Fabrication and cutting performance of cemented tungsten carbide micro-cutting tools

We have developed cemented tungsten carbide (CTC) micro-cutting tools of 3 μm diameter by electrical discharge machining (EDM). Microdrilling and micromilling were carried out using the developed tools, and their cutting performance was investigated. Cutting was performed in free-cutting brass plates. Ultrasonic oscillation was employed to lower the cutting resistance. As a result, holes and a slot of 3 μm depth were successfully fabricated using tools made of CTC with 0.6 μm grain size, indicating that successful cutting with 3 μm-diameter tools was accomplished for the first time. Furthermore, CTC with 90 nm grain size was used as a tool material to improve the tool breakage resistance and tool form accuracy. The drilling performance of tools made of this ultrafine-grain-sized CTC was also investigated and found to exhibit a considerably improved average tool life.     

Wear behavior and cutting performance of nanostructured hard coatings on cemented carbide cutting tools in hard milling

The influence of nanolayer AlTiN/TiN and multilayer nanocomposite TiAlSiN/TiSiN/TiAlN hard coatings on the wear behavior and cutting performance of carbide cutting tools was investigated in face milling of hardened AISI O2 cold work tool steel (∼58 HRC) at dry conditions. Characterization of the coatings was performed using nanoindentation, scratch test, reciprocating multi-pass wear test. The chips forming during cutting process were also analyzed. Results showed that abrasive and oxidation wear are dominant tool failures. The nanolayer AlTiN/TiN coating gives the best adhesion to the substrate, the best wear resistance in machining and thus provides the longest lifetime with carbide inserts.     

晶粒长大抑制剂对超细硬质合金刀具磨损性能的影响

对添加和不添加晶粒长大抑制剂的WC-10Co超细硬质合金刀具,分别进行了切削高温合金GH2132的刀具磨损试验,并对试验结果进行线性回归,建立了刀具寿命TL与切削速度v之间关系的经验公式,利用ZEISS连续变倍体视显微镜及显微摄影系统观察了刀具刃口和后刀面的磨损形貌,并对达到磨钝标准时的刀具后刀面磨损微区成分进行了电子探针能谱分析,探讨晶粒长大抑制剂对刀具磨损性能的影响机理。结果表明:晶粒长大抑制剂可以提高超细硬质合金刀具的耐磨性,不但使抗粘接磨损的能力得到提高,而且使抗磨料磨损、撕裂剥落和扩散磨损的能力也得到了提高。     

硬质合金刀具干切削TC4钛合金耐用度的研究

通过对YT15、YG8、YW2这3种牌号的硬质合金刀具干切削TC4钛合金的试验,分析了3种刀具的磨损形貌及特征,并研究了切削速度对刀具耐用度的影响,建立了刀具耐用度T与切削速度v之间的泰勒公式.结果表明,随切削速度增加YT15刀具耐用度降低最快,YG8刀具的耐用度次之,YW2刀具的耐用度降低最慢.     

Dynamic reliability sensitivity of cemented carbide cutting tool

Influence of geometric and cutting parameters of cemented carbide cutting tool on reliability of cutting tool has become more and more mature, yet influence of its physical and material parameters on reliability is still blank. In view of this, cutting test and fatigue crack growth test of YT05 cemented carbide cutting tool are conducted to measure such data as the original crack size, growth size, times of impact loading, number and time of cutting tool in failure, and stress distribution of cutting tool is also obtained by simulating cutting process of tools. Mathematical models on dynamic reliability and dynamic reliability sensitivity of cutting tool are derived respectively by taking machining time and times of impact loading into account, thus change rules of dynamic reliability sensitivity to physical and material parameters can be obtained. Theoretical and experimental results show that sensitive degree on each parameter of tools increases gradually with the increase of machining time and times of impact loading, especially for parameters such as fracture toughness, shape parameter, and cutting stress. This proposed model solves such problems as how to determine the most sensitive parameter and influence degree of physical parameters and material parameters to reliability, which is sensitivity, and can provide theoretical foundation for improving reliability of cutting tool system.     

Processes involved in the wear of cemented carbide tools

Studies were made of the initial cratering wear and subsequent wear propagation of WC-(Ti, Ta, W)C-Co tools used to cut carbon steel. Using mechanically polished tools and short cutting times (1–11 s), microstructural and chemical changes involved in the initial wear process were identified and used as a basis for evaluating several wear models. Making use of iron-coated and diffusion-annealed tools, the wear propagation process was similarly evaluated in tests of up to 6 min duration.Microscopic examination shows that WC grains fracture intragranularly, consequently generating fine WC wear debris. Analysis of chip material reveals the size of WC wear debris to be an order of magnitude less than the original grain size. The (Ti, Ta, W)C wear debris size was found to be of the order of the original grain size. Adhesion seems to be the most likely mechanism of wear. Abrasive wear seems to be inconsistent with the observed similarity between results for inclusion-containing 52100 steel and 1045 steel relatively free of inclusions. Despite evidence of substantial diffusion, diffusional wear models seem inapplicable owing to the relative wear rates of coated and uncoated tools and to the absence of intergranular failure. Dissolution models seem inconsistent with the observed coexistence of the iron coating and the WC particles.     

Failure analyses of cemented tungsten carbide extrusion die

Abstract

In this study, the failure of a cemented tungsten carbide extrusion die (WC–Co) which was designed for the production of 55 000 components but failed during production of third component has been investigated. The die is used for cold extrusion of auto parts components as sizing die. Sizes achieved by forging process are further refined to required fine tolerance. The component size is required to be controlled within ±20 μm. The investigations revealed that the failure is due to abusive machining of cemented tungsten carbide. Detail studies under different electrical discharge machining conditions have been made to investigate the formation of cracks and their morphology. The major cause of the failure is established as abusive electrical discharge machining conditions with higher pulse current, which lead to micro- to macrocracks at the machining stage. These cracks further enlarged under load conditions when extrusion was done. Based on this study experiments were performed under different machining conditions on the WC–Co material. Optimum parameters were established for machining and accordingly new die was designed and fabricated which is performing very well.     

Oxidation and wear behaviour of carbide cutting tools

The oxidation and wear behaviour of carbide cutting tools was studied by service simulation tests and the machining of cast iron was examined in an oxidising environment and the presence of a direct electric current. The oxides were investigated by chemical analysis, X-ray diffraction and optical microscopy. The rate of oxidation increases with increase in current flow and the composition of the oxide depends upon the magnitude of the current. The oxide structure is affected by the amount of current.     

Friction characteristics of coated tungsten carbide cutting tools

A series of experiments has been carried out to explain the lower frictional characteristics of carbide tools coated with TiN relative to those coated with TiC. The reason for the higher friction of TiC appears to lie in the tendency for C to diffuse from the TiC coating into the thin layer of steel that transfers to the tool surface, thus strengthening it. No such strengthening mechanism is evident when TiN is the coating.     

An analytical and experimental investigation of the wear of cemented carbide cutting tools in the presence of dilute organic acids

A simple theoretical analysis of the tool wear process that applies to cutting green wood with cemented carbide tools is described. The analysis, which indicates the important parameters in the wear process, is used to predict the effect of binder volume fraction, carbide particle size, toolworkpiece contact force and the chemical reaction rate constant on wear rate. Comparisons are made between the predicted and experimentally determined wear rates for two types of cemented carbide tools in the presence of weak organic acids. Good agreement, is found that is thought to lend strong justification for the analysis.     

纳米硬质合金刀具切削Al/SiC_p复合材料的实验

针对SiC颗粒硬度高,切削Al/SiCp复合材料时刀具磨损剧烈,本文提出用具有较高硬度、韧性及良好抗磨损能力的WC-7Co制备纳米硬质合金刀具,并对Al/SiCp复合材料进行了切削实验。研究了纳米硬质合金刀具磨损机理和Al/SiCp复合材料的切屑去除机理,以及刀尖处后刀面磨损值。研究认为,纳米硬质合金刀具磨损的机理为SiC颗粒的微切削作用引起的磨料磨损,及SiC颗粒对刀尖刃口的高频、断续冲击引起的微崩刃及微破损;Al/SiCp复合材料的切削实质是断续切削;去除机理为切屑的崩碎去除;纳米硬质合金后刀面磨损值较普通硬质合金小30%～50%。实验表明,纳米硬质合金较普通硬质合金更适于加工Al/SiCp复合材料。     

Machining of austenitic stainless steels using CVD multi-layer coated cemented carbide tools

This paper presents the results of experimental work in dry turning of austenitic stainless steels (AISI 304 and AISI 316) using CVD multi-layer coated cemented carbide tools. The turning tests were conducted at four different cutting speeds (120, 150, 180 and 210 m/min) while feed rate and depth of cut were kept constant at 0.16 mm/rev and 1 mm, respectively. The cutting tools used were TiC/TiCN/TiN and TiCN/TiC/Al₂O₃ coated cementide carbides. The influences of cutting speed, cutting tool coating top layer and workpiece material were investigated on the machined surface roughness and the cutting forces. The worn parts of the cutting tools were also examined under scanning electron microscope (SEM). The results showed that cutting speed significantly affected the machined surface roughness values. With increasing cutting speed, the surface roughness values decreased until a minimum value is reached beyond which they increased.     

Characterization of multilayer pvd nanocoatings deposited on tungsten carbide cutting tools

The present trends in the coating technologies are gradient coatings, metastable coatings, multicomponaent coatings and multilayer or super lattice coatings. The physical vapour deposition (PVD) process is well-suited technology for these advanced coating technologies. The performance of the coated tools can be improved considerably using multi-layer micro and nanocoatings. The present paper discusses the deposition and characterization of multilayer TiN/Al₂O₃ coatings on cemented tungsten carbide cutting tools using reactive sputtering. The characterization of the coatings was carried out using X-ray diffraction (XRD) for phase analysis, chemical composition using EDAX, adhesion and toughness evaluation using Rockwell indentation test and surface roughness. It was observed that with decrease in thickness of each alumina layer to nanolevel in multilayer coating system results considerable improvement in final surface finish, adhesion and toughness of the coating. The experimental results are presented and analyzed in this paper.     

整体硬质合金刀具参数化直接建模的研究与实现

针对整体硬质合金刀具曲面结构复杂、参数化直接建模难以实现的问题,对整体硬质合金立铣刀的三维参数化直接建模进行了研究。分析了整体硬质合金立铣刀中包含的复杂曲线与曲面,将立铣刀的三维模型划分为5个重要特征,在三维建模过程中对每个特征根据刀具的设计规则进行了详细的数学建模,提取出了影响特征生成的关键几何设计参数,为每个特征建立了通用数学模型,通过UG/Open二次开发工具完成了立铣刀参数化界面设计,并在UG环境下建立了整体硬质合金刀具参数化设计系统。研究结果表明,整体硬质合金刀具参数化设计系统实现了复杂曲面刀具的参数化直接建模,节约了曲面方程的计算时间,有效提高了刀具设计与建模效率。     

Elliptical vibration cutting of hardened die steel with coated carbide tools

Elliptical vibration cutting of hardened die steel with coated carbide tools is examined in this research in order to achieve low-cost high-precision machining. Diamond coated tools are applied because of superior hardness of their polycrystalline diamond coating and its low manufacturing cost. TiN coated tools are also tested, since they are widely used for conventional machining of steels. Machinability of hardened die steel by the elliptical vibration cutting with coated carbide tools is discussed in three aspects in this study, i.e. transferability of cutting edge profile to cut surface, cutting force, and tool life. The transferability is evaluated quantitatively by calculating correlation coefficients of measured roughness profiles. It is clarified that the diamond coated tools have high transferability which leads to diffraction of light on the surface machined at micro-scale pick feed. Total cutting forces including ploughing components are measured at various feed rates, and then shearing components and ploughing components are separated utilizing linear regression. The measured results indicate, for example, that the all forces become considerably smaller only when elliptical vibration is applied to the TiN coated tool without cutting fluid. It is also found that this considerable reduction of forces interestingly corresponds to higher friction coefficient, which is identified from the ploughing components. Tool life tests are carried out by various machining methods, i.e. elliptical vibration/ordinary wet/dry cutting with diamond/TiN coated tools. The result shows, for example, that the flank wear is smallest in the wet elliptical vibration cutting with the diamond coated tool.