铍青铜微细切削性能研究

通过对比聚晶金刚石(PCD)、硬质合金、立方氮化硼(CBN)刀具在微细切削铍青铜时的切削性能,研究了不同刀具微细切削铍青铜时的表面粗糙度以及表面纹理,分析了不同刀具微细切削铍青铜时的刀具磨损状况,主要包括前刀面、切削刃以及后刀面。研究表明,PCD刀具在进行微细切削时表现出优良且稳定的切削性能,不仅表面粗糙度R_a值低、切削力小,而且刀具磨损量最小;硬质合金刀具在本次试验中切削性能仅次于PCD刀具,考虑到刀具成本,硬质合金刀具具有极高的性价比;CBN刀具则由于容易产生大型的积屑瘤从而导致切削过程极不稳定,表面粗糙和切削力过大,而被证明不适合用于铍青铜材料的微细切削过程。同时对PCD刀具微细切削铍青铜的切削参数进行了优化。     

基于MATLAB的积屑瘤图像处理与分析

在金属切削中,积屑瘤对刀具使用寿命和工件表面质量有很大的影响,应用MATLAB对由机器视觉系统获得的刀具二维图像进行边缘检测,并采用图像相减法来计算积屑瘤的面积,获得了清晰的刀具轮廓图像和积屑瘤大小随时间的变化曲线,实现了刀具积屑瘤变化的在机监测。     

TiN涂层对积屑瘤和表面粗糙度的影响

工业技术的发展,使得对零件表面质量的要求越来越高。对于钢类材料的精加工,特别是拉削和齿轮切削等,由于在生产常用的切削条件下,积屑瘤难以避免,导致零件的已加工表面质量常常难以令人满意。对于由主切削刃形成已加工表面的加工工艺,积屑瘤是影响表面粗糙度的主要因素。为了降低工件的表面粗糙度,人们往往着眼于合理选择刀具几何角度,切削用量和切削液,但是由于积屑瘤是被切削材料在刀具前刀面上冷焊粘结形成的,所以,要想有效地降低已加工表面粗糙度,必须从根本上改善前刀面上刀具与切屑之间的摩擦粘结状况,抑制或消除积屑     

PCBN刀具和硬质合金刀具铣削GCr15的对比试验研究

在干式切削的条件下,采用单因素试验法,比较分析了PCBN刀具和硬质合金刀具铣削轴承钢GCr15的差异。结果表明:PCBN刀具在铣削过程中不产生积屑瘤,可获得更好的表面粗糙度,后刀面的磨损较小。     

用金刚石端铣刀高速加工铝材

试验用设计的金刚石端铣刀进行了铝合金铣削试验,在常规的切削速度下用普通刀具加工零件,由于积屑瘤和毛刺的形成,往往引起刀具寿命短,加工表面质量差及切削刃质量差.在许多行业的铝合金加工技术中,较高的表面光洁度及切削刃质量很重要,也很需要.本试验的结果揭示出使用新设计的金刚石端铣刀高速切削铝合金,能加工出镜面表面,而不产生积屑瘤和毛刺.     

单晶金刚石刀具切削有色金属磨损机理研究

研究单晶金刚石刀具切削有色金属的磨损机理,分析切削过程影响加工工件表面粗糙度的影响因素和切削速度、进给量、背吃刀量等因素对积屑瘤生成的影响,以及积屑瘤对刀具切削力的影响。给出了切削过程中刀具与工件接触区温度和压力过高,导致金刚石刀具刃口发生石墨化、溶解、崩刃等磨损破损。前后刀面磨损、崩刃是金刚石刀具磨损主要形态。金刚石刀具磨损是微观磨损的不断积累,其磨损程度与磨损速度取决于金刚石碳原子在有色金属或在其它非金属材料原子中的溶解率。     

积屑瘤对精加工的影响

通常在切削过程中,用中等或低的切削速度切削钢、铝或其他塑性金属时,会发现一小块金属牢固地粘附在所用刀具的前刀面上,这一小块金属就是积屑瘤,如图1所示。积屑瘤是被切金属在切削区的高压和大摩擦力作用下与刀具刃口附近的前刀面上粘结形成的。这图1块金属受到加工硬化的影响,其硬度可比基体高2~3倍,因此可以代替刀刃切削。积屑瘤在切削过程中是不稳定的。它开始生长到达一定高度以后,发生脆裂,被工件和切屑带走而消失,以后又开始生长,从小到大,又破碎消失,周而复始地循环。由于它时现时失、时大时小,使工件表面呈高低不平,使表面粗糙度…     

基于机器视觉的积屑瘤在线监测装置

现代切削工艺中,产生积屑瘤对切削过程和加工表面质量的影响不容忽视,对积屑瘤的在线监测显得尤为重要。设计制作了一种基于机器视觉技术的积屑瘤在线监测装置,能够方便地在机获取切削加工中积屑瘤变化的清晰图像。实验结果表明,该装置简便可靠,为于最终实现刀具磨损在线监测提供了手段。     

激光照射加热切削

通过高温切削改善难切削材料的切削加工性能,具体地说,在高温下材料的塑性流动变得容易,以便有助于减少磨损和摩擦。结果是减小了切削阻力,防止积屑瘤的产生,改善刀具寿命,提高切削效率,从而使加工表面的粗糙度得到改善。     

微切削镍基高温合金表面质量的研究

镍基高温合金是一种难加工金属材料,加工后表面质量很难保证。而表面质量是微切削加工追求的重要内容,其对加工后零件的耐磨性、耐腐蚀性和热传导性能都有很大的影响。在分析切削实验结果基础上,进行微切削仿真,深入研究镍基高温合金微切削时的表面质量。结果表明:微切削过程中切屑层晶粒破碎并由于产生的高温软化在前刀面形成积屑瘤,积屑瘤软化从下刀面流出,残留在加工表面形成硬点毛刺。由于微切削刀具刃口钝圆半径尺寸不能忽略,进而产生犁耕现象,即在进行微切削的过程中,钝圆前方的晶粒被刀具刃口挤压,压入加工表面,在加工表面形成凹陷。由仿真现象发现,锯齿形切屑的形成有利于减少犁耕现象。     

Built-up edge effects on process outputs of titanium alloy micro milling

Built-up edge (BUE) is generally known to cause surface finish problems in the micro milling process. The loose particles from the BUE may be deposited on the machined surface, causing surface roughness to increase. On the other hand, a stable BUE formation may protect the tool from rapid tool wear, which hinders the productivity of the micro milling process. Despite its common presence in practice, the influence of BUE on the process outputs of micro milling has not been studied in detail. This paper investigates the relationship between BUE formation and process outputs in micro milling of titanium alloy Ti6Al4V using an experimental approach. Micro end mills used in this study are fabricated to have a single straight edge using wire electrical discharge machining. An initial experimental effort was conducted to study the relationship between micro cutting tool geometry, surface roughness, and micro milling process forces and hence conditions to form stable BUE on the tool tip have been identified. The influence of micro milling process conditions on BUE size, and their combined effect on forces, surface roughness, and burr formation is investigated. Long-term micro milling experiment was performed to observe the protective effect of BUE on tool life. The results show that tailored micro cutting tools having stable BUE can be designed to machine titanium alloys with long tool life with acceptable surface quality.     

Study on the protective effect of built-up layer in dry cutting of stainless steel SUS304

This work presents a systematic and comprehensive investigation of the protective effect of built-up layer (BUL) in dry cutting of stainless steel SUS304. A detailed examination of BUL and built-up edge (BUE) formation conditions, their formation mechanisms, and their protective effect was carried out at different cutting speeds (5–140 m/min), and different feed rates (0.02–0.1 mm/rev). The uncoated cemented carbide tool was used as a cutting tool. The dimensions of BUL/BUE and tool wear were measured by scanning electron microscope (SEM) and laser confocal microscopy (LCM). The protective effect of BUL/BUE was characterized using flank wear progression, as well as crater wear progression, cutting force analysis, and surface roughness analysis. As a result, it was found that BUE forms around the cutting edge at low cutting speeds (5–20 m/min), and BUL, which resembles a water drop, forms on the tool rake face at cutting speeds equal to or above 40 m/min. And a thin layer of flank built-up (FBU) can form on the tool flank face as the cutting speed increases from 40 m/min to 140 m/min. The BUL/BUE formation mechanism was also confirmed. It was revealed that BUL can be considered as a protective layer, which can not only prevent the tool rake face from wear but also decrease the tool flank wear, but BUE can only prevent the crater wear; and to a certain extent, the thin layer of FBU can also work as a protecting layer on the worn tool flank face in dry cutting of SUS304. It was also revealed that the height of BUL plays a very important role in its protective effect. Meanwhile, it was found that BUL and the thin layer of FBU have no or few influences on the amplitude variation of cutting forces and on the surface roughness. These results indicated that BUL can be used to realize the self-protective tool (SPT) in cutting of difficult-to-cut material such as SUS034. In addition, the research also proved that it is necessary to take the influences of BUL, BUE, and FBU formations on tool wear into account in the tool wear model in order to achieve high-precision prediction.     

基于声发射技术的微切削加工表面形貌监测

采用声发射技术对工件材料为A16061-T6的微切削表面轮廓进行了实时测量.采集监控微切削加工表面时产生的声发射均方根信号,并与表面轮廓仪测得的结果进行对比.研究表明,声发射均方根信号与微切削表面形貌很好的相对应,因此,声发射技术适于微切削表面形貌的监测.研究了切削用量(每齿进给量和主轴转速)与表面形貌之间的关系,微切削的每齿进给量对表面粗糙度影响较大.     

The performance Of DLC-coated and uncoated ultra-fine carbide tools in micromilling of Inconel 718

Coating is an important factor that affects cutting-tool performance. In particular, it directly affects surface quality and burr formation in the micro milling process. After the micromechanical machining process, surface quality is very hard to increase by a second process (grinding, etc.). In addition, in micromechanical machining, the cutting tool needs to have a good resistance to wear, owing to the fact that the cutting process is carried out at high speed. In this study, the machinability of Inconel 718 superalloy was investigated, using a Diamond Like Carbon (DLC) coated tool. The experimental tests were carried out in dry cutting conditions for different feed rates and depth of cuts. It was found that the dominant wear mechanism for all cutting parameters was identified to be abrasive and diffusive wear. Besides, a significantly Built Up Edge (BUE) formation was observed in uncoated tool. The results clearly show that DLC coating significantly decreased BUE. In addition, a smaller cutting force and better surface roughness were obtained with a DLC-coated tool. In conclusion, DLC coating can be used in micro milling of Inconel 718. It reduces the BUE and burr formation, improves surface roughness.     

Fundamental analysis of the mechanism of built-up edge formation based on direct scanning electron microscope observation

Direct scanning electron microscope (SEM) observation of the dynamic behaviour of the built-up edge (BUE) and local strain analysis around the BUE were carried out to investigate fundamentally the mechanism of BUE formation for low carbon steel. There are two types of crack which play significant roles in the mechanism of BUE formation: one forms below the flank face of the tool and the other forms subsequently ahead of the rake face of the tool. The former starts at the machined surface, a few tens of micrometres from the cutting edge of the tool, and grows in the primary shear zone accompanied by severe strain concentration. The latter occurs along the secondary shear zone and is caused by extensive shearing a certain distance away from the cutting edge of the tool. The morphology of the BUE is determined by the formation of both cracks, its growth depending on the strain concentration and the growth of the cracks.     

Influence of turning parameters on the machinability of homogenized Al–Cu/TiB2 in situ metal matrix composites

The increasing demand for high-strength and lightweight materials in automobile, defense, and aerospace applications necessitates the development of new composite materials and their machinability studies with wide spectrum. In this aspect, an attempt has been made to investigate the machinability characteristics of homogenized Al–Cu/TiB₂ in situ metal matrix composites. The effect of parameters, such as cutting speed, feed, and depth of cut, on performance measures, such as cutting force and surface roughness, were investigated during turning operations. As a secondary objective, the built-up edge (BUE) and chip formation are also examined. Experimental results show that better surface finish is obtained at higher cutting speed and low feed. BUE formation is observed only at low cutting speed. The chip breakability is improved due to the presence of reinforcement.     

In-cycle detection of built-up edge (BUE) from 2-D images of cutting tools using machine vision

The built-up edge (BUE) phenomenon that appears under certain machining condition, such as low-to-moderate cutting speed, high depth of cut, dry cutting, cutting of ductile material, etc. is known to have a major effect on the surface quality of the finished workpiece. In the published literature, BUE has been measured using scanning electron microscope and optical microscopes to study its effect on tool life and surface quality. Such measurement methods are only applicable in off-the-machine inspection. Since the BUE extending beyond the tool nose alters the tool geometry and, thus, influences the workpiece roughness profile, detection of BUE outside the nose region is important. This research proposes a new method for detecting BUE from 2-D images of the nose region of the tool using a machine vision approach. Two methods of determining the BUE area are proposed—the subtraction method and polar-radius transformation method. Application of both methods is successfully demonstrated using simulated and real cutting tool images.     

A new quantitative evaluation for characteristic of surface roughness in turning

With turning as the aim, a method for quantitatively evaluating the stability of cutting phenomena and a machining system from the machined surface profile (primary profile and roughness profile) is proposed, based on the hypothesis that when the ideal cutting is achieved, the form of the cutter should be perfectly copied on the machined surface and the process can be replicated. Therefore, if the form and the position of the cutter (normally known) are estimated, should be possible to quantitatively evaluate the stability of the cutting phenomena, including adhesion and built-up edge, based on the difference between the actual machined surface and the position of the cutter estimated. Moreover, due to the estimated positional accuracy of the adjoining cutting edges, it should be possible to evaluate the stability of the machining system based on the vibration and the accuracy of spindle rotation. In this study, a method for estimating a cutting edge during machining from a surface profile was developed. Furthermore, the proposed method was applied to evaluate three elements: a virtually ideal machining surface with good transferability, a machining surface with poor transferability, wherein feed marks are clear, and a surface with variable transferability and feed marks due to chatter or adhesion. The results indicated that the proposed method can be successfully used to extract these characteristics.     

Dry machining of aluminum for proper selection of cutting tool: tool performance and tool wear

Machining of aluminum and its alloy is very difficult due to the adhesion and diffusion of aluminum, thus the formation of built-up edge (BUE) on the surface. The BUE, which affects the surface integrity and tool life significantly, affects the service and performance of the workpiece. The minimization of BUE was carried out by selection of proper cutting speed, feed, depth of cut, and cutting tool material. This paper presents machining of rolled aluminum at cutting speeds of 336, 426, and 540 m/min, the feeds of 0.045, 0.06, and 0.09 mm/rev, and a constant depth of cut of 0.2 mm in dry condition. Five cutting tools WC SPUN grade, WC SPGN grade, WC + PVD (physical vapor deposition) TiN coating, WC + Ti (C, N) + Al₂O₃ PVD multilayer coatings, and PCD (polycrystalline diamond) were utilized for the experiments. The surface roughness produced, total flank wear, and cut chip thicknesses were measured. The characterization of the tool was carried out by a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) pattern. The chip underface was analyzed for the study of chip deformation produced after machining. The results indicated that the PCD tool provides better results in terms of roughness, tool wear, and smoother chip underface. It provides promising results in all aspects.