Friction drilling of austenitic stainless steel by uncoated and PVD AlCrN- and TiAlN-coated tungsten carbide tools

Friction drilling utilizes the heat generated from the friction between the tool and the thin workpiece to form a bush for fixtures such as screw threads in plastic deformation process. This process produces no chip, shortens the time required for hole-making and incurs less tool wear, thus lengthening the service life of the drill. In this study, tungsten carbide drills with and without coating were employed to make holes in AISI 304 stainless steel, which is known to have high ductility, low thermal conductivity and great hardness. TiAIN and AlCrN were coated onto the drill surface by physical vapor deposition (PVD). Performance of coated and uncoated cutting tools was examined for drillings made under different spindle speeds. Changes in relationship between drill surface temperature, tool wear and axial thrust force during machining were also explored. Experimental results reveal that lubricating effect of the coating and low thermal conductivity of AlCrN caused AlCrN-coated drill to produce the highest surface temperature but the lowest axial thrust force with the least tool wear. However, the difference in performance between coated and uncoated drills diminished with increase in number of holes drilled.     

Wear characteristics of the cemented carbide blades in drilling limestone with water jet

Drilling hard rock with water jet is considered to be an efficient way to improve the work life of the cemented carbide blade. In this paper, cemented carbide material YG-6 is used on the drill bit in limestone drilling with water jet. Wear characteristics of the cemented carbide blades in drilling limestone with water jet is studied. Experiment results showed that the water jet pressure and nozzle diameter played an important influence on the wear rates of the cemented carbide blades in the drill bits. The wear rates of YG-6 blades decreased when the jet pressure increased. But the decline speed of wear rates was not even, it declined more and more slowly when the jet pressure upon 10 MPa. It was also showed that wear rates decrease with the increase of the nozzle diameter in the drill bit, for the bigger nozzle diameter could provide more impact force which could reduce the mechanical force on the YG-6 blades. SEM photographs were taken to characterize the wear mechanism of the cemented carbide blades in limestone drilling with water jet. Surface analysis demonstrated that cemented carbide blades in limestone drilling with water jet showed circular action of brittle fracture, grain pullout and polishing, which induced material removal process.     

Temperature of internally-cooled diamond-coated tools for dry-cutting titanium

The role of cutting fluids is well known for the importance of removing heat from the cutting edge, lubricating the sliding chip contact and transporting the metal chips away from the cutting zone. Dry machining leads to increased cutting temperatures and higher wear rates resulting in shorter tool life; this is particularly evident in the cutting of high strength materials. Diamond coated cutting inserts are not usually considered for machining titanium due to rapid oxidation of the coating at the temperatures typical of titanium machining. This paper examines the formation of hot-spots on the rake face during dry and near-dry turning of titanium using conventional cemented carbide inserts. Machining performance is assessed by measurement of tool wear and tool life. Trials with an internally cooled tool with a specially designed, diamond coated insert have shown that the heat from the cutting operation can be rapidly diffused over the entire surface of the insert and thus successfully drawn away from the tool via closed loop recirculation of coolant through the tool holder. This enables wear to be inhibited by management of rake face temperature to keep it below the critical temperatures at which these prominent wear mechanisms operate. Measurements of change in coolant temperature before and after circulation are used to quantify the heat removed from the cutting process. The low friction coefficient and high thermal conductivity of diamond, assisted by the indirect cooling, results in longer tool life whilst maintaining high standards of surface finish.     

Optimization of guide pads for the BTA deep hole drilling of high alloyed steels by microfinishing

The boring and trepanning association deep hole drilling of materials with a high tendency to adhesion, such as high alloyed-steels, is characterized by a poor surface quality of the bore hole. Material particles adhere to the guide pads that are positioned on the circumference of the drill head and that are normally responsible for the outstanding workpiece quality. In order to prevent this mechanism the guide pads were coated with an innovative amorphous and tetrahedral bonded (ta-C)-coating. This coating has a reduced friction coefficient of 0.1 against steel and a hardness coefficient of about 7,000 HV. To use the benefits of this ta-C-coating the pre- and the after-treatment of the uncoated carbide substrate and ta-C-coated guide pads are essential. For these process steps a microfinishing process was carried out as an alternative to the conventional treatment by polishing and brushing. The microfinishing of the uncoated guide pads effects a smooth surface that is necessary for an optimum bonding strength of the ta-C-coating at the carbide substrate. Furthermore the chamfer edge in the lead-in-area is rounded which reduces the mechanical load at this specific area during the process. The finishing process of the coated guide pads reduces the coating defects and improves the friction coefficient. Thus, the wear behavior of the guide pads is improved because of the better friction conditions during the drilling process of high alloyed steels.     

麻花钻几何参数对不锈钢钻削性能影响的研究

采用ProE和Deform-3D软件分析了影响麻花钻钻411性能关健的几何参数,主要研究麻花钻横刃和顶角对不锈钢钻削过程中切削力、扭矩、刀具磨损的影响.介绍了缩短横刃长度和采用S形横刃螺旋面钻尖对不锈钢钻削力和扭矩的影响.重点分析了顶角影响主切削刃的长度、单位刃长的切削负荷、切削层中切削宽度与切削厚度的比例、切削中轴向力与扭矩、切屑形成与排屑情况.对于在钻削中,如何提高钻头的寿命,提高钻削加工的生产率和孔的加工质量具有重要的指导意义.     

Nanocrystalline CVD diamond coatings for drilling of WC-Co parts

Drilling of pre-sintered cemented carbide parts is a challenging task due to the high hardness and abrasive nature of the WC grains. This operation is commonly done using uncoated cemented carbide drill bits but the tool life is very limited requiring tool re-sharpening after a few holes. A solution for the improvement of the tool performance is here exploited by the use of nanocrystalline diamond (NCD) films as high abrasion resistant coatings. These coatings were grown in a hot filament chemical vapor deposition (HFCVD) reactor. Filament temperatures in the range of 1940-1980 °C were crucial to obtain highly adherent and very uniform coatings at the cutting edge and on the surfaces of the flutes. The performance of the coated tools was evaluated in through-hole drilling of a pre-sintered cemented carbide showing outstanding cutting efficiency when compared to that of an uncoated tool: maximal 940 mm/min infeed rates (app. 1 s to drill 17 mm) instead of 20 mm/min for the latter; absence of tool wear in contrast to a flank wear of about 50 μm in the uncoated tool after only 4 holes; hole edge integrity even at the highest infeed rates while grain decohesion at the hole edge takes place when using bare drill bits.     

Experimental and finite element simulation based investigations on micro-milling Ti-6Al-4V titanium alloy: Effects of cBN coating on tool wear

Micro-milling process is a direct and flexible fabrication method in producing functional three dimensional micro-products. The advance of micro-milling process ultimately depends on the development of micro cutting tools since it is a tool-based process. Therefore, in this study an attempt to improve the performance of carbide micro-end mills by applying cubic boron nitride (cBN) coating was carried out. Experiments and finite element method (FEM) based simulations were used to study the effect of cBN coated tool in micro-machining of Ti-6Al-4V titanium alloy. The experiments were conducted to compare the performance of cBN coated and uncoated micro-end mills in terms of surface roughness, burr formation and tool wear. FE simulations were employed to investigate chip formation process in micro-milling to reveal the effects of cBN coated micro-end mills with increased edge radius in terms of cutting force generation, tool temperature and contact pressure, sliding velocity and hence tool wear rate. The simulation results were further utilized for estimating tool life using a sliding wear rate model and compared with experiments. This study clearly showed that the cBN coated carbide tool outperformed the uncoated carbide tool in generation of tool wear and cutting temperature.     

Thrust force, torque, and tool wear in drilling the bulk metallic glass

The thrust force, torque, and tool wear in drilling of Zr-based bulk metallic glass (BMG) material are investigated. Drilling the BMG at high speed generates the chip light emission, high tool temperature, and severe tool wear. At low spindle speed, the BMG work-material builds up at the major and margin cutting edges and may break the drill. A range of feasible spindle speed and feed rate for the efficient drilling of BMG without the detrimental chip light emission and cutting edge work-material build-up has been identified in this study. Under the same drilling condition, the WC-Co tool generally requires less thrust force and about the same torque than the high-speed steel tool. The progressive wear of the major and margin cutting edges for BMG drilling is examined. Severe drill wear is associated with the bright BMG chip light emission. Without chip light emission, the drill wear is visible but not severe. This study concluded that precision holes in BMG could be generated with proper selection of tooling and process parameters.     

Design characteristics of new types of drill and evaluation of their performance drilling cast iron—II. Drills with three major cutting edges

This paper describes the performance characteristics of a new type of carbide head twist drill with four flutes, four major cutting edges, and one chisel edge. This drill shows great potential for significantly improving drilling accuracy and productivity. The drill produces holes that are as good as reamed holes. The body and point geometries and the cutting characteristics of the four-flute drill are described, along with the accuracies of hole location, angularity, size and roundness. Cutting forces, drill wear and chip morphology during cast iron drilling are also discussed. The four-flute drill deflects and vibrates much less than two-flute drills, especially in interrupted cutting cases. A patent is pending for this drill.     

钎焊金刚石磨粒钻钻削C/SiC陶瓷基复合材料孔时切屑对钻削过程的影响

钎焊金刚石磨粒钻适合钻削碳纤维增强碳化硅陶瓷基复合材料孔,但大量切屑会对孔的钻削过程产生不利影响。为此,针对切屑排出过程,分析切屑形貌,研究钻削时切屑对轴向钻削力、孔加工质量、钻头磨损的影响。结果表明：切屑对轴向钻削力有影响,尤其钻削深孔时影响显著。切屑对孔进口的加工质量几乎没有影响,只表现为孔进口处的轻微崩边;切屑对孔出口的加工质量影响显著,可引起严重的纤维断裂、撕裂缺陷以及基体的大区域脱落。同时,切屑加剧钻头磨损,使钻头不仅出现崩刃、微裂纹等轻微磨损,而且还产生基体剥落、金刚石剥落等严重磨损行为。     

Effect of deviation on delamination by saw drill

Various cutting techniques are available to drill holes, but drilling is the most common way in secondary machining of composite materials owing to the need for structure joining. Twist drills are widely used in the industry to produce holes rapidly and economically. Since the twist drill has a chisel edge, increasing the length of a chisel edge will result in an increase in the thrust force generated. Whereas, a saw drill has no chisel edge; it utilizes the peripheral distribution of the thrust force for drilling. As a result, the saw drill can achieve better a machining quality in drilling composite laminates than twist drill. The deviation of cutting edge that occurs in saw drill would result in an increase of thrust force during drilling, causing delamination damage when drilling composite materials in particular. A comprehensive model concerning delamination induced by the thrust force of a deviation saw drill during drilling composite materials has been established in the present study. For a deviation saw drill, the critical thrust force that triggers delamination increases with increasing β. A lower feed rate has to be used with an increasing deviation saw drill in order to prevent delamination damage. The results agree with real industrial experience. A guide for avoiding the drill deviation during drill regrinding or drill wear has been proved analytically by the proposed model, especially when the deviation ratio (β) affects the critical thrust force. This approach can be extended to examine similar deviation effects of various drills.     

A numerical simulator to predict the dynamical behavior of the self-vibratory drilling head

The manufacturing of deep holes has to face problems to evacuate chips, especially for small diameters. Such problems induce frequent tool breakage and poor surface quality. The vibratory drilling enables the chip to be split into small elements thanks to the axial vibrations of the drill, self-maintained by the cutting energy. Thus, chips are easily evacuated from the hole. A specific tool holder with an adapted axial stiffness has been developed in order to investigate this drilling process. The cutting conditions are predetermined in order to lead to axial vibrations with a stable frequency and amplitude. During a period, the amplitude of the vibrations is higher than the feed per revolution, which enables the cutting edges to jump out of the work material. The vibrations are self-maintained and remain stable if some disturbances are absent or very limited such as the friction of the drill against the work material along its margins, the ploughing force induced by the chisel edge, the ploughing force induced by clearance face, etc. The objectives of this paper are (i) to model the dynamical behavior of the self-vibrating drilling head, the cutting and ploughing forces, and the material removal, (ii) to foresee with a numerical simulator the cutting conditions which generate good vibrations, (iii) to validate the numerical simulator with a experimental round of test. This work has also shown that the productivity of the drilling is improved by the use of the vibratory drilling. Deep hole (ratio deep/drill diameter >20) can be drilled with this new technology without any coolant and any retreat cycle with the same quality as a conventional drilling operation.     

PVD涂层刀具高速铣削CoCrMo合金的性能研究

目的为了提高涂层硬质合金刀具的切削性能,研究了物理气相沉积PVD法制备的涂层硬质合金铣刀在高速干式环境下的铣削性能。方法采用阴极电弧技术制备了TiN、TiAlN以及TiAlSiN涂层硬质合金铣刀刀头,通过一同沉积涂层的硬质合金圆片,间接测量得出涂层的显微硬度、厚度和平均摩擦系数,并以CoCrMo合金为切削对象,进行了PVD涂层与无涂层刀具高速铣削下的对比试验。结果TiAlSiN显微硬度最高达3800HV,摩擦系数达0.3,TiAlN涂层平均膜厚为2μm,间接测得TiN、TiAlN以及TiAlSiN涂层的结合力依次为60、58、42N。在三者的切削性能中,TiAlSiN涂层的切削性能比TiAlN和TiN涂层的好,同等切削参数时,TiN刀具的高速铣削时间最短,TiAlSiN涂层的平均磨损值为0.1895,TiN的平均磨损值为0.3047。结论涂层中添加Al、Si,极大地提高了刀具的使用性能,改善了刀具切削过程中的耐磨性、红硬性,极大地延长了刀具的使用寿命。TiAlSiN涂层的硬度高,耐磨损性好,切削性能好,适合高速铣削加工。     

石墨烯涂层刀具的研究现状

针对高效干式切削加工中润滑能力不足,将自润滑性能优良的石墨烯粒子原位生长或者以复合材料的形式沉积于硬质合金刀具基体表面,有望弥补传统干切削中刀具使用寿命和加工性能偏低的不足。介绍了石墨烯材料在金属切削刀具领域中的研究和应用的现状,解读使用不同的工艺制备方法获得原生石墨烯涂层或者石墨烯复合超硬材料,并用其进行金属切削加工和摩擦磨损的试验。结果表明：石墨烯涂层刀具具备优良的润滑性能,能有效降低刀具的摩擦因数和磨损率,提高其使用寿命。     

Drilling thick fabric woven CFRP laminates with double point angle drills

Carbon fiber reinforced plastics (CFRPs) have many desirable properties, including high strength-to-weight ratio, high stiffness-to-weight ratio, high corrosion resistance, and low thermal expansion. These properties make CFRP suitable for use in structural components for aerospace applications. Drilling is the most common machining process applied to CFRP laminates, and it is difficult due to the extremely abrasive nature of the carbon fibers and low thermal conductivity of CFRP. It is a challenge for manufacturers to drill CFRP materials without causing any delamination on the work part while also considering the economics of the process. The subject of this study is the drilling of fabric woven type CFRP laminates which are known to be more resistant to delamination than unidirectional type CFRP laminates. The objective of this study is to investigate the influence of double point angle drill geometry on drilling performance through an experimental approach. An uncoated carbide and two diamond coated carbide drills with different drill tip angles are employed in drilling experiments of aerospace quality thick fabric woven CFRP laminates. Force and torque measurements are used to investigate appropriate drilling conditions based on drill geometry and ideal drilling parameters are determined. Tool life tests of the drills were conducted and the condition of the diamond coating is examined as a function of drilling operational parameters. High feed rate drilling experiments are observed to be favorable in terms of drill wear. Feed is observed to be more important than speed, and the upper limit of feed is dictated by the drill design and the rigidity of the machine drill. Hole diameter variation due to drill wear is monitored to determine drill life. At high feeds, hole diameter tolerance is observed to be more critical than hole exit delamination during drilling of fabric woven CFRP laminates.     

Modes of failure of cemented tungsten carbide tool bits (WC/Co): A study of wear parts

Cemented tungsten carbide (WC/Co) holds a successful past as abrasion and wear-resistant components in mining industries for their wonderful combination of very high hardness and good fracture toughness as well as comparatively extraordinary wear resistance. Generally, the tungsten carbide drill bits/blades are used in rock drilling, mineral cutting, gas oil drilling and even tunneling industries. The service environments of the WC/Co tool bits are terribly complicated because of totally different hardness of the drilling objectives at different working conditions, consequence various movement patterns of the WC/Co drill bits. As a result, the failure mechanism of the tool bits is quite different. The mechanism of hole drilling and different mining operation and processes, a tool-bit gradually degrades till it breaks at the end of its life. Replacing a drill-bit once its breakage is often expensive in certain special applications. At the same time an early tool replacement decision could lead to cause of lower tools life. This type of claims is marking the ways that modify the accurate prediction of tool failures. In circumstances, where degradation signals using the appropriate features are utilized to make the tool replacement decision. Intensive investigation of the performance of tungsten carbide tools in hard metal industries and tool industries is being conducted worldwide. Tungsten carbide alloyed with cobalt (WC/Co) shows unique characteristics like high strength at elevated temperature and high mechanical and chemical resistance that makes carbide tools appropriate for cutting, drilling, mining and machining operation. A whole failure study is revealed within the paper. This study also discusses the failure mode of a tungsten carbide tools, its prediction and remedies.     

钻削B4C颗粒增强铝合金工艺参数对刀具磨损和孔尺寸精度影响的分析和优化

基于刀具磨损和钻孔尺寸误差等多个性能指标,对B4C颗粒增强铝合金切削加工参数进行评估和优化。通过Taguchi的L27,3水平4因子正交阵列进行实验设计。研究结果表明：磨粒磨损和积屑瘤一般在刀具磨损时形成,同时,边角磨损也具有重大意义。影响切削刀具的侧面磨损主要决定因素是合金中的颗粒质量分数,其次分别是进给速率、钻头的硬度和主轴转速。在所有使用的刀具中,有TiAlN涂层的硬质合金钻头在刀具磨损以及孔尺寸方面具有最佳性能。灰关系分析表明：钻头材料的影响比进给速度和主轴转速的影响更大。在最佳的钻探参数下可以得到最小的刀具磨损和孔直径误差。     

Cutting edge rounding: An innovative tool wear criterion in drilling CFRP composite laminates

An evenly and smoothly distributed abrasion wear, observed along the entire cutting edge of an uncoated carbide drill bit in drilling CFRPs, is due to the highly abrasive nature of the carbon fibres. A very few researchers have only quoted this wear mode as being responsible for giving rise to the rounding of the cutting edge, or its bluntness. However, this wear feature has seldom been investigated, unlike the conventional flank wear in practice. This paper offers a new approach in unveiling and introducing the cutting edge rounding (CER) – a latent wear characteristic as a measure of sharpness/bluntness – of uncoated cemented carbide tools during drilling CFRP composite laminates. Four different types of drills (conventional and specialised) were tested to assess the applicability and relevance of this new wear feature. Mechanical loads (drilling thrust and torque) were recorded, and the hole entry and exit delamination were quantified. For the utilised tools, the accruing magnitude of CER was also recorded, in parallel with studying their conventional flank wear. Very appreciable correlations between the CER and the drilling loads, and also the quantitative delamination results are observed. Results reveal that this new wear type develops almost similarly for the selected tools and is practically independent of their respective conventional flank wear patterns. Moreover, a distinct, non-zero magnitude of the CER for a very fresh tool state may provide researchers with some lucid information in further studying the results during wear tests, more emphatically. The CER correlations with quantitative delamination results are noticed quite comparable to those of the conventional flank wear via statistical linear regression analyses.     

金刚石涂层刀具加工石墨的切削性能

为充分对比不同类型金刚石涂层刀具的切削性能,定制几种不同类型金刚石涂层刀具进行等静压石墨切削加工,并与WC硬质合金刀具和TiAlN涂层刀具的切削情况对比,分析不同类型金刚石涂层刀具的涂层形貌、切削寿命、加工后的表面质量以及切削力。结果表明:制备的金刚石涂层刀具的涂层形貌主要为纳米晶和微晶,其寿命是硬质合金和TiAlN涂层刀具的10倍以上,且几种不同类型的金刚石涂层刀具寿命差异较小;金刚石涂层表面的晶粒细化可以降低加工表面的粗糙度和切削力,涂层脱落是金刚石刀具的主要磨损形式。      

Performance of cryogenically treated WC drill using tool wear measurements on the cutting edge and hole surface topography when drilling CFRP

Drilling CFRP poses major challenges from the perspective of rapid tool wear and poor hole quality, with the development of higher strength fibers further accentuating these problems. Cryogenic treatment is one way of increasing tool hardness thereby improving tool life and hole quality through longer retention of cutting edge sharpness. In this study, tool wear is monitored by measuring flank wear, cutting edge flatting (CEF), peak flatting (PF) and cutting edge surface roughness (CESR). While flank wear is unable to distinguish the better performance of the cryo-treated drill from the untreated drill, the other wear parameters are able to account for the better hole quality (exit delamination) produced by this drill. CEF and PF are direct measures of the extent of cutting edge blunting unlike flank wear which measures wear along the flank due to rubbing. Fiber pullout is the primary reason for deterioration in surface finish and Rz and Rv are better measures than Ra in estimating surface quality.