高速车削钛合金时PCBN刀具寿命的研究

采用对角正交回归试验法,研究了用PCBN刀具高速车削钛合金TC4时切削用量对刀具寿命的影响,并分析工件已加工表面粗糙度。通过扫描电镜观察分析,证实刀具的磨损机理主要是前后刀面的粘结磨损及氧化磨损、后刀面磨损以及切削深度线处的沟槽磨损。     

Analysis of tool wear and surface finish in hard turning

Hard turning is a profitable alternative to finish grinding. The ultimate aim of hard turning is to remove work piece material in a single cut rather than a lengthy grinding operation in order to reduce processing time, production cost, surface roughness, and setup time, and to remain competitive. In recent years, interrupted hard turning, which is the process of turning hardened parts with areas of interrupted surfaces, has also been encouraged. The process of hard turning offers many potential benefits compared to the conventional grinding operation. Additionally, tool wear, tool life, quality of surface turned, and amount of material removed are also predicted. In this analysis, 18 different machining conditions, with three different grades of polycrystalline cubic boron nitride (PCBN), cutting tool are considered. This paper describes the various characteristics in terms of component quality, tool life, tool wear, effects of individual parameters on tool life and material removal, and economics of operation. The newer solution, a hard turning operation, is performed on a lathe. In this study, the PCBN tool inserts are used with a WIDAX PT GNR 2525 M16 tool holder. The hardened material selected for hard turning is commercially available engine crank pin material.     

The monitoring of flank wear on the CBN tool in the hard turning process

In precision hard turning, tool flank wear is one of the major factors contributing to the geometric error and thermal damage in a machined workpiece. Tool wear not only directly reduces the part geometry accuracy but also increases the cutting forces drastically. The change in cutting forces causes instability in the tool motion, and in turn, more inaccuracy. There are demands for reliably monitoring the progress of tool wear during a machining process to provide information for both correction of geometric errors and to guarantee the surface integrity of the workpiece. A new method for tool wear monitoring in precision hard turning is presented in this paper. The flank wear of a CBN tool is monitored by feature parameters extracted from the measured passive force, by the use of a force dynamometer. The feature parameters include the passive force level, the frequency energy and the accumulated cutting time. An ANN model was used to integrate these feature parameters in order to obtain more reliable and robust flank wear monitoring. Finally, the results from validation tests indicate that the developed monitoring system is robust and consistent for tool wear monitoring in precision hard turning.     

Experimental investigations while hard machining of DIEVAR tool steel (50 HRC)

This paper describes hard machining which offers many potential benefits over traditional manufacturing techniques. In this work, investigations were carried out on end milling of hardened tool steel DIEVAR (hardness 50 HRC), a newly developed tool steel material used by tool- and die-making industries. The objective of the present investigation was to study the performance characteristics of machining parameters such as cutting speed, feed, depth of cut and width of cut with due consideration to multiple responses, i.e. volume of material removed, tool wear, tool life and surface finish. Performance evaluation of physical vapour deposition-coated carbide inserts, ball end mill cutter and polycrystalline cubic boron nitride inserts (PCBN) was done for rough and finish machining on the basis of flank wear, tool life, volume of material removed, surface roughness and chip formation. It has been observed from investigations that chipping, diffusion and adhesion were active tool wear mechanisms and saw-toothed chips were formed whilst machining DIEVAR hard steel. PCBN inserts give an excellent performance in terms of tool life and surface finish in comparison with carbide-coated inserts. End milling technique using PCBN inserts could be a viable alternative to grinding in comparison to ball end mill cutter in terms of surface finish and tool life.     

Tool wear, chip formation and workpiece surface issues in CBN hard turning: A review

Steel parts that carry critical loads in everything from automotive drive trains and jet engines to industrial bearings and metal-forming machinery are normally produced by a series of processes, including time-consuming and costly grinding and polishing operations. Due to the advent of super-hard materials such as polycrystalline cubic boron nitride (PCBN) cutting tools and improved machine tool designs, hard turning has become an attractive alternative to grinding for steel parts. The potential of hard turning to eliminate the costs associated with additional finishing processes in conventional machining is appealing to industry. The objective of this paper, is to survey the recent research progress in hard turning with CBN tools in regard of tool wear, surface issues and chip formation. A significant pool of CBN turning studies has been surveyed in an attempt to achieve better understanding of tool wear, chip formation, surface finish, white layer formation, micro-hardness variation and residual stress on the basis of varying CBN content, binder, tool edge geometry, cooling methods and cutting parameters. Further important modeling techniques based on finite element, soft computing and other mathematical approaches used in CBN turning are reviewed. In conclusion, a summary of the CBN turning and modeling techniques is outlined and the scope of future work is presented.     

Surface layer microhardness changes with high-speed turning of hardened steels

In high-speed cutting of hardened steels, the surface layer is strongly affected by thermal effects and mechanical forces. Due to this, the surface layer of the machined material changes noticeably. Microhardness, one parameter of the surface integrity, is the most important. This paper deals with an investigation of microhardness. Measuring results are presented, and reasons for the sometimes significant changes in microhardness are analysed. It is proved on which part of the cutting edge the material removal will not take place but the cutting edge deforms the material plastically and how this part of the cutting edge can be reduced. With the measurement of the cutting force, the hypothesis is proved that the values of the cutting force components related to each other are different compared to the traditional turning. The passive force is 1.88?C2.25 times higher than the main cutting force. Hence, the force taking place on the flank face of the cutting tool is very high and the friction power significantly influences the cutting temperature. The friction taking place on the flank face of the cutting tool generates 2.8?C3.9 times higher heat than the cutting force. Due to the changes that occur in the surface layer, the hardness of this layer is higher with 100?C150?HV in depth of 0.1?mm than the original hardness or the hardness prescribed in the technical drawings. This phenomenon can be observed not only in internal hard turning but also machining of external and conical surfaces. Microhardness is compared after hard turning and after grinding. According to the measurements, the ground surface has not become a harder surface layer but softer. As an average result of many measurements, it has been proven that the original hardness (700?HV) after case hardening will increase to 800?C850?HV after hard turning and will decrease to 500?C550?HV after grinding. Microhardness changes are analysed considering the typical chip removal characteristics of hard turning. In this article, the focus is on how changes in microhardness influence the functional behaviour of the components and may affect their lifetimes. In this article, it has been proven that independently from the surface of the machined gear (bore, conical or face surface) the changes in the surface layer regarding microhardness do not differ.     

精密干式硬态车削淬硬工具钢加工表面温度参数优化

使用PCBN刀具对不同淬硬状态工具钢Cr12MoV进行精密干式硬态车削试验,运用极差法分析切削速度、走刀量、切削深度、试件硬度、刀尖圆弧半径五个因素对工件表面温度影响的显著性,并得到了最优车削参数。试验表明：影响工件表面温度最显著的因素是工件淬火硬度,切削深度与走刀量的影响相当,刀尖圆弧半径的影响最小。     

Tool wear and tool life characteristics of unconventional sintered carbides in the intermittent cutting of hardened steel

Carbides coated with TiC, TiN, TiC/TiN or TiC/Al₂O₃ coatings on a tough hard material base and TiC-containing hard material of modified composition and structure were used to investigate tool-wear and tool-life characteristics in face milling of martensitic steel of hardness 300–600 HV. Tool-life behaviour with increasing hardness and cutting speed was determined. Characteristic wear mechanisms are discussed on the basis of light and scanning electron microscopy observations.     

CBN tool wear in hard turning: a survey on research progresses

Direct machining steel parts at a hardened state, known as hard turning, offers a number of potential benefits over traditional grinding in some applications. In addition, hard turning has several unique process characteristics, e.g., segmented chip formation and microstructural alterations at the machined surfaces, fundamentally different from conventional turning. Hard turning is, therefore, of a great interest to both the manufacturing industry and research community. Development of superhard materials such as polycrystalline cubic boron nitride (known as CBN) has been a key to enabling hard turning technology. A significant pool of CBN tool wear studies has been surveyed, in an attempt to achieve better processing and tooling applications, and discussed from the tool wear pattern and mechanism perspectives. Although various tool wear mechanisms, or a combination of several, coexist and dominate in CBN turning of hardened steels, it has been suggested that abrasion, adhesion (possibly complicated by tribochemical interactions), and diffusion may primarily govern the CBN tool wear in hard turning. Further, wear rate modeling including one approach developed in a recent study, on both crater and flank wear, is discussed as well. In conclusion, a summary of the CBN tool wear survey and the future work are outlined.     

Wear of CBN Tools in Ultra-Precision Machining of STAVAX

CBN cutting tools are widely used in ultra-precision machining of STAVAX (specialized stainless steel) mould inserts for injection moulding of optical lenses. This paper will report on experiments carried out to investigate the wear of CBN tools with different grain sizes and various CBN/TiN ratios in ultra-precision machining of STAVAX. The tool-wear characteristics were observed to be greatly dependent on the tool type, hardness of the STAVAX and cutting parameters used. In the machining of STAVAX with a hardness of 55 HRC, fine-scale cavities were formed on the rake face and as such the surface damage acted like a chip breaker resulting in formation of cracks. While the flank faces of all tool types showed a similar wear resistance, it was observed that a combination of a higher percentage of TiN binder and smaller grain size led to greater wear resistance on the rake face. It was found that the formation of cracks on the rake faces could be prevented by means of either increasing the cutting speed or reducing the hardness of the machined workpiece.     

Influence of tool wear on surface roughness in hard turning using differently shaped ceramic tools

Hard turning has been applied in many cases in producing bearings, gears, cams, shafts, axels, and other mechanical components since the early 1980s. Mixed ceramics (aluminum oxide plus TiC or TiCN) is one of the two cutting tool materials (apart from PCBN) widely used for finish machining of hardened steel (HRC 50–65) parts, especially under dry machining conditions and moderate cutting speed ranging from 90 to 120 m/min. This paper reports an extensive characterization of the surface roughness generated during hard turning (HT) operations performed with conventional and wiper ceramic tools at variable feed rate and its changes originated from tool wear. Moreover, it compares some predominant tool wear patterns produced on the two types of ceramic inserts and their influence on the alteration of surface profiles. After the hard turning tests, the relevant changes of surface profiles and surface roughness parameters were successively registered and measured by a stylus profilometer. In this investigation, a set of 2D surface roughness parameters, as well as profile and surface characteristics, such as the amplitude distribution functions, bearing area curves and symmetrical curves of geometrical contact obtained for the machined surface, were determined and analyzed. A novel aspect of this research is that the notch wear progress at the secondary cutting (trailing) edges was found to produce the substantial modifications of the individual irregularities, and constitute the altered surface profiles. Moreover, this research contributes to practical aspects of HT technology due to exploring the relations between the tool state at different times within the tool life and the relevant surface roughness characterization.     

用PCBN刀具精密切削GCr15淬硬轴承钢

通过切削试验研究了PCBN刀具精密切削GCr15淬硬轴承钢时的切削力特征、切屑形态、刀具磨损特性等切削性能 ,并从表面粗糙度、硬化层深度、亚表层白层现象、残余应力分布等方面研究了PCBN刀具精密切削淬硬轴承钢的加工表面质量     

Flank wear prediction of ceramic tools in hard turning

Due to technical and economical factors, hard turning is competing successfully with the grinding process in the industries. Many practical applications require components to be hardened in order to improve their wear behavior. Higher productivity and good surface quality are the requirements of the modern industries. However, tool wear is the major problem in hard turning. The tool wear models, used to assess the performance of hard turning process, play an important role in predicting the surface quality. So, in the present work, an attempt has been made to develop an analytical tool wear model for the mixed ceramic inserts during the hard turning of bearing steel incorporating abrasion, adhesion, and diffusion wear mechanisms. The new model developed can reliably be used to assess the wear of the mixed ceramic tools within the domain of the parameters. It has been observed that tool wear is increasing with the increase in cutting speed, feed, and effective rake angle. However, it has been found to be slightly decreasing with the increase in nose radius. The proposed model was validated by conducting experiments. It could be seen that the model was capable of predicting the flank wear using the cutting parameters and tool geometry.     

激光超声复合切削硬质合金的刀具磨损及其对工件表面质量的影响

基于激光加热辅助切削和超声椭圆振动切削提出了激光超声复合切削加工工艺。采用聚晶立方氮化硼(PCBN)刀具对YG10硬质合金进行了常规切削,超声椭圆振动切削,激光加热辅助切削和激光超声复合切削对比试验。检测了刀具磨损量、刀具磨损形貌、工件表面粗糙度以及工件表面形貌,并通过扫描电镜(SEM)对刀具磨损区域进行了能谱分析,同时研究了激光超声复合切削硬质合金时PCBN刀具的磨损及其对工件表面质量的影响。最后,与常规切削、超声振动切削及激光加热辅助切削进行了对比试验。结果表明:激光超声复合切削时刀具使用寿命显著增加,加工后的工件表面粗糙度平均值分别降低了79%、60%和64%,且工件表面更加平整光滑。激光超声复合切削硬质合金时,PCBN刀具的前刀面磨损表现为平滑且均匀的月牙洼磨损,后刀面磨损表现为较窄的三角形磨损带和较浅的凹坑和划痕;刀具的失效机理主要为黏接磨损、氧化磨损和磨粒磨损的综合作用。     

深冷处理对PCBN刀具切削性能的影响研究

针对PCBN刀具在硬切削加工中磨损严重、切削寿命短的问题,开展了PCBN刀具深冷处理试验和经深冷处理的PCBN刀具高速硬车削AISI 4340钢的试验,研究深冷处理对PCBN刀具表面完整性(包括微观形貌、粗糙度、显微硬度和残余应力)及切削性能的影响规律,探究提高PCBN刀具耐磨性和刀具寿命的方法。研究结果表明,经过深冷处理之后,刀具表面缩松缩孔等缺陷明显减少甚至消失,表面形貌得到改善,但刀具表面粗糙度增大;刀具表面显微硬度、残余应力均得到提高;表面形貌和表面残余应力对刀具寿命影响较大,其次是表面显微硬度,表面粗糙度对刀具寿命影响较小。深冷处理后,刀具黏结、氧化磨损减少,刀具寿命较未处理刀具提高24.78%,可见,深冷处理可有效改善PCBN刀具表面完整性,从而提高刀具寿命。     

Experimental investigation of the three-component forces in finish dry hard turning of hardened tool steel at different hardness levels

In this paper, the effects of cutting speed, depth of cut, feed, workpiece hardness (51, 55, 58, 62, and 65?±?1 HRC), tool flank wear, and nose radius on three-component forces in finish dry hard turning (FDHT) of the hardened tool steel AISI D2 were experimentally investigated by utilizing the PCBN inserts. Experimental results showed that the feed force is the lowest in three-component forces and influence of cutting parameters on it is less than two others in the FDHT of AISI D2. Values of the radial force are higher than those of the cutting force when cutting speed, depth of cut, and feed range from 75 to 301 m/min, and 0.10 to 0.40 and 0.05 to 0.20 mm, respectively, but lower in the range between 0.8- and 1.6-mm nose radius. Values of the cutting force are higher than those of the radial force as the workpiece hardness varies from 51 to 58?±?1 HRC while lower in the range between 62 and 65?±?1 HRC. Besides, there are relations between the changing laws of three-component forces and the softening effect of chip, cohesion effect in the tool–chip junction zone, and intenerating effect of metal in the workpiece surface. The high flank wear formation increases the contact with workpiece surface and hence induces tearing–drawing and welding effect duo to instantaneous high temperature.     

渐变强化刃刀具硬切削过程切屑流动和刀具磨损研究

刃口倒棱结构在提升切削刃强度的同时也进一步增大了切削过程中的热力载荷,进而影响着硬切削加工的切屑流动、刀具磨损和加工表面质量。利用高速摄影方法,对比分析了渐变强化刃和定值倒棱两种结构PCBN刀具的切屑流动特性,发现渐变强化刃结构具有协调切屑流动的作用,能有效地解决硬切削过程切屑积聚问题。结合硬切削试验,开展了渐变强化刃刀具磨损特性研究,结果表明：与定值倒棱刀具相对集中的磨损带不同,渐变强化刃刀具磨损区域则更为狭长,后刀面磨损带呈现为长三角形,具备了更为优异的刃口保持性和耐用度,当进入到刃形改变阶段,其磨损机制由磨粒磨损机制逐渐变化为磨粒、氧化和扩散等多种机制的混合形式。渐变强化刃结构刀具在改善切屑流动和提升刀具耐用度方面均体现出了明显的优势,具备了良好的推广应用前景。     

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.     

PCBN刀具断续切削磨损机理的研究

研究了BN250断续车削淬火钢SAE8822十字轴的磨损现象。试验结果显示微崩刃是断续车削中导致刀具失效的主要因素,工件与BN250刀具元素之间的化学反应和扩散作用削弱了结合剂与CBN基体直接的结合强度,是导致刀具破损发生的主要因素。     

Modeling and experimentation on multistage work-hardening mechanism in machining with nose-radiused tools and its influence on machined subsurface quality and tool wear

The paper reports on the modeling and respective experimental validation for the formation of the machined subsurface layer in turning with nose-radiused and round tools. An experimental work on the mechanisms of work-hardening of the machined surface and related wear of the cutting tools was conducted for high-speed turning of aged Inconel 718 with whisker-reinforced alumina tools. The model shows that multiple deformations of the machined surface occur when machining with small feeds and tools with large nose radius, thus changing the mechanics of surface formation. Experimental results confirm the localized increase in subsurface hardness in the vicinity of the tool tip. The variation in the degree of work-hardening and the extent of the area affected by it fully agree with the predictions of the model. The model also shows that a significant part of the cutting tool may cut through the extra work-hardened material. Tool wear tests show that the local increase in workpiece hardness results in a localized increase in the wear rate of the cutting tools.