination of coatings on carbide cutting tools

A new combination of two- and three-layer coatings on carbide-cutting instruments can be obtained by forming a boride-containing underlayer (CoWB) by a diffusion process, and by chemical vapour deposition (CVD) of TiC-TiCN or TiC-Al₂O₃ on the CoWB.The effect is shown of the thickened cobalt net structure on the increase in WC grains and on the decrease in contact surface between the grains of (Ti, Ta, W)C after repeated heating and chemical treatment of the carbide alloy.Comparative tests of cutting on steel and cast iron were carried out using various types of coated cutting plates. Combined coatings are found to prolong the lifetime of carbide instruments by more than 200% in comparison with the coating obtained by CVD alone.     

恒温时间对PCD刀具焊接性能的影响

本文通过PCD复合片与YG8硬质合金的高频感应钎焊试验,研究了恒温时间对PCD刀具钎焊接头强度及钎缝宽度的影响,并用扫描电镜观察了钎焊接头的显微结构,用电子探针分析了接头界面元素分布情况。试验结果表明：随着恒温时间的增加,钎焊接头的剪切强度先增大后减小,而钎缝宽度先减小后增大。当恒温时间为16S时,剪切强度达340MPa,钎缝宽度仅有25μm。No2试样中钎料元素发生了不同程度的扩散,Mn元素的氧化和Zn元素的挥发不明显,C元素有一定程度的扩散,说明钎焊工艺参数选择合理。     

Performance evaluation of cryogenically treated tungsten carbide tools in turning

This paper describes a study on the effects of cryogenic treatment of tungsten carbide. Cryogenic treatment has been acknowledged by some as a means of extending the tool life of many cutting tool materials, but little is known about the mechanism behind it. Thus far, detailed studies pertaining to cryogenic treatment have been conducted only on tool steels. However, tungsten carbide cutting tools are now in common use. The main aim of this study is to analyze the differences in tool performance between cryogenically treated and untreated tool inserts during orthogonal turning of steel. This will aid in the quest for optimal cutting conditions for the turning of steel using these inserts, and will also enhance the understanding of the mechanism behind the cryogenic treatment of tungsten carbide, and the changes in its properties after cryogenic treatment. In the process of ascertaining these findings, it was shown in this study that under certain conditions, cryogenic treatment can be detrimental to tool life and performance. It was also shown that cryogenically treated tools perform better while performing intermittent cutting operations.     

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.