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.     

Microstructure of fast tool servo machining on copper alloy

The development of the fast tool servo (FTS) for precision machining was investigated.The micron machining performance of a piezoelectric-assisted FTS on copper alloy was evaluated.The results indicate that the quality of the microstructure depends mainly on two important factors:the cutting speed (or spindle speed) and the driving frequency of the FTS.The excessive driving frequency increases the formation of burrs.The effect of the clearance angle of the diamond tool on the microstructure machining precision was also investigated.     

Nanocrystalline diamond coating tools for machining high-strength Al alloys

Diamond coating tools have been increasingly used for machining advanced materials. Recently, a microwave plasma-assisted chemical vapor deposition (CVD) technology was developed to produce diamond coatings which consist of nano-diamond crystals embedded into a hard amorphous diamond-like carbon matrix. In this study, the nanocrystalline diamond (NCD) coating tools were evaluated in machining high-strength aluminum (Al) alloy. The conventional CVD microcrystalline diamond coating (MCD) tools and PCD tools were also tested for performance comparisons. In addition, stress distributions in diamond coating tools, after deposition and during machining, were analyzed using a 2D finite element (FE) thermomechanical model.

The results show that catastrophic failures, reached in all except one machining conditions, limit the NCD tool life, which is primarily affected by the cutting speed. In addition, coating delamination in the worn NCD tools is clearly evident from scanning electron microscopy (SEM) and force monitoring in machining can capture the delamination incident. At a high feed, coating delamination may extend to the rake face. Furthermore, SEM observations of coating failure boundaries show intimate coating-substrate contact. Though the NCD tools are inferior to the PCD tools, they substantially outperform the MCD tools, which failed by premature delamination. The diamond coating tools can have high residual stresses from the deposition and stresses at the cutting edge are highly augmented. Further machining loading causes the stress reversal pattern which seems to correlate with the tool wear severity.     

激光选区熔化钛合金超声辅助铣削性能研究

目的 针对激光选区熔化钛合金开展超声振动辅助铣削性能和作用机理研究,提高增材制造钛合金表面加工质量、加工精度及加工效率,推动增材制造钛合金构件在高端装备业领域的广泛应用。方法 在传统铣削和超声振动辅助铣削下,采用聚晶金刚石刀具开展激光选区熔化钛合金铣削试验研究,分析不同条件下的表面硬度、切削力、表面形貌、表面粗糙度和切屑黏结的差异性。结果 激光选区熔化钛合金硬度单次测量及其平均值均高于传统钛合金。常规干铣削激光选区熔化钛合金时,切削力随着转速的增大而呈现下降趋势,随着进给速度和切削深度的增加表现出逐渐增大的趋势。在传统铣削下,传统钛合金表面形貌存在明显的刀具划痕,而超声振动铣削时,激光选区熔化钛合金表面形貌总体表现出更加的光滑和平整。激光选区熔化钛合金在常规铣削和超声辅助铣削过程中,刀具前后刀面都出现了严重的钛合金切屑黏结现象。结论 激光选区熔化钛合金常规干铣削时,增大转速或降低进给速度和切削深度能够降低切削力。在相同切削参数下,激光选区熔化钛合金超声铣削质量优于传统钛合金常规铣削表面质量。激光选区熔化钛合金表面质量改善的作用机理主要归因于激光选区熔化钛合金的金相组织特性及超声振动时断...     

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。      

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.     

Quality of Trimming and its Effect on Stretch Flanging of Automotive Panels

Traditional trimming requires accurate alignment of the die shearing edges, typically 5–10% of the blank thickness. Increasing the clearance above the recommended value often leads to generation of burrs on the trimmed surface. These burrs may create difficulties for flanging and hemming operations. Details of trimming technology for panels made out of aluminum sheet AA6111-T4 with elastic offal support will be discussed, including such factors as die radii of the tooling, effect of tooling wear, and trimming angle on the quality of trimmed surface. Also, imperfections on the trimmed edge of the panel may result in reduced formability in stretched flanging and hemming operations. Experimental results quantifying the behavior of trimmed surface in stretching will be provided for both a conventional trimming process and a newly developed process. This article was presented at Materials Science & Technology 2007, Automotive and Ground Vehicles symposium held September 16-20, 2007, in Detroit, MI.     

Material transfer during machining of aluminum alloys with polycrystalline diamond cutting tools

An analysis of a polycrystalline diamond (PCD)-tipped tool after drilling 40,000 holes in aluminum (Al) 319 alloy under fully lubricated conditions is reported. It is found that aluminum adheres to the PCD tip surface during the machining process under lubricated condition. The aluminum transferring leads to poor surface finishing. Surface morphology analysis and element mapping suggests that the cobalt (Co) binder in the PCD tips is responsible for the adhesion of aluminum to the PCD surface, due to the chemical affinity between aluminum and cobalt. Approaches to prevent the adhesion of aluminum to the tool are discussed.     

CVD金刚石刀具微铣削AA356铝合金的磨损分析

AA356铝合金已广泛应用于航空航天等领域,但其在微细加工过程中刀具磨损严重且相关机理尚不明晰.为揭示工艺参数对CVD金刚石刀具微铣削AA356铝合金的刀具磨损影响机制,基于正交试验和响应曲面法开展了微细加工试验,采用最小二乘法和粒子群优化算法建立刀具磨损的预测方程,分析刀具的磨损形貌和切削用量对刀具磨损的影响规律.结...     

Precision machining of small holes by the hybrid process of electrochemical removal and grinding

This paper presents a hybrid process of grinding and electrochemical removal for machining of precision small holes with hard-to-machine materials. In the process, a metal rod with coated abrasives as cathode tool rotates at high speed and removes material electrochemically and mechanically for a pre-machined pilot hole. The effects of process parameters on the hole surface quality and dimensional accuracy were demonstrated experimentally. Material removals on grinding and electrochemical machining are well balanced by rationally determining machining voltage, tool rotation speed and feed rate. Precision holes of diameters down to 0.6 mm with sharp edges and without burrs have been produced.     

Micro-texture at the coated tool face for high performance cutting

This paper describes the effect of micro surface texture on the lubrication conditions at the tool rake face in machining aluminum alloy. For this purpose, four types of micro surface texture were fabricated at the tool faces of cemented carbide through spattering, photolithography and wet etching, and the micro-textured tool faces were coated with diamond like carbon (DLC) or TiN. Then, orthogonal cutting experiments of aluminum alloy were conducted using the coated tools with and without micro-texture. The normal and friction forces and the coefficient of friction were obtained from the measured cutting forces. In addition, tool surface conditions were inspected with a CCD microscope after machining. As a result, it was found that parallel type and square-dot type of micro-textures improved effectively the lubrication conditions in machining aluminum alloy A6061-T6. It was also found that micro-texture was likely to improve the lubrication conditions more effectively as the pattern of texture became smaller and deeper.     

基于旋转超声振动的氧化锆陶瓷小孔磨削加工质量研究

针对陶瓷材料小孔加工质量较差以及加工成本较高等问题,设计一种基于旋转超声辅助的氧化锆陶瓷小孔磨削加工工艺。首先分析旋转超声加工原理,然后在超声振动条件下利用金刚石刀具对氧化锆陶瓷小孔进行单因素磨削加工试验,并对小孔的内壁进行形貌分析和粗糙度检测,最后研究主轴转速、超声功率以及进给速度对小孔表面粗糙度的影响规律。研究结果表明:与普通磨削方式相比,在旋转超声辅助加工条件下,小孔表面质量和残余应力都得到较大改善,当超声功率达到300 W时,加工后的小孔表面粗糙度下降了52%,加工精度明显提高。      

基于碳化硅纤维丝束不规则运动的多孔薄板类零件表面抛光理论与实验研究

汽车空调压缩机用多孔类阀板表面多采用硬研磨工艺进行光整加工,存在表面粗糙度大、孔边有毛刺、阀片与阀板配合表面密封不严等问题。为解决以上问题,提出利用碳化硅纤维丝束抛光替代传统的研磨。完成应用碳化硅纤维丝束进行抛光的运动轨迹的理论分析,采用MATLAB软件对运动参数进行优化仿真,对比分析了毛刷头和工件不同速度对运动轨迹的影响规律。设计制作了双面智能抛光机,并通过实验对运动参数和抛光效果进行验证。结果表明:此种方法将阀板表面的抛光轨迹变成小的均匀曲线交叉网格,消除孔边毛刺并对孔边进行了倒小圆角,提高了阀板表面质量。     

钎焊金刚石工具磨削CFRP的试验研究

为改善碳纤维增强树脂基复合材料(CFRP)的磨边质量及提高刀具的使用寿命,本研究基于"以磨代切"的思想,制备了钎焊金刚石磨头并对CFRP进行了磨边试验。为了评价CFRP磨边的加工质量,定义了CFRP磨边质量的评价参数——毛边因子,分析了主轴转速以及金刚石粒度对CFRP磨边质量的影响。试验结果表明:在相同的磨削深度、工件进给速度下,主轴转速的增加有助于提高CFRP磨边质量;金刚石粒径越小加工质量越好,细颗粒磨头的加工表面粗糙度更低。     

The preparation of cutting edges using a marking laser

During the machining process, high mechanical and thermal loads occur at the cutting edge. Such loads can cause tool failure. Specifically non-uniform and sharp cutting edges that have a low cutting edge stability lead to such failures. In order to enhance the tool performance, the cutting edges are prepared by manufacturing both a pre-defined cutting edge geometry, and an appropriate cutting edge roughness. This paper describes the use of a low-cost marking laser for the preparation of cutting edges as an alternative to conventional preparation techniques, such as brushing or blasting. Cutting edge radii of 9?C47 ??m can be prepared with a machining accuracy of 1.5 ??m. The maximum preparation time for an individual cutting edge is approximately 10 s. Uncoated indexable inserts manufactured in this way were tested in a face milling operation. The results of these investigations (using prepared cutting edges) show both an increase in tool life and an improved surface roughness of the machined workpieces compared to those using non-prepared cutting edges.     

Comparison of the machinabilities of Ti6Al4V and TIMETAL® 54M using uncoated WC–Co tools

Single-point turning tests of cylindrical bars were undertaken to analyse and compare the machinability of Ti6Al4V, the most common titanium alloy, and TIMETAL^® 54M, a newly developed alloy with similar mechanical properties as Ti6Al4V but with better machinability. Conventional cooling and uncoated WC–Co tool inserts were used in the study, because they are the most recommended for machining these materials. The feed and the depth of cut were maintained constant, and only the cutting speed was varied because it is the most affecting parameter. Adhesion of workpiece material in the form of a built-up edge appeared in all the cutting inserts after machining both alloys, which was removed for flank- and crater-wear measurements. Lower wear rates were observed for the Ti54M alloy, especially at high cutting speeds. In the same manner, cutting-force measurements showed lower specific cutting- and feed-force values for the Ti54M alloy. Adiabatic shear bands, a typical feature in the machining of titanium alloys, were observed in chips from both alloys under all cutting conditions. Finally, scanning electron microscopy observations were carried out to analyse the adhered material on the cutting edges of the worn tools where signs of diffusion and attrition were detected.     

Optimization of surface roughness in an end-milling operation using nested experimental design

This paper presents an experimental study to optimize the surface quality of an end-milled surface on a Vertical Machining Centre using Taguchi’s nested experimental design. The effect of various machining parameters on surface roughness was investigated on two different work piece materials, Aluminium alloy and Plain Carbon Steel. Other control factors, namely, feed rate and spindle speed, depth of cut and radial engagement of tool were varied in the experiment to measure surface roughness at four different positions on the work piece. Position was taken as an uncontrollable noise factor. Depth of cut was observed to be the most significant factor that affecting the surface roughness. Also, better surface finish was obtained while machining aluminum alloy as compared to plain carbon steel. Spindle speed and feed rate were the other two significant factors while machining aluminum alloy parts, although these factors did not significantly affect the finish for steel. Radial engagement of tool had no impact on the surface finish for aluminium alloy, while it had a significant impact for plain carbon steel. Further, the analysis of results shows that position P2 (middle of the milled surface) had the best surface finish while position P1 (at beginning of the cut) had relatively poorer finish.     

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.     

Micro milling of titanium alloy Ti-6Al-4V: 3-D finite element modeling for prediction of chip flow and burr formation

Cutting process of titanium alloy Ti-6Al-4V is considered difficult due to chemical affinity between tool and work material, adhesion, built-up edge and burr formation, and tool wear resulting in loss of productivity. Three dimensional (3-D) chip flow together with local field variables such as temperature, elastic/plastic strain, strain-rate and velocity in the shear zones during micro milling process can be predicted using continuum-mechanics based 3-D Finite Element (FE) modelling and simulation of elastic/viscoplastic work material deformations. This paper provides much needed process insight for chip flow, built-up edge and burr formation by using modeling work with experimental validation. Scanning electron microscopic (SEM) observation of the 3-D chip morphology and burrs demonstrate ductile fractured surfaces together with localized instability and failure behaviors. FE simulations are utilized to investigate the effects of micro milling operation i.e. up and down milling and tool edge radius on 3-D chip flow, built-up edge, and 3-D burr formation. Simulated results are compared with measurements of chip morphology, shape, and dimensions together with tool edge condition of built-up edge and chip adhesion yielding to good agreements.     

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。